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13492586
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2012-11-21T11:46:34.830
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2012-11-21T11:46:34.830
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There are a couple of different ways to support this use case. <hr> OPTION #1 - DOM Approach You could always use a DOM parser to convert the XML to a <code>Document</code> perform an XPath against it to get the value of the <code>id</code> element and then unmarshal the document based on the result <hr> OPTION #2 - SAX Approach LookAheadUnmarshallerHandler You could leverage a SAX parser and JAXB's <code>UnmarshallerHandler</code> mechanism and do the following: <ul> <li>Create a <code>ContentHandler</code> that queues up SAX events until the necessary information is discovered.</li> <li>Create/retrieve a <code>JAXBContext</code> based on the value of the <code>id</code> element.</li> <li>Create an <code>UnmarshallerHandler</code> from the <code>JAXBContext</code>.</li> <li>Call the queued events on the <code>UnmarshallerHandler</code>.</li> <li>Set the <code>UnmarshallerHandler</code> on the <code>XMLReader</code> as the <code>ContentHandler</code>.</li> <li>Retrieve the unmarshalled object from the <code>UnmarshallerHandler</code>.</li> </ul> <pre class="lang-java prettyprint-override"><code>package forum13397834; import java.util.*; import javax.xml.bind.*; import org.xml.sax.*; import org.xml.sax.helpers.DefaultHandler; public class LookAheadUnmarshallerHandler extends DefaultHandler { private XMLReader xmlReader; private List<Event> events = new ArrayList<Event>(); private UnmarshallerHandler unmarshallerHandler; public LookAheadUnmarshallerHandler(XMLReader xmlReader) { this.xmlReader = xmlReader; } @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { events.add(new StartElement(uri, localName, qName, attributes)); } @Override public void endElement(String uri, String localName, String qName) throws SAXException { if("id".equals(localName) || "id".equals(qName)) { Characters characters = (Characters) events.get(events.size() - 1); String value = characters.getString(); JAXBContext jc; try { if("1234".equals(value)) { jc = JAXBContext.newInstance(Root1.class); } else if("5678".equals(value)) { jc = JAXBContext.newInstance(Root2.class); } else { jc = JAXBContext.newInstance(Root3.class); } unmarshallerHandler = jc.createUnmarshaller().getUnmarshallerHandler(); } catch(JAXBException e) { throw new RuntimeException(e); } unmarshallerHandler.startDocument(); for(Event event : events) { event.event(unmarshallerHandler); } unmarshallerHandler.endElement(uri, localName, qName); xmlReader.setContentHandler(unmarshallerHandler); } else { events.add(new EndElement(uri, localName, qName)); } } @Override public void characters(char[] ch, int start, int length) throws SAXException { events.add(new Characters(ch, start, length)); } public Object getResult() throws JAXBException { return unmarshallerHandler.getResult(); } private static abstract class Event { public abstract void event(ContentHandler contentHandler) throws SAXException; } private static class StartElement extends Event { private String uri; private String localName; private String qName; private Attributes attributes; public StartElement(String uri, String localName, String qName, Attributes attributes) { this.uri = uri; this.localName = localName; this.qName = qName; this.attributes = attributes; } @Override public void event(ContentHandler contentHandler) throws SAXException { contentHandler.startElement(uri, localName, qName, attributes); } } private static class Characters extends Event { private char[] ch; private int start; private int length; public Characters(char[] ch, int start, int length) { this.ch = ch; this.start = start; this.length = length; } @Override public void event(ContentHandler contentHandler) throws SAXException { contentHandler.characters(ch, start, length); } public String getString() { return new String(ch, start, length); } } private static class EndElement extends Event { private String uri; private String localName; private String qName; public EndElement(String uri, String localName, String qName) { this.uri = uri; this.localName = localName; this.qName = qName; } @Override public void event(ContentHandler contentHandler) throws SAXException { contentHandler.endElement(uri, localName, qName); } } } </code></pre> JAVA MODEL The following object model is based on the classes you mention in your question. UserA <pre class="lang-java prettyprint-override"><code>package forum13397834; import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement(name="root") public class UserA { } </code></pre> UserB <pre class="lang-java prettyprint-override"><code>package forum13397834; import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement(name="root") public class UserB { } </code></pre> UserC <pre class="lang-java prettyprint-override"><code>package forum13397834; import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement(name="root") public class UserC { } </code></pre> INPUT (input.xml) We will use the XML document from your question as the input for this example. <pre><code><root> <user> <id>1234</id> </user> <XMLelements> ... </XMLelements> </root> </code></pre> DEMO CODE <pre class="lang-java prettyprint-override"><code>package forum13397834; import javax.xml.parsers.SAXParserFactory; import org.xml.sax.*; public class Demo { public static void main(String[] args) throws Exception { SAXParserFactory spf = SAXParserFactory.newInstance(); spf.setNamespaceAware(true); XMLReader xmlReader = spf.newSAXParser().getXMLReader(); LookAheadUnmarshallerHandler handler = new LookAheadUnmarshallerHandler(xmlReader); xmlReader.setContentHandler(handler); xmlReader.parse(new InputSource("src/forum13397834/input.xml")); Object object = handler.getResult(); System.out.println(object.getClass()); } } </code></pre> Output <pre><code>class forum13397834.UserA </code></pre>
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1. POHow do unmarshalling to different objects depending on the XML received?
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1. USBlaise Doughan
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1. POHow do unmarshalling to different objects depending on the XML received?
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1. COThank you Blaise, It seems what I'm looking for. I have to integrate it with Spring framework and I'll see if It works correctly
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