A sample using Hibernate and Spring on Z2¶

This sample is very similar to Sample-hibernate-basic but differs in that we use the Spring framework throughout...

• for assembly within the modules and to wire services between modules
• for declarative transaction demarcation
• for JPA entity manager injection

This is another practical application of How to Spring.

This sample is stored in z2-samples.spring-hibernate.

Prerequisites¶

You need the z_tx_tests database on a local MySQL database system. Start the MySQL client as the root user and run:

create database z_tx_tests;
grant all on z_tx_tests.* to tx@localhost identified by 'tx';

Run it¶

Like all samples, also this sample can be run as in How to run a sample. If you have the database, the fastest way to verify whether it runs is:

mkdir install
cd install 
git clone -b master http://git.z2-environment.net/z2-base.core
git clone -b master http://git.z2-environment.net/z2-samples.spring-hibernate

# on Linux / Mac OS:
cd z2-base.core/run/bin
./gui.sh

# on Windows:
cd z2-base.core\run\bin
gui.bat

When running, go to http://localhost:8080/spring-hibernate. You should see this:

Details¶

Similar to Sample-hibernate-basic, the assumption of this example is that of a re-use domain module com.zfabrik.samples.spring-hibernate.domain that implements a "Thingy Repository" and is used from a web application that is in another module com.zfabrik.samples.spring-hibernate.web. The domain module exposes the Thingy Repository as a Z2 component - from a Spring application context defined bean - that is imported into the application context of the Web application and injected into the controller filter by Spring. The controller uses declarative transaction demarcation.

The domain module makes use of Hibernate's JPA implementation using Spring's entity manager injection and integrates with the transaction management provided by com.zfabrik.jta.

The domain module and its persistence context¶

The domain module com.zfabrik.samples.spring-hibernate.domain defines a persistence unit "thingies" in java/src.impl/META-INF/persistence.xml, i.e. in its implementation. That makes sense, as the XML file will be looked up with a class loader and we do not intent to retrieve from another module. Or, put differently, the persistence unit is not part of the module's API.

In order to integrate with the built-in transaction management the persistence.xml declares the JTA data source

<jta-data-source>components:com.zfabrik.samples.hibernate-basic.domain/DB</jta-data-source>

and the Transaction Manager Lookup

<property name="hibernate.transaction.manager_lookup_class" value="com.zfabrik.hibernate.TransactionManagerLookup" />

The former points to the data source component com.zfabrik.samples.spring-hibernate.domain/DB, while the latter makes sure Hibernate can register with the transaction manager implementation.

The persistence unit defines only one entity. The Thingy as in Thingy.java. That is an API-exposed type. We use the simplified pattern of exposing persistent objects in the API rather than using Data Transfer Objects (DTOs).

The application context of the module is defined in java/src.impl/META-INF/applicationContext.xml and looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx" 
    xmlns:context="http://www.springframework.org/schema/context" 
    xmlns:aop="http://www.springframework.org/schema/aop" 
    xsi:schemaLocation=" 
    http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd  
    http://www.springframework.org/schema/context  http://www.springframework.org/schema/context/spring-context-3.0.xsd  
    http://www.springframework.org/schema/tx  http://www.springframework.org/schema/tx/spring-tx-3.0.xsd  
    http://www.springframework.org/schema/aop  http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">

    <!-- annotation based config -->
    <context:component-scan base-package="com.zfabrik.samples.spring_hibernate" />
    <context:annotation-config />

    <!-- EntityManager injection -->
    <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />

    <!-- The actual EMF we use -->
    <bean id="entityManagerFactory"    class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="persistenceUnitName" value="thingies" />
    </bean>

</beans>

In short:

• We make sure we can use annotations
• We enable entity manager injection
• We initialize the entity manager factory from Spring

In the implementation class ThingyRepositoryImpl we make use of these capabilities and declare a Spring bean "thingyRepository":

@Repository("thingiesRepository")
public class ThingyRepositoryImpl implements ThingyRepository {
    @PersistenceContext
    private EntityManager em;

    @Override
    public void store(Thingy thingy) {
        this.em.persist(thingy);
    }

    @SuppressWarnings("unchecked")
    @Override
    public Collection<Thingy> findAll() {
        return this.em.createQuery("select t from Thingy t").getResultList();
    }

    @Override
    public void delete(int id) {
        Thingy t = this.em.find(Thingy.class, id);
        if (t != null) {
            this.em.remove(t);
        }
    }
}

In order to expose that bean as a Z2 component for re-use from other modules, we declare a component com.zfabrik.samples.spring-hibernate/repository:

com.zfabrik.component.type=org.springframework.bean

#
# Expose Spring defined data source
#

#
# the context that defines the bean (more than one
# bean can be exposed like this)
#
bean.context=com.zfabrik.samples.spring-hibernate.domain/applicationContext

#
# the bean name
#
bean.name=thingiesRepository

that is based on the application context component com.zfabrik.samples.spring-hibernate/applicationContext:

com.zfabrik.component.type=org.springframework.context

#
# context config location is where the context is 
# actually defined. 
#
context.contextConfigLocation=classpath:META-INF/applicationContext.xml

See also How to Spring for more details on these component types.

The web module, transaction boundaries, and service re-use¶

Let's turn to the Web application in com.zfabrik.samples.spring-hibernate.web/web. This one is also Spring configured. In contrast to the service module, its application context is not initialized from a Z2 component but rather from the Web app context (see web/WebContent/WEB-INF/web.xml). It is stored in web/WebContent/WEB-INF/applicationContext.xml and looks like this:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:tx="http://www.springframework.org/schema/tx" 
    xmlns:context="http://www.springframework.org/schema/context" 
    xmlns:aop="http://www.springframework.org/schema/aop" xmlns:security="http://www.springframework.org/schema/security" 
    xsi:schemaLocation="http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-3.0.xsd  
    http://www.springframework.org/schema/context  http://www.springframework.org/schema/context/spring-context-3.0.xsd  
    http://www.springframework.org/schema/tx  http://www.springframework.org/schema/tx/spring-tx-3.0.xsd  
    http://www.springframework.org/schema/aop  http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
    http://www.springframework.org/schema/security http://www.springframework.org/schema/security/spring-security-3.0.3.xsd">

    <!-- Annotation Support -->
    <context:component-scan base-package="com.zfabrik.samples.spring_hibernate" />
    <context:spring-configured />
    <context:annotation-config />        

    <!--  
    This binds to java:comp/UserTransaction, which is ok in a Web app and considering
    that we configured Jetty JTA (see the transaction manager how-to in the Z2 Wiki and check environment/webServer/jetty.xml)
    -->

    <tx:jta-transaction-manager/>

    <!-- outside of a web app we would bind to com.zfabrik.jta transaction manager like this

    <bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager">
        <property name="userTransaction">
            <bean class="com.zfabrik.tx.UserTransaction"/>
        </property>
    </bean>
     -->

    <!-- make sure we can use @transactional with the Spring aspect -->
    <tx:annotation-driven transaction-manager="transactionManager" mode="aspectj"/>

    <!-- import external services -->
    <bean id="thingyRepository" class="com.zfabrik.springframework.ComponentFactoryBean">
        <property name="componentName"  value="com.zfabrik.samples.spring-hibernate.domain/repository" />
        <property name="className"  value="com.zfabrik.samples.spring_hibernate.thingies.ThingyRepository" />
    </bean>

</beans>

In short:

• We enable annotation based configuration
• We make the transaction manager available (for in-depth details see How to transaction management)
• We enabled annotation based transaction demarcation (i.e. the use of @transactional)
• We import the Thingy Repository as a bean into this context.

The ControllerFilter is configured by Spring, although it is instantiated by the Jetty Web container. That is happening because we use the Spring aspect (see How to Spring once more) and it is annotated with @configurable. We let Spring inject the Thingy Repository and we mark the doFilter method as transactional. Here is its skeleton:

@Configurable
public class ControllerFilter implements Filter {

  @Autowired
  private ThingyRepository thingyRepository;

  @Transactional
  public void doFilter(ServletRequest sreq, ServletResponse sres,    FilterChain chain) throws IOException, ServletException {

    // do some work here

  }

  @Override
  public void init(FilterConfig cfg) throws ServletException {}

  @Override
  public void destroy() {}
}

A final word¶

A lot of what happens here requires the right libraries to be available in the sample modules. These are provided via the references in the z.properties files in the respective Java modules.
In other words: There is some non-trivial mechanics going on here that - in the long run - you should be aware of and try to read carefully through How to Spring. As a result you get a lot of coding and modularization convenience in the combination of Spring and Z2.