Generate Java classes from .XSD files...?

Question

JAXB does EXACTLY what you want. It's built into the JRE/JDK starting at 1.6

To expand on the "use JAXB" comments above,

In Windows "%java_home%\bin\xjc" -p [your namespace] [xsd_file].xsd

e.g., "%java_home%\bin\xjc" -p com.mycompany.quickbooks.obj quickbooks.xsd

Wait a bit, and if you had a well-formed XSD file, you will get some well-formed Java classes

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 http://simple.sourceforge.net/download/stream/doc/tutorial/tutorial.php

However, if you are really keen on learning JAXB, here's an excellent tutorial http://blogs.oracle.com/teera/entry/jaxb_for_simple_java_xml

Contents of tutorial:

JAXB for simple Java-XML serialization

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.

JAXB contains a lot of useful features, you can check out the reference implementation here. Kohsuke's Blog 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.

POJO to XML

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

From the code

• @XmlRootElement(name="Item") indicates that I want to be the root element.
• @XmlType(propOrder = {"name", "price"}) indicates the order that I want the element to be arranged in XML output.
• @XmlAttribute(name="id", ...) indicates that id is an attribute to root element.
• @XmlElement(....) indicates that I want price and name to be element within Item.

My Item.java is ready. I can then go ahead and create JAXB script for marshaling Item.

//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"));

For complete code Listing please see Code Listing 2 main.java. The output Code Listing 3 item.xml file is created. It looks like this:

<?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>

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

...
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);

XML to POJO

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

<?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>

I can then unmarshal this xml code to Item object by

...
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;
...

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:

...
unmarshaller.unmarshal(new File("Item.xml")); // reading from file
...
// inputStream is an instance of java.io.InputStream, reading from stream
unmarshaller.unmarshal(inputStream);

Validation with XML Schema

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.

...
Schema schema = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI)
.newSchema(new File("Item.xsd"));
unmarshaller.setSchema(schema); //register item.xsd shcema for validation
...

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).

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'.]

Here I change the 'id' attribute to string instead of integer.

If XML input is valid against the schema, the XML data will be unmarshalled to Item.java object successfully.

Using Eclipse IDE:-

1. copy the xsd into a new/existing project.
2. Make sure you have JAXB required JARs in you classpath. You can download one here.
3. Right click on the XSD file -> Generate -> JAXB classes.

the easiest way is using command line. Just type in directory of your .xsd file:

xjc myFile.xsd.

So, the java will generate all Pojos.