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copied!<p>If you want to start coding Java to XML and XML to Java in less than 5 minutes, try Simple XML Serialization. Don't spend hours learning the JAXB API <a href="http://simple.sourceforge.net/download/stream/doc/tutorial/tutorial.php" rel="nofollow noreferrer"> <a href="http://simple.sourceforge.net/download/stream/doc/tutorial/tutorial.php" rel="nofollow noreferrer">http://simple.sourceforge.net/download/stream/doc/tutorial/tutorial.php</a></a></p> <p>However, if you are really keen on learning JAXB, here's an excellent tutorial <a href="http://blogs.oracle.com/teera/entry/jaxb_for_simple_java_xml" rel="nofollow noreferrer"><a href="http://blogs.oracle.com/teera/entry/jaxb_for_simple_java_xml" rel="nofollow noreferrer">http://blogs.oracle.com/teera/entry/jaxb_for_simple_java_xml</a></a></p> <p>Contents of tutorial:</p> <p><strong>JAXB for simple Java-XML serialization</strong></p> <p>There're a number of way to do XML serialization in Java. If you want fine-grained control over parsing and serialization you can go for SAX, DOM, or Stax for better performance. Yet, what I often want to do is a simple mapping between POJOs and XML. However, creating Java classes to do XML event parsing manually is not trivial. I recently found JAXB to be a quick and convenient Java-XML mapping or serialization.</p> <p>JAXB contains a lot of useful features, you can check out the reference implementation here. <a href="https://www.java.net/blogs/kohsuke/" rel="nofollow noreferrer">Kohsuke's Blog</a> is also a good resource to learn more about JAXB. For this blog entry, I'll show you how to do a simple Java-XML serialization with JAXB.</p> <p><strong>POJO to XML</strong></p> <p>Let's say I have an Item Java object. I want to serialize an Item object to XML format. What I have to do first is to annotate this POJO with a few XML annotation from javax.xml.bind.annotation.* package. See code listing 1 for Item.java</p> <p>From the code</p> <ul> <li><code>@XmlRootElement(name="Item")</code> indicates that I want to be the root element.</li> <li><code>@XmlType(propOrder = {"name", "price"})</code> indicates the order that I want the element to be arranged in XML output.</li> <li><code>@XmlAttribute(name="id", ...)</code> indicates that id is an attribute to root element.</li> <li><code>@XmlElement(....)</code> indicates that I want price and name to be element within Item.</li> </ul> <p>My <code>Item.java</code> is ready. I can then go ahead and create JAXB script for marshaling Item.</p> <pre><code>//creating Item data object Item item = new Item(); item.setId(2); item.setName("Foo"); item.setPrice(200); ..... JAXBContext context = JAXBContext.newInstance(item.getClass()); Marshaller marshaller = context.createMarshaller(); //I want to save the output file to item.xml marshaller.marshal(item, new FileWriter("item.xml")); </code></pre> <p>For complete code Listing please see Code Listing 2 <code>main.java</code>. The output Code Listing 3 <code>item.xml</code> file is created. It looks like this:</p> <pre><code><?xml version="1.0" encoding="UTF-8" standalone="yes"?> <ns1:item ns1:id="2" xmlns:ns1="http://blogs.sun.com/teera/ns/item"> <ns1:itemName>Foo</ns1:itemName> <ns1:price>200</ns1:price> </ns1:item> </code></pre> <p>Easy right? You can alternatively channel the output XML as text String, Stream, Writer, ContentHandler, etc by simply change the parameter of the marshal(...) method like</p> <pre><code>... JAXBContext context = JAXBContext.newInstance(item.getClass()); Marshaller marshaller = context.createMarshaller(); // save xml output to the OutputStream instance marshaller.marshal(item, <java.io.OutputStream instance>); ... JAXBContext context = JAXBContext.newInstance(item.getClass()); Marshaller marshaller = context.createMarshaller(); StringWriter sw = new StringWriter(); //save to StringWriter, you can then call sw.toString() to get java.lang.String marshaller.marshal(item, sw); </code></pre> <p><strong>XML to POJO</strong></p> <p>Let's reverse the process. Assume that I now have a piece of XML string data and I want to turn it into Item.java object. XML data (Code listing 3) looks like</p> <pre><code><?xml version="1.0" encoding="UTF-8" standalone="yes"?> <ns1:item ns1:id="2" xmlns:ns1="http://blogs.sun.com/teera/ns/item"> <ns1:itemName>Bar</ns1:itemName> <ns1:price>80</ns1:price> </ns1:item> </code></pre> <p>I can then unmarshal this xml code to Item object by</p> <pre><code>... ByteArrayInputStream xmlContentBytes = new ByteArrayInputStream (xmlContent.getBytes()); JAXBContext context = JAXBContext.newInstance(Item.getClass()); Unmarshaller unmarshaller = context.createUnmarshaller(); //note: setting schema to null will turn validator off unmarshaller.setSchema(null); Object xmlObject = Item.getClass().cast(unmarshaller.unmarshal(xmlContentBytes)); return xmlObject; ... </code></pre> <p>For complete code Listing please see Code Listing 2 (main.java). The XML source can come in many forms both from Stream and file. The only difference, again, is the method parameter:</p> <pre><code>... unmarshaller.unmarshal(new File("Item.xml")); // reading from file ... // inputStream is an instance of java.io.InputStream, reading from stream unmarshaller.unmarshal(inputStream); </code></pre> <p><strong>Validation with XML Schema</strong></p> <p>Last thing I want to mention here is validating input XML with schema before unmarshalling to Java object. I create an XML schema file called item.xsd. For complete code Listing please see Code Listing 4 (Item.xsd). Now what I have to do is register this schema for validation.</p> <pre><code>... Schema schema = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI) .newSchema(new File("Item.xsd")); unmarshaller.setSchema(schema); //register item.xsd shcema for validation ... </code></pre> <p>When I try to unmarshal XML data to POJO, if the input XML is not conformed to the schema, exception will be caught. For complete code Listing please see Code Listing 5 (invalid_item.xml).</p> <pre><code>javax.xml.bind.UnmarshalException - with linked exception: javax.xml.bind.JAXBException caught: null [org.xml.sax.SAXParseException: cvc-datatype-valid.1.2.1: 'item1' is not a valid value for 'integer'.] </code></pre> <p>Here I change the 'id' attribute to string instead of integer.</p> <p>If XML input is valid against the schema, the XML data will be unmarshalled to Item.java object successfully.</p>

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