mybatis读写分离

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

<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"/>
 <!-- 配置获取连接等待超时的时间 -->
 <property name="maxWait" value="60000"/>
 <!-- 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒 -->
 <property name="timeBetweenEvictionRunsMillis" value="60000"/>
 <!-- 配置一个连接在池中最小生存的时间，单位是毫秒 -->
 <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"/>
 <!-- 打开PSCache，并且指定每个连接上PSCache的大小 -->
 <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="readDataSource" parent="abstractDataSource">
 <!-- 基本属性 url、user、password -->
 <property name="url" value="${read.jdbc.url}"/>
 <property name="username" value="${read.jdbc.user}"/>
 <property name="password" value="${read.jdbc.password}"/>
 <!-- 配置初始化大小、最小、最大 -->
 <property name="initialSize" value="${read.jdbc.initPoolSize}"/>
 <property name="minIdle" value="10"/>
 <property name="maxActive" value="${read.jdbc.maxPoolSize}"/>
</bean>
<bean id="writeDataSource" parent="abstractDataSource">
 <!-- 基本属性 url、user、password -->
 <property name="url" value="${write.jdbc.url}"/>
 <property name="username" value="${write.jdbc.user}"/>
 <property name="password" value="${write.jdbc.password}"/>
 <!-- 配置初始化大小、最小、最大 -->
 <property name="initialSize" value="${write.jdbc.initPoolSize}"/>
 <property name="minIdle" value="10"/>
 <property name="maxActive" value="${write.jdbc.maxPoolSize}"/>
</bean>
<bean id="readSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
 <!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
 <property name="dataSource" ref="readDataSource"/>
 <property name="mapperLocations" value="classpath:mapper/read/*.xml"/>
</bean>
<bean id="writeSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
 <!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
 <property name="dataSource" ref="writeDataSource"/>
 <property name="mapperLocations" value="classpath:mapper/write/*.xml"/>
</bean>

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"/>
 <!-- 配置获取连接等待超时的时间 -->
 <property name="maxWait" value="60000"/>
 <!-- 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒 -->
 <property name="timeBetweenEvictionRunsMillis" value="60000"/>
 <!-- 配置一个连接在池中最小生存的时间，单位是毫秒 -->
 <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"/>
 <!-- 打开PSCache，并且指定每个连接上PSCache的大小 -->
 <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"/>
 <!-- 基本属性 url、user、password -->
 <property name="url" value="${read1.jdbc.url}"/>
 <property name="username" value="${read1.jdbc.user}"/>
 <property name="password" value="${read1.jdbc.password}"/>
 <!-- 配置初始化大小、最小、最大 -->
 <property name="initialSize" value="${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"/>
 <!-- 基本属性 url、user、password -->
 <property name="url" value="${read2.jdbc.url}"/>
 <property name="username" value="${read2.jdbc.user}"/>
 <property name="password" value="${read2.jdbc.password}"/>
 <!-- 配置初始化大小、最小、最大 -->
 <property name="initialSize" value="${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"/>
 <!-- 基本属性 url、user、password -->
 <property name="url" value="${write.jdbc.url}"/>
 <property name="username" value="${write.jdbc.user}"/>
 <property name="password" value="${write.jdbc.password}"/>
 <!-- 配置初始化大小、最小、最大 -->
 <property name="initialSize" value="${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>
 <!--轮询方式-->
 <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>
 <!-- 针对myBatis的配置项 -->
 <!-- 配置sqlSessionFactory -->
 <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
 <!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
 <property name="dataSource" ref="dataSource"/>
 <property name="mapperLocations" value="classpath:mapper/*.xml"/>
 </bean>
 <!-- 配置扫描器 -->
 <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
 <!-- 扫描包以及它的子包下的所有映射接口类 -->
 <property name="basePackage" value="com.test.api.dao.inte"/>
 <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
 </bean>
 <!-- 配置数据库注解aop -->
 <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>
 <!-- 配置数据库注解aop -->
</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"/>
  <!-- 配置获取连接等待超时的时间 -->
  <property name="maxWait" value="60000"/>
  <!-- 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位是毫秒 -->
  <property name="timeBetweenEvictionRunsMillis" value="60000"/>
  <!-- 配置一个连接在池中最小生存的时间，单位是毫秒 -->
  <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"/>
  <!-- 打开PSCache，并且指定每个连接上PSCache的大小 -->
  <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"/>
  <!-- 基本属性 url、user、password -->
  <property name="url" value="${read1.jdbc.url}"/>
  <property name="username" value="${read1.jdbc.user}"/>
  <property name="password" value="${read1.jdbc.password}"/>
  <!-- 配置初始化大小、最小、最大 -->
  <property name="initialSize" value="${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"/>
  <!-- 基本属性 url、user、password -->
  <property name="url" value="${read2.jdbc.url}"/>
  <property name="username" value="${read2.jdbc.user}"/>
  <property name="password" value="${read2.jdbc.password}"/>
  <!-- 配置初始化大小、最小、最大 -->
  <property name="initialSize" value="${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"/>
  <!-- 基本属性 url、user、password -->
  <property name="url" value="${write.jdbc.url}"/>
  <property name="username" value="${write.jdbc.user}"/>
  <property name="password" value="${write.jdbc.password}"/>
  <!-- 配置初始化大小、最小、最大 -->
  <property name="initialSize" value="${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>
  <!--轮询方式-->
  <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>
 <!-- 针对myBatis的配置项 -->
 <!-- 配置sqlSessionFactory -->
 <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
  <!-- 实例化sqlSessionFactory时需要使用上述配置好的数据源以及SQL映射文件 -->
  <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>
 <!-- 通过扫描的模式，扫描目录下所有的mapper， 根据对应的mapper.xml为其生成代理类-->
 <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) {
  //
 }
}