This chapter describes the Java Database Connectivity (JDBC) support for user-defined object types. It discusses functionality of the generic, weakly typed oracle.sql.STRUCT
class, as well as how to map to custom Java classes that implement either the JDBC standard SQLData
interface or the Oracle ORAData
interface.
The following topics are covered:
Oracle object types provide support for composite data structures in the database. For example, you can define a Person
type that has the attributes name
of CHAR
type, phoneNumber
of CHAR
type, and employeeNumber
of NUMBER
type.
Oracle provides tight integration between its Oracle object features and its JDBC functionality. You can use a standard, generic JDBC type to map to Oracle objects, or you can customize the mapping by creating custom Java type definition classes.
Note:
In this book, Java classes that you create to map to Oracle objects will be referred to as custom Java classes or, more specifically, custom object classes. This is as opposed to custom references classes, which are Java classes that map to object references, and custom collection classes, which are Java classes that map to Oracle collections.Custom object classes can implement either a standard JDBC interface or an Oracle extension interface to read and write data. JDBC materializes Oracle objects as instances of particular Java classes. Two main steps in using JDBC to access Oracle objects are:
Creating the Java classes for the Oracle objects
Populating these classes. You have the following options:
Let JDBC materialize the object as a STRUCT
object.
Explicitly specify the mappings between Oracle objects and Java classes.
This includes customizing your Java classes for object data. The driver then must be able to populate instances of the custom object classes that you specify. This imposes a set of constraints on the Java classes. To satisfy these constraints, you can define your classes to implement either the JDBC standard java.sql.SQLData
interface or the Oracle extension oracle.sql.ORAData
interface.
You can use the Oracle JPublisher utility to generate custom Java classes.
Note:
When you use theSQLData
interface, you must use a Java type map to specify your SQL-Java mapping, unless weakly typed java.sql.Struct
objects will suffice.If you choose not to supply a custom Java class for your SQL-Java mapping for an Oracle object, then Oracle JDBC will materialize the object as an instance of the oracle.sql.STRUCT
class.
You would typically want to use STRUCT
objects, instead of custom Java objects, in situations where you do not know the actual SQL type. For example, your Java application might be a tool to manipulate arbitrary object data within the database, as opposed to being an end-user application. You can select data from the database into STRUCT
objects and create STRUCT
objects for inserting data into the database. STRUCT
objects completely preserve data, because they maintain the data in SQL format. Using STRUCT
objects is more efficient and more precise in situations where you do not need the information in an application specific form.
This section covers the following topics:
This section discusses standard versus Oracle-specific features of the oracle.sql.STRUCT
class, introduces STRUCT
descriptors, and lists methods of the STRUCT
class to give an overview of its functionality.
Standard java.sql.Struct Methods
If your code must comply with standard JDBC 2.0, then use a java.sql.Struct
instance and use the following standard methods:
getAttributes(map)
This method retrieves the values of the attributes, using entries in the specified type map to determine the Java classes to use in materializing any attribute that is a structured object type. The Java types for other attribute values would be the same as for a getObject
call on data of the underlying SQL type.
getAttributes
This method is the same as the preceding getAttributes(map)
method, except it uses the default type map for the connection.
This method returns a Java String
that represents the fully qualified name of the Oracle object type that this Struct
represents.
Oracle oracle.sql.STRUCT Class Methods
If you want to take advantage of the extended functionality offered by Oracle-defined methods, then use an oracle.sql.STRUCT
instance.
The oracle.sql.STRUCT
class implements the java.sql.Struct
interface and provides extended functionality beyond the JDBC 2.0 standard.
The STRUCT
class includes the following methods in addition to standard Struct
functionality:
Retrieves the values of the values array as oracle.sql.*
objects
Returns the StructDescriptor
object for the SQL type that corresponds to this STRUCT
object
Returns the current connection instance
Consults the default type map of the connection to determine what class to map to and, then, uses toClass
Consults the specified type map to determine what class to map to, and then uses toClass
Creating and using a STRUCT
object requires a descriptor, which is an instance of the oracle.sql.StructDescriptor
class, to exist for the SQL type that will correspond to the STRUCT
object. You need only one StructDescriptor
object for any number of STRUCT
objects that correspond to the same SQL type.
If your application is fetching objects from the database as STRUCT
, then the Oracle JDBC drivers will construct the necessary STRUCT
descriptors for you. You only need to construct your own STRUCT
descriptors if you are creating STRUCT
values yourself for use in a setObject
call.
This section discusses how to retrieve and manipulate Oracle objects and their attributes, using either Oracle-specific features or JDBC 2.0 standard features.
Note:
The JDBC driver seamlessly handles embedded objects, that is,STRUCT
objects that are attributes of STRUCT
objects, in the same way that it normally handles objects. When the JDBC driver retrieves an attribute that is an object, it follows the same rules of conversion by using the type map, if it is available, or by using default mapping.Retrieving an Oracle Object as an oracle.sql.STRUCT Object
You can retrieve an Oracle object directly into an oracle.sql.STRUCT
instance. In the following example, getObject
is used to get a type_struct
object from the col1
column of the table struct_table
. Because getObject
returns an Object
type, the return is cast to oracle.sql.STRUCT
. This example assumes that the Statement
object stmt
has already been created.
String cmd; cmd = "CREATE TYPE type_struct AS object (field1 NUMBER,field2 DATE)"; stmt.execute(cmd); cmd = "CREATE TABLE struct_table (col1 type_struct)"; stmt.execute(cmd); cmd = "INSERT INTO struct_table VALUES (type_struct(10,'01-apr-01'))"; stmt.execute(cmd); cmd = "INSERT INTO struct_table VALUES (type_struct(20,'02-may-02'))"; stmt.execute(cmd); ResultSet rs= stmt.executeQuery("SELECT * FROM struct_table"); oracle.sql.STRUCT oracleSTRUCT=(oracle.sql.STRUCT)rs.getObject(1);
Another way to return the object as a STRUCT
object is to cast the result set to OracleResultSet
and use the Oracle extension getSTRUCT
method:
oracle.sql.STRUCT oracleSTRUCT=((OracleResultSet)rs).getSTRUCT(1);
Retrieving an Oracle Object as a java.sql.Struct Object
Alternatively, in the preceding example, you can use standard JDBC functionality, such as getObject
, to retrieve an Oracle object from the database as an instance of java.sql.Struct
. Because getObject
returns a java.lang.Object
, you must cast the output of the method to Struct
. For example:
ResultSet rs= stmt.executeQuery("SELECT * FROM struct_table"); java.sql.Struct jdbcStruct = (java.sql.Struct)rs.getObject(1);
Retrieving Attributes as oracle.sql Types
If you want to retrieve Oracle object attributes from a STRUCT
or Struct
instance as oracle.sql
types, then use the getOracleAttributes
method of the oracle.sql.STRUCT
class, as follows:
oracle.sql.Datum[] attrs = oracleSTRUCT.getOracleAttributes();
or:
oracle.sql.Datum[] attrs = ((oracle.sql.STRUCT)jdbcStruct).getOracleAttributes();
Retrieving Attributes as Standard Java Types
If you want to retrieve Oracle object attributes as standard Java types from a STRUCT
or Struct
instance, use the standard getAttributes
method:
Object[] attrs = jdbcStruct.getAttributes();
Note:
The Oracle JDBC drivers cache array and structure descriptors. This provides enormous performance benefits. However, it means that if you change the underlying type definition of a structure type in the database, the cached descriptor for that structure type will become stale and your application will receive aSQLException
.This section describes how to create STRUCT
objects and descriptors and lists useful methods of the StructDescriptor
class.
Note:
If you have already fetched from the database aSTRUCT
of the appropriate SQL object type, then the easiest way to get a STRUCT
descriptor is to call getDescriptor
on one of the fetched STRUCT
objects. Only one STRUCT
descriptor is needed for any one SQL object type.Steps in Creating StructDescriptor and STRUCT Objects
To create a STRUCT
object, you must:
Create a StructDescriptor
object for the given Oracle object type, if it does not already exist.
Use the StructDescriptor
to construct the STRUCT
object.
A StructDescriptor
is an instance of the oracle.sql.StructDescriptor
class and describes a type of Oracle object. Only one StructDescriptor
is necessary for each Oracle object type. The driver caches StructDescriptor
objects to avoid re-creating them if the type has already been encountered.
Before you can construct a STRUCT
object, a StructDescriptor
must first exist for the given Oracle object type. If a StructDescriptor
object does not exist, then you can create one by calling the static StructDescriptor.createDescriptor
method. This method requires you to pass in the SQL type name of the Oracle object type and a connection object, as follows:
StructDescriptor structdesc = StructDescriptor.createDescriptor (sql_type_name, connection);
The sql_type_name
parameter is a Java String
containing the name of the Oracle object type, such as EMPLOYEE
, and connection
is the connection object.
Once you have your StructDescriptor
object for the Oracle object type, you can construct the STRUCT
object. To do this, provide the Connection
object, the StructDescriptor
object, and an array of Java objects containing the attributes you want the STRUCT
to contain.
The following constructors of STRUCT
are available:
STRUCT(Connection conn, java.sql.StructDescriptor structDesc, Object[] attributes) STRUCT(Connection conn, java.sql.StructDescriptor structDesc, java.util.Map map)
The structDesc
parameter is the StructDescriptor
object created previously and conn
is your Connection
object. The attributes can be passed as an array of java.lang.Object
or as a java.util.Map
object.
The following code illustrates the use of the constructor that takes an Object
array:
... Object[] attributes = {"attribute1", null}; STRUCT struct = new STRUCT(connection, structDescriptor, attributes); ...
The following code illustrates the use of the constructor that takes a Map
object:
... HashMap map = new HashMap(1); map.put("A1","attribute1"); STRUCT struct = new STRUCT(connection, structDescriptor, map); ...
Using StructDescriptor Methods
A StructDescriptor
can be thought of as a type object. This means that it contains information about the object type, including the type code, the type name, and how to convert to and from the given type. Remember, there should be only one StructDescriptor
object for any one Oracle object type. You can then use that descriptor to create as many STRUCT
objects as you need for that type.
The StructDescriptor
class includes the following methods:
getName
This method returns the fully qualified SQL type name of the Oracle object.
getLength
This method returns the number of fields in the object type.
getMetaData
This method returns the meta data regarding this type. The returned ResultSetMetaData
object contains the attribute name, attribute type code, and attribute type precision information. The column index in the ResultSetMetaData
object maps to the position of the attribute in the STRUCT
, with the first attribute being at index 1.
Serializable STRUCT Descriptors
When you create a STRUCT
object, you must first create a StructDescriptor
object. You can do this by calling the StructDescriptor.createDescriptor
method. The oracle.sql.StructDescriptor
class is serializable. This means that you can write the complete state of a StructDescriptor
object to an output stream for later use. You can re-create the StructDescriptor
object by reading its serialized state from an input stream. This is referred to as deserializing. With the StructDescriptor
object serialized, you do not need to call the StructDescriptor.createDescriptor
method, instead you deserialize the StructDescriptor
object.
It is advisable to serialize a StructDescriptor
object when the object type is complex but not changed often.
If you create a StructDescriptor
object through deserialization, you must supply the appropriate database connection instance for the StructDescriptor
object, using the setConnection
method.
The following code provides the connection instance for a StructDescriptor
object:
public void setConnection (Connection conn) throws SQLException
Note:
The JDBC driver does not verify that the connection object from thesetConnection
method connects to the same database from which the type descriptor was initially derived.To bind an oracle.sql.STRUCT
object to a prepared statement or callable statement, you can either use the standard setObject
method (specifying the type code), or cast the statement object to an Oracle statement type and use the Oracle extension setOracleObject
method. For example:
PreparedStatement ps= conn.prepareStatement("text_of_prepared_statement");
STRUCT mySTRUCT = new STRUCT (...);
ps.setObject(1, mySTRUCT, Types.STRUCT);
or:
PreparedStatement ps= conn.prepareStatement("text_of_prepared_statement");
STRUCT mySTRUCT = new STRUCT (...);
((OraclePreparedStatement)ps).setOracleObject(1, mySTRUCT);
The Oracle JDBC driver furnishes public methods to enable and disable buffering of STRUCT
attributes.
See Also:
"ARRAY Automatic Element Buffering"The following methods are included with the oracle.sql.STRUCT
class:
The setAutoBuffering(boolean)
method enables or disables auto-buffering. The getAutoBuffering
method returns the current auto-buffering mode. By default, auto-buffering is disabled.
It is advisable to enable auto-buffering in a JDBC application when the STRUCT
attributes will be accessed more than once by the getAttributes
and getArray
methods, presuming the ARRAY
data is able to fit into the Java virtual machine (JVM) memory without overflow.
Note:
Buffering the converted attributes may cause the JDBC application to consume a significant amount of memory.When you enable auto-buffering, the oracle.sql.STRUCT
object keeps a local copy of all the converted attributes. This data is retained so that subsequent access of this information does not require going through the data format conversion process.
If you want to create custom object classes for your Oracle objects, then you must define entries in the type map that specify the custom object classes that the drivers will instantiate for the corresponding Oracle objects.
You must also provide a way to create and populate instances of the custom object class from the Oracle object and its attribute data. The driver must be able to read from a custom object class and write to it. In addition, the custom object class can provide get
XXX
and set
XXX
methods corresponding to the attributes of the Oracle object, although this is not necessary. To create and populate the custom classes and provide these read/write capabilities, you can choose between the following interfaces:
The JDBC standard SQLData
interface
The ORAData
and ORADataFactory
interfaces provided by Oracle
The custom object class you create must implement one of these interfaces. The ORAData
interface can also be used to implement the custom reference class corresponding to the custom object class. However, if you are using the SQLData
interface, then you can use only weak reference types in Java, such as java.sql.Ref
or oracle.sql.REF
. The SQLData
interface is for mapping SQL objects only.
As an example, assume you have an Oracle object type, EMPLOYEE
, in the database that consists of two attributes: Name
, which is of the CHAR
type and EmpNum
, which is of the NUMBER
type. You use the type map to specify that the EMPLOYEE
object should map to a custom object class that you call JEmployee
. You can implement either the SQLData
or ORAData
interface in the JEmployee
class.
You can create custom object classes yourself, but the most convenient way to create them is to use the Oracle JPublisher utility to create them for you. JPublisher supports the standard SQLData
interface as well as the Oracle-specific ORAData
interface, and is able to generate classes that implement either one.
This section covers the following topics:
In deciding which of the two interface implementations to use, you need to consider the advantages of ORAData
and SQLData
.
The SQLData
interface is for mapping SQL objects only. The ORAData
interface is more flexible, enabling you to map SQL objects as well as any other SQL type for which you want to customize processing. You can create a ORAData
object from any data type found in Oracle Database. This could be useful, for example, for serializing RAW
data in Java.
The advantages of ORAData
are:
It does not require an entry in the type map for the Oracle object.
It has awareness of Oracle extensions.
You can construct an ORAData
from an oracle.sql.STRUCT
. This is more efficient because it avoids unnecessary conversions to native Java types.
You can obtain the corresponding Datum
object from the ORAData
object, using the toDatum
method.
It provides better performance. ORAData
works directly with Datum
types, which is the internal format used by the driver to hold Oracle objects.
SQLData
is a JDBC standard that makes your code portable.
If you use the SQLData
interface in a custom object class, then you must create type map entries that specify the custom object class to use in mapping the Oracle object type to Java. You can either use the default type map of the connection object or a type map that you specify when you retrieve the data from the result set. The getObject
method of the ResultSet
interface has a signature that lets you specify a type map. You can use either of the following:
rs.getObject(int columnIndex); rs.getObject(int columnIndex, Map map);
When using a SQLData implementation, if you do not include a type map entry, then the object will map to the oracle.sql.STRUCT
class by default. ORAData
implementations, by contrast, have their own mapping functionality so that a type map entry is not required. When using an ORAData
implementation, use the Oracle getORAData
method instead of the standard getObject
method.
The type map relates a Java class to the SQL type name of an Oracle object. This one-to-one mapping is stored in a hash table as a keyword-value pair. When you read data from an Oracle object, the JDBC driver considers the type map to determine which Java class to use to materialize the data from the Oracle object type. When you write data to an Oracle object, the JDBC driver gets the SQL type name from the Java class by calling the getSQLTypeName
method of the SQLData
interface. The actual conversion between SQL and Java is performed by the driver.
The attributes of the Java class that corresponds to an Oracle object can use either Java native types or Oracle native types to store attributes.
When using a SQLData
implementation, the JDBC applications programmer is responsible for providing a type map, which must be an instance of a class that implements the standard java.util.Map
interface.
You have the option of creating your own class to accomplish this, but the standard java.util.Hashtable
class meets the requirement.
Note:
If you are migrating from Java Development Kit (JDK) 1.1.x to JDK 1.2.x, then you must ensure that your code uses a class that implements theMap
interface. If you were using the java.util.Hashtable
class under 1.1.x, then no change is necessary.Hashtable
and other classes used for type maps implement a put
method that takes keyword-value pairs as input, where each key is a fully qualified SQL type name and the corresponding value is an instance of a specified Java class.
A type map is associated with a connection instance. The standard java.sql.Connection
interface and the Oracle-specific oracle.jdbc.OracleConnection
interface include a getTypeMap
method. Both return a Map
object.
This section covers the following topics:
When a connection instance is first established, the default type map is empty. You must populate it.
Perform the following general steps to add entries to an existing type map:
Use the getTypeMap
method of your OracleConnection
object to return the type map object of the connection. The getTypeMap
method returns a java.util.Map
object. For example, presuming an OracleConnection
instance oraconn
:
java.util.Map myMap = oraconn.getTypeMap();
Note:
If the type map in theOracleConnection
instance has not been initialized, then the first call to getTypeMap
returns an empty map.Use the put
method of the type map to add map entries. The put
method takes two arguments: a SQL type name string and an instance of a specified Java class that you want to map to.
myMap.put(sqlTypeName, classObject);
The sqlTypeName
is a string that represents the fully qualified name of the SQL type in the database. The classObject
is the Java class object to which you want to map the SQL type. Get the class object with the Class.forName
method, as follows:
myMap.put(sqlTypeName, Class.forName(className));
For example, if you have a PERSON
SQL data type defined in the CORPORATE
database schema, then map it to a Person
Java class defined as Person
with this statement:
myMap.put("CORPORATE.PERSON", Class.forName("Person"));
The map has an entry that maps the PERSON
SQL data type in the CORPORATE
database to the Person
Java class.
Note:
SQL type names in the type map must be all uppercase, because that is how the Oracle Database stores SQL names.Perform the following general steps to create a new type map. This example uses an instance of java.util.Hashtable
, which extends java.util.Dictionary
and, under JDK 1.2.x, also implements java.util.Map
.
Create a new type map object.
Hashtable newMap = new Hashtable();
Use the put
method of the type map object to add entries to the map. For example, if you have an EMPLOYEE
SQL type defined in the CORPORATE
database, then you can map it to an Employee
class object defined by Employee.java
, as follows:
newMap.put("CORPORATE.EMPLOYEE", class.forName("Employee"));
When you finish adding entries to the map, use the setTypeMap
method of the OracleConnection
object to overwrite the existing type map of the connection. For example:
oraconn.setTypeMap(newMap);
In this example, setTypeMap
overwrites the original map of the oraconn
connection object with newMap
.
Note:
The default type map of a connection instance is used when mapping is required but no map name is specified, such as for a result setgetObject
call that does not specify the map as input.If you do not provide a type map with an appropriate entry when using a getObject
call, then the JDBC driver will materialize an Oracle object as an instance of the oracle.sql.STRUCT
class. If the Oracle object type contains embedded objects and they are not present in the type map, then the driver will materialize the embedded objects as instances of oracle.sql.STRUCT
as well. If the embedded objects are present in the type map, then a call to the getAttributes
method will return embedded objects as instances of the specified Java classes from the type map.
One of the choices in making an Oracle object and its attribute data available to Java applications is to create a custom object class that implements the SQLData
interface. Note that if you use this interface, you must supply a type map that specifies the Oracle object types in the database and the names of the corresponding custom object classes that you will create for them.
The SQLData
interface defines methods that translate between SQL and Java for Oracle database objects. Standard JDBC provides a SQLData
interface and companion SQLInput
and SQLOutput
interfaces in the java.sql
package.
If you create a custom object class that implements SQLData
, then you must provide a readSQL
method and a writeSQL
method, as specified by the SQLData
interface.
The JDBC driver calls your readSQL
method to read a stream of data values from the database and populate an instance of your custom object class. Typically, the driver would use this method as part of an OracleResultSet
object getObject
call.
Similarly, the JDBC driver calls your writeSQL
method to write a sequence of data values from an instance of your custom object class to a stream that can be written to the database. Typically, the driver would use this method as part of an OraclePreparedStatement
object setObject
call.
Understanding the SQLInput and SQLOutput Interfaces
The JDBC driver includes classes that implement the SQLInput
and SQLOutput
interfaces. It is not necessary to implement the SQLOutput
or SQLInput
objects. The JDBC drivers will do this for you.
The SQLInput
implementation is an input stream class, an instance of which is passed to the readSQL
method. SQLInput
includes a read
XXX
method for every possible Java type that attributes of an Oracle object may be converted to, such as readObject
, readInt
, readLong
, readFloat
, readBlob
, and so on. Each read
XXX
method converts SQL data to Java data and returns it as the result with the corresponding Java type. For example, readInt
returns an int
.
The SQLOutput
implementation is an output stream class, an instance of which is passed in to the writeSQL
method. SQLOutput
includes a write
XXX
method for each of these Java types. Each write
XXX
method converts Java data to SQL data, taking as input a parameter of the relevant Java type. For example, writeString
would take as input a String
attribute from your Java class.
Implementing readSQL and writeSQL Methods
When you create a custom object class that implements SQLData
, you must implement the readSQL
and writeSQL
methods, as described here.
You must implement readSQL
as follows:
public void readSQL(SQLInput stream, String sql_type_name) throws SQLException
The readSQL
method takes as input a SQLInput
stream and a string that indicates the SQL type name of the data, that is, the name of the Oracle object type, such as EMPLOYEE
.
When your Java application calls getObject
, the JDBC driver creates a SQLInput
stream object and populates it with data from the database. The driver can also determine the SQL type name of the data when it reads it from the database. When the driver calls readSQL
, it passes in these parameters.
For each Java data type that maps to an attribute of the Oracle object, readSQL
must call the appropriate read
XXX
method of the SQLInput
stream that is passed in.
For example, if you are reading EMPLOYEE
objects that have an employee name as a CHAR
variable and an employee number as a NUMBER
variable, then you must have a readString
call and a readInt
call in your readSQL
method. JDBC calls these methods according to the order in which the attributes appear in the SQL definition of the Oracle object type.
The readSQL
method takes the data that the read
XXX
methods read and convert and assigns them to the appropriate fields or elements of a custom object class instance.
You must implement writeSQL
as follows:
public void writeSQL(SQLOutput stream) throws SQLException
The writeSQL
method takes as input a SQLOutput
stream.
When your Java application calls setObject
, the JDBC driver creates a SQLOutput
stream object. When the driver calls writeSQL
, it passes in this stream parameter.
For each Java data type that maps to an attribute of the Oracle object, writeSQL
must call the appropriate write
XXX
method of the SQLOutput
stream that is passed in.
For example, if you are writing to EMPLOYEE
objects that have an employee name as a CHAR
variable and an employee number as a NUMBER
variable, then you must have a writeString
call and a writeInt
call in your writeSQL
method. These methods must be called according to the order in which attributes appear in the SQL definition of the Oracle object type.
The writeSQL
method then writes the data to the SQLOutput
stream by calling the write
XXX
methods so that it can be sent to the database once you execute the prepared statement.
This section describes how to read data from an Oracle object or write data to an Oracle object if your corresponding Java class implements SQLData
.
Reading SQLData Objects from a Result Set
The following text summarizes the steps to read data from an Oracle object into your Java application when you choose the SQLData
implementation for your custom object class.
These steps assume you have already defined the Oracle object type, created the corresponding custom object class, updated the type map to define the mapping between the Oracle object and the Java class, and defined a statement object stmt
.
Query the database to read the Oracle object into a JDBC result set.
ResultSet rs = stmt.executeQuery("SELECT emp_col FROM personnel");
The PERSONNEL
table contains one column, EMP_COL
, of SQL type EMP_OBJECT
. This SQL type is defined in the type map to map to the Java class Employee
.
Use the getObject
method of your result set to populate an instance of your custom object class with data from one row of the result set. The getObject
method returns the user-defined SQLData
object because the type map contains an entry for Employee
.
if (rs.next()) Employee emp = (Employee)rs.getObject(1);
Note that if the type map did not have an entry for the object, then getObject
would return an oracle.sql.STRUCT
object. Cast the output to type STRUCT
, because the getObject
method signature returns the generic java.lang.Object
type.
if (rs.next()) STRUCT empstruct = (STRUCT)rs.getObject(1);
The getObject
method calls readSQL
, which, in turn, calls read
XXX
from the SQLData
interface.
Note:
If you want to avoid using the defined type map, then use thegetSTRUCT
method. This method always returns a STRUCT
object, even if there is a mapping entry in the type map.If you have get
methods in your custom object class, then use them to read data from your object attributes. For example, if EMPLOYEE
has the attributes EmpName
of type CHAR
and EmpNum
of type NUMBER
, then provide a getEmpName
method that returns a Java String
and a getEmpNum
method that returns an int
value. Then call them in your Java application, as follows:
String empname = emp.getEmpName(); int empnumber = emp.getEmpNum();
Retrieving SQLData Objects from a Callable Statement OUT Parameter
Consider you have an OracleCallableStatement
instance, ocs
, that calls a PL/SQL function GETEMPLOYEE
. The program passes an employee number to the function. The function returns the corresponding Employee
object. To retrieve this object you do the following:
Prepare an OracleCallableStatement
to call the GETEMPLOYEE
function, as follows:
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{ ? = call GETEMPLOYEE(?) }");
Declare the empnumber
as the input parameter to GETEMPLOYEE
. Register the SQLData
object as the OUT
parameter, with the type code OracleTypes.STRUCT
. Then, run the statement. This can be done as follows:
ocs.setInt(2, empnumber); ocs.registerOutParameter(1, OracleTypes.STRUCT, "EMP_OBJECT"); ocs.execute();
Use the getObject
method to retrieve the employee object. The following code assumes that there is a type map entry to map the Oracle object to the Java type Employee
:
Employee emp = (Employee)ocs.getObject(1);
If there is no type map entry, then getObject
would return an oracle.sql.STRUCT
object. Cast the output to the STRUCT
type, because the getObject
method returns an instance of the generic java.lang.Object
class. This is done as follows:
STRUCT emp = (STRUCT)ocs.getObject(1);
Passing SQLData Objects to a Callable Statement as an IN Parameter
Suppose you have a PL/SQL function addEmployee(?)
that takes an Employee
object as an IN
parameter and adds it to the PERSONNEL
table. In this example, emp
is a valid Employee
object.
Prepare an OracleCallableStatement
to call the addEmployee(?)
function.
OracleCallableStatement ocs = (OracleCallableStatement) conn.prepareCall("{ call addEmployee(?) }");
Use setObject
to pass the emp
object as an IN
parameter to the callable statement. Then, call the statement.
ocs.setObject(1, emp); ocs.execute();
Writing Data to an Oracle Object Using a SQLData Implementation
This following text describes the steps in writing data to an Oracle object from your Java application when you choose the SQLData
implementation for your custom object class.
This description assumes you have already defined the Oracle object type, created the corresponding Java class, and updated the type map to define the mapping between the Oracle object and the Java class.
If you have set
methods in your custom object class, then use them to write data from Java variables in your application to attributes of your Java data type object.
emp.setEmpName(empname); emp.setEmpNum(empnumber);
This statement uses the emp
object and the empname
and empnumber
variables assigned in the preceding example.
Prepare a statement that updates an Oracle object in a row of a database table, as appropriate, using the data provided in your Java data type object.
PreparedStatement pstmt = conn.prepareStatement ("INSERT INTO PERSONNEL VALUES (?)");
This assumes conn
is your connection object.
Use the setObject
method of the prepared statement to bind your Java data type object to the prepared statement.
pstmt.setObject(1, emp);
Run the statement, which updates the database.
pstmt.executeUpdate();
One of the choices in making an Oracle object and its attribute data available to Java applications is to create a custom object class that implements the oracle.sql.ORAData
and oracle.sql.ORADataFactory
interfaces. The ORAData
and ORADataFactory
interfaces are supplied by Oracle and are not a part of the JDBC standard.
Note:
The JPublisher utility supports the generation of classes that implement theORAData
and ORADataFactory
interfaces.Understanding ORAData Features
The ORAData
interface has the following advantages:
It recognizes Oracle extensions to the JDBC. ORAData
uses oracle.sql.Datum
types directly.
It does not require a type map to specify the names of the Java custom classes you want to create.
It provides better performance. ORAData
works directly with Datum
types, the internal format the driver uses to hold Oracle objects.
The ORAData
and ORADataFactory
interfaces do the following:
The toDatum
method of the ORAData
class transforms the data into an oracle.sql.*
representation.
ORADataFactory
specifies a create
method equivalent to a constructor for your custom object class. It creates and returns an ORAData
instance. The JDBC driver uses the create
method to return an instance of the custom object class to your Java application or applet. It takes as input an oracle.sql.Datum
object and an integer indicating the corresponding SQL type code as specified in the OracleTypes
class.
ORAData
and ORADataFactory
have the following definitions:
public interface ORAData { Datum toDatum (OracleConnection conn) throws SQLException; } public interface ORADataFactory { ORAData create (Datum d, int sql_Type_Code) throws SQLException; }
Where conn
represents the Connection object, d
represents an object of type oracle.sql.Datum
and sql_Type_Code
represents the SQL type code of the Datum
object.
Retrieving and Inserting Object Data
The JDBC drivers provide the following methods to retrieve and insert object data as instances of ORAData
.
You can retrieve the object data in one of the following ways:
Use the following getORAData
method of the Oracle-specific OracleResultSet
class:
ors.getORAData (int col_index, ORADataFactory factory);
This method takes as input the column index of the data in your result set and a ORADataFactory
instance. For example, you can implement a getORAFactory
method in your custom object class to produce the ORADataFactory
instance to input to getORAData
. The type map is not required when using Java classes that implement ORAData
.
Use the standard getObject(
index
,
map
)
method specified by the ResultSet
interface to retrieve data as instances of ORAData
. In this case, you must have an entry in the type map that identifies the factory class to be used for the given object type and its corresponding SQL type name.
You can insert object data in one of the following ways:
Use the following setORAData
method of the Oracle-specific OraclePreparedStatement
class:
ops.setORAData (int bind_index, ORAData custom_obj);
This method takes as input the parameter index of the bind variable and the name of the object containing the variable.
Use the standard setObject
method specified by the PreparedStatement
interface. You can also use this method, in its different forms, to insert ORAData
instances without requiring a type map.
The following sections describe the getORAData
and setORAData
methods.
To continue the example of an Oracle object EMPLOYEE
, you might have something like the following in your Java application:
ORAData datum = ors.getORAData(1, Employee.getORAFactory());
In this example, ors
is an Oracle result set, getORAData
is a method in the OracleResultSet
class used to retrieve a ORAData
object, and the EMPLOYEE
is in column 1 of the result set. The static
Employee.getORAFactory
method will return a ORADataFactory
to the JDBC driver. The JDBC driver will call create(
) from this object, returning to your Java application an instance of the Employee
class populated with data from the result set.
Notes:
ORAData
and ORADataFactory
are defined as separate interfaces so that different Java classes can implement them if you wish.
To use the ORAData
interface, your custom object classes must import oracle.sql.*
.
This section describes how to read data from an Oracle object or write data to an Oracle object if your corresponding Java class implements ORAData
.
Reading Data from an Oracle Object Using a ORAData Implementation
The following text summarizes the steps in reading data from an Oracle object into your Java application. These steps apply whether you implement ORAData
manually or use JPublisher to produce your custom object classes.
These steps assume you have already defined the Oracle object type, created the corresponding custom object class or had JPublisher create it for you, and defined a statement object stmt
.
Query the database to read the Oracle object into a result set, casting it to an Oracle result set.
OracleResultSet ors = (OracleResultSet)stmt.executeQuery ("SELECT Emp_col FROM PERSONNEL");
Where PERSONNEL
is a one-column table. The column name is Emp_col
of type Employee_object
.
Use the getORAData
method of your Oracle result set to populate an instance of your custom object class with data from one row of the result set. The getORAData
method returns an oracle.sql.ORAData
object, which you can cast to your specific custom object class.
if (ors.next()) Employee emp = (Employee)ors.getORAData(1, Employee.getORAFactory());
or:
if (ors.next()) ORAData datum = ors.getORAData(1, Employee.getORAFactory());
This example assumes that Employee
is the name of your custom object class and ors
is the name of your OracleResultSet
object.
In case you do not want to use getORAData
, the JDBC drivers let you use the getObject
method of a standard JDBC ResultSet
to retrieve ORAData
data. However, you must have an entry in the type map that identifies the factory class to be used for the given object type and its corresponding SQL type name.
For example, if the SQL type name for your object is EMPLOYEE
, then the corresponding Java class is Employee
, which will implement ORAData
. The corresponding Factory class is EmployeeFactory
, which will implement ORADataFactory
.
Use this statement to declare the EmployeeFactory
entry for your type map:
map.put ("EMPLOYEE", Class.forName ("EmployeeFactory"));
Then use the form of getObject
where you specify the map object:
Employee emp = (Employee) rs.getObject (1, map);
If the default type map of the connection already has an entry that identifies the factory class to be used for the given object type and its corresponding SQL type name, then you can use this form of getObject
:
Employee emp = (Employee) rs.getObject (1);
If you have get
methods in your custom object class, then use them to read data from your object attributes into Java variables in your application. For example, if EMPLOYEE
has EmpName
of type CHAR
and EmpNum
of type NUMBER
, provide a getEmpName
method that returns a Java String
and a getEmpNum
method that returns an integer. Then call them in your Java application as follows:
String empname = emp.getEmpName(); int empnumber = emp.getEmpNum();
Note:
Alternatively, you can fetch data using a callable statement object. TheOracleCallableStatement
class also has a getORAData
method.Writing Data to an Oracle Object Using a ORAData Implementation
The following text summarizes the steps in writing data to an Oracle object from your Java application. These steps apply whether you implement ORAData
manually or use JPublisher to produce your custom object classes.
These steps assume you have already defined the Oracle object type and created the corresponding custom object class.
Note:
The type map is not used when you are performing databaseINSERT
and UPDATE
operations.If you have set
methods in your custom object class, then use them to write data from Java variables in your application to attributes of your Java data type object.
emp.setEmpName(empname); emp.setEmpNum(empnumber);
Write an Oracle prepared statement that updates an Oracle object in a row of a database table, as appropriate, using the data provided in your Java data type object.
OraclePreparedStatement opstmt = conn.prepareStatement ("UPDATE PERSONNEL SET Employee = ? WHERE Employee.EmpNum = 28959);
This assumes conn
is your Connection
object.
Use the setORAData
method of the Oracle prepared statement to bind your Java data type object to the prepared statement.
opstmt.setORAData(1, emp);
The setORAData
method calls the toDatum
method of the custom object class instance to retrieve an oracle.sql.STRUCT
object that can be written to the database.
In this step you could also use the setObject
method to bind the Java data type. For example:
opstmt.setObject(1,emp);
Note:
You can use your Java data type objects as eitherIN
or OUT
bind variables.The ORAData
interface offers far more flexibility than the SQLData
interface. The SQLData
interface is designed to let you customize the mapping of only Oracle object types to Java types of your choice. Implementing the SQLData
interface lets the JDBC driver populate fields of a custom Java class instance from the original SQL object data, and the reverse, after performing the appropriate conversions between Java and SQL types.
The ORAData
interface goes beyond supporting the customization of Oracle object types to Java types. It lets you provide a mapping between Java object types and any SQL type supported by the oracle.sql
package.
It may be useful to provide custom Java classes to wrap oracle.sql.*
types and perhaps implement customized conversions or functionality as well. The following are some possible scenarios:
Performing encryption and decryption or validation of data
Performing logging of values that have been read or are being written
Parsing character columns, such as character fields containing URL information, into smaller components
Mapping character strings into numeric constants
Making data into more desirable Java formats, such as mapping a DATE
field to java.util.Date
format
Customizing data representation, for example, data in a table column is in feet but you want it represented in meters after it is selected
Serializing and deserializing Java objects
For example, use ORAData
to store instances of Java objects that do not correspond to a particular SQL object type in the database in columns of SQL type RAW
. The create
method in ORADataFactory
would have to implement a conversion from an object of type oracle.sql.RAW
to the desired Java object. The toDatum
method in ORAData
would have to implement a conversion from the Java object to an oracle.sql.RAW
object. This can be done, for example, by using Java serialization.
Upon retrieval, the JDBC driver transparently retrieves the raw bytes of data in the form of an oracle.sql.RAW
and calls the create
method of ORADataFactory
to convert the oracle.sql.RAW
object to the desired Java class.
When you insert the Java object into the database, you can simply bind it to a column of type RAW
to store it. The driver transparently calls the ORAData
.toDatum
method to convert the Java object to an oracle.sql.RAW
object. This object is then stored in a column of type RAW
in the database.
Support for the ORAData
interfaces is also highly efficient because the conversions are designed to work using oracle.sql.*
formats, which happen to be the internal formats used by the JDBC drivers. Moreover, the type map, which is necessary for the SQLData
interface, is not required when using Java classes that implement ORAData
.
See Also:
"Understanding the ORAData Interface"After the oracle.jdbc
interfaces were introduced in Oracle9i Database as an alternative to the oracle.jdbc.driver
classes, the oracle.sql.CustomDatum
and oracle.sql.CustomDatumFactory
interfaces, formerly used to access customized objects, were deprecated. Oracle recommends you use the new interfaces, oracle.sql.ORAData
and oracle.sql.ORADataFactory
.
Object-type inheritance allows a new object type to be created by extending another object type. The new object type is then a subtype of the object type from which it extends. The subtype automatically inherits all the attributes and methods defined in the supertype. The subtype can add attributes and methods and overload or override methods inherited from the supertype.
Object-type inheritance introduces substitutability. Substitutability is the ability of a slot declared to hold a value of type T
in addition to any subtype of type T
. Oracle JDBC drivers handle substitutability transparently.
A database object is returned with its most specific type without losing information. For example, if the STUDENT_T
object is stored in a PERSON_T
slot, the Oracle JDBC driver returns a Java object that represents the STUDENT_T
object.
This section covers the following topics:
Create custom object classes if you want to have Java classes that explicitly correspond to the Oracle object types. If you have a hierarchy of object types, you may want a corresponding hierarchy of Java classes.
The most common way to create a database subtype in JDBC is to run a SQL CREATE TYPE
command using the execute
method of the java.sql.Statement
interface. For example, you want to create a type inheritance hierarchy for:
PERSON_T | STUDENT_T | PARTTIMESTUDENT_T
The JDBC code for this can be as follows:
Statement s = conn.createStatement(); s.execute ("CREATE TYPE Person_T (SSN NUMBER, name VARCHAR2(30), address VARCHAR2(255))"); s.execute ("CREATE TYPE Student_T UNDER Person_t (deptid NUMBER, major VARCHAR2(100))"); s.execute ("CREATE TYPE PartTimeStudent_t UNDER Student_t (numHours NUMBER)");
In the following code, the foo
member procedure in type ST
is overloaded and the member procedure print
overwrites the copy it inherits from type T
.
CREATE TYPE T AS OBJECT (..., MEMBER PROCEDURE foo(x NUMBER), MEMBER PROCEDURE Print(), ... NOT FINAL; CREATE TYPE ST UNDER T (..., MEMBER PROCEDURE foo(x DATE), <-- overload "foo" OVERRIDING MEMBER PROCEDURE Print(), <-- override "print" STATIC FUNCTION bar(...) ... ... );
Once the subtypes have been created, they can be used as both columns of a base table as well as attributes of a object type.
In most cases, a customized Java class represents a database object type. When you create a customized Java class for a subtype, the Java class can either mirror the database object type hierarchy or not.
You can use either the ORAData
or SQLData
solution in creating classes to map to the hierarchy of object types.
This section covers the following topics:
Customized mapping where Java classes implement the oracle.sql.ORAData
interface is the recommended mapping. ORAData
mapping requires the JDBC application to implement the ORAData
and ORADataFactory
interfaces. The class implementing the ORADataFactory
interface contains a factory method that produces objects. Each object represents a database object.
The hierarchy of the class implementing the ORAData
interface can mirror the database object type hierarchy. For example, the Java classes mapping to PERSON_T
and STUDENT_T
are as follows:
Code for the Person.java
class which implements the ORAData
and ORADataFactory
interfaces:
class Person implements ORAData, ORADataFactory { static final Person _personFactory = new Person(); public NUMBER ssn; public CHAR name; public CHAR address; public static ORADataFactory getORADataFactory() { return _personFactory; } public Person () {} public Person(NUMBER ssn, CHAR name, CHAR address) { this.ssn = ssn; this.name = name; this.address = address; } public Datum toDatum(OracleConnection c) throws SQLException { StructDescriptor sd = StructDescriptor.createDescriptor("SCOTT.PERSON_T", c); Object [] attributes = { ssn, name, address }; return new STRUCT(sd, c, attributes); } public ORAData create(Datum d, int sqlType) throws SQLException { if (d == null) return null; Object [] attributes = ((STRUCT) d).getOracleAttributes(); return new Person((NUMBER) attributes[0], (CHAR) attributes[1], (CHAR) attributes[2]); } }
Student.java extending Person.java
Code for the Student.java
class, which extends the Person.java
class:
class Student extends Person { static final Student _studentFactory = new Student (); public NUMBER deptid; public CHAR major; public static ORADataFactory getORADataFactory() { return _studentFactory; } public Student () {} public Student (NUMBER ssn, CHAR name, CHAR address, NUMBER deptid, CHAR major) { super (ssn, name, address); this.deptid = deptid; this.major = major; } public Datum toDatum(OracleConnection c) throws SQLException { StructDescriptor sd = StructDescriptor.createDescriptor("SCOTT.STUDENT_T", c); Object [] attributes = { ssn, name, address, deptid, major }; return new STRUCT(sd, c, attributes); } public CustomDatum create(Datum d, int sqlType) throws SQLException { if (d == null) return null; Object [] attributes = ((STRUCT) d).getOracleAttributes(); return new Student((NUMBER) attributes[0], (CHAR) attributes[1], (CHAR) attributes[2], (NUMBER) attributes[3], (CHAR) attributes[4]); } }
Customized classes that implement the ORAData
interface do not have to mirror the database object type hierarchy. For example, you could have declared the Student
class without a superclass. In this case, Student
would contain fields to hold the inherited attributes from PERSON_T
as well as the attributes declared by STUDENT_T
.
The JDBC application uses the factory class in querying the database to return instances of Person
or its subclasses, as in the following example:
ResultSet rset = stmt.executeQuery ("select person from tab1"); while (rset.next()) { Object s = rset.getORAData (1, PersonFactory.getORADataFactory()); ... }
A class implementing the ORADataFactory
interface should be able to produce instances of the associated custom object type, as well as instances of any subtype, or at least all the types you expect to support.
In the following example, the PersonFactory.getORADataFactory
method returns a factory that can handle PERSON_T
, STUDENT_T
, and PARTTIMESTUDENT_T
objects, by returning person
, student
, or parttimestudent
Java instances.
class PersonFactory implements ORADataFactory { static final PersonFactory _factory = new PersonFactory (); public static ORADataFactory getORADataFactory() { return _factory; } public ORAData create(Datum d, int sqlType) throws SQLException { STRUCT s = (STRUCT) d; if (s.getSQLTypeName ().equals ("SCOTT.PERSON_T")) return Person.getORADataFactory ().create (d, sqlType); else if (s.getSQLTypeName ().equals ("SCOTT.STUDENT_T")) return Student.getORADataFactory ().create(d, sqlType); else if (s.getSQLTypeName ().equals ("SCOTT.PARTTIMESTUDENT_T")) return ParttimeStudent.getORADataFactory ().create(d, sqlType); else return null; } }
The following example assumes a table tabl1
, such as the following:
CREATE TABLE tabl1 (idx NUMBER, person PERSON_T); INSERT INTO tabl1 VALUES (1, PERSON_T (1000, 'Scott', '100 Oracle Parkway')); INSERT INTO tabl1 VALUES (2, STUDENT_T (1001, 'Peter', '200 Oracle Parkway', 101, 'CS')); INSERT INTO tabl1 VALUES (3, PARTTIMESTUDENT_T (1002, 'David', '300 Oracle Parkway', 102, 'EE'));
The customized classes that implement the java.sql.SQLData
interface can mirror the database object type hierarchy. The readSQL
and writeSQL
methods of a subclass typically call the corresponding superclass methods to read or write the superclass attributes before reading or writing the subclass attributes. For example, the Java classes mapping to PERSON_T
and STUDENT_T
are as follows:
Code for the Person.java
class, which implements the SQLData
interface:
import java.sql.*; public class Person implements SQLData { private String sql_type; public int ssn; public String name; public String address; public Person () {} public String getSQLTypeName() throws SQLException { return sql_type; } public void readSQL(SQLInput stream, String typeName) throws SQLException { sql_type = typeName; ssn = stream.readInt(); name = stream.readString(); address = stream.readString(); } public void writeSQL(SQLOutput stream) throws SQLException { stream.writeInt (ssn); stream.writeString (name); stream.writeString (address); } }
Student.java extending Student.java
Code for the Student.java
class, which extends the Person.java
class:
import java.sql.*; public class Student extends Person { private String sql_type; public int deptid; public String major; public Student () { super(); } public String getSQLTypeName() throws SQLException { return sql_type; } public void readSQL(SQLInput stream, String typeName) throws SQLException { super.readSQL (stream, typeName); // read supertype attributes sql_type = typeName; deptid = stream.readInt(); major = stream.readString(); } public void writeSQL(SQLOutput stream) throws SQLException { super.writeSQL (stream); // write supertype // attributes stream.writeInt (deptid); stream.writeString (major); } }
Although not required, it is recommended that the customized classes, which implement the SQLData
interface, mirror the database object type hierarchy. For example, you could have declared the Student
class without a superclass. In this case, Student
would contain fields to hold the inherited attributes from PERSON_T
as well as the attributes declared by STUDENT_T
.
Code for the Student.java
class, which does not extend the Person.java
class, but implements the SQLData interface directly:
import java.sql.*; public class Student implements SQLData { private String sql_type; public int ssn; public String name; public String address; public int deptid; public String major; public Student () {} public String getSQLTypeName() throws SQLException { return sql_type; } public void readSQL(SQLInput stream, String typeName) throws SQLException { sql_type = typeName; ssn = stream.readInt(); name = stream.readString(); address = stream.readString(); deptid = stream.readInt(); major = stream.readString(); } public void writeSQL(SQLOutput stream) throws SQLException { stream.writeInt (ssn); stream.writeString (name); stream.writeString (address); stream.writeInt (deptid); stream.writeString (major); } }
Even though you can manually create customized classes that implement the SQLData
, ORAData
, and ORADataFactory
interfaces, it is recommended that you use Oracle JPublisher to automatically generate these classes. The customized classes generated by Oracle JPublisher that implement the SQLData
, ORAData
, and ORADataFactory
interfaces, can mirror the inheritance hierarchy.
In a typical JDBC application, a subtype object is returned as one of the following:
A query result
A PL/SQL OUT
parameter
A type attribute
You can use either the default mapping or the SQLData
mapping or the ORAData
mapping to retrieve a subtype.
By default, a database object is returned as an instance of the oracle.sql.STRUCT
class. This instance may represent an object of either the declared type or subtype of the declared type. If the STRUCT
class represents a subtype object in the database, then it contains the attributes of its supertype as well as those defined in the subtype.
The Oracle JDBC driver returns database objects in their most specific type. The JDBC application can use the getSQLTypeName
method of the STRUCT
class to determine the SQL type of the STRUCT
object. The following code shows this:
// tab1.person column can store PERSON_T, STUDENT_T and PARTIMESTUDENT_T objects ResultSet rset = stmt.executeQuery ("select person from tab1"); while (rset.next()) { oracle.sql.STRUCT s = (oracle.sql.STRUCT) rset.getObject(1); if (s != null) System.out.println (s.getSQLTypeName()); // print out the type name which // may be SCOTT.PERSON_T, SCOTT.STUDENT_T or SCOTT.PARTTIMESTUDENT_T }
With SQLData
mapping, the JDBC driver returns the database object as an instance of the class implementing the SQLData
interface.
To use SQLData
mapping in retrieving database objects, do the following:
Implement the wrapper classes that implement the SQLData
interface for the desired object types.
Populate the connection type map with entries that specify what custom Java type corresponds to each Oracle object type.
Use the getObject
method to access the SQL object values.
The JDBC driver checks the type map for an entry match. If one exists, then the driver returns the database object as an instance of the class implementing the SQLData
interface.
The following code shows the whole SQLData customized mapping process:
// The JDBC application developer implements Person.java for PERSON_T, // Student.java for STUDENT_T // and ParttimeStudent.java for PARTTIMESTUDEN_T. Connection conn = ...; // make a JDBC connection // obtains the connection typemap java.util.Map map = conn.getTypeMap (); // populate the type map map.put ("SCOTT.PERSON_T", Class.forName ("Person")); map.put ("SCOTT.STUDENT_T", Class.forName ("Student")); map.put ("SCOTT.PARTTIMESTUDENT_T", Class.forName ("ParttimeStudent")); // tab1.person column can store PERSON_T, STUDENT_T and PARTTIMESTUDENT_T objects ResultSet rset = stmt.executeQuery ("select person from tab1"); while (rset.next()) { // "s" is instance of Person, Student or ParttimeStudent Object s = rset.getObject(1); if (s != null) { if (s instanceof Person) System.out.println ("This is a Person"); else if (s instanceof Student) System.out.println ("This is a Student"); else if (s instanceof ParttimeStudent) System.out.pritnln ("This is a PartimeStudent"); else System.out.println ("Unknown type"); } }
The JDBC drivers check the connection type map for each call to the following:
getObject
method of the java.sql.ResultSet
and java.sql.CallableStatement
interfaces
getAttribute
method of the java.sql.Struct
interface
getArray
method of the java.sql.Array
interface
getValue
method of the oracle.sql.REF
interface
With ORAData
mapping, the JDBC driver returns the database object as an instance of the class implementing the ORAData
interface.
The Oracle JDBC driver needs to be informed of what Java class is mapped to the Oracle object type. The following are the two ways to inform the Oracle JDBC drivers:
The JDBC application uses the getORAData(int idx, ORADataFactory f)
method to access database objects. The second parameter of the getORAData
method specifies an instance of the factory class that produces the customized class. The getORAData
method is available in the OracleResultSet
and OracleCallableStatement
classes.
The JDBC application populates the connection type map with entries that specify what custom Java type corresponds to each Oracle object type. The getObject
method is used to access the Oracle object values.
The second approach involves the use of the standard getObject
method. The following code example demonstrates the first approach:
// tab1.person column can store both PERSON_T and STUDENT_T objects ResultSet rset = stmt.executeQuery ("select person from tab1"); while (rset.next()) { Object s = rset.getORAData (1, PersonFactory.getORADataFactory()); if (s != null) { if (s instanceof Person) System.out.println ("This is a Person"); else if (s instanceof Student) System.out.println ("This is a Student"); else if (s instanceof ParttimeStudent) System.out.pritnln ("This is a PartimeStudent"); else System.out.println ("Unknown type"); } }
There are cases where JDBC applications create database subtype objects with JDBC drivers. These objects are sent either to the database as bind variables or are used to exchange information within the JDBC application.
With customized mapping, the JDBC application creates either SQLData
- or ORAData
-based objects, depending on the approach you choose, to represent database subtype objects. With default mapping, the JDBC application creates STRUCT
objects to represent database subtype objects. All the data fields inherited from the supertype as well as all the fields defined in the subtype must have values. The following code demonstrates this:
Connection conn = ... // make a JDBC connection StructDescriptor desc = StructDescriptor.createDescriptor ("SCOTT.PARTTIMESTUDENT", conn); Object[] attrs = { new Integer(1234), "Scott", "500 Oracle Parkway", // data fields defined in // PERSON_T new Integer(102), "CS", // data fields defined in // STUDENT_T new Integer(4) // data fields defined in // PARTTIMESTUDENT_T }; STRUCT s = new STRUCT (desc, conn, attrs);
s
is initialized with data fields inherited from PERSON_T
and STUDENT_T
, and data fields defined in PARTTIMESTUDENT_T
.
In a typical JDBC application, a Java object that represents a database object is sent to the databases as one of the following:
A data manipulation language (DML) bind variable
A PL/SQL IN
parameter
An object type attribute value
The Java object can be an instance of the STRUCT
class or an instance of the class implementing either the SQLData
or ORAData
interface. The Oracle JDBC driver will convert the Java object into the linearized format acceptable to the database SQL engine. Binding a subtype object is the same as binding a normal object.
While the logic to access subtype data fields is part of the customized class, this logic for default mapping is defined in the JDBC application itself. The database objects are returned as instances of the oracle.sql.STRUCT
class. The JDBC application needs to call one of the following access methods in the STRUCT
class to access the data fields:
Object[] getAttribute()
oracle.sql.Datum[] getOracleAttribute()
Subtype Data Fields from the getAttribute Method
The getAttribute
method of the java.sql.Struct
interface is used in JDBC 2.0 to access object data fields. This method returns a java.lang.Object
array, where each array element represents an object attribute. You can determine the individual element type by referencing the corresponding attribute type in the JDBC conversion matrix, as listed in Table 5-1. For example, a SQL NUMBER
attribute is converted to a java.math.BigDecimal
object. The getAttribute
method returns all the data fields defined in the supertype of the object type as well as data fields defined in the subtype. The supertype data fields are listed first followed by the subtype data fields.
Subtype Data Fields from the getOracleAttribute Method
The getOracleAttribute
method is an Oracle extension method and is more efficient than the getAttribute
method. The getOracleAttribute
method returns an oracle.sql.Datum
array to hold the data fields. Each element in the oracle.sql.Datum
array represents an attribute. You can determine the individual element type by referencing the corresponding attribute type in the Oracle conversion matrix, as listed in Table 5-1. For example, a SQL NUMBER
attribute is converted to an oracle.sql.NUMBER
object. The getOracleAttribute
method returns all the attributes defined in the supertype of the object type, as well as attributes defined in the subtype. The supertype data fields are listed first followed by the subtype data fields.
The following code shows the use of the getAttribute
method:
// tab1.person column can store PERSON_T, STUDENT_T and PARTIMESTUDENT_T objects
ResultSet rset = stmt.executeQuery ("select person from tab1");
while (rset.next())
{
oracle.sql.STRUCT s = (oracle.sql.STRUCT) rset.getObject(1);
if (s != null)
{
String sqlname = s.getSQLTypeName();
Object[] attrs = s.getAttribute();
if (sqlname.equals ("SCOTT.PERSON")
{
System.out.println ("ssn="+((BigDecimal)attrs[0]).intValue());
System.out.println ("name="+((String)attrs[1]));
System.out.println ("address="+((String)attrs[2]));
}
else if (sqlname.equals ("SCOTT.STUDENT"))
{
System.out.println ("ssn="+((BigDecimal)attrs[0]).intValue());
System.out.println ("name="+((String)attrs[1]));
System.out.println ("address="+((String)attrs[2]));
System.out.println ("deptid="+((BigDecimal)attrs[3]).intValue());
System.out.println ("major="+((String)attrs[4]));
}
else if (sqlname.equals ("SCOTT.PARTTIMESTUDENT"))
{
System.out.println ("ssn="+((BigDecimal)attrs[0]).intValue());
System.out.println ("name="+((String)attrs[1]));
System.out.println ("address="+((String)attrs[2]));
System.out.println ("deptid="+((BigDecimal)attrs[3]).intValue());
System.out.println ("major="+((String)attrs[4]));
System.out.println ("numHours="+((BigDecimal)attrs[5]).intValue());
}
else
throw new Exception ("Invalid type name: "+sqlname);
}
}
rset.close ();
stmt.close ();
conn.close ();
Oracle JDBC drivers provide a set of meta data methods to access inheritance properties. The inheritance meta data methods are defined in the oracle.sql.StructDescriptor
and oracle.jdbc.StructMetaData
classes.
The oracle.sql.StructDescriptor
class provides the following inheritance meta data methods:
String[] getSubtypeNames()
Returns the SQL type names of the direct subtypes.
boolean isFinalType()
Indicates whether the object type is a final type. An object type is FINAL
if no subtypes can be created for this type; the default is FINAL
, and a type declaration must have the NOT FINAL
keyword to be subtypable.
boolean isSubTyp()
Indicates whether the object type is a subtype.
boolean isInstantiable()
Indicates whether the object type is instantiable. An object type is NOT INSTANTIABLE
if it is not possible to construct instances of this type.
String getSupertypeName()
Returns the SQL type names of the direct supertype.
int getLocalAttributeCount()
Returns the number of attributes defined in the subtype.
The StructMetaData
class provides inheritance meta data methods for subtype attributes. The getMetaData
method of the StructDescriptor
class returns an instance of StructMetaData
of the type. The StructMetaData
class contains the following inheritance meta data methods:
int getLocalColumnCount()
Returns the number of attributes defined in the subtype, which is similar to the getLocalAttributeCount()
method of the StructDescriptor
class.
boolean isInherited(int column)
Indicates whether the attribute is inherited. The value for the column
attribute begins from 1
.
A convenient way to create custom object classes, as well as other kinds of custom Java classes, is to use the Oracle JPublisher utility. It generates a full definition for a custom Java class, which you can instantiate to hold the data from an Oracle object. JPublisher-generated classes include methods to convert data from SQL to Java and from Java to SQL, as well as getter and setter methods for the object attributes.
This section covers the following topics:
See Also:
Oracle Database JPublisher User's Guide.You can direct JPublisher to create custom object classes that implement either the SQLData
interface or the ORAData
interface, according to how you set the JPublisher type mappings.
If you use the ORAData
interface, then JPublisher will also create a custom reference class to map to object references for the Oracle object type. If you use the SQLData
interface, then JPublisher will not produce a custom reference class. You would use standard java.sql.Ref
instances instead.
If you want additional functionality, you can subclass the custom object class and add features as desired. When you run JPublisher, there is a command-line option for specifying both a generated class name and the name of the subclass you will implement. For the SQL-Java mapping to work properly, JPublisher must know the subclass name, which is incorporated into some of the functionality of the generated class.
Note:
Hand-editing the JPublisher-generated class, instead of subclassing it, is not recommended. If you hand-edit this class and later have to re-run JPublisher for some reason, you would have to re-implement your changes.JPublisher offers various choices for how to map user-defined types and their attribute types between SQL and Java. This section lists categories of SQL types and the mapping options available for each category.
JPublisher categorizes SQL types into the following groups, with corresponding JPublisher options as specifies:
User-defined types (UDT)
This includes Oracle objects, references, and collections. You use the JPublisher -usertypes
option to specify the type-mapping implementation for UDTs, either a standard SQLData
implementation or an Oracle-specific ORAData
implementation.
Numeric types
This includes anything stored in the database as the NUMBER
SQL type. You use the JPublisher -numbertypes
option to specify type-mapping for numeric types.
Large object (LOB) types
This includes the SQL types, BLOB
and CLOB
. You use the JPublisher -lobtypes
option to specify type-mapping for LOB types.
Built-in types
This includes anything stored in the database as a SQL type not covered by the preceding categories. For example, CHAR
, VARCHAR2
, LONG
, and RAW
. You use the JPublisher -builtintypes
option to specify type-mapping for built-in types.
JPublisher defines the following type-mapping modes, two of which apply to numeric types only:
Uses standard default mappings between SQL types and Java native types. For a custom object class, uses a SQLData
implementation.
Oracle mapping (setting oracle
)
Uses corresponding oracle.sql
types to map to SQL types. For a custom object, reference, or collection class, uses a ORAData
implementation.
Object-JDBC mapping (setting objectjdbc
)
Is an extension of the JDBC mapping. Where relevant, object-JDBC mapping uses numeric object types from the standard java.lang
package, such as java.lang.Integer
, Float
, and Double
, instead of primitive Java types, such as int
, float
, and double
. The java.lang
types are nullable, while the primitive types are not.
BigDecimal
mapping (setting bigdecimal
)
Uses java.math.BigDecimal
to map to all numeric attributes. This is appropriate if you are dealing with large numbers but do not want to map to the oracle.sql.NUMBER
class.
Note:
UsingBigDecimal
mapping can significantly degrade performance.Mapping the Oracle object type to Java
Use the JPublisher -usertypes
option to determine how JPublisher will implement the custom Java class that corresponds to a Oracle object type:
A setting of -usertypes=oracle
, which is the default setting, instructs JPublisher to create a ORAData
implementation for the custom object class. This will also result in JPublisher producing a ORAData
implementation for the corresponding custom reference class.
A setting of -usertypes=jdbc
instructs JPublisher to create a SQLData
implementation for the custom object class. No custom reference class can be created. You must use java.sql.Ref
or oracle.sql.REF
for the reference type.
Note:
You can also use JPublisher with a-usertypes=oracle
setting in creating ORAData
implementations to map SQL collection types.
The -usertypes=jdbc
setting is not valid for mapping SQL collection types. The SQLData
interface is intended only for mapping Oracle object types.
Mapping Attribute Types to Java
If you do not specify mappings for the attribute types of the Oracle object type, then JPublisher uses the following defaults:
For numeric attribute types, the default mapping is object-JDBC.
For LOB attribute types, the default mapping is Oracle.
For built-in type attribute types, the default mapping is JDBC.
If you want alternate mappings, then use the -numbertypes
, -lobtypes
, and -builtintypes
options, as necessary, depending on the attribute types you have and the mappings you desire.
If an attribute type is itself an Oracle object type, then it will be mapped according to the -usertypes
setting.
Important:
Be aware that if you specify anSQLData
implementation for the custom object class and want the code to be portable, then you must be sure to use portable mappings for the attribute types. The defaults for numeric types and built-in types are portable, but for LOB types you must specify -lobtypes=jdbc
.Summary of SQL Type Categories and Mapping Settings
Table 15-1 summarizes JPublisher categories for SQL types, the mapping settings relevant for each category, and the default settings.
Table 15-1 JPublisher SQL Type Categories, Supported Settings, and Defaults
SQL Type Category | JPublisher Mapping Option | Mapping Settings | Default |
---|---|---|---|
UDT types |
-usertypes |
oracle, jdbc |
oracle |
numeric types |
-numbertypes |
oracle, jdbc, objectjdbc, bigdecimal |
objectjdbc |
LOB types |
-lobtypes |
oracle, jdbc |
oracle |
built-in types |
-builtintypes |
oracle, jdbc |
jdbc |
Oracle JDBC includes functionality to retrieve information about a structured object type regarding its attribute names and types. This is similar conceptually to retrieving information from a result set about its column names and types, and in fact uses an almost identical method.
This section covers the following topics:
The oracle.sql.StructDescriptor
class includes functionality to retrieve meta data about a structured object type. The StructDescriptor
class has a getMetaData
method with the same functionality as the standard getMetaData
method available in result set objects. It returns a set of attribute information, such as attribute names and types. Call this method on a StructDescriptor
object to get meta data about the Oracle object type that the StructDescriptor
object describes.
The signature of the StructDescriptor
class getMetaData
method is the same as the signature specified for getMetaData
in the standard ResultSet
interface. The signature is as follows:
ResultSetMetaData getMetaData() throws SQLException
However, this method actually returns an instance of oracle.jdbc.StructMetaData
, a class that supports structured object meta data in the same way that the standard java.sql.ResultSetMetaData
interface specifies support for result set meta data.
The StructMetaData
class includes the following standard methods that are also specified by ResultSetMetaData
:
String getColumnName(int column) throws SQLException
This returns a String
that specifies the name of the specified attribute, such as salary
.
int getColumnType(int column) throws SQLException
This returns an int
that specifies the type code of the specified attribute, according to the java.sql.Types
and oracle.jdbc.OracleTypes
classes.
String getColumnTypeName(int column) throws SQLException
This returns a string that specifies the type of the specified attribute, such as BigDecimal
.
int getColumnCount() throws SQLException
This returns the number of attributes in the object type.
The following method is also supported by StructMetaData
:
String getOracleColumnClassName(int column) throws SQLException
This method returns the fully-qualified name of the oracle.sql.Datum
subclass whose instances are manufactured if the OracleResultSet
class getOracleObject
method is called to retrieve the value of the specified attribute. For example, oracle.sql.NUMBER
.
To use the getOracleColumnClassName
method, you must cast the ResultSetMetaData
object, which that was returned by the getMetaData
method, to StructMetaData
.
Note:
In all the preceding method signatures,column
is something of a misnomer. Where you specify a value of 4 for column
, you really refer to the fourth attribute of the object.Use the following steps to obtain meta data about a structured object type:
Create or acquire a StructDescriptor
instance that describes the relevant structured object type.
Call the getMetaData
method on the StructDescriptor
instance.
Call the meta data getter methods, getColumnName
, getColumnType
, and getColumnTypeName
, as desired.
Note:
If one of the structured object attributes is itself a structured object, repeat steps 1 through 3.The following method shows how to retrieve information about the attributes of a structured object type. This includes the initial step of creating a StructDescriptor
instance.
// // Print out the ADT's attribute names and types // void getAttributeInfo (Connection conn, String type_name) throws SQLException { // get the type descriptor StructDescriptor desc = StructDescriptor.createDescriptor (type_name, conn); // get type meta data ResultSetMetaData md = desc.getMetaData (); // get # of attrs of this type int numAttrs = desc.length (); // temporary buffers String attr_name; int attr_type; String attr_typeName; System.out.println ("Attributes of "+type_name+" :"); for (int i=0; i<numAttrs; i++) { attr_name = md.getColumnName (i+1); attr_type = md.getColumnType (i+1); System.out.println (" index"+(i+1)+" name="+attr_name+" type="+attr_type); // drill down nested object if (attrType == OracleTypes.STRUCT) { attr_typeName = md.getColumnTypeName (i+1); // recursive calls to print out nested object meta data getAttributeInfo (conn, attr_typeName); } } }