多数据源的配置，详细（新手，错误之处，请指正）
大型应用为了实现读写分离，便于数据的管理，提高系统的水平伸缩性，往往会用到多数据源。
1，数据源是对应不同数据库的，为了方便操作可以写一个数据库的配置文件
UPDATE_MYSQL.type=mysql
UPDATE_MYSQL.autoCommitOnClose=false
UPDATE_MYSQL.driverClassName=com.mysql.jdbc.Driver
UPDATE_MYSQL.url=jdbc:mysql://192.168.1.139:3306/testdatabase?useUnicode=true&characterEncoding=UTF-8&useOldAliasMetadataBehavior=true
UPDATE_MYSQL.username=xccmysql
UPDATE_MYSQL.password=xccW7W8
UPDATE_MYSQL.initialPoolSize=5
SELECT_MYSQL.type=mysql
SELECT_MYSQL.autoCommitOnClose=false
SELECT_MYSQL.driverClassName=com.mysql.jdbc.Driver
SELECT_MYSQL.url=jdbc:mysql://192.168.1.139:3306/testmuti?useUnicode=true&characterEncoding=UTF-8&useOldAliasMetadataBehavior=true
SELECT_MYSQL.username=root
SELECT_MYSQL.password=xcc2009081231
SELECT_MYSQL.initialPoolSize=5
2，然后再spring的配置文件里添加不同的数据源
<!-- 数据源的配置 -->
<bean id ="update_dataSource" class= "org.apache.commons.dbcp.BasicDataSource" destroy-method="close" >
<property name ="driverClassName" value= "${UPDATE_MYSQL.driverClassName}" />
<property name ="url" value="${UPDATE_MYSQL.url}" />
<property name ="username" value= "${UPDATE_MYSQL.username}" />
<property name ="password" value= "${UPDATE_MYSQL.password}" />
<!-- data source configuration -->
<property name ="initialSize" value= "${UPDATE_MYSQL.initialPoolSize}" /> <!-- initial connections -->
<property name ="maxActive" value="10" /><!-- MAX connections -->
<property name ="maxIdle" value="10" /><!-- MAX idle connections -->
<property name ="minIdle" value="5" /><!-- MIN idle connections -->
<!-- 处理mysql 8小时自动断开连接的问题 -->
<property name ="testWhileIdle" value= "true" />
<property name ="testOnBorrow" value= "false" />
<property name ="testOnReturn" value= "false" />
<property name ="validationQuery" value= "select 1" />
<property name ="timeBetweenEvictionRunsMillis" value= "20000" />
<property name ="numTestsPerEvictionRun" value= "100" />
</bean >
<bean id ="select_dataSource" class= "org.apache.commons.dbcp.BasicDataSource" destroy-method="close" >
<property name ="driverClassName" value= "${UPDATE_MYSQL.driverClassName}" />
<property name ="url" value="${SELECT_MYSQL.url}" />
<property name ="username" value= "${SELECT_MYSQL.username}" />
<property name ="password" value= "${SELECT_MYSQL.password}" />
<!-- data source configuration -->
<property name ="initialSize" value= "${SELECT_MYSQL.initialPoolSize}" /> <!-- initial connections -->
<property name ="maxActive" value="10" /><!-- MAX connections -->
<property name ="maxIdle" value="10" /><!-- MAX idle connections -->
<property name ="minIdle" value="5" /><!-- MIN idle connections -->
<!-- 处理mysql 8小时自动断开连接的问题 -->
<property name ="testWhileIdle" value= "true" />
<property name ="testOnBorrow" value= "false" />
<property name ="testOnReturn" value= "false" />
<property name ="validationQuery" value= "select 1" />
<property name ="timeBetweenEvictionRunsMillis" value= "20000" />
<property name ="numTestsPerEvictionRun" value= "100" />
</bean >
3，数据源准备好之后，基本工作，已完成，先放在一边，我们去java里面写数据源的名称常量类
package org.iwall.muti.datasource;
/**
*
* @author Lee
*
*/
public class DataSourceNames {
public static final String UPDATE_MYSQL="update_dataSource" ;
public static final String SELECT_MYSQL = "select_dataSource";
}
4，建立一个类，负责改变数据源的名称（其实可使用spring的注解切换不同的数据源）
package org.iwall.muti.datasource;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* 获得和设置上下文环境 主要负责改变上下文数据源的名称
* @author Lee
*
*/
public class DataSourceContextHolder {
private static final ThreadLocal contextHandler = new ThreadLocal(); // 线程本地环境
public static Log log = LogFactory.getLog(DataSourceContextHolder.class);
// 设置数据源类型
public static void setDataSourceType(String dataSourceType) {
log.info("set dataSource:" + dataSourceType);
contextHandler.set(dataSourceType);
}
// 获取数据源类型
public static String getDataSourceType() {
return (String) contextHandler.get();
}
// 清除数据源类型
public static void clearDataSourceType() {
contextHandler.remove();
}
}
5，建立动态数据源，主要实现 determineCurrentLookupKey这个方法
package org.iwall.muti.datasource;
import java.util.Map;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
import org.springframework.jdbc.datasource.lookup.DataSourceLookup;
/**
*
* @author Lee
*
*/
public class DynamicDataSource extends AbstractRoutingDataSource implements InitializingBean {
private Log log = LogFactory.getLog(DynamicDataSource.class);
/*
* 该方法必须要重写 方法是为了根据数据库标示符取得当前的数据库 既是获得数据源类型
*/
@Override
public Object determineCurrentLookupKey() {
log.info("starting determineCurrentLookupKey:" + DataSourceContextHolder.getDataSourceType());
return DataSourceContextHolder.getDataSourceType();
}
@Override
public void setDataSourceLookup(DataSourceLookup dataSourceLookup) {
log.info("starting setDataSourceLookup:" + DataSourceContextHolder.getDataSourceType());
super.setDataSourceLookup(dataSourceLookup);
}
@Override
public void setDefaultTargetDataSource(Object defaultTargetDataSource) {
log.info("starting setDefaultTargetDataSource:" + DataSourceContextHolder.getDataSourceType());
super.setDefaultTargetDataSource(defaultTargetDataSource);
}
@Override
public void setTargetDataSources(Map targetDataSources) {
System.out.println("starting setTargetDataSources:" + DataSourceContextHolder.getDataSourceType());
super.setTargetDataSources(targetDataSources);
//重点
super.afterPropertiesSet();
}
}
6，数据源配置完了，java对应的类也写完了，就需要写映射关系了，其中key是对应java类里的数据源常量名，value是配置文件里的数据源名
<bean id= "dynamicDataSource" class= "org.iwall.muti.datasource.DynamicDataSource" >
<!-- 通过key-value的形式来关联数据源 -->
<property name ="targetDataSources">
<map key-type ="java.lang.String">
<entry key ="update_dataSource" value-ref="update_dataSource" ></entry>
<entry key ="select_dataSource" value-ref="select_dataSource" ></entry>
</map>
</property>
<property name ="defaultTargetDataSource" ref= "update_dataSource">
</property>
</bean >
7，如果没有使用hibernate，mybatis等数据交互的框架，用spring的模板jdbc的话，注入一下就好
<bean id= "jdbcTemplate" class= "org.springframework.jdbc.core.JdbcTemplate" >
<constructor-arg ref ="dynamicDataSource" />
</bean >
8，总结下，这种方式，便于维护，基本只用修改数据库配置文件和spring配置文件即可。但是多个用户访问会争抢datasource，系统性能
会降低，（没测试过）。
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