XVisitor: Visitor Pattern for JAXB

XVisitor is a plugin for the xjc code generator to enrich the JAXB model generated from an XML schema so that users can work with the Visitor pattern on this model.

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JAXB Marshalling with Custom Namespace Prefixes

The Problem

• You have an XML schema with multiple XML namespaces.
• You generate a JAXB model with xjc.
• You build a JAXB document model and use the JAXB Marshaller to create XML from the model.
• You want to override the default namespace prefixes ns1, ns2, ... created by the Marshaller.

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Java XML Binding with Property Change Support

In an earlier post, I was talking about generating Java classes with xjc with property change support which is not enabled by default. This post explains the details, an in fact the Maven build explained below is a lot a easier than my original approch with Ant which required some downloads to set things up.

The general idea is same as described by Kohsuke Kawaguchi in a post of 2007, but his POM is broken with the current stage of the Maven repositories. In addition, there is a tweak with the PropertyListener customization.

So here is a little example schema:

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema" xmlns:tns="http://www.example.org/person/" targetNamespace="http://www.example.org/person/">
    <complexType name="Person">
      <sequence>
        <element name="firstName" type="string"></element>
        <element name="lastName" type="string"></element>
        <element name="address" type="tns:Address"></element>
      </sequence>
    </complexType>

    <complexType name="Address">
      <sequence>
        <element name="street" type="string"></element>
        <element name="houseNumber" type="string"></element>
        <element name="city" type="string"></element>
        <element name="postalCode" type="string"></element>
        <element name="country" type="string"></element>
      </sequence>
    </complexType>
</schema>

We use the following file bindings.xjb to customize the Java classes generated by xjc. We make all classes serializable and include support for PropertyChangeListeners.

<?xml version="1.0" encoding ="UTF-8"?>
<jaxb:bindings
    schemaLocation="person.xsd"
    version="2.1"
    xmlns:li="http://jaxb.dev.java.net/plugin/listener-injector"
    xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
    xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <jaxb:bindings node="/xs:schema">
    <jaxb:globalBindings>
      <jaxb:serializable uid="1" />
    </jaxb:globalBindings>
    <li:listener>java.beans.PropertyChangeListener</li:listener>    
  </jaxb:bindings>
</jaxb:bindings>

The following POM takes care of the code generation:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>jaxb-properties</groupId>
  <artifactId>jaxb-properties</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>JAXB PropertyListener Demo</name>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.3</version>
        <configuration>
          <source>1.6</source>
          <target>1.6</target>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.jvnet.jaxb2.maven2</groupId>
        <artifactId>maven-jaxb2-plugin</artifactId>
        <version>0.7.3</version>
        <executions>
          <execution>
            <goals>
              <goal>generate</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <extension>true</extension>
          <generatePackage>com.example.jaxb</generatePackage>
          <schemaIncludes>
            <schemaInclude>person.xsd</schemaInclude>
          </schemaIncludes>
          <bindingIncludes>
            <bindingInclude>bindings.xjb</bindingInclude>
          </bindingIncludes>
          <args>
            <arg>-Xinject-listener-code</arg>
          </args>
        </configuration>
        <dependencies>
          <dependency>
            <groupId>com.sun.xml.bind</groupId>
            <artifactId>jaxb-xjc</artifactId>
            <version>2.1.13</version>
          </dependency>
          <dependency>
            <groupId>org.jvnet.jaxb2-commons</groupId>
            <artifactId>property-listener-injector</artifactId>
            <version>1.1-SNAPSHOT</version>
            <exclusions>
              <exclusion>
                <groupId>com.sun.xml.bind</groupId>
                <artifactId>jaxb-xjc</artifactId>
              </exclusion>
            </exclusions>
          </dependency>
        </dependencies>
      </plugin>

    </plugins>
  </build>
</project>

You do need to use the 1.1-SNAPSHOT version of the property-listener-injector, as the 1.0 release only supports VetoableChangeListeners and not the PropertyChangeListeners we want to use. The <li:listener> element in the bindings file is used to define the listener class.

It is important to exclude the jaxb-xjc dependency from the property-listener-injector, or else it will try to download an non-existing snapshot version. Looks like something is broken in the java.net repository, but then again, working with snapshot releases is always dangerous....