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Oracle® XML Developer's Kit Programmer's Guide
12c Release 1 (12.1)

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8 Using XQuery API for Java to Access Oracle XML DB

This chapter provides information about using XQJ to access Oracle XML DB. It includes these sections:

Introduction to Oracle XML DB Support for XQJ

XQuery API for Java (XQJ), also known as JSR-225, provides an industry-standard way for Java programs to access XML data using XQuery. It lets you evaluate XQuery expressions against XML data sources and process the results as XML data.

Oracle provides two XQuery engines for evaluating XQuery expressions: one in Oracle XML DB, for use with XML data in the database, and one in Oracle XML Developer's Kit (XDK), for use with XML data outside the database. (See Chapter 7 for information about the XQuery engine for Oracle XDK).

Oracle provides two different XQJ implementations for accessing these two XQuery engines. Both implementations are part of Oracle XDK, enabling you to use XDK to access XML data with a standard XQJ API whether that data resides in the database or elsewhere.

The queries executed by XQJ are written in standard W3C XQuery 1.0 language, as supported by Oracle XML DB. A typical use case for this feature is to access XML data stored in remote databases (in Oracle XML DB) from a local Java program.

General information about XQuery and XQJ is documented outside of this manual.

See Also:

Prerequisites

You must have Java Runtime Environment 1.6 to use XQJ with Oracle XML DB.

In addition, the required JAR files listed in Introduction to the XQuery Processor for Java and these JAR files must be in the CLASSPATH environment variable (or passed using the command-line option classpath):

  • jdbc/lib/ojdbc6.jar

  • rdbms/jlib/xdb6.jar

The directory paths for these JAR files are relative to the ORACLE_HOME directory of your database installation.

Examples: Using XQJ to Query XML DB

You can use XQJ to query and retrieve data in Oracle XML DB, as illustrated by the examples in this section.

Example 8-1 shows how to use XQJ to query data from a table in Oracle XML DB. It uses the WAREHOUSES table in the Order Entry (OE) database sample schema. The OE sample schema contains XML documents with warehouse information in the WAREHOUSES table. The WAREHOUSES table contains an XMLType column warehouse_spec and other columns. (See the discussion about standard database schemas in Oracle XML DB Developer's Guide for more information about the data used in this example.)

Specifically, Example 8-1 shows how to perform these steps:

  1. Obtain an XQJ connection to Oracle XML DB

    Every program using XQJ to connect to Oracle XML DB must first create an OXQDDataSource object. Then, OXQDDataSource must be initialized with the required property values before obtaining an XQJ connection to the Oracle XML DB instance.

  2. Prepare an XQuery expression

  3. Submit the XQuery expression for evaluation

  4. Print each item in the resulting XQuery sequence

Example 8-1 Using XQJ to Query an XML DB Table with XQuery

import oracle.xml.xquery.xqjdb.OXQDDataSource;
 
import javax.xml.xquery.XQItemType;
import javax.xml.xquery.XQResultSequence;
import javax.xml.xquery.XQConnection;
import javax.xml.xquery.XQPreparedExpression;
 
import javax.xml.namespace.QName;
 
public class example1
{
  public static void main(String argv[])
  {
 
    try
    {
      // Create a new OXQDDataSource for connecting to Oracle XML DB
      OXQDDataSource oxqDS = new OXQDDataSource();
 
      // Set appropriate connection information for the database instance.
      // Must use the thin driver
      oxqDS.setProperty("driver", "jdbc:oracle:thin");
 
      oxqDS.setProperty("dbusername", "oe");
      oxqDS.setProperty("dbpassword", "oe");
 
      // Machine hostname
      oxqDS.setProperty("dbserver", "myserver");
 
      // Database instance port number
      oxqDS.setProperty("dbport", "6479");
 
      // Database instance port number
      oxqDS.setProperty("serviceName", "mydbinstance");
      XQConnection conn = oxqDS.getConnection();
 
      XQItemType  itemTypeInt = conn.createAtomicType(XQItemType.XQBASETYPE_INT);
 
      XQPreparedExpression expr = conn.prepareExpression("declare variable $x as
        xs:int external; for $i in fn:collection('oradb:/OE/WAREHOUSES') where
          $i/ROW/WAREHOUSE_ID < $x return $i/ROW/WAREHOUSE_SPEC/Warehouse");
 
      expr.bindInt(new QName("x"), 3, itemTypeInt);
 
      XQResultSequence xqSeq = expr.executeQuery();
 
      while (xqSeq.next())
         System.out.println (xqSeq.getItemAsString(null));
 
     }
     catch (Exception e)
     {
      e.printStackTrace();
     }
  }
}

In Example 8-1, the XQuery expression accesses the WAREHOUSES table through the use of the URI scheme oradb. (See the discussion about the URI scheme oradb in Oracle XML DB Developer's Guide for more information about using XQuery with XML DB to query table or view data.)

Example 8-1 also shows how to bind external variable values in XQJ. The query has an external variable $x, which is used to filter the returned rows from the WAREHOUSES table, by WAREHOUSE_ID.

Example 8-1 generates this output (reformatted for better readability):

<Warehouse><Building>Owned</Building><Area>25000</Area><Docks>2</Docks>
 <DockType>Rearload</DockType><WaterAccess>Y</WaterAccess>
 <RailAccess>N</RailAccess><Parking>Street</Parking>
 <VClearance>10 ft</VClearance></Warehouse>

<Warehouse><Building>Rented</Building><Area>50000</Area><Docks>1</Docks>
 <DockType>Sideload</DockType><WaterAccess>Y</WaterAccess>
 <RailAccess>N</RailAccess><Parking>Lot</Parking>
 <VClearance>12 ft</VClearance></Warehouse>

Example 8-2 shows how to use XQJ to retrieve data from the Oracle XML DB repository. This example assumes that two files, depts.xml and emps.xml, have been uploaded into the XML DB repository under the folder /public. For example, you can use FTP to upload the two files into the Oracle XML DB repository. (See the discussion about using the Oracle XML DB repository in Oracle XML DB Developer's Guide for more information about storing data in and using the Oracle XML DB repository.)

The content of depts.xml is as follows:

depts.xml:
 
<?xml version="1.0"?>
     <depts>
       <dept deptno="10" dname="Administration"/>
       <dept deptno="20" dname="Marketing"/>
       <dept deptno="30" dname="Purchasing"/>
     </depts>

The content of emps.xml is as follows:

emps.xml:
 
<?xml version="1.0"?>
   <emps>
    <emp empno="1" deptno="10" ename="John"  salary="21000"/>
       <emp empno="2" deptno="10" ename="Jack" salary="310000"/>
       <emp empno="3" deptno="20" ename="Jill" salary="100001"/>
     </emps>

You can use the fn:doc and fn:collection functions to query the data in the Oracle XML DB repository with XQuery. Example 8-2 shows how to use the fn:doc function within XQuery to access the repository. (See the discussion about querying XML data in the Oracle XML DB repository in Oracle XML DB Developer's Guide for more information about using these XQuery functions.)

Example 8-2 Using XQJ to Query the XML DB Repository with XQuery

import oracle.xml.xquery.xqjdb.OXQDDataSource;
 
import javax.xml.xquery.XQItemType;
import javax.xml.xquery.XQResultSequence;
import javax.xml.xquery.XQConnection;
import javax.xml.xquery.XQPreparedExpression;
 
import javax.xml.namespace.QName;
 
public class example2
{
  public static void main(String argv[])
  {
 
    try
    {
      // Create a new OXQDDataSource for connecting to Oracle XML DB
      OXQDDataSource oxqDS = new OXQDDataSource();
 
      // Set appropriate connection information for the database instance.
      // Must use the thin driver
      oxqDS.setProperty("driver", "jdbc:oracle:thin");
 
      oxqDS.setProperty("dbusername", "oe");
      oxqDS.setProperty("dbpassword", "oe");
 
      // Machine hostname
      oxqDS.setProperty("dbserver", "myserver");
 
      // Database instance port number
      oxqDS.setProperty("dbport", "6479");
 
      // Database instance port number
      oxqDS.setProperty("serviceName", "mydbinstance");
 
      XQConnection conn = oxqDS.getConnection();
 
      XQPreparedExpression expr = conn.prepareExpression("for $e in
        doc(\"/public/emps.xml\")/emps/emp let $d :=
        doc(\"/public/depts.xml\")//dept[@deptno = $e/@deptno]/@dname where
        $e/@salary > 100000 order by $e/@empno return 
        <emp ename=\"{$e/@ename}\" dept=\"{$d}\"/>");
 
      XQResultSequence xqSeq = expr.executeQuery();
 
      while (xqSeq.next())
         System.out.println (xqSeq.getItemAsString(null));
 
     }
     catch (Exception e)
     {
      e.printStackTrace();
     }
  }
}

Example 8-2 generates this output:

<emp ename="Jack" dept="Administration"/>
<emp ename="Jill" dept="Marketing"/>

XQJ Support for Oracle XML DB

The two Oracle XQJ implementations differ in some respects. Oracle XML DB support for XQJ is described in this section. Chapter 7 provides information about using XQJ to access the mid-tier XQuery engine.

Table 8-1 describes the OXQDDataSource properties to be used for connection to Oracle XML DB. To create an XQJ connection to Oracle XML DB, you must set the values for these properties. You must set either the dbname or the serviceName property value, and all the other OXQDDataSource property values listed in Table 8-1.

Table 8-1 OXQDDataSource Properties

Property Value Get Method Set Method

driver

jdbc:oracle:thin

getDriver

setDriver

dbusername

Database schema (user) name

getDBUserName

setDBUserName

dbpassword

Password for database schema

getDBPassword

setDBPassword

dbserver

Host name for the database instance

getDBServer

setDBServer

dbport

Port number of the database instance for XQJ connection

getDBPort

setDBPort

dbname

Database instance name (service id)Foot 1 

getDBName

setDBName

serviceName

Service nameFootref 1

getServiceName

setServiceName


Footnote 1 You can identify the database using either the service id or the service name.

Table 8-2 describes the Oracle XML DB support for optional XQJ features. Note that the Oracle XML DB support for some XQJ features differs from their support by the mid-tier XQuery engine. In particular, the Oracle XML DB XQJ implementation does not support the use of user-defined types.

Table 8-2 Oracle XML DB Support for Optional XQJ Features

XQJ Feature Oracle XML DB Support

Class name of XQDataSource implementation

oracle.xml.xquery.xqjdb.OXQDDataSource

JDBC connections

Not supported.

Properties defined on OXQDDataSource (connection information)

See Table 8-1.

Commands

Not supported.

XQPreparedExpression.cancel (cancelling of query execution)

Not supported.

Serialization

Only parameter method with value xml and parameter encoding with value UTF-8 or UTF-16.

Additional StAX and SAX events

Not supported.

User-defined schema types

Not supported.

Node identity, document order, and full-node context preservation when a node is bound to an external variable

Not supported.

Login timeout

Not supported.

Transactions

Not supported.

Behavior of XQItemAccessor method getNodeUri() when the input node is not a document node

Return NULL.

Behavior of XQItemType method getTypeName() for anonymous types

Return false.

Behavior of XQItemType method getSchemaURI()

Return NULL or the schema URI provided during type creation. Currently, the Oracle XML DB XQJ implementation does not use the schema URI to obtain type information, and user-defined types are not supported.

Behavior of XQDataFactory methods createItemFromDocument() and bindDocument() if the input is not a well-formed XML document

Raise an exception.

Additional error codes returned from XQQueryException

Not supported.

Interfaces ConnectionPoolXQDataSource, PooledXQConnection, XQConnectionEvent, XQConnectionEventListener

Not supported.

XQDataSource.getConnection(
  java.sql.Connection)

Not supported. (JDBC connections are not supported.)

XQDataSource.getConnection(
  java.lang.String,
  java.lang.String)

Same as getConnection() with no arguments: the arguments are ignored.


See Also:

Oracle XML DB Developer's Guide for information about using the XQuery language with Oracle XML DB

Other Oracle XML DB XQJ Support Limitations

Oracle XML DB support for XQJ has the following limitations. None of these limitations apply to mid-tier XQuery engine support for XQJ.

  • All Oracle XML DB XQuery support limitations apply to Oracle XML DB support for XQJ as well.

  • Only the Oracle XDK DOM is supported. Use of any other DOM can result in errors.

  • Do not expect the Oracle XML DB XQJ implementation to be interoperable with another XQJ implementation, including the Oracle XDK Java implementation of XQJ. (See the XQJ standard (JSR-225) for the meaning of "interoperable".)

  • XQDataSource methods getLogWriter and setLogWriter have no effect (they are ignored).

  • XQStaticContent methods getBoundarySpacePolicy, setBoundarySpacePolicy, getDefaultCollation, and setDefaultCollation have no effect (they are ignored).

  • The copy namespaces mode for XQStaticContent methods setCopyNamespacesModPreserve and setCopyNamespacesModeInherit has no effect (it is ignored). The values used are always preserve and inherit, respectively.

  • Use of XQDynamicContext methods to bind DocumentFragment objects is not supported.

  • Values of type xs:duration are not supported. Using an XQDynamicContext method to bind xs:duration, or accessing an xs:duration value, raises an error.

  • The year of a xs:date, xs:dateTime, xs:gYear, and xs:gYearMonth value must be from -4712 to 9999, inclusive. Using a year outside this range can raise an error or produce unpredictable results.

XQJ Performance Considerations for Use with Oracle XML DB

To fetch a sequence of items from the database, use XQResultSequence method next() to retrieve a single item at a time; then use an XQItemAccessor method to fetch all data corresponding to that item.

This provides better performance than using the following whole-sequence fetch methods, which each materialize the entire sequence before returning any data.

  • getSequenceAsStream()

  • getSequenceAsString(java.util.Properties props)

  • writeSequence(java.io.OutputStream os, java.util.Properties props)

  • writeSequence(java.io.Writer ow, java.util.Properties props)

  • writeSequenceToResult(javax.xml.transform.Result result)

  • writeSequenceToSAX(org.xml.sax.ContentHandler saxhdlr)

For example, if you call getSequenceAsStream(), all of the XQuery result sequence data is fetched from the database before the XMLStreamReader instance that is built from it is returned to your program.

Be aware also that items themselves are not streamable: the item accessor methods always materialize an entire item before outputting any part of it.

For inputting, all bind methods defined on XQDynamicContext fully materialize the input data before passing it to the database.

For example, when you call bindDocument(javax.xml.namespace.QName varName, javax.xml.stream.XMLStreamReader value, XQItemType type), all the data that is referenced by the input XMLStreamReader instance is processed before the external XQuery variable is bound to it.