Can I use one hibernate persistence unit on tomcat and share it between deployed wars?

Question

I have an application running on tomcat where we have multiple wars.

1. War1 is a web app that is used to provision the database.
2. War2 is for uploading data via a web service.
3. War3 is for getting data via a web service.
4. War4 is another web app that is used to view the data in a dashboard.

We use hibernate/jpa and spring. The classes are annotated and we don't have a persistence.xml for any of them. All configuration is in the spring context file and the annotations. Here's the spring file:

<?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:jpa="http://www.springframework.org/schema/data/jpa"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:flow="http://www.springframework.org/schema/webflow-config"
       xmlns:lang="http://www.springframework.org/schema/lang"
       xmlns:osgi="http://www.springframework.org/schema/osgi"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:util="http://www.springframework.org/schema/util"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:cache="http://www.springframework.org/schema/cache"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-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/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
          http://www.springframework.org/schema/webflow-config http://www.springframework.org/schema/webflow-config/spring-webflow-config-2.0.xsd
          http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-3.0.xsd
          http://www.springframework.org/schema/osgi http://www.springframework.org/schema/osgi/spring-osgi-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/util http://www.springframework.org/schema/util/spring-util-3.0.xsd
          http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa.xsd
          http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd
">
    <tx:annotation-driven transaction-manager="transactionManager"/>
    <!-- Directory to scan for repository classes -->
    <jpa:repositories
        base-package="com.blah.db.model.repository" />
    <bean id="propertyConfigurer"
          class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations">
            <list>
                <value>/WEB-INF/configuration.properties</value>
            </list>
        </property>
    </bean>
    <cache:annotation-driven />
        <bean id="cacheManager" class="org.springframework.cache.ehcache.EhCacheCacheManager" p:cache-manager-ref="ehcache"/>
        <bean id="ehcache" class="org.springframework.cache.ehcache.EhCacheManagerFactoryBean"
                    p:config-location="/WEB-INF/ehcache.xml"
                    p:shared="true"/>
    <context:component-scan base-package="com.blah.db.model.service" />
    <context:component-scan base-package="com.blah.business.objects" />
    <context:component-scan base-package="com.blah.data.access.objects" />
    <context:component-scan base-package="com.blah.common" />

    <bean class="org.springframework.orm.jpa.JpaTransactionManager"
      id="transactionManager">
        <property name="entityManagerFactory"
            ref="entityManagerFactory" />
        <property name="jpaDialect">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaDialect" />
        </property>
    </bean>
    <bean id="entityManagerFactory"
      class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="packagesToScan" value="com.blah.db.model"  />
        <property name="dataSource" ref="dataSource" />
        <property name="jpaVendorAdapter">
            <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
                <property name="generateDdl" value="${hibernate.generate.ddl}" />
                <property name="database" value="${hibernate.database}" />
                <property name="showSql" value="${show.sql}" />
            </bean>
        </property>
        <property name="jpaProperties">
            <map>
                <entry key="hibernate.default_schema" value="${default.schema}"/>
                <entry key="hibernate.dialect" value="${jdbc.hibernate.dialect}"/>
                <entry key="hibernate.id.new_generator_mappings" value="${new.generator.mappings}"/>
                <entry key="hibernate.cache.region.factory_class" value="${hibernate.cache.factory.class}"/>
                <entry key="hibernate.cache.use_second_level_cache" value="${hibernate.use.second.level.cache}"/>
                <entry key="hibernate.cache.use_query_cache" value="${hibernate.use.query.cache}"/>
                <entry key="net.sf.ehcache.configurationResourceName" value="${ehcache.config.file}"/>
            </map>
        </property>
    </bean>
    <bean id="dataSource"
      class="org.apache.commons.dbcp.BasicDataSource"
      destroy-method="close">
        <property name="driverClassName" value="org.postgresql.Driver" />
        <property name="url" value="jdbc:postgresql://127.0.0.1:5432/blah" />
        <property name="username" value="postgres" />
        <property name="password" value="password" />
    </bean>
    <bean id="openSessionInViewInterceptor" class="org.springframework.orm.jpa.support.OpenEntityManagerInViewInterceptor">
        <property name="entityManagerFactory">
            <ref local="entityManagerFactory"/>
        </property>
        <property name="jpaProperties">
            <map>
                <entry key="singleSession" value="true"/>
                <entry key="flushModeName" value="FLUSH_AUTO"/>
            </map>
        </property>
    </bean>
</beans>

How do I ensure that all the wars use a single persistence unit? I want to be able to use ehcache, but I know I can't use it if they all use their own PU.

Is my only option moving to JavaEE and packaging it all in an EAR?

Thanks!

Answer 1

Sharing a persistance unit between applications means deploying your common classes in the shared tomcat folder, which is as safe as cleaning a loaded shotgun with your tonge.

If you need to share a cache, with ehcache, use terracotta as an off heap cache. This solution will be simples and definitely less risky.

Another option is to merge those 4 apps into a bigger app, which might make sense if all of them share the same data.