经常可以在Spring Roo论坛上看到一个经常的问题。问题是“如何配置使得应用可以处理两个数据库”。
这对Spring Roo来说，是足够麻烦的问题，这个问题涉及了JPA和Spring持久化栈。所以，我相信这对所有的Spring开发社区都要处理这个问题。
假设读者是Java开发人员，对Spring Roo有些熟悉。我关注如何获取配置。查看帮助，请访问http://www.springsource.org/roo。
解决问题
创建了以下最小的Roo项目。修改配置，每个实体都来自于不同的独立的数据库。
project --topLevelPackage org.pragmatikroo.twodbpersistence setup --provider HIBERNATE --database MYSQL --userName <username> --password <password> --databaseName twodbonelogging setup --level DEBUG --package PERSISTENCEentity --class ~.domain.DbOnefield string --fieldName nameentity --class ~.domain.DbTwofield string --fieldName nameperform cleanperform eclipseexit
原始Database.properties文件
database.password=<password>database.url=jdbc\:mysql\://localhost\:3306/twodbdatabase.username=<username>database.driverClassName=com.mysql.jdbc.Driver
修改后的Database.properties文件
database.password1=<password1>database.url1=jdbc\:mysql\://localhost\:3306/twodbonedatabase.username1=<username1>database.password2=<password1>database.url2=jdbc\:mysql\://localhost\:3306/twodbtwodatabase.username2=<username2>database.driverClassName=com.mysql.jdbc.Driver
基本上，我已经从原始文件复制了一个拷贝定义第二个数据库。对其他文件的模式也是重复的。
修改后的Persistence.xml文件
<persistence-unit name="persistenceUnit1" transaction-type="RESOURCE_LOCAL"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <class>org.josean.twodb.domain.DbOne</class> <exclude-unlisted-classes>true</exclude-unlisted-classes> <properties> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/> <!-- value="create" to build a new database on each run; value="update" to modify an existing database; value="create-drop" means the same as "create" but also drops tables when Hibernate closes; value="validate" makes no changes to the database --> <property name="hibernate.hbm2ddl.auto" value="update"/> <property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.ImprovedNamingStrategy"/> <property name="hibernate.connection.charSet" value="UTF-8"/> <!-- Uncomment the following two properties for JBoss only --> <!-- property name="hibernate.validator.apply_to_ddl" value="false" /--> <!-- property name="hibernate.validator.autoregister_listeners" value="false" /--> </properties></persistence-unit><persistence-unit name="persistenceUnit2" transaction-type="RESOURCE_LOCAL"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <class>org.josean.twodb.domain.DbTwo</class> <exclude-unlisted-classes>true</exclude-unlisted-classes> <properties> <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/> <!-- value="create" to build a new database on each run; value="update" to modify an existing database; value="create-drop" means the same as "create" but also drops tables when Hibernate closes; value="validate" makes no changes to the database --> <property name="hibernate.hbm2ddl.auto" value="update"/> <property name="hibernate.ejb.naming_strategy" value="org.hibernate.cfg.ImprovedNamingStrategy"/> <property name="hibernate.connection.charSet" value="UTF-8"/> <!-- Uncomment the following two properties for JBoss only --> <!-- property name="hibernate.validator.apply_to_ddl" value="false" /--> <!-- property name="hibernate.validator.autoregister_listeners" value="false" /--> </properties></persistence-unit>
为第二个数据库复制持久化单元代码，定义了唯一的id。重要的是：添加
修改后的ApplicationContext.xml文件
<bean class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" id="dataSource1"> <property name="driverClassName" value="${database.driverClassName}"/> <property name="url" value="${database.url1}"/> <property name="username" value="${database.username1}"/> <property name="password" value="${database.password1}"/> <property name="validationQuery" value="SELECT 1 FROM DUAL"/> <property name="testOnBorrow" value="true"/></bean><bean class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean" id="entityManagerFactory1"> <property name="dataSource" ref="dataSource1"/> <property name="persistenceUnitName" value="persistenceUnit1"/></bean><tx:annotation-driven mode="aspectj" transaction-manager="transactionManager1" /><bean class="org.springframework.orm.jpa.JpaTransactionManager" id="transactionManager1"> <property name="entityManagerFactory" ref="entityManagerFactory1" /></bean><bean class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close" id="dataSource2"> <property name="driverClassName" value="${database.driverClassName}"/> <property name="url" value="${database.url2}"/> <property name="username" value="${database.username2}"/> <property name="password" value="${database.password2}"/> <property name="validationQuery" value="SELECT 1 FROM DUAL"/> <property name="testOnBorrow" value="true"/></bean><bean class="org.springframework.orm.jpa.JpaTransactionManager" id="transactionManager2"> <property name="entityManagerFactory" ref="entityManagerFactory2"/></bean><tx:annotation-driven mode="aspectj" transaction-manager="transactionManager2" /><bean class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean" id="entityManagerFactory2"> <property name="dataSource" ref="dataSource2"/> <property name="persistenceUnitName" value="persistenceUnit2"/></bean>其他文件的处理过程类似。添加属性到entityManagerFactory beans中。
修改后的Web.xml文件
<filter> <filter-name>Spring OpenEntityManagerInViewFilter1</filter-name> <filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class> <init-param> <param-name>entityManagerFactoryBeanName</param-name> <param-value>entityManagerFactory1</param-value> </init-param></filter><filter> <filter-name>Spring OpenEntityManagerInViewFilter2</filter-name> <filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class> <init-param> <param-name>entityManagerFactoryBeanName</param-name> <param-value>entityManagerFactory2</param-value> </init-param></filter>
就是这样！应用可以部署和测试了。
总结
已经演示了如何安装Spring web应用的上下文，使得应用可以访问第二个数据库，尤其对Spring Roo开发人员有用。
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