Spring+MyBatis实现数据库读写分离方案

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

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) {
        //
    }
}