Spring(AbstractRoutingDataSource)实现动态数据源切换
来源:互联网 发布:java continue跳几层 编辑:程序博客网 时间:2024/06/11 14:42
原始出处:http://linhongyu.blog.51cto.com/6373370/1615895
一、前言
近期一项目A需实现数据同步到另一项目B数据库中,在不改变B项目的情况下,只好选择项目A中切换数据源,直接把数据写入项目B的数据库中。这种需求,在数据同步与定时任务中经常需要。
那么问题来了,该如何解决多数据源问题呢?不光是要配置多个数据源,还得能灵活动态的切换数据源。以spring+hibernate框架项目为例(引用:http://blog.csdn.net/wangpeng047/article/details/8866239博客的图片):
单个数据源绑定给sessionFactory,再在Dao层操作,若多个数据源的话,那不是就成了下图:
可见,sessionFactory都写死在了Dao层,若我再添加个数据源的话,则又得添加一个sessionFactory。所以比较好的做法应该是下图:
接下来就为大家讲解下如何用spring来整合这些数据源,同样以spring+hibernate配置为例。
二、实现原理
1、扩展Spring的AbstractRoutingDataSource抽象类(该类充当了DataSource的路由中介, 能有在运行时, 根据某种key值来动态切换到真正的DataSource上。)
从AbstractRoutingDataSource的源码中:
public abstract class AbstractRoutingDataSource extends AbstractDataSource implements InitializingBean
public Connection getConnection() throws SQLException { returndetermineTargetDataSource().getConnection(); } public Connection getConnection(String username, String password) throwsSQLException { returndetermineTargetDataSource().getConnection(username, password); }
获取连接的方法中,重点是determineTargetDataSource()方法,看源码:
/** * Retrieve the current target DataSource. Determines the * {@link #determineCurrentLookupKey() current lookup key}, performs * a lookup in the {@link #setTargetDataSources targetDataSources} map, * falls back to the specified * {@link #setDefaultTargetDataSource default target DataSource} if necessary. * @see #determineCurrentLookupKey() */ protectedDataSource determineTargetDataSource() { Assert.notNull(this.resolvedDataSources,"DataSource router not initialized"); Object lookupKey = determineCurrentLookupKey(); DataSource dataSource = this.resolvedDataSources.get(lookupKey); if (dataSource == null && (this.lenientFallback || lookupKey ==null)) { dataSource = this.resolvedDefaultDataSource; } if (dataSource == null) { throw new IllegalStateException("Cannot determine target DataSource for lookup key ["+ lookupKey + "]"); } return dataSource; }
看完源码,应该有点启发了吧,没错!你要扩展AbstractRoutingDataSource类,并重写其中的determineCurrentLookupKey()方法,来实现数据源的切换:
package com.datasource.test.util.database;import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;/*** 获取数据源(依赖于spring)* @author linhy*/public class DynamicDataSource extendsAbstractRoutingDataSource{ @Override protectedObject determineCurrentLookupKey() { return DataSourceHolder.getDataSource(); }}
package com.datasource.test.util.database;/*** 数据源操作* @author linhy*/public class DataSourceHolder { //线程本地环境 privatestatic final ThreadLocal<String> dataSources = new ThreadLocal<String>(); //设置数据源 publicstatic void setDataSource(String customerType) { dataSources.set(customerType); } //获取数据源 publicstatic String getDataSource() { return (String) dataSources.get(); } //清除数据源 publicstatic void clearDataSource() { dataSources.remove(); }}
2、有人就要问,那你setDataSource这方法是要在什么时候执行呢?当然是在你需要切换数据源的时候执行啦。手动在代码中调用写死吗?这是多蠢的方法,当然要让它动态咯。所以我们可以应用spring aop来设置,把配置的数据源类型都设置成为注解标签,在service层中需要切换数据源的方法上,写上注解标签,调用相应方法切换数据源咯(就跟你设置事务一样):
@DataSource
(name=DataSource.slave1)
public
List getProducts(){
当然,注解标签的用法可能很少人用到,但它可是个好东西哦,大大的帮助了我们开发:
package com.datasource.test.util.database;import java.lang.annotation.*;@Target({ElementType.METHOD, ElementType.TYPE})@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @interface DataSource { String name()default DataSource.master; publicstatic String master ="dataSource1"; publicstatic String slave1 ="dataSource2"; publicstatic String slave2 ="dataSource3";}
三、配置文件
为了精简篇幅,省略了无关本内容主题的配置。
项目中单独分离出application-database.xml,关于数据源配置的文件。
<?xmlversion="1.0"encoding="UTF-8"?><!-- Spring 数据库相关配置 放在这里 --><beansxmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"> <beanid = "dataSource1" class = "com.mysql.jdbc.jdbc2.optional.MysqlDataSource"> <propertyname="url"value="${db1.url}"/> <propertyname = "user" value = "${db1.user}"/> <propertyname = "password" value = "${db1.pwd}"/> <propertyname="autoReconnect"value="true"/> <propertyname="useUnicode" value="true"/> <propertyname="characterEncoding"value="UTF-8"/> </bean> <beanid = "dataSource2" class = "com.mysql.jdbc.jdbc2.optional.MysqlDataSource"> <propertyname="url"value="${db2.url}"/> <propertyname = "user" value = "${db2.user}"/> <propertyname = "password" value = "${db2.pwd}"/> <propertyname="autoReconnect"value="true"/> <propertyname="useUnicode" value="true"/> <propertyname="characterEncoding"value="UTF-8"/> </bean> <beanid = "dataSource3" class = "com.mysql.jdbc.jdbc2.optional.MysqlDataSource"> <propertyname="url"value="${db3.url}"/> <propertyname = "user" value = "${db3.user}"/> <propertyname = "password" value = "${db3.pwd}"/> <propertyname="autoReconnect"value="true"/> <propertyname="useUnicode" value="true"/> <propertyname="characterEncoding"value="UTF-8"/> </bean> <!-- 配置多数据源映射关系 --> <beanid="dataSource"class="com.datasource.test.util.database.DynamicDataSource"> <propertyname="targetDataSources"> <map key-type="java.lang.String"> <entrykey="dataSource1"value-ref="dataSource1"></entry> <entry key="dataSource2"value-ref="dataSource2"></entry> <entry key="dataSource3"value-ref="dataSource3"></entry> </map> </property> <!-- 默认目标数据源为你主库数据源 --> <propertyname="defaultTargetDataSource"ref="dataSource1"/> </bean> <beanid="sessionFactoryHibernate"class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <propertyname="dataSource"ref="dataSource"/> <propertyname="hibernateProperties"> <props> <prop key="hibernate.dialect">com.datasource.test.util.database.ExtendedMySQLDialect</prop> <prop key="hibernate.show_sql">${SHOWSQL}</prop> <prop key="hibernate.format_sql">${SHOWSQL}</prop> <prop key="query.factory_class">org.hibernate.hql.classic.ClassicQueryTranslatorFactory</prop> <prop key="hibernate.connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</prop> <prop key="hibernate.c3p0.max_size">30</prop> <prop key="hibernate.c3p0.min_size">5</prop> <prop key="hibernate.c3p0.timeout">120</prop> <prop key="hibernate.c3p0.idle_test_period">120</prop> <prop key="hibernate.c3p0.acquire_increment">2</prop> <prop key="hibernate.c3p0.validate">true</prop> <prop key="hibernate.c3p0.max_statements">100</prop> </props> </property> </bean> <beanid="hibernateTemplate"class="org.springframework.orm.hibernate3.HibernateTemplate"> <propertyname="sessionFactory"ref="sessionFactoryHibernate"/> </bean> <beanid="dataSourceExchange"class="com.datasource.test.util.database.DataSourceExchange"/> <beanid="transactionManager"class="org.springframework.orm.hibernate3.HibernateTransactionManager"> <propertyname="sessionFactory"ref="sessionFactoryHibernate"/> </bean> <tx:adviceid="txAdvice"transaction-manager="transactionManager"> <tx:attributes> <tx:method name="insert*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="add*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="update*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="modify*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="edit*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="del*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="save*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="send*"propagation="NESTED"rollback-for="Exception"/> <tx:method name="get*"read-only="true"/> <tx:method name="find*"read-only="true"/> <tx:method name="query*"read-only="true"/> <tx:method name="search*"read-only="true"/> <tx:method name="select*"read-only="true"/> <tx:method name="count*"read-only="true"/> </tx:attributes> </tx:advice> <aop:config> <aop:pointcut id="service"expression="execution(* com.datasource..*.service.*.*(..))"/> <!-- 关键配置,切换数据源一定要比持久层代码更先执行(事务也算持久层代码) --> <aop:advisor advice-ref="txAdvice"pointcut-ref="service"order="2"/> <aop:advisor advice-ref="dataSourceExchange"pointcut-ref="service"order="1"/> </aop:config></beans>
四、疑问
多数据源切换是成功了,但牵涉到事务呢?单数据源事务是ok的,但如果多数据源需要同时使用一个事务呢?这个问题有点头大,网络上有人提出用atomikos开源项目实现JTA分布式事务处理。你怎么看?
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