【Mybatis】MyBatis之配置多数据源（十）

　　在做项目的过程中，有时候一个数据源是不够，那么就需要配置多个数据源。本例介绍mybatis多数据源配置

前言

　　一般项目单数据源，使用流程如下：

　　　　

　　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

　　　　

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

　　2、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：

 public Connection getConnection() throws SQLException {
     return determineTargetDataSource().getConnection();
 }  

 public Connection getConnection(String username, String password) throws SQLException {
      return determineTargetDataSource().getConnection(username, password);
 }

　　3、 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()
      */
     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

案例

　　1、搭建一个Springmvc + Spring + Mybatis  maven项目，POM文件中引入AOP相关依赖，参考：【Mybatis】MyBatis之整合Spring（八）

 <project xmlns="http://maven.apache.org/POM/4.0.0"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.test</groupId>
     <artifactId>test-spring-mybatis</artifactId>
     <packaging>war</packaging>
     <version>1.0.0-SNAPSHOT</version>
     <url>http://maven.apache.org</url>

     <!-- 定义maven变量 -->
     <properties>
         <!-- spring -->
         <spring.version>5.1.4.RELEASE</spring.version>

         <!-- Mybatis -->
         <mybatis.version>3.5.0</mybatis.version>
         <!-- Mybatis 整合 Spring -->
         <mybatis-spring.version>2.0.0</mybatis-spring.version>

         <!-- mysql -->
         <mysql.version>8.0.13</mysql.version>

         <!-- c3p0 连接池 -->
         <c3p0.version>0.9.5.4</c3p0.version>

         <!-- logback -->
         <slf4j-api.version>1.7.5</slf4j-api.version>
         <logback.version>0.9.30</logback.version>

         <!-- Servlet -->
         <servlet.version>3.0.1</servlet.version>
         <jsp-api.version>2.2</jsp-api.version>

         <!-- jstl -->
         <jstl.version>1.2</jstl.version>
         <standard.version>1.1.2</standard.version>

         <!-- test junit -->
         <junit.version>3.8.1</junit.version>

         <!-- jdk -->
         <jdk.version>1.8</jdk.version>
         <maven.compiler.plugin.version>2.3.2</maven.compiler.plugin.version>
     </properties>

     <dependencies>

         <!-- Spring IOC 核心容器 -->
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-core</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-beans</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-context</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-expression</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <!-- Spring AOP 切面 模块 -->
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-aop</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <dependency>
             <groupId>org.aspectj</groupId>
             <artifactId>aspectjrt</artifactId>
             <version>1.9.2</version>
         </dependency>

         <dependency>
             <groupId>org.aspectj</groupId>
             <artifactId>aspectjweaver</artifactId>
             <version>1.9.2</version>
         </dependency>

         <!-- Spring WEB MVC 模块 -->
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-web</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-webmvc</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <!-- Spring 事物 模块 -->
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-tx</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <!-- Spring ORM 对象关系映射 模块 -->
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-orm</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <!-- Spring JDBC 模块 -->
         <dependency>
             <groupId>org.springframework</groupId>
             <artifactId>spring-jdbc</artifactId>
             <version>${spring.version}</version>
         </dependency>

         <!-- Mybatis -->
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis</artifactId>
             <version>${mybatis.version}</version>
         </dependency>

         <!-- Mybatis 整合 Spring -->
         <dependency>
             <groupId>org.mybatis</groupId>
             <artifactId>mybatis-spring</artifactId>
             <version>${mybatis-spring.version}</version>
         </dependency>

         <!-- mysql -->
         <dependency>
             <groupId>mysql</groupId>
             <artifactId>mysql-connector-java</artifactId>
             <version>${mysql.version}</version>
         </dependency>

         <!-- c3p0 连接池 -->
         <!-- https://mvnrepository.com/artifact/c3p0/c3p0 -->
         <dependency>
             <groupId>com.mchange</groupId>
             <artifactId>c3p0</artifactId>
             <version>${c3p0.version}</version>
         </dependency>

         <!-- logback -->
         <dependency>
             <groupId>org.slf4j</groupId>
             <artifactId>slf4j-api</artifactId>
             <version>${slf4j-api.version}</version>
             <type>jar</type>
             <scope>compile</scope>
         </dependency>

         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-core</artifactId>
             <version>${logback.version}</version>
             <type>jar</type>
         </dependency>

         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-classic</artifactId>
             <version>${logback.version}</version>
             <type>jar</type>
         </dependency>

         <dependency>
             <groupId>ch.qos.logback</groupId>
             <artifactId>logback-access</artifactId>
             <version>${logback.version}</version>
         </dependency>

         <!-- Servlet -->
         <dependency>
             <groupId>javax.servlet</groupId>
             <artifactId>javax.servlet-api</artifactId>
             <version>${servlet.version}</version>
             <scope>provided</scope>
         </dependency>
         <dependency>
             <groupId>javax.servlet.jsp</groupId>
             <artifactId>jsp-api</artifactId>
             <version>${jsp-api.version}</version>
             <scope>provided</scope>
         </dependency>

         <!-- jstl -->
         <dependency>
             <groupId>javax.servlet</groupId>
             <artifactId>jstl</artifactId>
             <version>${jstl.version}</version>
         </dependency>

         <dependency>
             <groupId>taglibs</groupId>
             <artifactId>standard</artifactId>
             <version>${standard.version}</version>
         </dependency>

         <!-- test -->
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
             <version>${junit.version}</version>
             <scope>test</scope>
         </dependency>

     </dependencies>

     <build>
         <plugins>
             <!-- define the project compile level -->
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>${maven.compiler.plugin.version}</version>
                 <configuration>
                     <source>${jdk.version}</source>
                     <target>${jdk.version}</target>
                 </configuration>
             </plugin>
         </plugins>
         <finalName>test_spring_mybatis</finalName>
     </build>
 </project>

pom.xml

　　2、编辑一个扩展AbstractRoutingDataSource类，DynamicDataSource.java

 package com.test.datasource;

 import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

 /**
  *     动态数据源（依赖于spring）
  * @author chenheng
  * @date 2019-08-03 17:27:35
  *
  */
 public class DynamicDataSource extends AbstractRoutingDataSource {

     @Override
     protected Object determineCurrentLookupKey() {
          return DataSourceHolder.getDataSource();
     }

 }

　　3、 封装一个的对数据源进行操作的类，DataSourceHolder.java

 package com.test.datasource;

 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();
     }
 }

　　4、当需要切换数据源的时候执行啦。手动在代码中调用写死吗？调用setDataSource方法

　　　　但是这种方法比较死板，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）

 @TargetDataSource(name=TargetDataSource.SLAVE)
 public List<Employee> getEmpsFromSalve()

　　　　编辑注解标签TargetDataSource.java

 package com.test.annotation;

 import java.lang.annotation.*;

 @Target({ElementType.METHOD, ElementType.TYPE})
 @Retention(RetentionPolicy.RUNTIME)
 @Documented
 public @interface TargetDataSource {

     String name() default TargetDataSource.MASTER;

     public static String MASTER = "dataSource1";

     public static String SLAVE = "dataSource2";

 }

　　5、编辑切面的Bean，DataSourceExchange.java

 package com.test.datasource;

 import java.lang.reflect.Method;

 import org.springframework.aop.AfterReturningAdvice;
 import org.springframework.aop.MethodBeforeAdvice;

 import com.test.annotation.TargetDataSource;

 public class DataSourceExchange implements MethodBeforeAdvice, AfterReturningAdvice {

     @Override
     public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
         DataSourceHolder.clearDataSource();
     }

     @Override
     public void before(Method method, Object[] args, Object target) throws Throwable {
         // 这里TargetDataSource是自定义的注解
         if (method.isAnnotationPresent(TargetDataSource.class)) {
             TargetDataSource datasource = method.getAnnotation(TargetDataSource.class);
             DataSourceHolder.setDataSource(datasource.name());
         } else {
             if(target.getClass().isAnnotationPresent(TargetDataSource.class))
             {
                 TargetDataSource datasource = target.getClass().getAnnotation(TargetDataSource.class);
                 DataSourceHolder.setDataSource(datasource.name());
             }
         }

     }
 } 

　　6、配置文件

 <?xml version="1.0" encoding="UTF-8"?>
 <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:context="http://www.springframework.org/schema/context"
     xmlns:mybatis-spring="http://mybatis.org/schema/mybatis-spring"
     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://mybatis.org/schema/mybatis-spring
         http://mybatis.org/schema/mybatis-spring.xsd
         http://www.springframework.org/schema/aop
         http://www.springframework.org/schema/aop/spring-aop.xsd
         http://www.springframework.org/schema/tx
         http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
         http://www.springframework.org/schema/context
         http://www.springframework.org/schema/context/spring-context-4.0.xsd">

     <!-- 引入数据库的配置文件 -->
     <context:property-placeholder location="classpath:dbconfig.properties" />

     <bean id="dataSource1" class="com.mchange.v2.c3p0.ComboPooledDataSource">
         <property name="jdbcUrl" value="${datasource1.jdbc.url}"></property>
         <property name="driverClass" value="${datasource1.jdbc.driver}"></property>
         <property name="user" value="${datasource1.jdbc.username}"></property>
         <property name="password" value="${datasource1.jdbc.password}"></property>
     </bean>

     <bean id="dataSource2" class="com.mchange.v2.c3p0.ComboPooledDataSource">
         <property name="jdbcUrl" value="${datasource2.jdbc.url}"></property>
         <property name="driverClass" value="${datasource2.jdbc.driver}"></property>
         <property name="user" value="${datasource2.jdbc.username}"></property>
         <property name="password" value="${datasource2.jdbc.password}"></property>
     </bean>

     <!-- 数据源：Spring用来控制业务逻辑。数据源、事务控制、aop -->
     <bean id="dataSource" class="com.test.datasource.DynamicDataSource">
         <property name="targetDataSources">
             <map key-type="java.lang.String">
                 <entry key="dataSource1" value-ref="dataSource1"></entry>
                 <entry key="dataSource2" value-ref="dataSource2"></entry>
             </map>
         </property>
         <!-- 默认目标数据源为你主库数据源 -->
         <property name="defaultTargetDataSource" ref="dataSource1"/>
     </bean>

     <!-- spring事务管理 -->
     <bean id="dataSourceTransactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
         <property name="dataSource" ref="dataSource"></property>
     </bean>

     <!-- 开启基于注解的事务 -->
     <tx:annotation-driven transaction-manager="dataSourceTransactionManager" order="2"/>

     <!--
     整合mybatis
         目的：1、spring管理所有组件。mapper的实现类。
                 service==>Dao   @Autowired:自动注入mapper；
             2、spring用来管理事务，spring声明式事务
     -->
     <!--创建出SqlSessionFactory对象  -->
     <bean id="sqlSessionFactoryBean" class="org.mybatis.spring.SqlSessionFactoryBean">
         <property name="dataSource" ref="dataSource"></property>
         <!-- configLocation指定全局配置文件的位置 -->
         <property name="configLocation" value="classpath:mybatis-config.xml"></property>
         <!--mapperLocations: 指定mapper文件的位置-->
         <property name="mapperLocations" value="classpath:mybatis/mapper/*.xml"></property>
     </bean>

     <!--配置一个可以进行批量执行的sqlSession  -->
     <bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">
         <constructor-arg name="sqlSessionFactory" ref="sqlSessionFactoryBean"></constructor-arg>
         <constructor-arg name="executorType" value="BATCH"></constructor-arg>
     </bean>

     <!-- 扫描所有的mapper接口的实现，让这些mapper能够自动注入；
     base-package：指定mapper接口的包名
      -->
     <mybatis-spring:scan base-package="com.test.dao"/>

     <!-- 配置切面的Bean -->
     <bean id="dataSourceExchange" class="com.test.datasource.DataSourceExchange"/>

     <!-- 配置AOP -->
     <aop:config>
         <!-- 配置切点表达式  -->
         <aop:pointcut id="servicePointcut" expression="execution(* com.test.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="servicePointcut" order="1"/>
     </aop:config>

 </beans>

　　注意：Spring中的事务是通过aop来实现的，当我们自己写aop拦截的时候，会遇到跟spring的事务aop执行的先后顺序问题，比如说动态切换数据源的问题，如果事务在前，数据源切换在后，会导致数据源切换失效，所以就用到了Order（排序）这个关键字

 <aop:advisor advice-ref="dataSourceExchange" pointcut-ref="servicePointcut" order="1"/>

 <!-- 开启基于注解的事务 -->
 <tx:annotation-driven transaction-manager="dataSourceTransactionManager" order="2"/>

　　7、在service上加上注解即可使用

 @Transactional
 @TargetDataSource(name=TargetDataSource.SLAVE)
 public int addEmployeeFromSalve(Employee employee) {

     return employeeMapper.insert(employee);
 }

　　　

　　

数据流转顺序：

　　1.xml<aop>拦截到数据源名称

　　2.执行切面DataSourceExchange中的before方法，将数据源名称放入 DataSourceHolder中

　　3.Spring 调用determineCurrentLookupKey()方法<DynamicDataSource中重写AbstractRoutingDataSource类中的方法> ，从DataSourceHolder取出当前的数据库名称，并返回

　　4.AbstractRoutingDataSource类中determineTargetDataSource()方法调用determineCurrentLookupKey()匹配到指定的数据库，并建立链接，即为切换到相应的数据库；

　　5.在指定的数据库中执行相应的sql