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:
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
我们可以看到,它继承了AbstractDataSource,而AbstractDataSource不就是javax.sql.DataSource的子类,So我们可以分析下它的getConnection方法:
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public Connection getConnection() throws SQLException { return determineTargetDataSource().getConnection(); } public Connection getConnection(String username, String password) throws SQLException { return determineTargetDataSource().getConnection(username, password); } |
获取连接的方法中,重点是determineTargetDataSource()方法,看源码:
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/** * 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() */ protected DataSource 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; } |
上面这段源码的重点在于determineCurrentLookupKey()方法,这是AbstractRoutingDataSource类中的一个抽象方法,而它的返回值是你所要用的数据源dataSource的key值,有了这个key值,resolvedDataSource(这是个map,由配置文件中设置好后存入的)就从中取出对应的DataSource,如果找不到,就用配置默认的数据源。
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:
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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 extends AbstractRoutingDataSource{ @Override protected Object determineCurrentLookupKey() { return DataSourceHolder.getDataSource(); } } |
DataSourceHolder这个类则是我们自己封装的对数据源进行操作的类:
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package com.datasource.test.util.database; /** * 数据源操作 * @author linhy */ public class DataSourceHolder { //线程本地环境 private static final ThreadLocal<String> dataSources = new ThreadLocal<String>(); //设置数据源 public static void setDataSource(String customerType) { dataSources.set(customerType); } //获取数据源 public static String getDataSource() { return (String) dataSources.get(); } //清除数据源 public static 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):
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@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:
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package com.datasource.test.util.database; import java.lang.annotation.*; @Target ({ElementType.METHOD, ElementType.TYPE}) @Retention (RetentionPolicy.RUNTIME) @Documented public @interface DataSource { String name() default DataSource.master; public static String master = "dataSource1" ; public static String slave1 = "dataSource2" ; public static 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。
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<? xml version = "1.0" encoding = "UTF-8" ?> <!-- Spring 数据库相关配置 放在这里 --> < beans xmlns = "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"> < bean id = "dataSource1" class = "com.mysql.jdbc.jdbc2.optional.MysqlDataSource" > < property name = "url" value = "${db1.url}" /> < property name = "user" value = "${db1.user}" /> < property name = "password" value = "${db1.pwd}" /> < property name = "autoReconnect" value = "true" /> < property name = "useUnicode" value = "true" /> < property name = "characterEncoding" value = "UTF-8" /> </ bean > < bean id = "dataSource2" class = "com.mysql.jdbc.jdbc2.optional.MysqlDataSource" > < property name = "url" value = "${db2.url}" /> < property name = "user" value = "${db2.user}" /> < property name = "password" value = "${db2.pwd}" /> < property name = "autoReconnect" value = "true" /> < property name = "useUnicode" value = "true" /> < property name = "characterEncoding" value = "UTF-8" /> </ bean > < bean id = "dataSource3" class = "com.mysql.jdbc.jdbc2.optional.MysqlDataSource" > < property name = "url" value = "${db3.url}" /> < property name = "user" value = "${db3.user}" /> < property name = "password" value = "${db3.pwd}" /> < property name = "autoReconnect" value = "true" /> < property name = "useUnicode" value = "true" /> < property name = "characterEncoding" value = "UTF-8" /> </ bean > <!-- 配置多数据源映射关系 --> < bean id = "dataSource" class = "com.datasource.test.util.database.DynamicDataSource" > < property name = "targetDataSources" > < map key-type = "java.lang.String" > < entry key = "dataSource1" value-ref = "dataSource1" ></ entry > < entry key = "dataSource2" value-ref = "dataSource2" ></ entry > < entry key = "dataSource3" value-ref = "dataSource3" ></ entry > </ map > </ property > <!-- 默认目标数据源为你主库数据源 --> < property name = "defaultTargetDataSource" ref = "dataSource1" /> </ bean > < bean id = "sessionFactoryHibernate" class = "org.springframework.orm.hibernate3.LocalSessionFactoryBean" > < property name = "dataSource" ref = "dataSource" /> < property name = "hibernateProperties" > < props > < prop key = "hibernate.dialect" >com.datasource.test.util.database.ExtendedMySQLDialect</ prop > < prop key = "hibernate.show_sql" >${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 > < bean id = "hibernateTemplate" class = "org.springframework.orm.hibernate3.HibernateTemplate" > < property name = "sessionFactory" ref = "sessionFactoryHibernate" /> </ bean > < bean id = "dataSourceExchange" class = "com.datasource.test.util.database.DataSourceExchange" /> < bean id = "transactionManager" class = "org.springframework.orm.hibernate3.HibernateTransactionManager" > < property name = "sessionFactory" ref = "sessionFactoryHibernate" /> </ bean > < tx:advice id = "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?
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。
原文链接:http://www.cnblogs.com/davidwang456/p/4318303.html