Hibernate, generate entities and database from mapping file

Question

I was wondering if it was possible to generate entities from hibernate mapping file. My ultimate goal is to programmaticaly create a mapping file, and then create the database from it. I know that I can use :

<prop key="hibernate.hbm2ddl.auto">create</prop>

To create database form entities, but is there a way, (without eclipse tool, I need to do it automatically in the application) to generate entities from mapping? (Or even directly database from mapping).

I don't know if other tools can do it, but I though I would use Hibernate because of the cross database compatibility.

Thank you! Guillaume

Answer 1

You can use maven with the help of mojo plugins to generate Java entities by providing your hibernate mapping files.

Here is a sample maven project:

Create your maven project of this structure:

¦pom.xml
¦
+---src
¦   +---main
¦       +---java
¦       +---resources
¦           ¦   hibernate.cfg.xml
¦           ¦
¦           +---hbmFiles
¦                   Person.hbm.xml

The hibernate configuration file hibernate.cfg.xml is placed in YourProject/src/main/java/resources

The mapping files should be placed in resources or sub-directory of resources folder.

Contents of Person.hbm.xml file:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="com.mypackage.Person" table="person">
   <id name="id" column="id" type="int"/>
   <property name="name" column="name" type="string"/>
</class>
</hibernate-mapping>

Contents of hibernate.cfg.xml file:

<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <mapping resource="hbmFiles/Person.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

Contents of pom.xml file:

<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.hibernate.tutorials</groupId>
  <artifactId>MyProject</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>MyProject</name>
  <url>http://maven.apache.org</url>
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  <build>
     <plugins>
        <plugin>
           <groupId>org.codehaus.mojo</groupId>
           <artifactId>hibernate3-maven-plugin</artifactId>
           <version>2.2</version>
           <executions>
             <execution>
              <phase>default</phase>
              <goals>
                <goal>hbm2java</goal>
              </goals>
             </execution>
            </executions>
           <configuration>
             <components>
              <component>
               <name>hbm2java</name>
               <implementation>configuration</implementation>
               <outputDirectory>generated-sources/hibernate3</outputDirectory>
              </component>
             </components>
             <componentProperties>
              <drop>true</drop>
              <ejb3>true</ejb3>
              <jdk5>true</jdk5>
             </componentProperties>
           </configuration>
        </plugin> 
     </plugins>
  </build>
</project>

The property - ejb3=true is useful if you need annotations in your generated java entity files. If annotations are not required then you can just remove the line - <ejb3>true</ejb3>

After creating these 3 file, you can run the command:

mvn clean hibernate3:hbm2java

Now maven generates the java entity files at path -

YourProject/generated-sources/hibernate3/..package_mentioned_in_hbm_files../Student.java