Configure Maven to generate classes from XML Schema using JAXB

In my previous post I showed how to create RESTful services using Spring Framework. For representation of resources in XML I used JAXB and I followed the bottom-up approach (I wrote the Java classes and I let to generate XML/XSD from Java classes). In this post I will demonstrate how you can generate the same Java classes (User and UserList) from XML Schema (XSD) during Maven build, therefore using a top-down approach. For generation of Java classes from XML Schema during Maven build I will use Java.net Maven 2 JAXB 2 Plugin.

Along with the default generation of Java classes from XML Schema using xjc tool, I will add the following customizations:

• Making all the generated classes to implement Serializable (useful when you want to use classes with some remote services: RMI, EJB, etc).
• Use java.util.Calendar instead of javax.xml.datatype.XMLGregorianCalendar for fields generated from elements of type xs:dateTime.
• Generated classes should also have a generated toString() method.
• Classes have to be annotated with XmlRootElement (required by Spring Framework when classes are used to represent state in RESTful services).
• You can further enhance and customize the generation of Java classes using various plugins.

Project sources are available for download. So let’s start, step by step:

1. Create Maven project. Below you can see the POM:

   <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/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <groupId>org.zmeu</groupId>
     <artifactId>zmeu-blog-maven-jaxb</artifactId>
     <version>1.0-SNAPSHOT</version>
     <name>ZMEU Blog Maven JAXB</name>
     <build>
       <plugins>
           <plugin>
             <artifactId>maven-compiler-plugin</artifactId>
             <configuration>
               <source>1.6</source>
               <target>1.6</target>
             </configuration>
           </plugin>
           <plugin>
             <groupId>org.jvnet.jaxb2.maven2</groupId>
             <artifactId>maven-jaxb2-plugin</artifactId>
             <version>0.8.0</version>
             <configuration>
               <schemaDirectory>src/main/resources/schema</schemaDirectory>
               <bindingDirectory>src/main/resources/schema</bindingDirectory>
               <generatePackage>org.zmeu.blog.jaxb</generatePackage>
               <strict>false</strict>
               <extension>true</extension>
               <plugins>
                 <plugin>
                   <groupId>org.jvnet.jaxb2_commons</groupId>
                   <artifactId>jaxb2-basics</artifactId>
                   <version>0.6.2</version>
                 </plugin>
                 <plugin>
                   <groupId>org.jvnet.jaxb2_commons</groupId>
                   <artifactId>jaxb2-basics-annotate</artifactId>
                   <version>0.6.2</version>
                 </plugin>
               </plugins>
               <args>
                 <arg>-Xannotate</arg>
                 <arg>-XtoString</arg>
               </args>
             </configuration>
             <executions>
               <execution>
                 <id>generate</id>
                 <goals>
                   <goal>generate</goal>
                 </goals>
               </execution>
             </executions>
           </plugin>
       </plugins>
     </build>
     <dependencies>
       <dependency>
         <groupId>org.jvnet.jaxb2_commons</groupId>
         <artifactId>jaxb2-basics-runtime</artifactId>
         <version>0.6.2</version>
       </dependency>
     </dependencies>
   </project>
   

2. Write XML Schema (schema.xsd):

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <xs:schema version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema">
   
       <xs:element name="user" type="user" />
       <xs:element name="userList" type="userList" />
   
       <xs:complexType name="user">
           <xs:all>
               <xs:element name="id" type="xs:long" minOccurs="0" />
               <xs:element name="name" type="xs:string" />
               <xs:element name="registrationDate" type="xs:dateTime" />
           </xs:all>
       </xs:complexType>
   
       <xs:complexType name="userList">
           <xs:sequence>
               <xs:element name="user" type="user" minOccurs="0"
                   maxOccurs="unbounded" />
           </xs:sequence>
       </xs:complexType>
       
   </xs:schema>
   

3. Customize JAXB Bindings (binding.xjb):

   <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
   <jaxb:bindings xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
       xmlns:xs="http://www.w3.org/2001/XMLSchema"
       xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:annox="http://annox.dev.java.net" 
       xsi:schemaLocation="http://java.sun.com/xml/ns/jaxb
           http://java.sun.com/xml/ns/jaxb/bindingschema_2_0.xsd"
       version="2.1">
       <jaxb:globalBindings>
           <!-- Use Calendar instead of XMLGregorianCalendar for xs:dateTime -->
           <jaxb:javaType name="java.util.Calendar" xmlType="xs:dateTime"
                   parseMethod="javax.xml.bind.DatatypeConverter.parseDateTime" 
                   printMethod="javax.xml.bind.DatatypeConverter.printDateTime" />
   
           <!-- Force all classes implements Serializable -->
           <xjc:serializable uid="1" />
       </jaxb:globalBindings>
   
       <!-- Annotate the following classes with XmlRootElement -->
       <jaxb:bindings schemaLocation="schema.xsd" node="/xs:schema">
           <jaxb:bindings node="xs:complexType[@name='user']">
               <annox:annotate>
                   <annox:annotate annox:class="javax.xml.bind.annotation.XmlRootElement"
                       name="user" />
               </annox:annotate>
           </jaxb:bindings>
           <jaxb:bindings node="xs:complexType[@name='userList']">
               <annox:annotate>
                   <annox:annotate annox:class="javax.xml.bind.annotation.XmlRootElement"
                       name="userList" />
               </annox:annotate>
           </jaxb:bindings>
       </jaxb:bindings>
   </jaxb:bindings>
   

4. Run the build using mvn clean install command. Build must be successful. Generated classes will be located in target/generated-sources/xjc directory. Below is a snippet from generated User class:

   .....
   
   @XmlAccessorType(XmlAccessType.FIELD)
   @XmlType(name = "user", propOrder = {})
   @XmlRootElement(name = "user")
   public class User implements Serializable, ToString {
       private final static long serialVersionUID = 1L;
       
       protected Long id;
       
       @XmlElement(required = true)
       protected String name;
       
       @XmlElement(required = true, type = String.class)
       @XmlJavaTypeAdapter(Adapter1 .class)
       @XmlSchemaType(name = "dateTime")
       protected Calendar registrationDate;
   
       .....
   }
   

5. You are done!

Update (01-Jun-2013): In case you have several schema files and you wish to generate java classes in different packages then you have the option to specify the package inside JAXB binding file (*.xjb). For this you have to:

• Remove generatePackage element from maven-jaxb2-plugin configuration. In our case remove the line: <generatePackage>org.zmeu.blog.jaxb</generatePackage>
• Add the desired package name for every schema file inside JAXB binding file (*.xjb) as follows (see the highlighted section):

  <jaxb:bindings schemaLocation="schema.xsd" node="/xs:schema">
      <jaxb:schemaBindings>
          <jaxb:package name="org.zmeu.blog.jaxb.user" />
      </jaxb:schemaBindings>
  
      <jaxb:bindings node="xs:complexType[@name='user']">
          <annox:annotate>
              <annox:annotate annox:class="javax.xml.bind.annotation.XmlRootElement"
                  name="user" />
          </annox:annotate>
      </jaxb:bindings>
      <jaxb:bindings node="xs:complexType[@name='userList']">
          <annox:annotate>
              <annox:annotate annox:class="javax.xml.bind.annotation.XmlRootElement"
                  name="userList" />
          </annox:annotate>
      </jaxb:bindings>
  </jaxb:bindings>