鉴于很多同学反应，在看的过程中，自己搭建的demo，没有成功。 首先附上本项目github地址，可以对照着看，看一下相关的配置是否正确配置。

本文介绍两种动态切换数据库的方法。
方法一：数据源信息配置在xml中，适用于一般数据库切换。执行完某操作，切换数据库，执行另一个操作。
方法二：数据源信息配置在默认数据源中，适用于切换数据库操作同一方法，相当于批量执行方法。

两种方法核心都是AbstractRoutingDataSource，由spring提供，用来动态切换数据源。我们需要继承它，来进行操作。本博客中，隐藏了部分spring相关的配置信息。

源码分析可以看下一篇文章源码分析

文章目录

• * 方法一：数据源信息都配置在xml中
  • 方法二：数据源信息配置在数据库中

方法一：数据源信息都配置在xml中

1…继承AbstractRoutingDataSource，重写determineCurrentLookupKey方法

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

public class MultiDataSource extends AbstractRoutingDataSource{

    /* ThreadLocal,叫线程本地变量或线程本地存储。
     * ThreadLocal为变量在每个线程中都创建了一个副本，那么每个线程可以访问自己内部的副本变量。
     * 这里使用它的子类InheritableThreadLocal用来保证父子线程都能拿到值。
     */
    private static final ThreadLocal<String> dataSourceKey = new InheritableThreadLocal<String>();

    /**
     * 设置dataSourceKey的值
     * @param dataSource
     */
    public static void setDataSourceKey(String dataSource) {
        dataSourceKey.set(dataSource);
    }
    /**
     * 清除dataSourceKey的值
     */
    public static void toDefault() {
        dataSourceKey.remove();
    }
    /**
     * 返回当前dataSourceKey的值
     */
    @Override
    protected Object determineCurrentLookupKey() {
        return dataSourceKey.get();
    }
}

2… 配置xml，这里将上面创建的MultiDataSource注入到spring容器中，这里主要用到AbstractRoutingDataSource的两个属性defaultTargetDataSource和targetDataSources。defaultTargetDataSource默认目标数据源，targetDataSources（map类型）存放用来切换的数据源。配置完以后，其他地方用到数据源的话，都引用multiDataSource。

<?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:context="http://www.springframework.org/schema/context"
    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/context http://www.springframework.org/schema/context/spring-context-4.2.xsd
        http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.2.xsd">


    <bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource"
        init-method="init" destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
            <property name="url" value="第一个数据库的url" />
            <property name="username" value="账号" />
            <property name="password" value="密码" />
            <property name="validationQuery" value="select 1"></property>
            <property name="testOnBorrow" value="true"></property>
    </bean>
        <bean id="dataSource2" class="com.alibaba.druid.pool.DruidDataSource"
        init-method="init" destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="第二个数据库的url" />
        <property name="username" value="账号" />
        <property name="password" value="密码" />
        <property name="validationQuery" value="select 1"></property>
        <property name="testOnBorrow" value="true"></property>
    </bean>
    <bean id="multiDataSource" class="com.wbb.dataSource.MultiDataSource">
        <property name="defaultTargetDataSource" ref="dataSource"></property>
        <property name="targetDataSources">
            <map>
                <entry key="dataSource2" value-ref="dataSource2"></entry>
            </map>
        </property>
    </bean>
    <!-- mybatis -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="multiDataSource"></property>
        <property name="configLocation" value="classpath:mybatis-config.xml"></property>
        <property name="mapperLocations" value="classpath:com/wbb/mapper/*.xml"></property>
    </bean>
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
        <property name="basePackage" value="com.wbb.mapper"></property>
    </bean>

    <!-- 添加事务管理 -->
    <tx:annotation-driven transaction-manager="transactionManager" />

    <bean id="transactionManager"
        class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="multiDataSource"></property>
    </bean>

</beans>

3…手动切换数据源，切换完以后，记得再切回默认数据库。

MultiDataSource.setDataSourceKey("dataSource2");//切换到dataSource2数据源
XXX在该数据源下的操作XXX
MultiDataSource.toDefault();//操作完以后，清除dataSourceKey的值，即切回默认数据源，原理后面会讲。

4… 利用aop切换数据源，这里记得开启aop，配置文件中使用
4.1首先定义一个注解，来调用注解切换数据库

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

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

    String value() default "dataSource";//本文默认dataSource

}

4.2 这里使用@Before和@After，在调用目标方法前，进行aop拦截，通过解析注解上的值来切换数据源。在调用方法结束后，切回默认数据源。如果目标方法无返回值，也可以使用@Around，调用ProceedingJoinPoint的proceed()方法前切换数据源，调用proceed()方法后切回默认数据源。

import java.lang.reflect.Method;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.After;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import com.wbb.annotation.DynamicRoutingDataSource;
import com.wbb.dataSource.MultiDataSource;

@Aspect
@Component
public class HandlerDataSourceAop {

    private static Logger logger = LoggerFactory.getLogger(HandlerDataSourceAop.class);
    /**
     * @within匹配类上的注解
     * @annotation匹配方法上的注解
     */
    @Pointcut("@within(com.wbb.annotation.DynamicRoutingDataSource)||@annotation(com.wbb.annotation.DynamicRoutingDataSource)")
    public void pointcut(){}

    @Before(value = "pointcut()")
    public void beforeOpt(JoinPoint joinPoint) {
    /** 先查找方法上的注解，没有的话再去查找类上的注解
    *-----------------------------------------------------------------------
     * 这里使用的是接口的模式，注解在实现类上，所以不能使用如下方式获取目标方法的对象，
    * 因为该方式获取的是该类的接口或者顶级父类的方法的对象.
    * MethodSignature methodSignature = (MethodSignature)point.getSignature();
     * Method method = methodSignature.getMethod();
     * DynamicRoutingDataSource annotation = method.getAnnotation(DynamicRoutingDataSource.class);
     * 通过上面代码是获取不到方法上的注解的，如果真要用上面代码来获取，可以修改aop代理模式，修改为cglib代理
     * 在xml配置文件修改为<aop:aspectj-autoproxy proxy-target-class="true" /> ，
     * proxy-target-class属性true为cglib代理，默认false为jdk动态代理 。
     * ---------------------------------------------------------
     * 本文使用是jdk动态代理， 这里使用反射的方式获取方法
    */
    //反射获取Method 方法一
    Object target = joinPoint.getTarget();
    Class<?> clazz = target.getClass();
    Method[] methods = clazz.getMethods();
    DynamicRoutingDataSource annotation = null;
    for (Method method : methods) {
        if (joinPoint.getSignature().getName().equals(method.getName())) {
            annotation = method.getAnnotation(DynamicRoutingDataSource.class);
            if (annotation == null) {
                annotation = joinPoint.getTarget().getClass().getAnnotation(DynamicRoutingDataSource.class);
                if (annotation == null) {
                    return;
                }
            }
        }
    }
    //  反射获取Method 方法二
    //      Object[] args = joinPoint.getArgs();
    //      Class<?>[] argTypes = new Class[joinPoint.getArgs().length];
    //      for (int i = 0; i < args.length; i++) {
    //          argTypes[i] = args[i].getClass();
    //      }
    //      Method method = joinPoint.getTarget().getClass().getMethod(joinPoint.getSignature().getName(), argTypes);
    //      DynamicRoutingDataSource annotation = method.getAnnotation(DynamicRoutingDataSource.class);
    //      if (annotation == null) {
    //          annotation = joinPoint.getTarget().getClass().getAnnotation(DynamicRoutingDataSource.class);
    //          if (annotation == null) {
    //              return;
    //          }
    //      }

        String dataSourceName = annotation.value();
        MultiDataSource.setDataSourceKey(dataSourceName);
        logger.info("切到" + dataSourceName + "数据库");
    }
    @After(value="pointcut()")
    public void afterOpt(){
        MultiDataSource.toDefault();
        logger.info("切回默认数据库");
    }
}

4.3 使用：只需要把@DynamicRoutingDataSource注解加到方法或者类上即可

@DynamicRoutingDataSource("dataSource2")

方法一到此就结束了

方法二：数据源信息配置在数据库中

1.xml的配置，这里只需要配置一个默认的数据源就行了，因为其他的数据源都是从该数据源的数据源表中读取。

    <?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:context="http://www.springframework.org/schema/context"
        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/context http://www.springframework.org/schema/context/spring-context-4.2.xsd
            http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.2.xsd">

        <bean id="defaultDataSource" class="com.alibaba.druid.pool.DruidDataSource"
            init-method="init" destroy-method="close">
            <property name="driverClassName" value="com.mysql.jdbc.Driver" />
            <property name="url" value="第一个数据库的url" />
            <property name="username" value="账号" />
            <property name="password" value="密码" />
            <property name="validationQuery" value="select 1"></property>
            <property name="testOnBorrow" value="true"></property>
        </bean>

        <!--动态数据源相关-->
        <bean id="dynamicDataSource" class="com.wbb.dataSource.dynamic.DynamicDataSource">
            <property name="targetDataSources">
                <map key-type="java.lang.String">
                    <entry key="defaultDataSource" value-ref="defaultDataSource"/>
                </map>
            </property>
            <property name="defaultTargetDataSource" ref="defaultDataSource"/>
        </bean>
        <!-- mybatis -->
        <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
            <property name="dataSource" ref="dynamicDataSource"></property>
            <property name="configLocation" value="classpath:mybatis-config.xml"></property>
            <property name="mapperLocations" value="classpath:com/wbb/mapper/*.xml"></property>
        </bean>
        <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
            <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
            <property name="basePackage" value="com.wbb.mapper"></property>
        </bean>

        <!-- 添加事务管理 -->
        <tx:annotation-driven transaction-manager="transactionManager" />

        <bean id="transactionManager"
            class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
            <property name="dataSource" ref="dynamicDataSource"></property>
        </bean>

    </beans>

2.数据源表的设计

DROP TABLE IF EXISTS `other_datasource`;
CREATE TABLE `other_datasource` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `datasource_name` varchar(64) DEFAULT NULL,
  `database_ip` varchar(64) DEFAULT NULL,
  `database_port` varchar(64) DEFAULT NULL,
  `database_name` varchar(64) DEFAULT NULL,
  `database_username` varchar(64) DEFAULT NULL,
  `database_password` varchar(64) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

3.数据源表对应的bean

/**
 * 数据源bean构建器
 */
public class DataSourceBean {

    private final String beanName;      //注册在spring中bean名字
    private final String driverClassName; 
    private final String url;
    private final String username;
    private final String password;
    private final String validationQuery;
    private final Boolean testOnBorrow;

    public String getBeanName() {
        return beanName;
    }

    public String getDriverClassName() {
        return driverClassName;
    }

    public String getUrl() {
        return url;
    }

    public String getUsername() {
        return username;
    }

    public String getPassword() {
        return password;
    }

    public String getValidationQuery() {
        return validationQuery;
    }

    public Boolean getTestOnBorrow() {
        return testOnBorrow;
    }

    public DataSourceBean(DataSourceBeanBuilder builder) {
        this.beanName = builder.getBeanName();
        this.driverClassName = builder.getDriverClassName();
        this.url = builder.getUrl();
        this.username = builder.getUsername();
        this.password = builder.getPassword();
        this.validationQuery = builder.getValidationQuery();
        this.testOnBorrow = builder.getTestOnBorrow();
    }

    public static class DataSourceBeanBuilder {
        private String beanName;
        private String driverClassName = "com.mysql.jdbc.Driver";
        private String url = "jdbc:mysql://%s:%s/%s";
        private String databaseIP;
        private String databasePort;
        private String databaseName;
        private String username;
        private String password;
        private String validationQuery = "select 1";
        private Boolean testOnBorrow = true;
        public DataSourceBeanBuilder(String beanName, String databaseIP, String databasePort, String databaseName,
                String username, String password) {
            super();
            this.beanName = beanName;
            this.databaseIP = databaseIP;
            this.databasePort = databasePort;
            this.databaseName = databaseName;
            this.username = username;
            this.password = password;
        }
        public DataSourceBeanBuilder() {
            super();
        }
        public DataSourceBeanBuilder driverClassName(String driverClassName) {
            this.driverClassName = driverClassName;
            return this;
        }
        public DataSourceBeanBuilder validationQuery(String validationQuery) {
            this.validationQuery = validationQuery;
            return this;
        }
        public DataSourceBeanBuilder testOnBorrow(Boolean testOnBorrow) {
            this.testOnBorrow = testOnBorrow;
            return this;
        }
        public String getUrl() {
            return String.format(url,this.databaseIP,this.databasePort,this.databaseName);
        }
        public String getBeanName() {
            return beanName;
        }
        public String getDriverClassName() {
            return driverClassName;
        }
        public String getDatabaseIP() {
            return databaseIP;
        }
        public String getDatabasePort() {
            return databasePort;
        }
        public String getDatabaseName() {
            return databaseName;
        }
        public String getUsername() {
            return username;
        }
        public String getPassword() {
            return password;
        }
        public String getValidationQuery() {
            return validationQuery;
        }
        public Boolean getTestOnBorrow() {
            return testOnBorrow;
        }
    }

4.这里将操作抽离出，建立数据源操作类，方便操作

/**
 * 数据源操作类
 */
public class DataSourceContext {

    private static ThreadLocal<DataSourceBean> threadLocal = new InheritableThreadLocal<DataSourceBean>();

    /**
     * 获取数据源
     */
    public static DataSourceBean getDataSource() {
        return threadLocal.get();
    }
    /**
     * 设置数据源
     */
    public static void setDataSource(DataSourceBean dataSourceBean) {
        threadLocal.set(dataSourceBean);
    }
    /**
     * 清除数据源
     * 清除后,数据源为默认时间
     */
    public static void toDefault() {
        threadLocal.remove();
    }
}

5.定义AbstractRoutingDataSource的继承类DynamicDataSource，同时实现ApplicationContextAware接口，因为该方法切换数据源，需要到spring上下文中生成和获取数据源bean。

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

import com.alibaba.druid.pool.DruidDataSource;


public class  DynamicDataSource extends AbstractRoutingDataSource implements ApplicationContextAware{

    private ApplicationContext applicationContext ;

    /**
     * 连接数据源前,调用该方法
     */
    @Override
    protected Object determineCurrentLookupKey() {
        //1.获取手动设置的数据源参数DataSourceBean
        DataSourceBean dataSourceBean = DataSourceContext.getDataSource();
        if(dataSourceBean == null) {
            return null;
        }
        try {
            //2.获取AbstractRoutingDataSource的targetDataSources属性,该属性存放数据源属性
            Map<Object, Object> targetSourceMap = getTargetSource();
            synchronized(this) {
                /*
                 * 3.判断targetDataSources中是否已经存在要设置的数据源bean
                 * 存在的话,则直接返回beanName
                 * 
                 */
                if(!targetSourceMap.keySet().contains(dataSourceBean.getBeanName())) {
                    /*不存在，则进行以下几步
                    3.1 先在spring容器中创建该数据源bean
                    */
                    Object dataSource = createDataSource(dataSourceBean);
                    //3.2 在创建后的bean,放入到targetDataSources Map中
                    targetSourceMap.put(dataSourceBean.getBeanName(), dataSource);
                    /*
                     * 3.3 通知spring有bean更新
                     * 主要更新AbstractRoutingDataSource的resolvedDefaultDataSource(Map)属性,
                     * 更新完以后,AbstractRoutingDataSource的determineTargetDataSource()中,才能找到数据源
                     * 代码如下：
                     * Object lookupKey = determineCurrentLookupKey();
                       DataSource dataSource = this.resolvedDataSources.get(lookupKey);
                     */
                    super.afterPropertiesSet();
                }
            }
            for(Map.Entry<Object, Object> entry : targetSourceMap.entrySet()) {
                System.out.println(entry.getKey()+"-"+entry.getValue());
            }
            return dataSourceBean.getBeanName();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
    /**
     * 根据数据源信息在spring中创建bean,并返回
     * @param dataSourceBean 数据源信息
     * @return
     * @throws IllegalAccessException
     */
    public Object createDataSource(DataSourceBean dataSourceBean) throws IllegalAccessException {
        //1.将applicationContext转化为ConfigurableApplicationContext
        ConfigurableApplicationContext context = (ConfigurableApplicationContext) applicationContext;
        //2.获取bean工厂并转换为DefaultListableBeanFactory
        DefaultListableBeanFactory beanFactory =  (DefaultListableBeanFactory) context.getBeanFactory();
        /*
         * 3.本文用的是DruidDataSource,所有在这里我们获取的是该bean的BeanDefinitionBuilder,
         * 通过BeanDefinitionBuilder来创建bean定义
         */
        BeanDefinitionBuilder beanDefinitionBuilder = BeanDefinitionBuilder.genericBeanDefinition(DruidDataSource.class);
        /**
         * 4.获取DataSourceBean里的属性和对应值,并将其交给BeanDefinitionBuilder创建bean的定义
         */
        Map<String, Object> propertyKeyValues = getPropertyKeyValues(DataSourceBean.class, dataSourceBean);
        for(Map.Entry<String,Object> entry : propertyKeyValues.entrySet()) {
            beanDefinitionBuilder.addPropertyValue(entry.getKey(), entry.getValue());
        }
        //5.bean定义创建好以后,将其交给beanFactory注册成bean对象，由spring容器管理
        beanFactory.registerBeanDefinition(dataSourceBean.getBeanName(), beanDefinitionBuilder.getBeanDefinition());
        //6.最后获取步骤5生成的bean,并将其返回
        return context.getBean(dataSourceBean.getBeanName());
    }
    //获取类属性和对应的值,放入Map中
    @SuppressWarnings("unused")
    private <T> Map<String, Object> getPropertyKeyValues(Class<T> clazz, Object object) throws IllegalAccessException {
       Field[] fields = clazz.getDeclaredFields();
       Map<String,Object> map = new HashMap<>();
       for (Field field : fields) {
           field.setAccessible(true);
           map.put(field.getName(), field.get(object));
       }
       map.remove("beanName");
       return map;
    }
    //通过反射获取AbstractRoutingDataSource的targetDataSources属性
    @SuppressWarnings("unchecked")
    public Map<Object, Object> getTargetSource() throws NoSuchFieldException, SecurityException, IllegalArgumentException, IllegalAccessException {
        Field field = AbstractRoutingDataSource.class.getDeclaredField("targetDataSources");
        field.setAccessible(true);
        return (Map<Object, Object>) field.get(this);
    }
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.applicationContext = applicationContext;
    }

}

6.测试用例测试一下

    @Test
    public void testDynamicDataSource() {
        1.从表中获取需要切换的数据源信息
        List<DataSourceDO> dataSourceDOList = dataSourceMapper.getAllDataSources();
        2.循环遍历,切换数据源,执行操作,切完就得切回默认数据源
        for (DataSourceDO dataSourceDO : dataSourceDOList) {
            DataSourceBean dataSourceBean = new DataSourceBean(new DataSourceBeanBuilder(dataSourceDO.getDatasourceName(),
                    dataSourceDO.getDatabaseIp(), dataSourceDO.getDatabasePort(), dataSourceDO.getDatabaseName(),
                    dataSourceDO.getUsername(), dataSourceDO.getPassword()));
            DataSourceContext.setDataSource(dataSourceBean);
            XXX你的操作XXX
            DataSourceContext.toDefault();
        }
    }

方法二部分参考https://blog.csdn.net/yizhenn/article/details/53965552该博客的思想。

源码分析可以看下一篇文章https://blog.csdn.net/u013034378/article/details/81661706

讲到这里，本篇文章到此也就结束了,如果文章中有问题,或者有一些不够严谨完善的地方,希望大家体谅体谅。欢迎大家留言,交流交流。
最后附上本项目github的地址