An XQJ Introduction

January 23, 2008 An XQJ Introduction The XQuery API for Java (XQJ), currently in development under the Java Community Process as JSR 225, lets programmers use XQuery for XML processing and data integration applications, with full support for the Java Standard Edition (Java SE) and Java Enterprise Edition (Java EE) platforms. XQJ allows a Java program to connect to XML data sources, prepare and issue XQueries, and process the results as XML. This functionality is similar to that of JDBC, but the query language for XQJ is XQuery.

]]> The XQuery language is designed specifically for XML programming and data integration, and programmers are more productive using XQuery for these tasks. However, many enterprise applications are built on the Java platform, and often require functionality not found in XQuery; for instance, many XML programs need to use the Web Services functionality of J2EE. On the Java platform, XML is accessed and manipulated as a DOM tree, a SAX stream, or as a StAX stream. The XQuery API for Java, currently under development as JSR 225, lets programmers have the best of both worlds, using XQuery for XML programming and data integration, with full access to the J2SE and J2EE platforms. XQJ allows a Java program to connect to XML data sources, prepare and issue XQueries, and process the results as XML. This functionality is similar to that of JDBC® Java API for SQL, but the query language for XQJ is XQuery. This article shows how XQJ is used to issue XQueries and obtain results. Next, it shows how XQJ can be used to query DOM trees, perform joins between XML and relational sources, obtain results using StAX, and issue prepared XQueries (similar to JDBC's prepared statements). Finally, we show four complete, working XQJ programs, including one that uses StAX to handle output. These programs are based on the Early Draft Review of JSR-225, released in May 2004. Code examples were tested with DataDirect XQuery™ 1.0, which implements XQuery and XQJ. <h2>Querying Relational Data to Create XML</h2> Although XQuery is a native XML query language, it is often used to query XML views of relational data to create XML results. Most Java programmers are familiar with the JDBC API. This example shows the similarities between JDBC and XQJ, using an XQJ connection to query a relational database and print out the results to the standard output. SQL/XML Views of the Tables The examples in this article are based on financial stock data, with a set of users and stock holdings for each user. DataDirect XQuery relational data using the SQL/XML mappings defined by SQL:2003. Here's the SQL/XML description of the USERS table (only a few rows are shown). <table bgcolor="#e6e6e6" ID="Table1"> <tbody> <tr> <td> <pre><USERS> <row> <USERID>Minollo</USERID> <FIRSTNAME>Carlo</FIRSTNAME> <LASTNAME>Innocenti</LASTNAME> <OTHERNAME/> <MEMBERSINCE>2004-07-16T00:00:00</MEMBERSINCE> </row> <row> <USERID>Jonathan</USERID> <FIRSTNAME>Jonathan</FIRSTNAME> <LASTNAME>Robie</LASTNAME> <OTHERNAME>William</OTHERNAME> <MEMBERSINCE>2004-04-03T00:00:00</MEMBERSINCE> </row> </USERS> </pre> </td> </tr> </tbody> </table> Here's the XML mapping of the HOLDINGS table, which contains the (fictional!) stock holdings for each user. Again, only a few rows are shown. <table bgcolor="#e6e6e6" ID="Table2"> <tbody> <tr> <td> <pre><HOLDINGS> <row> <USERID>Jonathan</USERID> <STOCKTICKER>AMZN</STOCKTICKER> <SHARES>3000.0000</SHARES> </row> <row> <USERID>Minollo</USERID> <STOCKTICKER>EBAY</STOCKTICKER> <SHARES>4000.0000</SHARES> </row> <row> <USERID>Jonathan</USERID> <STOCKTICKER>IBM</STOCKTICKER> <SHARES>2500.0000</SHARES> </row> <row> <USERID>Minollo</USERID> <STOCKTICKER>LU</STOCKTICKER> <SHARES>40000.0000</SHARES> </row>  </HOLDINGS> </pre> </td> </tr> </tbody> </table> Querying SQL/XML Views For relational data, XQuery often is used as a reporting language, combining data to display on a web page or for use in a web message. Here's an XQuery that returns results that show the stocks held by each user. <table bgcolor="#e6e6e6" ID="Table3"> <tbody> <tr> <td> <pre>for $u in collection("USERS")/USERS/row return <user> <name> { $u/FIRSTNAME, $u/LASTNAME } </name> { for $h in collection("HOLDINGS")/HOLDINGS/row where $h/USERID = $u/USERID return <stock> { $h/STOCKTICKER, $h/SHARES } </stock> } </user> </pre> </td> </tr> </tbody> </table> This query uses an XQuery function named collection() to address tables-the collection() function accepts a string and returns a sequence of nodes. In this sample query, we bind the variables $u and $h to the SQL/XML view of rows in the USERS and HOLDINGS tables. January 23, 2008 Configuring XQJ Connections The XQuery in the previous section uses the collection() function to access relational data, but XQuery has no notion of a relational database or a connection. To make this work, we use XQJ to specify the required database connections and associate these names with the tables. A connection is created from a <code>XQDataSource</code>. Each vendor must provide some way of creating and parameterizing their own XQDataSource objects - the following two lines do this for DataDirect XQuery™, which uses a JDBC URL to describe connections. <table bgcolor="#e6e6e6" ID="Table1"> <tbody> <tr> <td> <pre>DDXQDataSource dataSource = new DDXQDataSource(); dataSource.setJdbcUrl("jdbc:xquery:sqlserver://server1:1433; databaseName=stocks"); </pre> </td> </tr> </tbody> </table> The getConnection() method can now be invoked to return a connection to the data source: <table bgcolor="#e6e6e6" ID="Table2"> <tbody> <tr> <td> <pre>XQConnection connection = dataSource.getConnection(); </pre> </td> </tr> </tbody> </table> The next step is to create an XQExpression object, which can execute an XQuery expression and return a sequence of results. An XQConnection can create an XQExpression. <table bgcolor="#e6e6e6" ID="Table3"> <tbody> <tr> <td> <pre> XQExpression xqExpression = connection.createExpression(); FileReader fileReader = new FileReader("xquerySourceFile.xq"); XQSequence xqSequence = xqExpression.executeQuery(fileReader); </pre> </td> </tr> </tbody> </table> For this example, we place the query in a separate file named xquerySourceFile.xq (another reasonable way would be to put the query in a String object). Now that the query results are in a sequence, we can serialize this sequence using the getSequenceAsString() method. <table bgcolor="#e6e6e6" ID="Table4"> <tbody> <tr> <td> <pre>System.out.println(xqSequence.getSequenceAsString()); </pre> </td> </tr> </tbody> </table> Here's an excerpt from the result of this query. NB: This is formatted for readability- whitespace has been modified <table bgcolor="#e6e6e6" ID="Table5"> <tbody> <tr> <td> <pre><user> <name> <FIRSTNAME>Jonathan</FIRSTNAME> <LASTNAME>Robie</LASTNAME> </name> <stock> <STOCKTICKER>AMZN</STOCKTICKER> <SHARES>3000.0000</SHARES> </stock> <stock> <STOCKTICKER>EBAY</STOCKTICKER> <SHARES>4000.0000</SHARES> </stock> <stock> <STOCKTICKER>IBM</STOCKTICKER> <SHARES>2500.0000</SHARES> </stock>  </user> </pre> </td> </tr> </tbody> </table> January 23, 2008 Querying Data from XML Files or Java XML API's In the previous query, our data was in a relational database. Now let's query an XML file. Suppose we want to query the users from a file named 'holdings.xml', which looks like this. <table bgcolor="#e6e6e6" ID="Table1"><tbody><tr><td> <pre><HOLDINGS> <row> <USERID>Jonathan</USERID> <STOCKTICKER>AMZN</STOCKTICKER> <SHARES>3000.0000</SHARES> </row> <row> <USERID>Minollo</USERID> <STOCKTICKER>EBAY</STOCKTICKER> <SHARES>4000.0000</SHARES> </row> </HOLDINGS> </pre> </td></tr></tbody></table> Here's an XQuery expression that returns the holdings for Jonathan. <table bgcolor="#e6e6e6" ID="Table2"><tbody><tr><td> <pre>doc("holdings.xml")//holding[USERID="Jonathan"] </pre> </td></tr></tbody></table> Obviously, Jonathan is not the only person whose holdings might interest us. If we write our XQuery with an external variable, the Java program can specify the name of the user before it executes the query. If we also use an external variable to represent the document, the Java program can pass any document to the query at runtime: <table bgcolor="#e6e6e6" ID="Table3"><tbody><tr><td> <pre>declare variable $u as xs:string external; declare variable $d as document-node(element(*,xdt:untyped)) external; $d//holding[USERID=$u] </pre> </td></tr></tbody></table> Now let's write the Java code to create a DOM tree and bind it to the variable $d. We start by creating a DOM tree. <table bgcolor="#e4e4e4" ID="Table4"><tbody><tr><td> <pre>DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); factory.setNamespaceAware(true); FileReader fileReader = new FileReader("holdings.xml"); Document document = parser.parse(fileReader); </pre></td></tr></tbody></table> Once we create a DOM tree, we can use XQJ to bind it to a variable and query it. First, let's create an expression object, and then bind the document to the variable $d for this expression. <table bgcolor="#e4e4e4" ID="Table5"><tbody><tr><td> <pre> XQConnection connection = dataSource.getConnection(); XQExpression xqExpression = connection.createExpression(); xqExpression.bindNode(new QName("d"), document); xqExpression.bindVariable(new QName("u"), "Jonathan")); </pre></td></tr></tbody></table> Now we can execute the expression and output the result. <table bgcolor="#e4e4e4" ID="Table6"><tbody><tr><td> <pre>FileReader fileReader = new FileReader("xquerySourceFile.xq"); XQSequence xqSequence = xqExpression.executeQuery(fileReader); System.out.println(xqSequence.getSequenceAsString()); </pre></td></tr></tbody></table> January 23, 2008 Joining XML and Relational Sources We have already explored how XQJ enables XQuery to operate on relational and XML file data stores. Now let's leverage that functionality to query both at the same time. We will use an incoming Web Service request that provides parameters for a query, and then query a database to create the Web Service response. Consider the following Web Service request: <table bgcolor="#e6e6e6" ID="Table1"><tbody><tr><td> <pre><request> <performance> <UserId>Jonathan</UserId> <start>2003-01-01</start> <end>2003-01-01</end> </performance> </request> </pre> </td></tr></tbody></table> The above example contains only the SOAP message payload - we left out the envelope to simplify the example, but the XQuery would be changed only slightly if it were in an envelope. This request asks for performance data on a user's portfolio within a specific date range. Let's compose an XQuery that uses the parameters from the request to create a performance report, which will report the performance of each stock held by each user during the given range. <table bgcolor="#e6e6e6" ID="Table2"><tbody><tr><td> <pre>let $request := doc("request.xml")/request for $user in $request/performance return <portfolio UserID="{$user/UserId}"> { $request } { for $h in collection("HOLDINGS")/row where $h/USERID = $user return <stock> { $h/STOCKTICKER, $h/SHARES } </stock> } </portfolio> </pre></td></tr></tbody></table> In keeping with our previous examples, we instantiate a XQDataSource instance and establish a connection to the data source. <table bgcolor="#e4e4e4" ID="Table3"><tbody><tr><td> <pre>XQConnection connection = dataSource.getConnection(); </pre> </td></tr></tbody></table> Again, we create an XQExpression object, which can execute the XQuery expression and return a sequence of results. <table bgcolor="#e4e4e4" ID="Table4"><tbody><tr><td> <pre>FileReader fileReader = new FileReader("xquerySourceFile.xq"); XQExpression xqExpression = connection.createExpression(); XQSequence xqSequence = xqExpression.executeQuery(fileReader); </pre> </td></tr></tbody></table> With our query results in a sequence, we can again serialize this sequence using the getSequenceAsString() method. <table bgcolor="#e4e4e4" ID="Table5"><tbody><tr><td> <pre>System.out.println(xqSequence.getSequenceAsString()); </pre> </td></tr></tbody></table> The result looks like this (whitespace has been modified for readability): <table bgcolor="#e4e4e4" ID="Table6"> <tbody><tr><td> <pre><portfolio UserID="Jonathan"> <request> <performance> <UserId>Jonathan</UserId> <start>2003-01-01</start> <end>2004-06-01</end> </performance> </request> <stock> <STOCKTICKER>PRGS</STOCKTICKER> <SHARES>23.0000</SHARES> </stock> <stock> <STOCKTICKER>AMZN</STOCKTICKER> <SHARES>3000.0000</SHARES> </stock> <stock> <STOCKTICKER>EBAY</STOCKTICKER> <SHARES>4000.0000</SHARES> </stock> <stock> <STOCKTICKER>IBM</STOCKTICKER> <SHARES>2500.0000</SHARES> <SHARES>2500.0000</SHARES> </stock> </portfolio> </pre></td></tr></tbody></table> January 23, 2008 Retrieving Results with Java XML API's Often, applications need to retrieve XQuery results as DOM, SAX, or StAX. The XQSequence interface has methods to support each of these APIs. XQJ provides two ways by which the result of an XQuery can be processed. We have already used the XQSequence level access, which permits the result as a direct mapping of the XQuery sequence. Within a XQSequence, zero or more XQItem objects represent each component in an XQuery sequence. Note that instantiating each item in a XQItem object is expensive because it requires the creation of multiple objects and should be used judiciously. The XQItemAccessor interface allows an XQuery result sequence to be divided and processed item by item. This is particularly useful when processing large result sequences. Importantly, both the XQSequence and XQItemAccessor result accessors interfaces allow processing using the SAX and StAX APIs. For example, if you want to retrieve your results as a StAX stream rather than a string, you simply replace the last line from the previous section with this: <table bgcolor="#e4e4e4" ID="Table1"><tbody><tr><td> <pre>XMLStreamReader reader = xqSequence.getSequenceAsStream(); </pre></td></tr></tbody></table> You can use this like any other StAX stream reader. For example, the following function reads one event at a time and prints the type of the event together with the associated names. Only a small excerpt is shown below-the complete program is here. <table bgcolor="#e4e4e4" ID="Table2"><tbody><tr><td> <pre>private static void formatOutput(XMLStreamReader reader) throws XMLStreamException { for (int event = reader.next(); even != XMLStreamConstants.END_DOCUMENT; event = reader.next()) { switch (event) { case XMLStreamConstants.START_ELEMENT: System.out.println("Start tag: "); printNames(reader); break; } } /* !!! SNIP !!! */ </pre></td></tr></tbody></table> January 24, 2008 Preparing XQuery statements When an XQuery is executed, the query generally is parsed and optimized before it is run. To avoid incurring this overhead each time the XQuery is used, XQJ allows queries to be prepared once and executed multiple times. Here's the code to create a prepared query-only the last line differs from the code used to create a query in our first example. <table bgcolor="#e6e6e6" ID="Table1"><tbody><tr><td> <pre>dataSource = new DDXQDataSource(new FileInputStream(configFile)); connection = dataSource.getConnection(); FileReader fileReader = new FileReader("xquerySourceFile.xq"); preparedExpression = connection.prepareExpression( fileReader); </pre></td></tr></tbody></table> Once the query is prepared, it is executed using the executeQuery() call. <table bgcolor="#e6e6e6" ID="Table2"><tbody><tr><td> <pre>XQSequence xqSequence = preparedExpression.executeQuery(); System.out.println(xqSequence.getSequenceAsString()); </pre></td></tr></tbody></table> Of course, queries often take parameters, and these parameters may need to be changed between executions. For example, we might want to prepare a query that selects items that match a particular value and change that value each time the query is executed. Suppose we want to use a query that returns the stock holdings for a given user. The user changes each time this XQuery is run. <table bgcolor="#e6e6e6" ID="Table3"><tbody><tr><td> <pre>declare variable $l as xs:string external; collection("HOLDINGS")/HOLDINGS[USERID=$l] </pre></td></tr> </tbody></table> The value of $l is set using XQJ. Let's run this twice, each time for different users. <table bgcolor="#e6e6e6" ID="Table4"><tbody><tr><td> <pre>preparedExpression.bindString(new QName("l"), "Jonathan"); xqSequence = preparedExpression.executeQuery(); System.out.println("\n\nHoldings for Jonathan:\n\n"); System.out.println(xqSequence.getSequenceAsString()); preparedExpression.bindString(new QName("l"), "Minollo"); xqSequence = preparedExpression.executeQuery(); System.out.println("\n\nHoldings for Minollo:\n\n"); System.out.println(xqSequence.getSequenceAsString()); </pre></td></tr></tbody></table> January 24, 2008 XQJ Code Listing - Executing XQJ This example shows how to execute an XQuery contained in a file. It is called with two parameters: : the name of the file that specifies the connections for the query and the name of the file that contains the query An optional, third parameter specifies the name of the file to which the output is written. <table bgcolor="#e4e4e4" ID="Table1"><tbody><tr><td> <pre> /* * DataDirect Technologies Corp 2005 */ package com.ddtek.xqj.examples; import java.io.FileInputStream; import java.io.FileReader; import java.io.FileWriter; import java.util.Properties; import com.ddtek.xquery.XQConnection; import com.ddtek.xquery.XQException; import com.ddtek.xquery.XQExpression; import com.ddtek.xquery.XQSequence; import com.ddtek.xquery.xqj.mediator.DDXQDataSource; /** * The purpose of this class is to serve as an example of using the XQJ * API to execute an XQuery query contained in a file. * This application is intended to be run as command-line Java, * the useage is: * java XQJExecute * There is an optional third argument that allows you * to specify an output file for the resulting XML: * java XQJExecute * where the final argument will write * XQuery results to the file specified. * (c)Copyright 2004-2005 DataDirect Technologies Corp. * @version 1.2 8.23.2005 */ public class XQJExecute extends Object { /** * Execute XQJExecute as a java console application. See the 'args' param * for startup arguments. * @param args - a list of three strings that represent the path to * the config file, the path to an XQuery source file, and the path * to a well-formed XML data file. The third argument is optional - if * left off, no file will be created and written, and the output will go * to the current System.out. */ public static void main(String[] args) throws Exception { DDXQDataSource dataSource = null; XQConnection connection = null; XQExpression xqExpression = null; XQSequence xqSequence = null; String configFile = ""; String xquerySourceFile = ""; if (args.length < 2 || args.length > 3) { String usage = "Usage:\n\n java XQJExecute [configfile] [queryfile]\n\n" " + [configfile] Source Configuration File\n" " + [queryfile] XQuery file" + "\n\n" + "or:\n" + "java XQJExecute [configfile] [queryfile]\n\n" + " [configfile] Source Configuration File\n" " + [queryfile] XQuery file" + " [resultoutputfile] result output file"; System.out.println(usage); System.out.println("Exiting XQJExecute..."); System.exit(1); } configFile = args[0]; xquerySourceFile = args[1]; try { //this property will be used with the results to //help the output be nice to read Properties indentationProperty = new Properties(); indentationProperty.setProperty("indent", "yes"); //get a connection, prepare the query dataSource = new DDXQDataSource(new FileInputStream(configFile)); //get a connection as configured by the XQDataSource connection = dataSource.getConnection(); //make an XQuery expression based on the new //connection xqExpression = connection.createExpression(); /* Get an XQuery sequence as a result of * the expression run of the query in the specified * file. */ xqSequence = xqExpression.executeQuery( new FileReader(xquerySourceFile)); /* If a third arg is supplied, attempt to write the * sequence as a string to a file by the given name. * Otherwise, print the sequence to the System's out * stream. */ if (args.length == 3) { FileWriter fileWriter = new FileWriter(args[2]); xqSequence.writeSequence(fileWriter, indentationProperty); fileWriter.close(); } else { //now use the indentation properties to get //the sequence to look nice when we ask the //sequence for a String representation drop //the output onto the System.out so we can //see what came back System.out.println( xqSequence.getSequenceAsString(indentationProperty)); } if (connection != null){ try { //close/free up resources connection.close(); } catch (XQException e) { e.printStackTrace(); } } } catch (Exception ex) { ex.printStackTrace(); } } } </pre></td></tr></tbody></table> January 24, 2008 XQJ Code Listing - Execute XQuery and Output result w/ StAX This example shows how to execute an XQuery and output the result using StAX. It is called with two parameters: the name of the file that specifies the connections for the query and the name of the file that contains the query. <table bgcolor="#e4e4e4" ID="Table1"><tbody><tr><td> <pre>package com.ddtek.xqj.examples; import java.io.*; import javax.xml.stream.XMLStreamConstants; import javax.xml.stream.XMLStreamException; import javax.xml.stream.XMLStreamReader; /* Import XQJ classes */ import com.ddtek.xquery.XQConnection; import com.ddtek.xquery.XQException; import com.ddtek.xquery.XQExpression; import com.ddtek.xquery.XQItem; import com.ddtek.xquery.XQSequence; import com.ddtek.xquery.xqj.mediator.DDXQDataSource; /** * The purpose of this class is to serve as an example of using the XQJ API to * query a stream from StAX (Streaming API for XML). * * This application is intended to be run as command-line Java, * the usage is: * * java StAXExample */ public class StAXExample { public static void main(String[] args) { DDXQDataSource dataSource = null; XQConnection connection = null; XQExpression xqExpression = null; XQSequence xqSequence = null; XMLStreamReader reader = null; String configFile = ""; String xquerySourceFile = ""; if (args.length != 2) { String usage = "Usage:\n\n java StAXExample [configfile] [queryfile]\n\n" + " [configfile] Source Configuration File\n" + " [queryfile] XQuery file"; System.out.println(usage); System.out.println("Exiting StAXExample..."); System.exit(1); } configFile = args[0]; xquerySourceFile = args[1]; try { dataSource = new DDXQDataSource(); dataSource.setConfigFile(configFile); connection = dataSource.getConnection(); xqExpression = connection.createExpression(); FileReader fileReader = new FileReader(xquerySourceFile); xqSequence = xqExpression.executeQuery(fileReader); reader = xqSequence.getSequenceAsStream(); formatOutput(reader); } catch (Exception ex) { ex.printStackTrace(); } finally { try { if (connection != null){ reader.close(); connection.close(); } } catch (XQException xqEx) { xqEx.printStackTrace(); } catch (XMLStreamException e) { e.printStackTrace(); } } } private static void formatOutput(XMLStreamReader reader) throws XMLStreamException { for (int event = reader.next(); event != XMLStreamConstants.END_DOCUMENT; event = reader.next()) { switch (event) { case XMLStreamConstants.START_ELEMENT: System.out.println("Start tag: "); printNames(reader); break; case XMLStreamConstants.END_ELEMENT: System.out.println("End tag"); printNames(reader); break; case XMLStreamConstants.CHARACTERS: System.out.println("Text"); printChars(reader); break; case XMLStreamConstants.CDATA: System.out.println("CDATA Section\n"); break; case XMLStreamConstants.COMMENT: System.out.println("Comment"); break; case XMLStreamConstants.DTD: System.out.println("Document type declaration\n"); break; case XMLStreamConstants.ENTITY_REFERENCE: System.out.println("Entity Reference\n"); break; case XMLStreamConstants.SPACE: System.out.println("Ignorable white space\n"); break; case XMLStreamConstants.PROCESSING_INSTRUCTION: System.out.println("Processing Instruction\n"); break; default: System.out.println("This can not happen."); } } } private static void printChars(XMLStreamReader aReader){ String textString = aReader.getText(); if(textString != null){ System.out.println("\tValue:" + textString); } } private static void printNames(XMLStreamReader reader) { String localName = reader.getLocalName(); String prefix = reader.getPrefix(); String uri = reader.getNamespaceURI(); if (localName != null){ System.out.println("\tLocal name: " + localName); } if (prefix != null) { System.out.println("\tPrefix: " + prefix); } if (uri != null) { System.out.println("\tNamespace URI: " + uri); } System.out.println(); } } </pre></td></tr></tbody></table> January 24, 2008 XQJ Code Listing - Prepare XQuery and execute w/ with variable bindings This example shows how to prepare a query and execute it with different variable bindings. It is called with two parameters: the name of the file that specifies the connections for the query and the name of the file that contains the query. <table bgcolor="#e4e4e4" ID="Table1"><tbody><tr><td> <pre>package com.ddtek.xqj.examples; import java.io.*; import javax.xml.namespace.QName; /* Import XQJ classes */ import com.ddtek.xquery.XQConnection; import com.ddtek.xquery.XQException; import com.ddtek.xquery.XQPreparedExpression; import com.ddtek.xquery.XQResultSequence; import com.ddtek.xquery.XQSequence; import com.ddtek.xquery.xqj.mediator.DDXQDataSource; /** * The purpose of this class is to serve as an example of using the XQJ API to * execute a prepared query. * * This application is intended to be run as command-line Java, * the usage is: * * java PreparedQuery */ public class PreparedQuery { public static void main(String[] args) throws Exception { DDXQDataSource dataSource = null; XQConnection connection = null; XQPreparedExpression preparedExpression = null; XQSequence xqSequence = null; String configFile = ""; String xquerySourceFile = ""; if (args.length != 2) { String usage = "Usage:\n\n java PreparedQuery [configfile]" + " [queryfile]\n\n" + " [configfile] Source Configuration File\n" + " [queryfile] XQuery file"; System.out.println(usage); System.out.println("Exiting PreparedQuery..."); return; } configFile = args[0]; xquerySourceFile = args[1]; try { /* Get a connection, prepare the query */ dataSource = new DDXQDataSource(); dataSource.setConfigFile(configFile); connection = dataSource.getConnection(); FileReader fileReader = new FileReader(xquerySourceFile); preparedExpression = connection.prepareExpression(fileReader); /* Bind variable $l to "Jonathan" and execute */ preparedExpression.bindString(new QName("l"), "Jonathan"); xqSequence = preparedExpression.executeQuery(); System.out.println("\n\nHoldings for Jonathan:\n\n"); System.out.println(xqSequence.getSequenceAsString()); /* Bind variable $l to "Minollo" and execute */ preparedExpression.bindString(new QName("l"), "Minollo"); xqSequence = preparedExpression.executeQuery(); System.out.println("\n\nHoldings for Minollo:\n\n"); System.out.println(xqSequence.getSequenceAsString()); } catch (Exception ex) { ex.printStackTrace(); } finally { if (connection != null){ try { connection.close(); } catch (XQException e) { e.printStackTrace(); } } } } } </pre></td></tr></tbody></table> January 24, 2008 XQJ Code Listing - Build a DOM tree and query it using XQuery This example shows how to build a DOM tree and query it using XQuery. It is called with two parameters: the name of the file that specifies the connections for the query and the name of the file that contains the query. <table bgcolor="#e6e6e6" ID="Table1"><tbody><tr><td> <pre>package com.ddtek.xqj.examples; import java.io.*; import javax.xml.namespace.QName; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.FactoryConfigurationError; import javax.xml.parsers.ParserConfigurationException; import javax.xml.transform.Result; import javax.xml.transform.Source; import javax.xml.transform.Transformer; import javax.xml.transform.TransformerFactory; import javax.xml.transform.dom.DOMSource; import javax.xml.transform.stream.StreamResult; import org.w3c.dom.Document; import org.xml.sax.SAXException; /* Import XQJ classes */ import com.ddtek.xquery.XQConnection; import com.ddtek.xquery.XQException; import com.ddtek.xquery.XQExpression; import com.ddtek.xquery.XQSequence; import com.ddtek.xquery.xqj.mediator.DDXQDataSource; /** * The purpose of this class is to provide an example of how to * use the XQJ API to query XML with a variable bound to a DOM. * * To use this application, execute the following from the command line: * * java BindDomToVariable * */ public class BindDomToVariable { /** * Execute BindDomToVariable as a java console application. See the * "args" param for startup arguments. * @param args - a list of three strings that represent the path to the * config file, the path to an XQuery source file, and the path to a * well-formed XML data file. */ public static void main(String[] args) { DDXQDataSource dataSource = null; XQConnection connection = null; XQExpression xqExpression = null; XQSequence xqSequence = null; String configFile = ""; String xquerySourceFile = ""; String xmlDataFile = ""; //we need all three args to run this example... if (args.length != 3) { System.out.println("Usage: java BindDomToVariable configfile xquery" + "xmldatafile"); System.out.println("Exiting BindDomToVariable..."); return; } configFile = args[0]; xquerySourceFile = args[1]; xmlDataFile = args[2]; try { /* Ask the DocumentBuilderFactory class for an instance * to help us make a DocumentBuilder parser. */ DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); /* Establish the aspect of namespace awareness * before the parser is created. */ factory.setNamespaceAware(true); /* Ask the DocumentBuilderFactory instance for a new * document builder parser */ DocumentBuilder parser = factory.newDocumentBuilder(); /* Create a DOM tree from the xml data file. */ Document document = parser.parse(xmlDataFile); /* Create a connection, then an expression */ dataSource = new DDXQDataSource(); dataSource.setConfigFile(configFile); connection = dataSource.getConnection(); xqExpression = connection.createExpression(); /* Bind the document to the external variable $d */ xqExpression.bindNode(new QName("d"), document); /* Execute the query - print the result */ FileReader fileReader = new FileReader(xquerySourceFile); xqSequence = xqExpression.executeQuery( fileReader); System.out.println(xqSequence.getSequenceAsString()); } catch (SAXException e) { System.out.println(xmlDataFile + " is not well-formed." + e); } catch (IOException e) { System.out.println( "Due to an IOException, the parser could not read " + xmlDataFile + ". " + e ); } catch (FactoryConfigurationError e) { System.out.println("Could not locate a factory class" + e); } catch (ParserConfigurationException e) { System.out.println("Could not locate a JAXP parser" + e); } catch (XQException e) { e.printStackTrace(); } finally { if (connection != null) { try { connection.close(); } catch (XQException e) { e.printStackTrace(); } } } } } </pre></td></tr></tbody></table> January 24, 2008 XQJ References <ol class="plain"> <li>XQuery 1.0: An XML Query Language, Working Draft 11th February 2005 <ul> <li><a href="http://www.w3.org/TR/xquery" target="_blank">http://www.w3.org/TR/xquery</a></li> </ul> </li> <li>JSR 225: XQuery API for Java™ (XQJ), Early Draft Review <ul> <li><a href="http://www.jcp.org/en/jsr/detail?id=225" target="_blank">http://www.jcp.org/en/jsr/detail?id=225</a></li> </ul> </li> <li>Document Object Model, DOM Level 3. <ul> <li><a href="http://www.w3.org/DOM/" target="_blank">http://www.w3.org/DOM/</a></li> </ul> </li> <li>JDBC API Specification 3.0 <ul> <li><a href="http://java.sun.com/products/jdbc" target="_blank">http://java.sun.com/products/jdbc</a></li> </ul> </li> <li>StAX - Stream API for XML <ul> <li><a href="http://dev2dev.bea.com/technologies/stax/index.jsp" target="_blank">http://dev2dev.bea.com/technologies/stax/index.jsp</a></li> </ul> </li> </ol>