Generating EJB3 classes from a database

Generating EJB3 classes from a database is not that hard. Yay! First you need to download and unzip hibernate tools. You'll want to have the hibernate tools docs at hand. Next you need to grab a bunch of jars. Almost all the jars can be found in /plugins/org.hibernate.eclipse.x.x.x/lib/tools/hibernate-tools.jar . Then download ejb3-persistence.jar. Below are all the jars I collected. Don't worry about overkill, you're not going to include any of these jars in your distribution.

antlr-2.7.6.jar    dom4j-1.6.1.jar    hibernate3.jar    jtidy-r8-20060801.jar
asm-attrs.jar    ehcache-1.2.3.jar   jaas.jar    log4j-1.2.15.jar
asm.jar     ejb3-persistence.jar   javassist.jar    lucene-core-2.2.0.jar
bsh-2.0b1.jar    freemarker.jar    jboss-cache.jar    oscache-2.1.jar
c3p0-0.9.1.jar    hibernate-annotations.jar  jboss-common.jar   postgresql-8.4-701.jdbc3.jar
cglib-2.1.3.jar    hibernate-commons-annotations.jar jboss-jmx.jar    proxool-0.8.3.jar
commons-collections-2.1.1.jar  hibernate-entitymanager.jar  jboss-system.jar   swarmcache-1.0rc2.jar
commons-logging-1.0.4.jar  hibernate-search.jar   jdbc2_0-stdext.jar
concurrent-1.3.2.jar   hibernate-tools.jar   jgroups-2.2.8.jar
connector.jar    hibernate-validator.jar   jta.jar

Now create your build.xml file:

<?xml version="1.0" encoding="UTF-8"?>
<project name="my-proj" default="gen_hibernate" basedir=".">
        <property name="src" location="src" />
        <property name="build" location="build" />
        <property name="generated" location="generated" />

        <path id="toolslib">
          <fileset dir="${basedir}">
             <include name="lib/*.jar"/>
          </fileset>
        </path>

        <taskdef name="hibernatetool"
                 classname="org.hibernate.tool.ant.HibernateToolTask"
                 classpathref="toolslib" />

        <target name="gen_hibernate">
                <hibernatetool>
                        <jdbcconfiguration
                                packagename="com.my.proj"
                            configurationfile="hibernate.cfg.xml"
                                detectManytoMany="true"
                                detectOptimisticLock="true">
                          </jdbcconfiguration>
                        <hbm2hbmxml destdir="${generated}" />
                </hibernatetool>
        </target>

        <target name="gen_java" depends="gen_hibernate">
                <hibernatetool destdir="${src}">
                        <annotationconfiguration configurationfile="hibernate.cfg.xml">
                                <fileset dir="${generated}">
                                <include name="**/*.hbm.xml"/>
                                </fileset>
                        </annotationconfiguration>
                        <hbm2java jdk5="true" ejb3="true"/>
                </hibernatetool>
        </target>

        <target name="compile" depends="gen_java">
                <mkdir dir="${build}/classes" />
                <javac srcdir="${src}" destdir="${build}/classes" classpathref="toolslib" />
        </target>

        <target name="jar" depends="compile">
                <jar destfile="my-proj.jar" basedir="${build}/classes" />
        </target>
        <target name="clean">
                <delete dir="${build}" />
                <delete dir="${src}" />
                <delete dir="${generated}" />
        </target>
</project>

If you're using postgres your hibernate.cfg.xml file should look like:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
                "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
                "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
        <session-factory name="myproj">
                <property name="hibernate.connection.driver_class">org.postgresql.Driver</property>
                <property name="hibernate.connection.url">jdbc:postgresql://your-url</property>
                <property name="hibernate.connection.username">your-username</property>
                <property name="hibernate.connection.password">your-password</property>
                <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
        </session-factory>
</hibernate-configuration>
</pre></blockquote>

run ant jar and you should be good to go!

Depending on how you're setup you should also consider running <hbm2cfgxml ejb3="true"> it creates a nice hibernate.cfg.xml file with all the classes and your DB connection info.