This chapter describes how to use Java Database Connectivity (JDBC) and the oracle.sql.*
classes to access and manipulate large object (LOB) and binary file (BFILE) locators and data. This chapter contains the following sections:
Notes:
In Oracle Database 10g, the Oracle JDBC drivers support the JDBC 3.0 java.sql.Clob
and java.sql.Blob
interfaces. Certain Oracle extensions made in oracle.sql.CLOB
and oracle.sql.BLOB
in earlier Oracle Database releases are no longer necessary and are deprecated. You should port your application to the standard JDBC 3.0 interface.
Prior to Oracle Database 10g, the maximum size of a LOB was 232 bytes. This restriction is removed in Oracle Database 10g, and the maximum size is now limited to the size of available physical storage. The Java LOB application programming interface (API) has not changed.
LOBs are stored in a way that optimizes space and provides efficient access. The JDBC drivers provide support for two types of LOB: binary large object (BLOB), which is used for unstructured binary data, and character large object (CLOB), which is used for character data. BLOB and CLOB data is accessed and referenced by using a locator that is stored in the database table and points to the BLOB or CLOB data, which is outside the table.
BFILEs are large binary data objects stored in operating system files outside of database tablespaces. These files use reference semantics. They can also be located on tertiary storage devices, such as hard disks, CD-ROMs, PhotoCDs, and DVDs. As with BLOBs and CLOBs, a BFILE is accessed and referenced by a locator which is stored in the database table and points to the BFILE data.
To work with LOB data, you must first obtain a LOB locator. Then you can read or write LOB data and perform data manipulation.
The JDBC drivers support the following oracle.sql.*
classes for BLOBs, CLOBs, and BFILEs:
oracle.sql.BLOB
oracle.sql.CLOB
oracle.sql.BFILE
The oracle.sql.BLOB
and oracle.sql.CLOB
classes implement the java.sql.Blob
and java.sql.Clob
interfaces, respectively. In contrast, BFILE
is an Oracle extension, without a corresponding java.sql
interface.
Instances of these classes contain only the locators for these data types, not the data. After accessing the locators, you must perform some additional steps to access the data.
Note:
Your code cannot call theBLOB
, CLOB
, or BFILE
constructors. To create a new LOB use the createTemporary
, getEmptyCLOB
, or getEmptyBLOB
methods.This section describes how to read and write data to and from BLOBs and CLOBs in Oracle Database, using LOB locators. This section covers the following topics:
Standard as well as Oracle-specific getter and setter methods are available for retrieving or passing LOB locators from or to the database. This section covers the following topics:
Given a standard JDBC result set or callable statement that includes BLOB or CLOB locators, you can access the locators by using standard getter methods. You can use the standard getBlob
and getClob
methods, which return java.sql.Blob
and Clob
objects, respectively.
Note:
All the standard and Oracle-specific getter methods discussed here take either anint
column index or a String
column name as input.If you retrieve or cast the result set or the callable statement to OracleResultSet
or OracleCallableStatement
, then you can use Oracle extensions, as follows:
You can use getBLOB
and getCLOB
, which return oracle.sql.BLOB
and CLOB
objects, respectively.
You can also use the getOracleObject
method, which returns an oracle.sql.Datum
object, and cast the output appropriately.
Example: Getting BLOB and CLOB Locators from a Result Set
Assume the database has a table called lob_table
with a column for a BLOB locator, blob_col
, and a column for a CLOB locator, clob_col
. This example assumes that you have already created the Statement
object, stmt
.
First, select the LOB locators into a standard result set, then get the LOB data into appropriate Java classes:
// Select LOB locator into standard result set.
ResultSet rs =
stmt.executeQuery ("SELECT blob_col, clob_col FROM lob_table");
while (rs.next())
{
// Get LOB locators into Java wrapper classes.
java.sql.Blob blob = (java.sql.Blob)rs.getObject(1);
java.sql.Clob clob = (java.sql.Clob)rs.getObject(2);
(...process...)
}
The output is cast to java.sql.Blob
and java.sql.Clob
. As an alternative, you can cast the output to oracle.sql.BLOB
and oracle.sql.CLOB
to take advantage of extended functionality offered by the oracle.sql.*
classes. For example, you can rewrite the preceding code to get the LOB locators as:
// Get LOB locators into Java wrapper classes.
oracle.sql.BLOB blob = (BLOB)rs.getObject(1);
oracle.sql.CLOB clob = (CLOB)rs.getObject(2);
(...process...)
Example: Getting a CLOB Locator from a Callable Statement
The callable statement methods for retrieving LOBs are identical to the result set methods.
For example, if you have an OracleCallableStatement
instance, ocs
, that calls a function func
that has a CLOB output parameter, then set up the callable statement as in the following example.
This example registers OracleTypes.CLOB
as the type code of the output parameter.
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{? = call func()}"); ocs.registerOutParameter(1, OracleTypes.CLOB); ocs.execute(); oracle.sql.CLOB clob = ocs.getCLOB(1);
Given a standard JDBC prepared statement or callable statement, you can use standard setter methods to pass LOB locators. These methods are defined as follows:
public void setBlob(int index, Blob value); public void setClob(int index, Clob value);
Note:
If you pass a BLOB to a PL/SQL procedure, then the BLOB must be no bigger than 32K - 7. If you pass a BLOB that exceeds this limit, then you will receive aSQLException
.Given an Oracle-specific OraclePreparedStatement
or OracleCallableStatement
, then you can use Oracle extensions as follows:
Use setBLOB
and setCLOB
, which take oracle.sql.BLOB
and CLOB
locators as input, respectively.
Use the setOracleObject
method, which simply specifies an oracle.sql.Datum
input.
Example: Passing a BLOB Locator to a Prepared Statement
If you have an OraclePreparedStatement
object ops
and a BLOB named my_blob
, then write the BLOB to the database as follows:
OraclePreparedStatement ops = (OraclePreparedStatement)conn.prepareStatement ("INSERT INTO blob_table VALUES(?)"); ops.setBLOB(1, my_blob); ops.execute();
Example: Passing a CLOB Locator to a Callable Statement
If you have an OracleCallableStatement
object ocs
and a CLOB named my_clob
, then input the CLOB to the stored procedure proc
as follows:
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{call proc(?))}"); ocs.setClob(1, my_clob); ocs.execute();
Once you have a LOB locator, you can use JDBC methods to read and write the LOB data. LOB data is materialized as a Java array or stream. However, unlike most Java streams, a locator representing the LOB data is stored in the table. Thus, you can access the LOB data at any time during the life of the connection.
To read and write the LOB data, use the methods in the oracle.sql.BLOB
or oracle.sql.CLOB
class, as appropriate. These classes provide functionality such as reading from the LOB into an input stream, writing from an output stream into a LOB, determining the length of a LOB, and closing a LOB.
Notes:
To write LOB data, the application must acquire a write lock on the LOB object. One way to accomplish this is through aSELECT FOR UPDATE
. Also, you must disable auto-commit mode.To read and write LOB data, you can use these methods:
To read from a BLOB, use the getBinaryStream
method of an oracle.sql.BLOB
object to retrieve the entire BLOB
as an input stream. This returns a java.io.InputStream
object.
As with any InputStream
object, use one of the overloaded read
methods to read the LOB data and use the close
method when you finish.
To write to a BLOB, use the setBinaryStream
method of an oracle.sql.BLOB
object to retrieve the BLOB as an output stream. This returns a java.io.OutputStream
object to be written back to the BLOB.
As with any OutputStream
object, use one of the overloaded write
methods to update the LOB data and use the close
method when you finish.
To read from a CLOB, use the getAsciiStream
or getCharacterStream
method of an oracle.sql.CLOB
object to retrieve the entire CLOB as an input stream. The getAsciiStream
method returns an ASCII input stream in a java.io.InputStream
object. The getCharacterStream
method returns a Unicode
input stream in a java.io.Reader
object.
As with any InputStream
or Reader
object, use one of the overloaded read
methods to read the LOB data and use the close
method when you finish.
You can also use the getSubString
method of oracle.sql.CLOB
object to retrieve a subset of the CLOB as a character string of type java.lang.String
.
To write to a CLOB, use the setAsciiStream
or setCharacterStream
method of an oracle.sql.CLOB
object to retrieve the CLOB as an output stream to be written back to the CLOB. The setAsciiStream
method returns an ASCII output stream in a java.io.OutputStream
object. The setCharacterStream
method returns a Unicode output stream in a java.io.Writer
object.
As with any Stream
or Writer
object, use one of the overloaded write
methods to update the LOB data and use the flush
and close
methods when you finish.
Notes:
The stream write methods described in this section write directly to the database when you write to the output stream. You do not need to run an UPDATE
to write the data. However, you need to call close
or flush
to ensure all changes are written. CLOBs and BLOBs are transaction controlled. After writing to either, you must commit the transaction for the changes to be permanent. BFILEs are not transaction controlled. Once you write to them the changes are permanent, even if the transaction is rolled back, unless the external file system does something else.
When writing to or reading from a CLOB, the JDBC drivers perform all character set conversions for you.
Use the getBinaryStream
method of the oracle.sql.BLOB
class to read BLOB data. The getBinaryStream
method provides access to the BLOB data through a binary stream.
The following example uses the getBinaryStream
method to read BLOB data through a byte stream and then reads the byte stream into a byte array, returning the number of bytes read, as well.
// Read BLOB data from BLOB locator. InputStream byte_stream = my_blob.getBinaryStream(1L); byte [] byte_array = new byte [10]; int bytes_read = byte_stream.read(byte_array); ...
The following example uses the getCharacterStream
method to read CLOB
data into a Unicode character stream. It then reads the character stream into a character array, returning the number of characters read, as well.
// Read CLOB data from CLOB locator into Reader char stream. Reader char_stream = my_clob.getCharacterStream(1L); char [] char_array = new char [10]; int chars_read = char_stream.read (char_array, 0, 10); ...
The next example uses the getAsciiStream
method of the oracle.sql.CLOB
class to read CLOB data through an ASCII character stream. It then reads the ASCII stream into a byte array, returning the number of bytes read, as well.
// Read CLOB data from CLOB locator into Input ASCII character stream Inputstream asciiChar_stream = my_clob.getAsciiStream(1L); byte[] asciiChar_array = new byte[10]; int asciiChar_read = asciiChar_stream.read(asciiChar_array,0,10);
Use the setBinaryOutputStream
method of an oracle.sql.BLOB
object to write BLOB data.
The following example reads a vector of data into a byte array, then uses the setBinaryOutputStream
method to write an array of character data to a BLOB.
java.io.OutputStream outstream; // read data into a byte array byte[] data = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; // write the array of binary data to a BLOB outstream = ((BLOB)my_blob).setBinaryOutputStream(1L); outstream.write(data); ...
Use the setCharacterStream
method or the setAsciiStream
method to write data to a CLOB. The setCharacterStream
method returns a Unicode
output stream. The setAsciiStream
method returns an ASCII output stream.
The following example reads a vector of data into a character array, then uses the setCharacterStream
method to write the array of character data to a CLOB.
java.io.Writer writer; // read data into a character array char[] data = {'0','1','2','3','4','5','6','7','8','9'}; // write the array of character data to a CLOB writer = ((CLOB)my_clob).setCharacterStream(); writer.write(data); writer.flush(); writer.close(); ...
The next example reads a vector of data into a byte array, then uses the setAsciiStream
method to write the array of ASCII data to a CLOB.
java.io.OutputStream out; // read data into a byte array byte[] data = {'0','1','2','3','4','5','6','7','8','9'}; // write the array of ascii data to a CLOB out = clob.setAsciiStream(); out.write(data); out.flush(); out.close();
Create and populate a BLOB
or CLOB
column in a table by using SQL statements.
Note:
You cannot construct a newBLOB
or CLOB
locator in your application with a Java new
statement. You must create the locator through a SQL operation, and then select it into your application or with the createTemporary
or empty_lob
methods.Create a BLOB
or CLOB
column in a table with the SQL CREATE TABLE
statement, then populate the LOB. This includes creating the LOB entry in the table, obtaining the LOB locator, and then copying the data into the LOB.
Creating a BLOB or CLOB Column in a New Table
To create a BLOB
or CLOB
column in a new table, run the SQL CREATE TABLE
statement. The following example code creates a BLOB
column in a new table. This example assumes that you have already created your Connection
object conn
and Statement
object stmt
:
String cmd = "CREATE TABLE my_blob_table (x VARCHAR2 (30), c BLOB)"; stmt.execute (cmd);
In this example, the VARCHAR2
column designates a row number, such as 1 or 2, and the BLOB
column stores the locator of the BLOB data.
Populating a BLOB or CLOB Column in a New Table
This example demonstrates how to populate a BLOB
or CLOB
column by reading data from a stream. These steps assume that you have already created your Connection
object conn
and Statement
object stmt
. The table my_blob_table
is the table that was created in the previous section.
The following example writes the john.gif
file to a BLOB:
Begin by using SQL statements to create the BLOB entry in the table. Use the empty_blob
function to create the BLOB locator.
stmt.execute ("INSERT INTO my_blob_table VALUES ('row1', empty_blob())");
Get the BLOB locator from the table.
BLOB blob; cmd = "SELECT * FROM my_blob_table WHERE X='row1' FOR UPDATE"; ResultSet rset = stmt.executeQuery(cmd); rset.next(); BLOB blob = ((OracleResultSet)rset).getBLOB(2);
Note:
You must disable auto-commit mode.Declare a file handler for the john.gif
file, then print the length of the file. This value will be used later to ensure that the entire file is read into the BLOB. Next, create a FileInputStream
object to read the contents of the file, and an OutputStream
object to retrieve the BLOB as a stream.
File binaryFile = new File("john.gif"); System.out.println("john.gif length = " + binaryFile.length()); FileInputStream instream = new FileInputStream(binaryFile); OutputStream outstream = blob.setBinaryStream(1L);
Call getBufferSize
to retrieve the ideal buffer size to use in writing to the BLOB, then create the buffer
byte array.
int size = blob.getBufferSize(); byte[] buffer = new byte[size]; int length = -1;
Use the read
method to read the file to the byte array buffer
, then use the write
method to write it to the BLOB. When you finish, close the input and output streams and commit the changes.
while ((length = instream.read(buffer)) != -1) outstream.write(buffer, 0, length); instream.close(); outstream.close(); conn.commit();
Once your data is in the BLOB or CLOB, you can manipulate the data.
Once you have your BLOB or CLOB locator in a table, you can access and manipulate the data to which it points. To access and manipulate the data, you first must select their locators from a result set or from a callable statement.
After you select the locators, you can retrieve the BLOB or CLOB data. You will usually want to cast the result set to OracleResultSet
, so that you can retrieve the data in oracle.sql.*
format. After retrieving the BLOB or CLOB data, you can manipulate it however you want.
This example is a continuation of the example in the previous section. It uses the SQL SELECT
statement to select the BLOB locator from the table my_blob_table
into a result set. The result of the data manipulation is to print the length of the BLOB in bytes.
// Select the blob - what we are really doing here // is getting the blob locator into a result set BLOB blob; cmd = "SELECT * FROM my_blob_table"; ResultSet rset = stmt.executeQuery (cmd); // Get the blob data - cast to OracleResult set to // retrieve the data in oracle.sql format String index = ((OracleResultSet)rset).getString(1); blob = ((OracleResultSet)rset).getBLOB(2); // get the length of the blob int length = blob.length(); // print the length of the blob System.out.println("blob length" + length); // read the blob into a byte array // then print the blob from the array byte bytes[] = blob.getBytes(1, length); blob.printBytes(bytes, length);
In addition to what has already been discussed in this chapter, the oracle.sql.BLOB
and oracle.sql.CLOB
classes have a number of methods for further functionality.
Note:
Theoracle.sql.CLOB
class supports all the character sets that the Oracle data server supports for CLOB types.The oracle.sql.BLOB
class includes the following methods:
close
Closes the BLOB associated with the locator.
freeTemporary
Frees the storage used by a temporary BLOB.
Returns the ideal buffer size, according to calculations by the JDBC driver, to use in reading and writing BLOB data. This value is a multiple of the chunk size and is close to 32K.
Reads from the BLOB data, starting at a specified point, into a supplied buffer. The method returns a byte
array which holds the contents of the BLOB.
Notes:
In releases prior to Oracle Database 10g release 2 (10.2), thegetBytes
method when used on a BLOB
column or output parameter incorrectly returns the bytes of the LOB
locator, which is internal data and should not be used by applications. However, in Oracle Database 10g release 2 (10.2) the getBytes
method returns a byte
array that holds the contents of the BLOB
.
This method can give errors for BLOB
data that exceed available memory or the size imposed by the Java language.
Returns the Oracle chunking size, which can be specified by the database administrator when the LOB column is first created. This value, in Oracle blocks, determines the size of the chunks of data read or written by the LOB data layer in accessing or modifying the BLOB value. Part of each chunk stores system-related information, and the rest stores LOB data. Performance is enhanced if read and write requests use some multiple of the chunk size.
isOpen
Returns true
if the BLOB was opened by calling the open
method; otherwise, it returns false
.
isTemporary
Returns true if the BLOB is a temporary BLOB.
Returns the length of the BLOB in bytes.
open
Opens the BLOB associated with the locator.
open(int)
Opens the BLOB associated with the locator in the mode specified by the argument.
Determines the byte position in the BLOB where a given pattern begins.
Returns the BLOB data for this Blob
instance as a stream of bytes beginning at the position in the BLOB specified in the argument.
Writes BLOB data, starting at a specified point, from a supplied buffer.
truncate(long)
Trims the value of the BLOB to the length specified by the argument.
The oracle.sql.CLOB
class includes the following methods:
close
Closes the CLOB associated with the locator.
freeTemporary
Frees the storage used by a temporary CLOB.
Returns the CLOB value designated by the Clob
object as a stream of ASCII bytes.
getAsciiStream(long)
Returns the CLOB value designated by the CLOB object as a stream of ASCII bytes, beginning at the position in the CLOB specified by the argument.
Returns the ideal buffer size, according to calculations by the JDBC driver, to use in reading and writing CLOB data. This value is a multiple of the chunk size and is close to 32K.
Returns the CLOB data as a stream of Unicode characters.
getCharacterStream(long)
Returns the CLOB data as a stream of Unicode characters beginning at the position in the CLOB specified by the argument.
Retrieves characters from a specified point in the CLOB data into a character array.
Returns the Oracle chunking size, which can be specified by the database administrator when the LOB column is first created. This value, in Oracle blocks, determines the size of the chunks of data read or written by the LOB data layer in accessing or modifying the CLOB value. Part of each chunk stores system-related information and the rest stores LOB data. Performance is enhanced if you make read and write requests using some multiple of the chunk size.
Retrieves a substring from a specified point in the CLOB data.
isOpen
Returns true
if the CLOB was opened by calling the open
method; otherwise, it returns false
.
isTemporary
Returns true
if and only if the CLOB is a temporary CLOB.
Returns the length of the CLOB in characters.
open
Opens the CLOB associated with the locator.
open(int)
Opens the CLOB associated with the locator in the mode specified by the argument.
Determines the character position in the CLOB at which a given substring begins.
Writes characters from a character array to a specified point in the CLOB data.
Returns a java.io.OutputStream
object to write data to the CLOB as a stream. The data is written beginning at the position in the CLOB specified by the argument.
Returns a java.io.Writer
object to write data to the CLOB as a stream. The data is written beginning at the position in the CLOB specified by the argument.
setString(long pos, String str)
Writes a string to a specified point in the CLOB data.
truncate(long)
Trims the value of the CLOB to the length specified by the argument.
Before writing data to an internal LOB, you must make sure the LOB column/attribute is not null
. It must contain a locator. You can accomplish this by initializing the internal LOB as an empty LOB in an INSERT
or UPDATE
statement, using the getEmpty
XXX
methods defined in the oracle.sql.BLOB
and oracle.sql.CLOB
classes:
public static BLOB getEmptyBLOB() throws SQLException
public static CLOB getEmptyCLOB() throws SQLException
A JDBC driver creates an empty LOB
instance without making database round trips. You can use empty LOBs in the following:
attributes of STRUCT
objects
elements of ARRAY
objects
Note:
Because agetEmpty
XXX
method creates a special marker that does not contain a locator, a JDBC application cannot read or write to it. The JDBC driver throws the exception ORA-17098 Invalid empty LOB operation
, if a JDBC application attempts to read or write to an empty LOB before it is stored in the database.The data interface for LOBs provides a streamlined mechanism for writing and reading the entire LOB contents. It is simpler to code and faster in many cases. It does not provide the random access capability or access beyond 2147483648 elements as do the standard java.sql.Blob
and java.sql.Clob
interfaces and the Oracle extensions, oracle.sql.BLOB
, oracle.sql.BFILE
, and oracle.sql.CLOB
.
In Oracle Database 10g release 2 (10.2), the setBytes
, setBinaryStream
, setString
, setCharacterStream
, and setAsciiStream
methods of PreparedStatement
are extended for BLOB
and CLOB
parameters.
For the JDBC Oracle Call Interface (OCI) and Thin drivers there is no limitation on the size of the byte
array or String
and no limit on the length specified for the stream functions except the limits imposed by the Java language, which is that array sizes are limited to positive Java int
or 2147483648 elements.
For the server side internal driver there is currently a limitation of 4000 bytes for operations on SQL statements, such as an INSERT
statement. The limitation does not apply for PL/SQL statements. There is a simple workaround for an INSERT
statement, which is to wrap it in a PL/SQL block, as follows:
BEGIN INSERT id, c INTO clob_tab VALUES(?,?); END;
You must bear in mind the following automatic switching of the input mode for large data:
For SQL statements:
setBytes
switches to setBinaryStream
for data larger than 2000 bytes
setString
switches to setCharacterStream
for data larger than 32766 characters
PL/SQL statements
setBytes
switches to setBinaryStream
for data larger than 2000 bytes and to setBytesForBlob
for data larger that 32512 bytes
setString
switches to setStringForClob
for string data larger than 32512 bytes in the database character set or national character set depending on whether setFormOfUse
has been used for NCLOB
parameters
This will have impact on some programs, which formerly got ORA-17157
errors for attempts to use setString
for String
values larger than 32766 characters. Now, depending on the type of the target parameter an error may occur while the application is executed or the operation may succeed.
Another impact is that the automatic switching may result in additional server side parsing to adapt to the change in the parameter type. This would result in a performance effect if the data sizes vary above and below the limit for repeated executions of the statement. Switching to the stream modes will effect batching as well.
Oracle Database 10g release 1 (10.1) has the SetBigStringTryClob
connection property. Setting this property causes the standard setString
method to switch to setStringForClob
method for large data. This property is no longer used or needed. The setBytesForBlob
and setStringForClob
methods create temporary LOBs, which are automatically freed when the statement is executed or closed before execution.
However, when a PL/SQL procedure or function is embedded in a SQL statement, data less than 4 KB is bound as String
, which is the standard. When data is greater than 4KB, the driver binds the data as a String
as for any SQL statement. This will throw an error. The workaround is to use setClob
or setCharacterStream
instead of setString
or setStringForClob
. You can also create a callable statement.
The getBytes
, getBinaryStream
, getSting
, getCharacterStream
, and getAsciiStream
methods of ResultSet
and CallableStatement
are extended to work with BLOB
, CLOB
, and BFILE
columns or OUT
parameters. These methods will work for any LOB of length less than 2147483648. This operates entirely on the client-side and will work with any supported version of the database, that is, Oracle Database 8.1.7 and later.
BLOB
, BFILE
, or CLOB
data can be read and written using the same streaming mechanism as for LONG RAW
and LONG
data. To read, use defineColumnType(nn, Types.LONGVARBINARY)
or defineColumnType(nn,Types.LONGVARCHAR)
on the column. This produces a direct stream on the data as if it were a LONG RAW
or LONG
column. This technique is limited to Oracle Database 10g release 1 (10.1) and later.
CallableSatement and IN OUT Parameter
It is a PL/SQL requirement that the Java types used as input and output for an IN OUT parameter must be the same. The automatic switching of types done by the extensions described in this chapter may cause problems with this.
Consider that you have an IN OUT CLOB
parameter of a stored procedure and you wish to use setString
for setting the value for this parameter. For any IN
and OUT
parameter, the binds must be of the same type. The automatic switching of the input mode will cause problems unless you are sure of the data sizes. For example, if it is known that neither the input nor output data will ever be larger than 32512 bytes, then you could use setString
for the input parameter and register the OUT
parameter as Types.VARCHAR
and use getString
for the output parameter.
A better solution is to change the stored procedure to have separate IN
and OUT
parameters. That is, if you have:
CREATE PROCEDURE clob_proc( c IN OUT CLOB );
then, change it to:
CREATE PROCEDURE clob_proc( c_in IN CLOB, c_out OUT CLOB );
Another workaround is to use a wrapper block to make the call. The clob_proc
procedure can be wrapped with a Java string to use for the prepareCall
statement, as follows:
"DECLARE c_temp; BEGIN c_temp := ?; clob_proc( c_temp); ? := c_temp; END;"
In either case you may use setString
on the first parameter and registerOutParameter
with Types.CLOB
on the second.
Please be aware of the effect on the performance of the Java memory management system due to creation of very large byte
array or String
. Please read the information provided by your Java virtual machine (JVM) vendor about the impact of very large data elements on memory management, and consider using the stream interfaces instead.
You can use temporary LOBs to store transient data. The data is stored in temporary table space rather than regular table space. You should free temporary LOBs after you no longer need them. If you do not, then the space the LOB consumes in temporary table space will not be reclaimed.
You can insert temporary LOBs into a table. When you do this, a permanent copy of the LOB is created and stored. Inserting a temporary LOB may be preferable for some situations. For example, if the LOB data is relatively small so that the overhead of copying the data is less than the cost of a database round trip to retrieve the empty locator. Remember that the data is initially stored in the temporary table space on the server and then moved into permanent storage.
You create a temporary LOB with the static
method createTemporary(Connection, boolean, int)
. This method is defined in both the oracle.sql.BLOB
and oracle.sql.CLOB
classes. You free a temporary LOB with the freeTemporary
method.
public static BLOB createTemporary(Connection conn, boolean isCached, int duration); public static CLOB createTemporary(Connection conn, boolean isCached, int duration);
The duration must be either DURATION_SESSION
or DURATION_CALL
as defined in the oracle.sql.BLOB
or oracle.sql.CLOB
class. In client applications, DURATION_SESSION
is appropriate. In Java stored procedures, you can use either DURATION_SESSION
or DURATION_CALL
, which ever is appropriate.
You can test whether a LOB is temporary by calling the isTemporary
method. If the LOB was created by calling the createTemporary
method, then the isTemporary
method returns true
, else it returns false
.
You can free a temporary LOB by calling the freeTemporary
method. Free any temporary LOBs before ending the session or call. Otherwise, the storage used by the temporary LOB will not be reclaimed.
Notes:
Failure to free a temporary LOB will result in the storage used by that LOB in the database being unavailable. Frequent failure to free temporary LOBs will result in filling up temporary table space with unavailable LOB storage.
When fetching data from a ReultSet
with columns that are temporary LOBs, use getClob
or getBlob
instead of getString
or getBytes
. Also invoke freeTemporary
to free the temporary LOBs.
You create temporary national character large objects (NCLOBs) using a variant of the createTemporary
method.
CLOB.createTemporary (Connection conn, boolean cache, int duration, short form);
The form
argument specifies whether the created LOB is a CLOB or an NCLOB. If form
equals oracle.jdbc.OraclePreparedStatement.FORM_NCHAR
, then the method creates an NCLOB. If form
equals oracle.jdbc.OraclePreparedStatement.FORM_CHAR
, then the method creates a CLOB.
You do not have to open and close your LOBs. You may choose to open and close them for performance reasons.
If you do not wrap LOB operations inside an Open/Close call operation, then each modification to the LOB will implicitly open and close the LOB, thereby firing any triggers on a domain index. Note that in this case, any domain indexes on the LOB will become updated as soon as LOB modifications are made. Therefore, domain LOB indexes are always valid and may be used at any time.
If you wrap your LOB operations inside the Open/Close call operation, then triggers will not be fired for each LOB modification. Instead, the trigger on domain indexes will be fired at the Close call. For example, you might design your application so that domain indexes are not be updated until you call the close
method. However, this means that any domain indexes on the LOB will not be valid in-between the Open/Close calls.
You open a LOB by calling the open
or open(int)
method. You may then read and write the LOB without any triggers associated with that LOB firing. When you are done accessing the LOB, close the LOB by calling the close
method. When you close the LOB, any triggers associated with the LOB will fire. You can see if a LOB is open or closed by calling the isOpen
method. If you open the LOB by calling the open(int)
method, the value of the argument must be either MODE_READONLY
or MODE_READWRITE
, as defined in the oracle.sql.BLOB
and oracle.sql.CLOB
classes. If you open the LOB with MODE_READONLY
, any attempt to write to the LOB will result in a SQL exception.
Note:
An error occurs if you commit the transaction before closing all LOBs that were opened by the transaction. The openness of the open LOBs is discarded, but the transaction is successfully committed. Hence, all the changes made to the LOB and non-LOB data in the transaction are committed, but the triggers for domain indexing are not fixed.This section describes how to read and write data to and from BFILEs, using file locators. This section covers the following topics:
Getter and setter methods are available for retrieving or passing BFILE locators from or to the database.
Given a standard JDBC result set or callable statement object that includes BFILE locators, you can access the locators by using the standard result set
getObject
method. This method returns an oracle.sql.BFILE
object.
You can also access the locators by casting your result set to OracleResultSet
or your callable statement to OracleCallableStatement
and using the getOracleObject
or getBFILE
method.
Notes:
In the OracleResultSet
and OracleCallableStatement
classes, getBFILE
and getBfile
both return oracle.sql.BFILE
. There is no java.sql
interface for BFILEs.
If using getObject
or getOracleObject
, remember to cast the output, as necessary.
Example: Getting a BFILE locator from a Result Set
Assume that the database has a table called bfile_table
with a single column for the BFILE locator bfile_col
. This example assumes that you have already created your Statement
object stmt
.
Select the BFILE locator into a standard result set. If you cast the result set to OracleResultSet
, then you can use getBFILE
to get the BFILE locator, as follows:
// Select the BFILE locator into a result set ResultSet rs = stmt.executeQuery("SELECT bfile_col FROM bfile_table"); while (rs.next()) { oracle.sql.BFILE my_bfile = ((OracleResultSet)rs).getBFILE(1); }
Note that as an alternative, you can use getObject
to return the BFILE locator. In this case, because getObject
returns a java.lang.Object
, cast the results to BFILE
. For example:
oracle.sql.BFILE my_bfile = (BFILE)rs.getObject(1);
Example: Getting a BFILE Locator from a Callable Statement
Assume you have an OracleCallableStatement
object ocs
that calls a function func
that has a BFILE
output parameter. The following code example sets up the callable statement, registers the output parameter as OracleTypes.BFILE
, runs the statement, and retrieves the BFILE locator:
OracleCallableStatement ocs = (OracleCallableStatement)conn.prepareCall("{? = call func()}"); ocs.registerOutParameter(1, OracleTypes.BFILE); ocs.execute(); oracle.sql.BFILE bfile = ocs.getBFILE(1);
To pass a BFILE locator to a prepared statement or callable statement, you can do one of the following:
Cast the statement to OraclePreparedStatement
or OracleCallableStatement
, and use the setOracleObject
or setBFILE
method.
These methods take the parameter index and an oracle.sql.BFILE
object as input.
Example: Passing a BFILE Locator to a Prepared Statement
Assume you want to insert a BFILE locator into a table, and you have an OraclePreparedStatement
object ops
to insert data into a table. The first column is a string, the second column is a BFILE, and you have a valid oracle.sql.BFILE
object, bfile
. Write the BFILE to the database, as follows:
OraclePreparedStatement ops = (OraclePreparedStatement)conn.prepareStatement ("INSERT INTO my_bfile_table VALUES (?,?)"); ops.setString(1,"one"); ops.setBFILE(2, bfile); ops.execute();
Example: Passing a BFILE Locator to a Callable Statement
Passing a BFILE locator to a callable statement is similar to passing it to a prepared statement. In this case, the BFILE locator is passed to the myGetFileLength
procedure, which returns the BFILE length as a numeric value.
OracleCallableStatement cstmt = (OracleCallableStatement)conn.prepareCall ("begin ? := myGetFileLength (?); end;"); try { cstmt.registerOutParameter (1, Types.NUMERIC); cstmt.setBFILE (2, bfile); cstmt.execute (); return cstmt.getLong (1); }
To read BFILE data, you must first get the BFILE locator. You can get the locator from either a callable statement or a result set. Once you obtain the locator, you can call a number of methods on the BFILE without opening it. For example, you can use the
oracle.sql.BFILE
methods fileExists()
and isFileOpen()
to determine whether the BFILE exists and if it is open. However, if you want to read and manipulate the data, then you must open and close the BFILE, as follows:
Use the openFile
method of the oracle.sql.BFILE
class to open a BFILE.
When you are done, use the closeFile
method of the BFILE
class.
BFILE data is through a Java stream. To read from a BFILE, use the getBinaryStream
method of an oracle.sql.BFILE
object to access the file as an input stream. This returns a java.io.InputStream
object.
As with any InputStream
object, use one of the overloaded read
methods to read the file data and use the close
method when you finish.
Notes:
BFILEs are read-only. You cannot insert data or otherwise write to a BFILE.
You can create a BFILE. However, you cannot create an operating system file that a BFILE would refer to. Those are created only externally.
The following example uses the getBinaryStream
method of an oracle.sql.BFILE
object to read BFILE data into a byte stream and then read the byte stream into a byte array. The example assumes that the BFILE has already been opened.
// Read BFILE data from a BFILE locator Inputstream in = bfile.getBinaryStream(); byte[] byte_array = new byte{10}; int byte_read = in.read(byte_array);
This section discusses how to create a BFILE
column in a table with SQL operations and specify the location where the BFILE resides. The examples in this section assume that you have already created your Connection
object conn
and Statement
object stmt
.
Creating a BFILE Column in a New Table
To work with BFILE data, create a BFILE
column in a table, and specify the location of the BFILE. To specify the location of the BFILE, use the SQL CREATE DIRECTORY
...AS
statement to specify an alias for the directory where the BFILE resides. In this example, the directory alias is test_dir
and the BFILE resides in the /home/work
directory.
String cmd; cmd = "CREATE DIRECTORY test_dir AS '/home/work'"; stmt.execute (cmd);
Use the SQL CREATE
TABLE
statement to create a table containing a BFILE
column. In this example, the name of the table is my_bfile_table
.
// Create a table containing a BFILE field cmd = "CREATE TABLE my_bfile_table (x varchar2 (30), b bfile)"; stmt.execute (cmd);
In this example, the VARCHAR2
column designates a row number and the BFILE
column stores the locator of the BFILE data.
Use the SQL INSERT INTO...VALUES
statement to populate the VARCHAR2
and BFILE
fields. The BFILE
column is populated with the locator to the BFILE data. To populate the BFILE
column, use the bfilename
function to specify the directory alias and the name of the BFILE file.
cmd ="INSERT INTO my_bfile_table VALUES ('one', bfilename(test_dir, 'file1.data'))"; stmt.execute (cmd); cmd ="INSERT INTO my_bfile_table VALUES ('two', bfilename(test_dir, 'jdbcTest.data'))"; stmt.execute (cmd);
In this example, the name of the directory alias is test_dir
. The locator of the BFILE file1.data
is loaded into the BFILE
column on row one
, and the locator of the BFILE
jdbcTest.data
is loaded into the bfile
column on row two
.
As an alternative, you may want to create the row for the row number and BFILE locator now, but wait until later to insert the locator. In this case, insert the row number into the table and null
as a place holder for the BFILE locator.
cmd ="INSERT INTO my_bfile_table VALUES ('three', null)"; stmt.execute(cmd);
Here, three
is inserted into the row number column and null
is inserted as the place holder. Later in your program, insert the BFILE locator into the table by using a prepared statement.
First get a valid BFILE locator into the bfile
object:
rs = stmt.executeQuery("SELECT b FROM my_bfile_table WHERE x='two'"); rs.next(); oracle.sql.BFILE bfile = ((OracleResultSet)rs).getBFILE(1);
Then, create your prepared statement. Note that because this example uses the setBFILE
method to identify the BFILE, the prepared statement must be cast to OraclePreparedStatement
:
OraclePreparedStatement ops = (OraclePreparedStatement)conn.prepareStatement (UPDATE my_bfile_table SET b=? WHERE x = 'three'); ops.setBFILE(1, bfile); ops.execute();
Now row two
and row three
contain the same BFILE.
Once you have the BFILE locators available in a table, you can access and manipulate the BFILE data.
Once you have the BFILE locator in a table, you can access and manipulate the data to which it points. To access and manipulate the data, you must first select its locator from a result set or a callable statement.
The following code continues the example from the preceding section, getting the locator of the BFILE from row two
of a table into a result set. The result set is cast to OracleResultSet
so that oracle.sql.*
methods can be used on it. Several of the methods applied to the BFILE, such as getDirAlias
and getName
, do not require you to open the BFILE. Methods that manipulate the BFILE data, such as reading, getting the length, and displaying, do require you to open the BFILE.
When you finish manipulating the BFILE data, you must close the BFILE.
// select the bfile locator cmd = "SELECT * FROM my_bfile_table WHERE x = 'two'"; rset = stmt.executeQuery (cmd); if (rset.next ()) BFILE bfile = ((OracleResultSet)rset).getBFILE (2); // for these methods, you do not have to open the bfile println("getDirAlias() = " + bfile.getDirAlias()); println("getName() = " + bfile.getName()); println("fileExists() = " + bfile.fileExists()); println("isFileOpen() = " + bfile.isFileOpen()); // now open the bfile to get the data bfile.openFile(); // get the BFILE data as a binary stream InputStream in = bfile.getBinaryStream(); int length ; // read the bfile data in 6-byte chunks byte[] buf = new byte[6]; while ((length = in.read(buf)) != -1) { // append and display the bfile data in 6-byte chunks StringBuffer sb = new StringBuffer(length); for (int i=0; i<length; i++) sb.append( (char)buf[i] ); System.out.println(sb.toString()); } // we are done working with the input stream. Close it. in.close(); // we are done working with the BFILE. Close it. bfile.closeFile();
In addition to the features already discussed in this chapter, the oracle.sql.BFILE
class has a number of methods for further functionality, including the following:
Closes the external file.
Returns the contents of the external file as a stream of bytes.
getBinaryStream(long)
Returns the contents of the external file as a stream of bytes beginning at the position in the external file specified by the argument.
Reads from the external file, starting at a specified point, into a supplied buffer.
Gets the name of the external file.
Gets the directory alias of the external file.
Determines whether the BFILE is open.
Returns the length of the BFILE in bytes.
Opens the external file for read-only access.
Determines the byte position at which the given byte pattern begins.