基于Spring和Mybatis拦截器实现数据库操作读写分离

首先需要配置好数据库的主从同步：

上一篇文章中有写到：https://www.cnblogs.com/xuyiqing/p/10647133.html

为什么要进行读写分离呢？

通常的Web应用大多数读操作次数远大于写操作

为了提高效率，我们可以考虑读写分离

读写分离可以采用DBProxy中间件，这里不谈这种方式

而是使用Mabatis拦截器

大体思路是：

得到SQL语句进行分析，如果是select那么分配从数据库数据源

反之，分配主数据库数据源

Spring重写路由：

package org.dreamtech.o2o.dao.split;

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

/**
 * 数据源路由重写，用于读写分离
 *
 * @author Xu Yiqing
 *
 */
public class DynamicDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
        return DynamicDataSourceHolder.getDbType();
    }

}

自定义工具类：

package org.dreamtech.o2o.dao.split;

/**
 * 辅助进行读写分离操作
 *
 * @author Xu Yiqing
 *
 */
public class DynamicDataSourceHolder {
    private static ThreadLocal<String> contextHolder = new ThreadLocal<String>();
    public static final String DB_MASTER = "master";
    public static final String DB_SLAVE = "slave";

    /**
     * 获取dbType
     *
     * @return dbType
     */
    public static String getDbType() {
        String db = contextHolder.get();
        if (db == null) {
            db = DB_MASTER;
        }
        return db;
    }

    /**
     * 设置线程的dbType
     *
     * @param str
     *            类型
     */
    public static void setDbType(String str) {
        contextHolder.set(str);
    }

    /**
     * 清理连接类型
     */
    public static void clearDBType() {
        contextHolder.remove();
    }

}

Mybatis过滤器：

package org.dreamtech.o2o.dao.split;

import java.util.Locale;
import java.util.Properties;

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.Interceptor;
import org.apache.ibatis.plugin.Intercepts;
import org.apache.ibatis.plugin.Invocation;
import org.apache.ibatis.plugin.Plugin;
import org.apache.ibatis.plugin.Signature;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;

import org.springframework.transaction.support.TransactionSynchronizationManager;

/**
 * Mybatis拦截器，实现读写分离
 *
 * @author Xu Yiqing
 *
 */
@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 DynamicDataSourceInterceptor implements Interceptor {
    private static final String REGEX = ".*insert\\u0020.*|.*delete\\u0020.*|.*update\\u0020.*";

    /**
     * 核心方法
     */
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        boolean synchronizationActive = TransactionSynchronizationManager.isActualTransactionActive();
        Object[] objects = invocation.getArgs();
        MappedStatement ms = (MappedStatement) objects[0];
        String lookupKey = DynamicDataSourceHolder.DB_MASTER;
        if (synchronizationActive != true) {
            if (ms.getSqlCommandType().equals(SqlCommandType.SELECT)) {
                if (ms.getId().contains(SelectKeyGenerator.SELECT_KEY_SUFFIX)) {
                    lookupKey = DynamicDataSourceHolder.DB_MASTER;
                } else {
                    BoundSql boundSql = ms.getSqlSource().getBoundSql(objects[1]);
                    String sql = boundSql.getSql().toLowerCase(Locale.CHINA).replaceAll("[\\t\\n\\r]", " ");
                    if (sql.matches(REGEX)) {
                        lookupKey = DynamicDataSourceHolder.DB_MASTER;
                    } else {
                        lookupKey = DynamicDataSourceHolder.DB_SLAVE;
                    }
                }
            }
        } else {
            lookupKey = DynamicDataSourceHolder.DB_MASTER;
        }
        DynamicDataSourceHolder.setDbType(lookupKey);
        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 arg0) {
    }

}

配置主从服务器的地址：

为了方便，他们的用户名和密码都是一样的

jdbc.properties：

jdbc.driver=com.mysql.jdbc.Driver
jdbc.master.url=jdbc:mysql://192.168.111.134:3306/o2o?useUnicode=true&characterEncoding=utf8
jdbc.slave.url=jdbc:mysql://192.168.111.135:3306/o2o?useUnicode=true&characterEncoding=utf8
jdbc.username=work
jdbc.password=xuyiqing

mybatis-config.xml：Mybatis配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
......
    <!-- 自定义拦截器 -->
    <plugins>
        <plugin interceptor="org.dreamtech.o2o.dao.split.DynamicDataSourceInterceptor" />
    </plugins>
......
</configuration>

spring-dao.xml配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-4.3.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop-4.3.xsd
        http://www.springframework.org/schema/tx
        http://www.springframework.org/schema/tx/spring-tx-4.3.xsd">
......
    <context:property-placeholder location="classpath:jdbc.properties" />
    <!-- 数据源 -->
    <bean id="abstractDataSource" abstract="true"
        class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
        <property name="maxPoolSize" value="30" />
        <property name="minPoolSize" value="10" />
        <property name="autoCommitOnClose" value="false" />
        <property name="checkoutTimeout" value="10000" />
        <property name="acquireRetryAttempts" value="2" />
    </bean>
    <!-- 主数据库 -->
    <bean id="master" parent="abstractDataSource">
        <property name="driverClass" value="${jdbc.driver}" />
        <property name="jdbcUrl" value="${jdbc.master.url}" />
        <property name="user" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>
    <!-- 从数据库 -->
    <bean id="slave" parent="abstractDataSource">
        <property name="driverClass" value="${jdbc.driver}" />
        <property name="jdbcUrl" value="${jdbc.slave.url}" />
        <property name="user" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>
    <!-- 配置动态数据源 -->
    <bean id="dynamicDataSource" class="org.dreamtech.o2o.dao.split.DynamicDataSource">
        <property name="targetDataSources">
            <map>
                <entry value-ref="master" key="master"></entry>
                <entry value-ref="slave" key="slave"></entry>
            </map>
        </property>
    </bean>
    <!-- 懒加载数据源 -->
    <bean id="dataSource"
        class="org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy">
        <property name="targetDataSource">
            <ref bean="dynamicDataSource" />
        </property>
    </bean>
......
</beans>