mybatis多數據源動態切換

•  首先在配置文件中配置多個數據源

	<!--數據庫配置一-->
    <bean id="dataSource1" class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName" value="${jdbc.driver}" />
        <property name="url" value="${dataSource1.jdbc.conn.url}" />
        <property name="username" value="${dataSource1.jdbc.conn.username}" />
        <property name="password" value="${dataSource1.jdbc.conn.password}" />
        <property name="initialSize" value="${jdbc.dbcp.initialSize}" />
        <property name="minIdle" value="${dataSource1.jdbc.dbcp.minIdle}" />
        <property name="maxIdle" value="${dataSource1.jdbc.dbcp.maxIdle}" />
        <property name="maxActive" value="${dataSource1.jdbc.dbcp.maxActive}" />
        <property name="maxWait" value="${jdbc.dbcp.maxWait}" />
    </bean>
	<!--數據庫配置二-->
    <bean id="dataSource2" class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName" value="${jdbc.driver}" />
        <property name="url" value="${dataSource2.jdbc.conn.url}" />
        <property name="username" value="${dataSource2.jdbc.conn.username}" />
        <property name="password" value="${dataSource2.jdbc.conn.password}" />
        <property name="initialSize" value="${jdbc.dbcp.initialSize}" />
        <property name="minIdle" value="${dataSource2.jdbc.dbcp.minIdle}" />
        <property name="maxIdle" value="${dataSource2.jdbc.dbcp.maxIdle}" />
        <property name="maxActive" value="${dataSource2.jdbc.dbcp.maxActive}" />
        <property name="maxWait" value="${jdbc.dbcp.maxWait}" />
    </bean>

•  自定義數據源MyDataSource ，用一個Map屬性存儲多個數據源，實現DataSource接口

public class MyDataSource implements DataSource {

    private Map<String, DataSource> dataSourceMap = new HashMap();
	
    public void setDataSourceMap(Map<String, DataSource> dataSourceMap) {
        this.dataSourceMap = dataSourceMap;
    }

	public Connection getConnection() throws SQLException {
        return this.getMyDataSource().getConnection();
    }
	
    public DataSource getMyDataSource() {
        String which = MyDataSourceContext.getContext().getWhich();
		if(StringUtils.equals(which, "dataSource1")) {
			return (DataSource)this.dataSourceMap.get("dataSource1");
		} else {
			return (DataSource)this.dataSourceMap.get("dataSource2");
		}
    }
}

•  加載自定義數據源，注入到數據庫操作Session工廠

    <!-- 自定義數據源 -->    
    <bean id="myDataSource" class="xxx.xxx.MyDataSource">
        <property name="dataSourceMap">
            <map>
                <entry key="dataSource1" value-ref="dataSource1"></entry>
                <entry key="dataSource2" value-ref="dataSource2"></entry>
            </map>
        </property>
    </bean>

	 <!-- 數據庫操作Session工廠 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="myDataSource"/>
        <property name="configLocation" value="classpath:/mybatis-config.xml"/>
        <property name="mapperLocations" value="classpath:/sqlMap/*Mapper.xml"/>
    </bean>

•  用線程本地變量（ThreadLocal）來支持每個線程可選擇自己的數據源

public class MyDataSourceContext {

    private static final ThreadLocal<MyDataSourceContext> localContext = new ThreadLocal();
	
    private String which = "dataSource2";

	private MyDataSourceContext() {
        localContext.set(this);
    }
	
    public String getWhich() {
        return this.which;
    }
	
	public String setWhich(String which) {
        this.which = which;
    }

	public static MyDataSourceContext getContext() {
        MyDataSourceContext context = (MyDataSourceContext)localContext.get();
        return context == null ? new MyDataSourceContext() : context;
    }

}

• 提供一個工具類，在每個線程執行數據庫操作之前，用工具類來修改自己的數據源。

public class DatasourceUtils {
    public static void switchDatasource(String datasource){
        MyDataSourceContext.getContext().setWhich(datasource);
    }
}

因爲每個線程的本地變量localContext 存的是MyDataSourceContext 的實例，也就是說每個線程都有自己的MyDataSourceContext 實例，所以調用setWhich()方法可以修改線程內實例的which 屬性值，這樣在執行數據庫操作時調用sqlSessionFactory中配置的dataSource（也就是myDataSource）的getConnection()時，根據線程的本地變量的屬性值選擇想要的數據源。