mybatis读写分离

约定不等于承诺〃 2022-03-28 09:46 210阅读 0赞

mybatis读写分离实现方式有很多种，当然如果没有太过复杂的处理，可以使用阿里云数据库自带的读写分离连接，那样会更加简洁。本文主要对mybatis实现读写分离。主要的实现方式有一下四种：

## 方案1 ##

通过MyBatis配置文件创建读写分离两个DataSource，每个SqlSessionFactoryBean对象的mapperLocations属性制定两个读写数据源的配置文件。将所有读的操作配置在读文件中，所有写的操作配置在写文件中。

**优点：**实现简单

**缺点：**维护麻烦，需要对原有的xml文件进行重新修改，不支持多读，不易扩展

## 方案2 ##

通过Spring AOP在业务层实现读写分离，在DAO层调用前定义切面，利用Spring的AbstractRoutingDataSource解决多数据源的问题，实现动态选择数据源

**优点：**通过注解的方法在DAO每个方法上配置数据源，原有代码改动量少，易扩展，支持多读

**缺点：**需要在DAO每个方法上配置注解，人工管理，容易出错

//定义枚举类型，读写
    public enum DynamicDataSourceGlobal {
     READ, WRITE;
    }

import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    /**
     * RUNTIME
     * 定义注解
     * 编译器将把注释记录在类文件中，在运行时 VM 将保留注释，因此可以反射性地读取。
     * @author shma1664
     *
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.METHOD)
    public @interface DataSource {
     public DynamicDataSourceGlobal value() default DynamicDataSourceGlobal.READ;
    }

/**
     * Created by IDEA
     * 本地线程设置和获取数据源信息
     * User: mashaohua
     * Date: 2016-07-07 13:35
     * Desc:
     */
    public class DynamicDataSourceHolder {
     private static final ThreadLocal<DynamicDataSourceGlobal> holder = new ThreadLocal<DynamicDataSourceGlobal>();
     public static void putDataSource(DynamicDataSourceGlobal dataSource){
     holder.set(dataSource);
     }
     public static DynamicDataSourceGlobal getDataSource(){
     return holder.get();
     }
     public static void clearDataSource() {
     holder.remove();
     }
    }

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import java.util.concurrent.ThreadLocalRandom;
    import java.util.concurrent.atomic.AtomicLong;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    /**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-07-14 10:56
     * Desc: 动态数据源实现读写分离
     */
    public class DynamicDataSource extends AbstractRoutingDataSource {
     private Object writeDataSource; //写数据源
     private List<Object> readDataSources; //多个读数据源
     private int readDataSourceSize; //读数据源个数
     private int readDataSourcePollPattern = 0; //获取读数据源方式，0：随机，1：轮询
     private AtomicLong counter = new AtomicLong(0);
     private static final Long MAX_POOL = Long.MAX_VALUE;
     private final Lock lock = new ReentrantLock();
     @Override
     public void afterPropertiesSet() {
     if (this.writeDataSource == null) {
      throw new IllegalArgumentException("Property 'writeDataSource' is required");
     }
     setDefaultTargetDataSource(writeDataSource);
     Map<Object, Object> targetDataSources = new HashMap<>();
     targetDataSources.put(DynamicDataSourceGlobal.WRITE.name(), writeDataSource);
     if (this.readDataSources == null) {
      readDataSourceSize = 0;
     } else {
      for(int i=0; i<readDataSources.size(); i++) {
      targetDataSources.put(DynamicDataSourceGlobal.READ.name() + i, readDataSources.get(i));
      }
      readDataSourceSize = readDataSources.size();
     }
     setTargetDataSources(targetDataSources);
     super.afterPropertiesSet();
     }
     @Override
     protected Object determineCurrentLookupKey() {
     DynamicDataSourceGlobal dynamicDataSourceGlobal = DynamicDataSourceHolder.getDataSource();
     if(dynamicDataSourceGlobal == null
      || dynamicDataSourceGlobal == DynamicDataSourceGlobal.WRITE
      || readDataSourceSize <= 0) {
      return DynamicDataSourceGlobal.WRITE.name();
     }
     int index = 1;
     if(readDataSourcePollPattern == 1) {
      //轮询方式
      long currValue = counter.incrementAndGet();
      if((currValue + 1) >= MAX_POOL) {
      try {
       lock.lock();
       if((currValue + 1) >= MAX_POOL) {
       counter.set(0);
       }
      } finally {
       lock.unlock();
      }
      }
      index = (int) (currValue % readDataSourceSize);
     } else {
      //随机方式
      index = ThreadLocalRandom.current().nextInt(0, readDataSourceSize);
     }
     return dynamicDataSourceGlobal.name() + index;
     }
     public void setWriteDataSource(Object writeDataSource) {
     this.writeDataSource = writeDataSource;
     }
     public void setReadDataSources(List<Object> readDataSources) {
     this.readDataSources = readDataSources;
     }
     public void setReadDataSourcePollPattern(int readDataSourcePollPattern) {
     this.readDataSourcePollPattern = readDataSourcePollPattern;
     }
    }

import org.apache.log4j.Logger;
    import org.aspectj.lang.JoinPoint;
    import org.aspectj.lang.reflect.MethodSignature;
    import java.lang.reflect.Method;
    /**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-07-07 13:39
     * Desc: 定义选择数据源切面
     */
    public class DynamicDataSourceAspect {
     private static final Logger logger = Logger.getLogger(DynamicDataSourceAspect.class);
     public void pointCut(){};
     public void before(JoinPoint point)
     {
     Object target = point.getTarget();
     String methodName = point.getSignature().getName();
     Class<?>[] clazz = target.getClass().getInterfaces();
     Class<?>[] parameterTypes = ((MethodSignature) point.getSignature()).getMethod().getParameterTypes();
     try {
      Method method = clazz[0].getMethod(methodName, parameterTypes);
      if (method != null && method.isAnnotationPresent(DataSource.class)) {
      DataSource data = method.getAnnotation(DataSource.class);
      DynamicDataSourceHolder.putDataSource(data.value());
      }
     } catch (Exception e) {
      logger.error(String.format("Choose DataSource error, method:%s, msg:%s", methodName, e.getMessage()));
     }
     }
     public void after(JoinPoint point) {
     DynamicDataSourceHolder.clearDataSource();
     }
    }

<?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:tx="http://www.springframework.org/schema/tx"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.1.xsd
    http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.1.xsd">
     <bean id="abstractDataSource" abstract="true" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
     <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
     
     <property name="maxWait" value="60000"/>
     
     <property name="timeBetweenEvictionRunsMillis" value="60000"/>
     
     <property name="minEvictableIdleTimeMillis" value="300000"/>
     <property name="validationQuery" value="SELECT 'x'"/>
     <property name="testWhileIdle" value="true"/>
     <property name="testOnBorrow" value="false"/>
     <property name="testOnReturn" value="false"/>
     
     <property name="poolPreparedStatements" value="true"/>
     <property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
     <property name="filters" value="config"/>
     <property name="connectionProperties" value="config.decrypt=true" />
     </bean>
     <bean id="dataSourceRead1" parent="abstractDataSource">
     <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
     
     <property name="url" value="${read1.jdbc.url}"/>
     <property name="username" value="${read1.jdbc.user}"/>
     <property name="password" value="${read1.jdbc.password}"/>
     
     <property name="initialSize" value="${read1.jdbc.initPoolSize}"/>
     <property name="minIdle" value="${read1.jdbc.minPoolSize}"/>
     <property name="maxActive" value="${read1.jdbc.maxPoolSize}"/>
     </bean>
     <bean id="dataSourceRead2" parent="abstractDataSource">
     <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
     
     <property name="url" value="${read2.jdbc.url}"/>
     <property name="username" value="${read2.jdbc.user}"/>
     <property name="password" value="${read2.jdbc.password}"/>
     
     <property name="initialSize" value="${read2.jdbc.initPoolSize}"/>
     <property name="minIdle" value="${read2.jdbc.minPoolSize}"/>
     <property name="maxActive" value="${read2.jdbc.maxPoolSize}"/>
     </bean>
     <bean id="dataSourceWrite" parent="abstractDataSource">
     <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
     
     <property name="url" value="${write.jdbc.url}"/>
     <property name="username" value="${write.jdbc.user}"/>
     <property name="password" value="${write.jdbc.password}"/>
     
     <property name="initialSize" value="${write.jdbc.initPoolSize}"/>
     <property name="minIdle" value="${write.jdbc.minPoolSize}"/>
     <property name="maxActive" value="${write.jdbc.maxPoolSize}"/>
     </bean>
     <bean id="dataSource" class="com.test.api.dao.datasource.DynamicDataSource">
     <property name="writeDataSource" ref="dataSourceWrite" />
     <property name="readDataSources">
      <list>
      <ref bean="dataSourceRead1" />
      <ref bean="dataSourceRead2" />
      </list>
     </property>
     
     <property name="readDataSourcePollPattern" value="1" />
     <property name="defaultTargetDataSource" ref="dataSourceWrite"/>
     </bean>
     <tx:annotation-driven transaction-manager="transactionManager"/>
     <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
     <property name="dataSource" ref="dataSource"/>
     </bean>
     
     
     <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
     
     <property name="dataSource" ref="dataSource"/>
     <property name="mapperLocations" value="classpath:mapper/*.xml"/>
     </bean>
     
     <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
     
     <property name="basePackage" value="com.test.api.dao.inte"/>
     <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
     </bean>
     
     <bean id="dynamicDataSourceAspect" class="com.test.api.dao.datasource.DynamicDataSourceAspect" />
     <aop:config>
     <aop:aspect id="c" ref="dynamicDataSourceAspect">
      <aop:pointcut id="tx" expression="execution(* com.test.api.dao.inte..*.*(..))"/>
      <aop:before pointcut-ref="tx" method="before"/>
      <aop:after pointcut-ref="tx" method="after"/>
     </aop:aspect>
     </aop:config>
     
    </beans>

## 方案3 ##

通过Mybatis的Plugin在业务层实现数据库读写分离，在MyBatis创建Statement对象前通过拦截器选择真正的数据源，在拦截器中根据方法名称不同（select、update、insert、delete）选择数据源。

**优点：**原有代码不变，支持多读，易扩展

/**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-07-19 15:40
     * Desc: 创建Connection代理接口
     */
    public interface ConnectionProxy extends Connection {
     /**
     * 根据传入的读写分离需要的key路由到正确的connection
     * @param key 数据源标识
     * @return
     */
     Connection getTargetConnection(String key);
    }

import java.lang.reflect.InvocationHandler;
    import java.lang.reflect.InvocationTargetException;
    import java.lang.reflect.Method;
    import java.lang.reflect.Proxy;
    import java.sql.Connection;
    import java.sql.SQLException;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.logging.Logger;
    import javax.sql.DataSource;
    import org.springframework.beans.factory.InitializingBean;
    import org.springframework.jdbc.datasource.AbstractDataSource;
    import org.springframework.jdbc.datasource.lookup.DataSourceLookup;
    import org.springframework.jdbc.datasource.lookup.JndiDataSourceLookup;
    import org.springframework.util.Assert;
    public abstract class AbstractDynamicDataSourceProxy extends AbstractDataSource implements InitializingBean {
     private List<Object> readDataSources;
     private List<DataSource> resolvedReadDataSources;
     private Object writeDataSource;
     private DataSource resolvedWriteDataSource;
     private int readDataSourcePollPattern = 0;
     private int readDsSize;
     private boolean defaultAutoCommit = true;
     private int defaultTransactionIsolation = Connection.TRANSACTION_READ_COMMITTED;
     public static final String READ = "read";
     public static final String WRITE = "write";
     private DataSourceLookup dataSourceLookup = new JndiDataSourceLookup();
     @Override
     public Connection getConnection() throws SQLException {
     return (Connection) Proxy.newProxyInstance(
    com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class.getClassLoader(),
      new Class[] {com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class},
      new RWConnectionInvocationHandler());
     }
     @Override
     public Connection getConnection(String username, String password)
      throws SQLException {
     return (Connection) Proxy.newProxyInstance( com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class.getClassLoader(),
      new Class[] {com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy.class},
      new RWConnectionInvocationHandler(username,password));
     }
     public int getReadDsSize(){
     return readDsSize;
     }
     public List<DataSource> getResolvedReadDataSources() {
     return resolvedReadDataSources;
     }
     public void afterPropertiesSet() throws Exception {
     if(writeDataSource == null){
      throw new IllegalArgumentException("Property 'writeDataSource' is required");
     }
     this.resolvedWriteDataSource = resolveSpecifiedDataSource(writeDataSource);
     resolvedReadDataSources = new ArrayList<DataSource>(readDataSources.size());
     for(Object item : readDataSources){
      resolvedReadDataSources.add(resolveSpecifiedDataSource(item));
     }
     readDsSize = readDataSources.size();
     }
     protected DataSource determineTargetDataSource(String key) {
     Assert.notNull(this.resolvedReadDataSources, "DataSource router not initialized");
     if(WRITE.equals(key)){
      return resolvedWriteDataSource;
     }else{
      return loadReadDataSource();
     }
     }
     public Logger getParentLogger() {
     // NOOP Just ignore
     return null;
     }
     /**
     * 获取真实的data source
     * @param dataSource (jndi | real data source)
     * @return
     * @throws IllegalArgumentException
     */
     protected DataSource resolveSpecifiedDataSource(Object dataSource) throws IllegalArgumentException {
     if (dataSource instanceof DataSource) {
      return (DataSource) dataSource;
     }
     else if (dataSource instanceof String) {
      return this.dataSourceLookup.getDataSource((String) dataSource);
     }
     else {
      throw new IllegalArgumentException(
       "Illegal data source value - only [javax.sql.DataSource] and String supported: " + dataSource);
     }
     }
     protected abstract DataSource loadReadDataSource();
     public void setReadDsSize(int readDsSize) {
     this.readDsSize = readDsSize;
     }
     public List<Object> getReadDataSources() {
     return readDataSources;
     }
     public void setReadDataSources(List<Object> readDataSources) {
     this.readDataSources = readDataSources;
     }
     public Object getWriteDataSource() {
     return writeDataSource;
     }
     public void setWriteDataSource(Object writeDataSource) {
     this.writeDataSource = writeDataSource;
     }
     public void setResolvedReadDataSources(List<DataSource> resolvedReadDataSources) {
     this.resolvedReadDataSources = resolvedReadDataSources;
     }
     public DataSource getResolvedWriteDataSource() {
     return resolvedWriteDataSource;
     }
     public void setResolvedWriteDataSource(DataSource resolvedWriteDataSource) {
     this.resolvedWriteDataSource = resolvedWriteDataSource;
     }
     public int getReadDataSourcePollPattern() {
     return readDataSourcePollPattern;
     }
     public void setReadDataSourcePollPattern(int readDataSourcePollPattern) {
     this.readDataSourcePollPattern = readDataSourcePollPattern;
     }
     /**
     * Invocation handler that defers fetching an actual JDBC Connection
     * until first creation of a Statement.
     */
     private class RWConnectionInvocationHandler implements InvocationHandler {
     private String username;
     private String password;
     private Boolean readOnly = Boolean.FALSE;
     private Integer transactionIsolation;
     private Boolean autoCommit;
     private boolean closed = false;
     private Connection target;
     public RWConnectionInvocationHandler() {
     }
     public RWConnectionInvocationHandler(String username, String password) {
      this();
      this.username = username;
      this.password = password;
     }
     public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      // Invocation on ConnectionProxy interface coming in...
      if (method.getName().equals("equals")) {
      // We must avoid fetching a target Connection for "equals".
      // Only consider equal when proxies are identical.
      return (proxy == args[0] ? Boolean.TRUE : Boolean.FALSE);
      }
      else if (method.getName().equals("hashCode")) {
      // We must avoid fetching a target Connection for "hashCode",
      // and we must return the same hash code even when the target
      // Connection has been fetched: use hashCode of Connection proxy.
      return new Integer(System.identityHashCode(proxy));
      }
      else if (method.getName().equals("getTargetConnection")) {
      // Handle getTargetConnection method: return underlying connection.
      return getTargetConnection(method,args);
      }
      if (!hasTargetConnection()) {
      // No physical target Connection kept yet ->
      // resolve transaction demarcation methods without fetching
      // a physical JDBC Connection until absolutely necessary.
      if (method.getName().equals("toString")) {
       return "RW Routing DataSource Proxy";
      }
      else if (method.getName().equals("isReadOnly")) {
       return this.readOnly;
      }
      else if (method.getName().equals("setReadOnly")) {
       this.readOnly = (Boolean) args[0];
       return null;
      }
      else if (method.getName().equals("getTransactionIsolation")) {
       if (this.transactionIsolation != null) {
       return this.transactionIsolation;
       }
       return defaultTransactionIsolation;
       // Else fetch actual Connection and check there,
       // because we didn't have a default specified.
      }
      else if (method.getName().equals("setTransactionIsolation")) {
       this.transactionIsolation = (Integer) args[0];
       return null;
      }
      else if (method.getName().equals("getAutoCommit")) {
       if (this.autoCommit != null)
       return this.autoCommit;
       return defaultAutoCommit;
       // Else fetch actual Connection and check there,
       // because we didn't have a default specified.
      }
      else if (method.getName().equals("setAutoCommit")) {
       this.autoCommit = (Boolean) args[0];
       return null;
      }
      else if (method.getName().equals("commit")) {
       // Ignore: no statements created yet.
       return null;
      }
      else if (method.getName().equals("rollback")) {
       // Ignore: no statements created yet.
       return null;
      }
      else if (method.getName().equals("getWarnings")) {
       return null;
      }
      else if (method.getName().equals("clearWarnings")) {
       return null;
      }
      else if (method.getName().equals("isClosed")) {
       return (this.closed ? Boolean.TRUE : Boolean.FALSE);
      }
      else if (method.getName().equals("close")) {
       // Ignore: no target connection yet.
       this.closed = true;
       return null;
      }
      else if (this.closed) {
       // Connection proxy closed, without ever having fetched a
       // physical JDBC Connection: throw corresponding SQLException.
       throw new SQLException("Illegal operation: connection is closed");
      }
      }
      // Target Connection already fetched,
      // or target Connection necessary for current operation ->
      // invoke method on target connection.
      try {
      return method.invoke(target, args);
      }
      catch (InvocationTargetException ex) {
      throw ex.getTargetException();
      }
     }
     /**
      * Return whether the proxy currently holds a target Connection.
      */
     private boolean hasTargetConnection() {
      return (this.target != null);
     }
     /**
      * Return the target Connection, fetching it and initializing it if necessary.
      */
     private Connection getTargetConnection(Method operation,Object[] args) throws SQLException {
      if (this.target == null) {
      String key = (String) args[0];
      // No target Connection held -> fetch one.
      if (logger.isDebugEnabled()) {
       logger.debug("Connecting to database for operation '" + operation.getName() + "'");
      }
      // Fetch physical Connection from DataSource.
      this.target = (this.username != null) ?
       determineTargetDataSource(key).getConnection(this.username, this.password) :
       determineTargetDataSource(key).getConnection();
      // If we still lack default connection properties, check them now.
      //checkDefaultConnectionProperties(this.target);
      // Apply kept transaction settings, if any.
      if (this.readOnly.booleanValue()) {
       this.target.setReadOnly(this.readOnly.booleanValue());
      }
      if (this.transactionIsolation != null) {
    this.target.setTransactionIsolation(this.transactionIsolation.intValue());
      }
      if (this.autoCommit != null && this.autoCommit.booleanValue() != this.target.getAutoCommit()) {
       this.target.setAutoCommit(this.autoCommit.booleanValue());
      }
      }
      else {
      // Target Connection already held -> return it.
      if (logger.isDebugEnabled()) {
       logger.debug("Using existing database connection for operation '" + operation.getName() + "'");
      }
      }
      return this.target;
     }
     }
    }

import javax.sql.DataSource;
    import java.util.concurrent.ThreadLocalRandom;
    import java.util.concurrent.atomic.AtomicLong;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    /**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-07-19 16:04
     * Desc:
     */
    public class DynamicRoutingDataSourceProxy extends AbstractDynamicDataSourceProxy {
     private AtomicLong counter = new AtomicLong(0);
     private static final Long MAX_POOL = Long.MAX_VALUE;
     private final Lock lock = new ReentrantLock();
     @Override
     protected DataSource loadReadDataSource() {
     int index = 1;
     if(getReadDataSourcePollPattern() == 1) {
      //轮询方式
      long currValue = counter.incrementAndGet();
      if((currValue + 1) >= MAX_POOL) {
      try {
       lock.lock();
       if((currValue + 1) >= MAX_POOL) {
       counter.set(0);
       }
      } finally {
       lock.unlock();
      }
      }
      index = (int) (currValue % getReadDsSize());
     } else {
      //随机方式
      index = ThreadLocalRandom.current().nextInt(0, getReadDsSize());
     }
     return getResolvedReadDataSources().get(index);
     }
    }

import org.apache.ibatis.executor.statement.RoutingStatementHandler;
    import org.apache.ibatis.executor.statement.StatementHandler;
    import org.apache.ibatis.mapping.MappedStatement;
    import org.apache.ibatis.mapping.SqlCommandType;
    import org.apache.ibatis.plugin.*;
    import java.sql.Connection;
    import java.util.Properties;
    /**
     * 拦截器
     */
    @Intercepts({ @Signature(type = StatementHandler.class, method = "prepare", args = { Connection.class }) })
    public class DynamicPlugin implements Interceptor {
     public Object intercept(Invocation invocation) throws Throwable {
     Connection conn = (Connection)invocation.getArgs()[0];
     //如果是采用了我们代理,则路由数据源
     if(conn instanceof com.autohome.api.dealer.tuan.dao.rwmybatis.ConnectionProxy){
      StatementHandler statementHandler = (StatementHandler) invocation
       .getTarget();
      MappedStatement mappedStatement = null;
      if (statementHandler instanceof RoutingStatementHandler) {
      StatementHandler delegate = (StatementHandler) ReflectionUtils
       .getFieldValue(statementHandler, "delegate");
      mappedStatement = (MappedStatement) ReflectionUtils.getFieldValue(
       delegate, "mappedStatement");
      } else {
      mappedStatement = (MappedStatement) ReflectionUtils.getFieldValue(
    statementHandler, "mappedStatement");
      }
      String key = AbstractDynamicDataSourceProxy.WRITE;
      if(mappedStatement.getSqlCommandType() == SqlCommandType.SELECT){
      key = AbstractDynamicDataSourceProxy.READ;
      }else{
      key = AbstractDynamicDataSourceProxy.WRITE;
      }
      ConnectionProxy connectionProxy = (ConnectionProxy)conn;
      connectionProxy.getTargetConnection(key);
     }
     return invocation.proceed();
     }
     public Object plugin(Object target) {
     return Plugin.wrap(target, this);
     }
     public void setProperties(Properties properties) {
     //NOOP
     }
    }

import org.apache.ibatis.logging.Log;
    import org.apache.ibatis.logging.LogFactory;
    import java.lang.reflect.*;
    public class ReflectionUtils {
     private static final Log logger = LogFactory.getLog(ReflectionUtils.class);
     /**
     * 直接设置对象属性值,无视private/protected修饰符,不经过setter函数.
     */
     public static void setFieldValue(final Object object, final String fieldName, final Object value) {
     Field field = getDeclaredField(object, fieldName);
     if (field == null)
      throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
     makeAccessible(field);
     try {
      field.set(object, value);
     } catch (IllegalAccessException e) {
     }
     }
     /**
     * 直接读取对象属性值,无视private/protected修饰符,不经过getter函数.
     */
     public static Object getFieldValue(final Object object, final String fieldName) {
     Field field = getDeclaredField(object, fieldName);
     if (field == null)
      throw new IllegalArgumentException("Could not find field [" + fieldName + "] on target [" + object + "]");
     makeAccessible(field);
     Object result = null;
     try {
      result = field.get(object);
     } catch (IllegalAccessException e) {
     }
     return result;
     }
     /**
     * 直接调用对象方法,无视private/protected修饰符.
     */
     public static Object invokeMethod(final Object object, final String methodName, final Class<?>[] parameterTypes,
      final Object[] parameters) throws InvocationTargetException {
     Method method = getDeclaredMethod(object, methodName, parameterTypes);
     if (method == null)
      throw new IllegalArgumentException("Could not find method [" + methodName + "] on target [" + object + "]");
     method.setAccessible(true);
     try {
      return method.invoke(object, parameters);
     } catch (IllegalAccessException e) {
     }
     return null;
     }
     /**
     * 循环向上转型,获取对象的DeclaredField.
     */
     protected static Field getDeclaredField(final Object object, final String fieldName) {
     for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass
      .getSuperclass()) {
      try {
      return superClass.getDeclaredField(fieldName);
      } catch (NoSuchFieldException e) {
      }
     }
     return null;
     }
     /**
     * 循环向上转型,获取对象的DeclaredField.
     */
     protected static void makeAccessible(final Field field) {
     if (!Modifier.isPublic(field.getModifiers()) || !Modifier.isPublic(field.getDeclaringClass().getModifiers())) {
      field.setAccessible(true);
     }
     }
     /**
     * 循环向上转型,获取对象的DeclaredMethod.
     */
     protected static Method getDeclaredMethod(Object object, String methodName, Class<?>[] parameterTypes) {
     for (Class<?> superClass = object.getClass(); superClass != Object.class; superClass = superClass
      .getSuperclass()) {
      try {
      return superClass.getDeclaredMethod(methodName, parameterTypes);
      } catch (NoSuchMethodException e) {
      }
     }
     return null;
     }
     /**
     * 通过反射,获得Class定义中声明的父类的泛型参数的类型.
     * eg.
     * public UserDao extends HibernateDao<User>
     *
     * @param clazz The class to introspect
     * @return the first generic declaration, or Object.class if cannot be determined
     */
     @SuppressWarnings("unchecked")
     public static <T> Class<T> getSuperClassGenricType(final Class clazz) {
     return getSuperClassGenricType(clazz, 0);
     }
     /**
     * 通过反射,获得Class定义中声明的父类的泛型参数的类型.
     * eg.
     * public UserDao extends HibernateDao<User>
     *
     * @param clazz The class to introspect
     * @return the first generic declaration, or Object.class if cannot be determined
     */
     @SuppressWarnings("unchecked")
     public static Class getSuperClassGenricType(final Class clazz, final int index) {
     Type genType = clazz.getGenericSuperclass();
     if (!(genType instanceof ParameterizedType)) {
      logger.warn(clazz.getSimpleName() + "'s superclass not ParameterizedType");
      return Object.class;
     }
     Type[] params = ((ParameterizedType) genType).getActualTypeArguments();
     if (index >= params.length || index < 0) {
      logger.warn("Index: " + index + ", Size of " + clazz.getSimpleName() + "'s Parameterized Type: "
       + params.length);
      return Object.class;
     }
     if (!(params[index] instanceof Class)) {
      logger.warn(clazz.getSimpleName() + " not set the actual class on superclass generic parameter");
      return Object.class;
     }
     return (Class) params[index];
     }
     /**
     * 将反射时的checked exception转换为unchecked exception.
     */
     public static IllegalArgumentException convertToUncheckedException(Exception e) {
     if (e instanceof IllegalAccessException || e instanceof IllegalArgumentException
      || e instanceof NoSuchMethodException)
      return new IllegalArgumentException("Refelction Exception.", e);
     else
      return new IllegalArgumentException(e);
     }
    }

<?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD SQL Map Config 3.0//EN" 
     "http://mybatis.org/dtd/mybatis-3-config.dtd">
    <configuration>
     <plugins>
      <plugin interceptor="com.test.api.dao.mybatis.DynamicPlugin">
      </plugin>
     </plugins>
    </configuration>

<?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:tx="http://www.springframework.org/schema/tx"
    xmlns:aop="http://www.springframework.org/schema/aop"
    xsi:schemaLocation="http://www.springframework.org/schema/beans  http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
    http://www.springframework.org/schema/tx
    http://www.springframework.org/schema/tx/spring-tx-4.1.xsd
    http://www.springframework.org/schema/aop  http://www.springframework.org/schema/aop/spring-aop-4.1.xsd">
     <bean id="abstractDataSource" abstract="true" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
      <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
      
      <property name="maxWait" value="60000"/>
      
      <property name="timeBetweenEvictionRunsMillis" value="60000"/>
      
      <property name="minEvictableIdleTimeMillis" value="300000"/>
      <property name="validationQuery" value="SELECT 'x'"/>
      <property name="testWhileIdle" value="true"/>
      <property name="testOnBorrow" value="false"/>
      <property name="testOnReturn" value="false"/>
      
      <property name="poolPreparedStatements" value="true"/>
      <property name="maxPoolPreparedStatementPerConnectionSize" value="20"/>
      <property name="filters" value="config"/>
      <property name="connectionProperties" value="config.decrypt=true" />
     </bean>
     <bean id="dataSourceRead1" parent="abstractDataSource">
      <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
      
      <property name="url" value="${read1.jdbc.url}"/>
      <property name="username" value="${read1.jdbc.user}"/>
      <property name="password" value="${read1.jdbc.password}"/>
      
      <property name="initialSize" value="${read1.jdbc.initPoolSize}"/>
      <property name="minIdle" value="${read1.jdbc.minPoolSize}"/>
      <property name="maxActive" value="${read1.jdbc.maxPoolSize}"/>
     </bean>
     <bean id="dataSourceRead2" parent="abstractDataSource">
      <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
      
      <property name="url" value="${read2.jdbc.url}"/>
      <property name="username" value="${read2.jdbc.user}"/>
      <property name="password" value="${read2.jdbc.password}"/>
      
      <property name="initialSize" value="${read2.jdbc.initPoolSize}"/>
      <property name="minIdle" value="${read2.jdbc.minPoolSize}"/>
      <property name="maxActive" value="${read2.jdbc.maxPoolSize}"/>
     </bean>
     <bean id="dataSourceWrite" parent="abstractDataSource">
      <property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver"/>
      
      <property name="url" value="${write.jdbc.url}"/>
      <property name="username" value="${write.jdbc.user}"/>
      <property name="password" value="${write.jdbc.password}"/>
      
      <property name="initialSize" value="${write.jdbc.initPoolSize}"/>
      <property name="minIdle" value="${write.jdbc.minPoolSize}"/>
      <property name="maxActive" value="${write.jdbc.maxPoolSize}"/>
     </bean>
     <bean id="dataSource" class="com.test.api.dao.datasource.DynamicRoutingDataSourceProxy">
      <property name="writeDataSource" ref="dataSourceWrite" />
      <property name="readDataSources">
       <list>
        <ref bean="dataSourceRead1" />
        <ref bean="dataSourceRead2" />
       </list>
      </property>
      
      <property name="readDataSourcePollPattern" value="1" />
     </bean>
     <tx:annotation-driven transaction-manager="transactionManager"/>
     <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
      <property name="dataSource" ref="dataSource"/>
     </bean>
     
     
     <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
      
      <property name="dataSource" ref="dataSource"/>
      <property name="mapperLocations" value="classpath:mapper/*.xml"/>
      <property name="configLocation" value="classpath:mybatis-plugin-config.xml" />
     </bean>
     <bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">
      <constructor-arg ref="sqlSessionFactory" />
     </bean>
     
     <bean id="mapper" class="org.mybatis.spring.mapper.MapperScannerConfigurer">
      <property name="basePackage" value="com.test.api.dao.inte" />
      <property name="sqlSessionTemplate" ref="sqlSessionTemplate"></property>
     </bean>
    </beans>

## 方案4 ##

如果你的后台结构是spring+mybatis，可以通过spring的AbstractRoutingDataSource和mybatis Plugin拦截器实现非常友好的读写分离，原有代码不需要任何改变。推荐第四种方案

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;
    import java.util.HashMap;
    import java.util.Map;
    /**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-07-14 10:56
     * Desc: 动态数据源实现读写分离
     */
    public class DynamicDataSource extends AbstractRoutingDataSource {
     private Object writeDataSource; //写数据源
     private Object readDataSource; //读数据源
     @Override
     public void afterPropertiesSet() {
      if (this.writeDataSource == null) {
       throw new IllegalArgumentException("Property 'writeDataSource' is required");
      }
      setDefaultTargetDataSource(writeDataSource);
      Map<Object, Object> targetDataSources = new HashMap<>();
      targetDataSources.put(DynamicDataSourceGlobal.WRITE.name(), writeDataSource);
      if(readDataSource != null) {
       targetDataSources.put(DynamicDataSourceGlobal.READ.name(), readDataSource);
      }
      setTargetDataSources(targetDataSources);
      super.afterPropertiesSet();
     }
     @Override
     protected Object determineCurrentLookupKey() {
      DynamicDataSourceGlobal dynamicDataSourceGlobal = DynamicDataSourceHolder.getDataSource();
      if(dynamicDataSourceGlobal == null
        || dynamicDataSourceGlobal == DynamicDataSourceGlobal.WRITE) {
       return DynamicDataSourceGlobal.WRITE.name();
      }
      return DynamicDataSourceGlobal.READ.name();
     }
     public void setWriteDataSource(Object writeDataSource) {
      this.writeDataSource = writeDataSource;
     }
     public Object getWriteDataSource() {
      return writeDataSource;
     }
     public Object getReadDataSource() {
      return readDataSource;
     }
     public void setReadDataSource(Object readDataSource) {
      this.readDataSource = readDataSource;
     }
    }

/**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-07-14 10:58
     * Desc:
     */
    public enum DynamicDataSourceGlobal {
     READ, WRITE;
    }

public final class DynamicDataSourceHolder {
     private static final ThreadLocal<DynamicDataSourceGlobal> holder = new ThreadLocal<DynamicDataSourceGlobal>();
     private DynamicDataSourceHolder() {
      //
     }
     public static void putDataSource(DynamicDataSourceGlobal dataSource){
      holder.set(dataSource);
     }
     public static DynamicDataSourceGlobal getDataSource(){
      return holder.get();
     }
     public static void clearDataSource() {
      holder.remove();
     }
    }

import org.apache.ibatis.executor.Executor;
    import org.apache.ibatis.executor.keygen.SelectKeyGenerator;
    import org.apache.ibatis.mapping.BoundSql;
    import org.apache.ibatis.mapping.MappedStatement;
    import org.apache.ibatis.mapping.SqlCommandType;
    import org.apache.ibatis.plugin.*;
    import org.apache.ibatis.session.ResultHandler;
    import org.apache.ibatis.session.RowBounds;
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    import org.springframework.transaction.support.TransactionSynchronizationManager;
    import java.util.Locale;
    import java.util.Map;
    import java.util.Properties;
    import java.util.concurrent.ConcurrentHashMap;
    /**
     * Created by IDEA
     * User: mashaohua
     * Date: 2016-08-10 11:09
     * Desc:
     */
    @Intercepts({
    @Signature(type = Executor.class, method = "update", args = {
      MappedStatement.class, Object.class }),
    @Signature(type = Executor.class, method = "query", args = {
      MappedStatement.class, Object.class, RowBounds.class,
      ResultHandler.class }) })
    public class DynamicPlugin implements Interceptor {
     protected static final Logger logger = LoggerFactory.getLogger(DynamicPlugin.class);
     private static final String REGEX = ".*insert\\u0020.*|.*delete\\u0020.*|.*update\\u0020.*";
     private static final Map<String, DynamicDataSourceGlobal> cacheMap = new ConcurrentHashMap<>();
     @Override
     public Object intercept(Invocation invocation) throws Throwable {
      boolean synchronizationActive = TransactionSynchronizationManager.isSynchronizationActive();
      if(!synchronizationActive) {
       Object[] objects = invocation.getArgs();
       MappedStatement ms = (MappedStatement) objects[0];
       DynamicDataSourceGlobal dynamicDataSourceGlobal = null;
       if((dynamicDataSourceGlobal = cacheMap.get(ms.getId())) == null) {
        //读方法
        if(ms.getSqlCommandType().equals(SqlCommandType.SELECT)) {
         //!selectKey 为自增id查询主键(SELECT LAST_INSERT_ID() )方法，使用主库
         if(ms.getId().contains(SelectKeyGenerator.SELECT_KEY_SUFFIX)) {
          dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
         } else {
          BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);
          String sql = boundSql.getSql().toLowerCase(Locale.CHINA).replaceAll("[\\t\\n\\r]", " ");
          if(sql.matches(REGEX)) {
           dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
          } else {
           dynamicDataSourceGlobal = DynamicDataSourceGlobal.READ;
          }
         }
        }else{
         dynamicDataSourceGlobal = DynamicDataSourceGlobal.WRITE;
        }
        logger.warn("设置方法[{}] use [{}] Strategy, SqlCommandType [{}]..", ms.getId(), dynamicDataSourceGlobal.name(), ms.getSqlCommandType().name());
        cacheMap.put(ms.getId(), dynamicDataSourceGlobal);
       }
       DynamicDataSourceHolder.putDataSource(dynamicDataSourceGlobal);
      }
      return invocation.proceed();
     }
     @Override
     public Object plugin(Object target) {
      if (target instanceof Executor) {
       return Plugin.wrap(target, this);
      } else {
       return target;
      }
     }
     @Override
     public void setProperties(Properties properties) {
      //
     }
    }