⭐⭐⭐ Spring Boot 项目实战	⭐⭐⭐ Spring Cloud 项目实战
《Dubbo 实现原理与源码解析 —— 精品合集》	《Netty 实现原理与源码解析 —— 精品合集》
《Spring 实现原理与源码解析 —— 精品合集》	《MyBatis 实现原理与源码解析 —— 精品合集》
《Spring MVC 实现原理与源码解析 —— 精品合集》	《数据库实体设计合集》
《Spring Boot 实现原理与源码解析 —— 精品合集》	《Java 面试题 + Java 学习指南》

摘要: 原创出处 jianshu.com/p/2222257f96d3 「蓝汀华韶」欢迎转载，保留摘要，谢谢！

🙂🙂🙂关注**微信公众号：【芋道源码】**有福利：

RocketMQ / MyCAT / Sharding-JDBC 所有源码分析文章列表

RocketMQ / MyCAT / Sharding-JDBC 中文注释源码 GitHub 地址

您对于源码的疑问每条留言都将得到认真回复。甚至不知道如何读源码也可以请教噢。

新的源码解析文章实时收到通知。每周更新一篇左右。

认真的源码交流微信群。

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
实现方式

<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
实现方式

//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
缺点：
实现方式

/**
 * 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.springframework.jdbc.datasource.DataSourceTransactionManager;
import org.springframework.transaction.TransactionDefinition;

/**
 * Created by IDEA
 * User: mashaohua
 * Date: 2016-08-10 14:34
 * Desc:
 */
public class DynamicDataSourceTransactionManager extends DataSourceTransactionManager {

    /**
     * 只读事务到读库，读写事务到写库
     * @param transaction
     * @param definition
     */
    @Override
    protected void doBegin(Object transaction, TransactionDefinition definition) {

        //设置数据源
        boolean readOnly = definition.isReadOnly();
        if(readOnly) {
            DynamicDataSourceHolder.putDataSource(DynamicDataSourceGlobal.READ);
        } else {
            DynamicDataSourceHolder.putDataSource(DynamicDataSourceGlobal.WRITE);
        }
        super.doBegin(transaction, definition);
    }

    /**
     * 清理本地线程的数据源
     * @param transaction
     */
    @Override
    protected void doCleanupAfterCompletion(Object transaction) {
        super.doCleanupAfterCompletion(transaction);
        DynamicDataSourceHolder.clearDataSource();
    }
}

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) {
        //
    }

推荐第四种：https://github.com/shawntime/shawn-rwdb

芋道源码 —— 纯源码解析博客

Spring + MyBatis 实现数据库读写分离方案

方案1

方案2

方案3

方案4