<meta attribute="???">xxxx</meta>的用法 - hibernate配置文件生成java类

With <meta attribute="class-code"> you can add additional methods on a given class. However,such <meta>attributes can not be used at a property scope level and Hibernate Tools does not provide such <meta>attributes.

A possible solution for this is to modify the Freemarker templates responsible for generating the POJOs. If you look inside the hibernate-tools.jar archive,you can find the template pojo/PojoPropertyAccessor.ftl.

As its name indicates,this file is used to generate property accessors for POJOs.

Extract the PojoPropertyAccessor.ftl file into a local folder e.g. ${hbm.template.path},respecting the whole path,for example: ${hbm.template.path}/pojo/PojoPropertyAccessor.ftl.

The contents of the file will be something like this:

<#foreach property in pojo.getAllPropertiesIterator()>
    ${pojo.getPropertyGetModifiers(property)} 
    ${pojo.getJavaTypeName(property,jdk5)} 
    ${pojo.getGetterSignature(property)}() {
        return this.${property.name};
    }
    
    ${pojo.getPropertySetModifiers(property)} void set${pojo.getPropertyName(property)}
        (${pojo.getJavaTypeName(property,jdk5)} ${property.name}) 
    {
        this.${property.name} = ${property.name};
    }
</#foreach>

We can add pre and post conditions on our set method generation just by adding a little Freemarker syntax to the above source code:

{pojo.getGetterSignature(property)}()
    {
        return this.${property.namE};
    }
    
    ${pojo.getPropertySetModifiers(property)} void set${pojo.getPropertyName(property)}
        (${pojo.getJavaTypename(property,jdk5)} ${property.namE}) 
        {
      <#if pojo.has@H_257_361@metaAttribute(property,"pre-cond")> 
       ${C2j.getMetaAsString(property,"pre-cond","\n")} 
      </#if>      
      this.${property.namE} = ${property.namE};
      <#if pojo.hasMetaAttribute(property,"post-cond")> 
       ${C2j.getMetaAsString(property,"post-cond","\n")} 
      </#if>        
}
</#foreach>

Now if in any .hbm.xml file we define the <meta> attributes: pre-cond or post-cond,and their contents will be generated into the body of the relevant set method.

As an example let us add a pre-condition for the name property which will prevent the Person class from having an empty name. To achieve this we have to modify the Person.hbm.xml file like so:

<hibernate-mapping>
  <class name="Person">
  <id name="id" type="long">        
      <generator class="increment"/>
  </id>
  <property name="firstName" type="string">
      <meta attribute="pre-cond">
      if ((firstName != null) &amp;&amp; (firstName.length() == 0) ) {
        throw new IllegalArgumentException("firstName can not be an empty String");
      }
      </meta>
  </property>
</class>
</hibernate-mapping>

Finally we have to generate the Person.java class. For this we can use either Eclipse or Ant,as long as you remember to set or fill in the templatepath setting. For Ant we configure the <hibernatetool> task via thetemplatepath attribute as in:

    <target name="hbm2java">
        <taskdef name="hibernatetool"
          classname="org.hibernate.tool.ant.HibernateToolTask"
          classpathref="lib.classpath"/>
        <hibernatetool destdir="${hbm2java.dest.dir}"
          templatepath="${hbm.template.path}">
          <classpath>
            <path refid="pojo.classpath"/>
          </classpath>        
          <configuration>
            <fileset dir="${hbm2java.src.dir}">
              <include name="**/*.hbm.xml"/>
            </fileset>
          </configuration>
          <hbm2java/>
        </hibernatetool>
    </target>

Invoking the target <hbm2java> will generate file Person.java in ${hbm2java.dest.dir}:

// default package
import java.io.Serializable;
public class Person implements Serializable {

    public Long id;

    public String name;

    public Person(java.lang.String name) {
        this.name = name;
    }

    public Person() {
    }

    public java.lang.Long getId() {
        return this.id;
    }

    public void setId(java.lang.Long id) {
        this.id = id;
    }
    
    public java.lang.String getName() {
        return this.name;
    }

    public void setName(java.lang.String name) {
        if ((name != null) && (name.length() == 0)) {
            throw new IllegalArgumentException("name can not be an empty String");
        }
        this.name = name;
    }
    }

In conclusion,this document is intended to introduce you to Hibernate plugin specific features related to tools both for the Eclipse and Ant tasks.

In @L_674_85@ you've learned about a set of wizards for creaTing Mapping files,Configuration files,Console Configurations,become familiar with Mapping and Configuration files editors,tooling for organizing and controlling Reverse ENGIneering,Hibernate Console and Mapping diagrams.

The rest chapters have explored the use of the Hibernate Tools™ via Ant tasks.

Please visit @L_696_89@ to leave questions or/and suggestions on the topic. Your FeedBACk is always appreciated.