I my previous post Creating Java classes from an XML schema I used xjc to generate the Java classes for a small project.

Ultimately I try to automate my tasks as much as possible and also don’t want to have to write a document with lots of steps when passing code onto others to use. So I decided it was time to get Maven to (as part of it’s process) automatically generate the classed for me using xjc.

So now when passing my app. to somebody else to take on, I just say run mvn install and it’ll do everything else for you.

To get this to work we need to use the xjc/jaxb-2 plugin.

In your pom.xml, add the following

<build>
   <pluginManagement>
      <plugins>
         <plugin>
           <groupId>org.apache.maven.plugins</groupId>
           <artifactId>maven-compiler-plugin</artifactId>
           <configuration>
              <source>1.7</source>
              <target>1.7</target>
           </configuration>
         </plugin>
     </plugins>
   </pluginManagement>
   <plugins>
      <plugin>
         <groupId>org.codehaus.mojo</groupId>
         <artifactId>jaxb2-maven-plugin</artifactId>
         <version>1.6</version>
         <executions>
            <execution>
               <id>request-xsd</id>
               <goals>
                  <goal>xjc</goal>
               </goals>
               <configuration>
                  <packageName>com.putridparrot.request</packageName>
                  <schemaDirectory>src/main/resources/xsd/request-xsd</schemaDirectory>
                  <clearOutputDir>false</clearOutputDir>
               </configuration>
            </execution>
            <execution>
               <id>request-xsd</id>
               <goals>
                  <goal>xjc</goal>
               </goals>
               <configuration>
                  <packageName>com.putridparrot.response</packageName>
                  <schemaDirectory>src/main/resources/xsd/response-xsd</schemaDirectory>
                  <clearOutputDir>false</clearOutputDir>
               </configuration>
            </execution>
         </executions>
      </plugin>
   </plugins>
</build>

In the above example, I actually have a request xsd and a response xsd for a webservice call. The problem (and hence why I have two separate execution sections) is that they have duplicate type names, which meant if I had them both in the same folder would end up with conflicts and an error for the class generation.

Note: The folder xsd can be named anything you like and contain the XSD’s themselves or contain folders, as I’m using.

The jaxb2-maven-plugin does all the work for us, it executes xjc, creates the package for out resultant classes (i.e. com.putridparrot.request and com.putridparrot.response). It generates the classes from the schema in the schemaDirectory (i.e. all XSD’s within that directory) and it’s doesn’t clear the output folder. This is not important if you are not outputting to the source folder or don’t want the output folder cleared when maybe not regenerating everything within it, but it’s very useful to stop you accidentally deleting all your source (as I did whilst outputting to the src/main/java folder initially!).

If you do not specify and output directory then the classes will be generated into your target folder, within target/generated-sources/jaxb/<you package names>.

These files are then compiled into your application and available to use in your source.