Frequently Asked Questions

A:

Java SE 6 or higher.

A:

This is no longer supported. However, you should be able to deploy http://search.maven.org/remotecontent?filepath=com/sun/xml/bind/jaxb1-impl/2.2.5-1/jaxb1-impl-2.2.5-1.jar with your with your application application.

A:

You need to recompile your schema with the newer JAXB 2.0 xjc and modify your application code to work with the new bindings.

A:

The JAXB Specification currently does not address the thread safety of any of the runtime classes. In the case of the Oracle JAXB RI, the JAXBContext class is thread safe, but the Marshaller, Unmarshaller, and Validator classes are not thread safe.

For example, suppose you have a multi-thread server application that processes incoming XML documents by JAXB. In this case, for the best performance you should have just one instance of JAXBContext in your whole application like this:

class MyServlet extends HttpServlet {
    static final JAXBContext context = initContext();

    private static JAXBContext initContext() {
        return JAXBContext.newInstance("....", MyServlet.class.getClassLoader());
    }
}

And each time you need to unmarshal/marshal/validate a document. Just create a new Unmarshaller/Marshaller/Validator from this context, like this:

public void doGet(HttpServletRequest req, HttpServletResponse resp) {
    Unmarshaller u = context.createUnmarshaller();
    u.unmarshal(...);
}

This is the simplest safe way to use the JAXB RI from multi-threaded applications.

If you really care about the performance, and/or your application is going to read a lot of small documents, then creating Unmarshaller could be relatively an expensive operation. In that case, consider pooling Unmarshaller objects. Different threads may reuse one Unmarshaller instance, as long as you don't use one instance from two threads at the same time.

A:

When you invoke JAXBContext.newInstance("aaa.bbb.ccc"), it tries to load classes and resources using the same classloader used to load the JAXBContext class itself. This classloader may be different from the classloader which was used to load your application (see the picture Parent/Child classloader). In this case, you'll see the above error. This problem is often seen with application servers, J2EE containers, Ant, JUnit, and other applications that use sophisticated class loading mechanisms.

Figure 1. Parent/Child classloader

With some applications, things get even more complicated when the JAXB-generated code can be loaded by either classloader. In this case, JAXBContext.newInstance("aaa.bbb.ccc") will work but the JVM ends up loading two copies of the generated classes for each class loader. As a result, unmarshalling works but an attempt to cast the returned object into the expected type will fail, even though its getClass().getName() returns the expected name.

The solution for both situations is to pass your curent class loader like this:

JAXBContext.newInstance("aaa.bbb.ccc", this.getClass().getClassLoader());

In general, if you are writing code that uses JAXB, it is always better to explicitly pass in a class loader, so that your code will work no matter where it is deployed.

A:

For JAXB 2.2.x:

$JAXB_HOME/mod/jakarta.xml.bind-api.jar
$JAXB_HOME/mod/jaxb-impl.jar

A:

This functionality is not available from JAXB directly, but you can configure an Apache Xerces-J XMLSerializer to produce CDATA blocks. Please review the JaxbCDATASample.java sample app for more detail.

A:

In JAXB 2.0, <xs:any/> is handled correctly without any customization.

A:

Run the following command

$ java -jar jaxb-xjc.jar -version

Alternatively, each JAXB jar has version information in its META-INF/MANIFEST.MF, such as this:

Manifest-Version: 1.0
Ant-Version: Apache Ant 1.8.2
Created-By: 1.6.0_29-b11 (Sun Microsystems Inc.)
Specification-Title: Java Architecture for XML Binding
Specification-Version: 2.2.6
Specification-Vendor: Oracle Corporation
Implementation-Title: JAXB Reference Implementation 
Implementation-Version: 2.2.5-SNAPSHOT
Implementation-Vendor: Oracle Corporation
Implementation-Vendor-Id: com.sun
Extension-Name: com.sun.xml.bind
Build-Id: 02/09/2012 01:42PM (hudson)
Class-Path: jakarta.xml.bind-api.jar