Maven JAXB2 Plugin and Configuring Package Names

Several Maven plugins exist for generating classes from a schema definition. One I have yet to try is the Maven JAXB2 Plugin. Below I'll show the minimum setup for using the plugin in your project, as well as a couple of methods for dealing with the package name assigned to the generated classes.

Given the simplistic schema below, placed in src/main/resources of the project:

  <?xml version="1.0" encoding="utf-8"?>
  <xsd:schema xmlns="http://example.org/message/1.0" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="message">
      <xsd:complexType>
        <xsd:sequence>
          <xsd:element name="text" type="xsd:string"/>
        </xsd:sequence>
      </xsd:complexType>    
    </xsd:element>
  </xsd:schema>

We can add the plugin definition to our POM:

  <plugin>
    <groupId>org.jvnet.jaxb2.maven2</groupId>
    <artifactId>maven-jaxb2-plugin</artifactId>
    <version>0.8.0</version>
    <executions>
      <execution>
        <goals>
          <goal>generate</goal>
        </goals>
      </execution>
    </executions>
  </plugin>

The classes generated by the plugin can be found in target/generated-sources/xjc. Below is the single class, Message.java, generated by the plugin (with the imports optimized and comments removed for brevity):

  package generated;

  import javax.xml.bind.annotation.*;

  @XmlAccessorType(XmlAccessType.FIELD)
  @XmlType(name = "", propOrder = {"text"})
  @XmlRootElement(name = "message")
  public class Message {

      @XmlElement(required = true)
      protected String text;

      public String getText() {
          return text;
      }

      public void setText(String value) {
          this.text = value;
      }
  }

The first thing that stands out to me is the package name of generated. This might be ok if I wanted to use the generated classes within a single project, but if I wanted to distribute them, a more useful package name might be helpful.

The user guide for the plugin describes a list of configuration options. The one we're looking for might just be generatePackage, which we can add:

  <plugin>
    <groupId>org.jvnet.jaxb2.maven2</groupId>
    <artifactId>maven-jaxb2-plugin</artifactId>
    <version>0.8.0</version>
    <executions>
      <!-- ... -->
    </executions>
    <configuration>
      <generatePackage>org.example.message</generatePackage>
    </configuration>
  </plugin>

The generated class can now be found in target/generated-sources/xjc/org/example/messsage/Message.java, with the new package name:

  package org.example.message;

  public class Message {
     // ...
  }

There are a couple more options for setting the package name, one is to add an annotation to the schema:

  <?xml version="1.0" encoding="utf-8"?>
  <xsd:schema xmlns="http://example.org/message"
      xmlns:xsd="http://www.w3.org/2001/XMLSchema" 
      xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc" 
      xmlns:jaxb="http://java.sun.com/xml/ns/jaxb" 
      jaxb:version="2.0">
    <xsd:annotation>
      <xsd:appinfo>
        <jaxb:schemaBindings>
          <jaxb:package name="org.example.test"/>
        </jaxb:schemaBindings>
      </xsd:appinfo>
    </xsd:annotation>
    <xsd:element name="message">
      <!-- ... -->
    </xsd:element>
  </xsd:schema>

If you find annotating a schema to for something like JAXB impurifies the schema, you could influence to derive a namespace by providing a targetNamespace attribute to the root element of the schema:

  <?xml version="1.0" encoding="utf-8"?>
  <xsd:schema xmlns="http://example.org/message"
      targetNamespace="http://example.org/message" ...>
      <!-- ... -->
  </xsd:schema>

If you have any other suggestions or feel like weighing in on the use of xjc annotations in schema definitions, please feel free to add a comment below.