spring aop实现数据库的读写分离

　　为了减轻数据库的压力，一般会使用数据库主从(master/slave)的方式，但是这种方式会给应用程序带来一定的麻烦，比如说，应用程序如何做到把数据写到master库，而读取数据的时候，从slave库读取。如果应用程序判断失误，把数据写入到slave库，会给系统造成致命的打击。

　　解决读写分离的方案很多，常用的有SQL解析、动态设置数据源。SQL解析主要是通过分析sql语句是insert/select/update/delete中的哪一种，从而对应选择主从。而动态设置数据源，则是通过拦截方法名称的方式来决定主从的，例如：save*(),insert*() 形式的方法使用master库，select()开头的，使用slave库。蛮多公司会使用在方法上标上自定义的@Master、@Slave之类的标签来选择主从，也有公司直接就调用setxxMaster,setxxSlave之类的代码进行主从选择。

本文基于spring AOP编写了一个简单的读写分离的demo

---

前提环境：eclipse 、maven、 mysql、mybatis

数据库信息：两个库 masterdb和slaverdb 偷懒放在同一台mysql了，可以用虚拟机模拟多台实例，这里简单弄一下

两个库都有一个user表：

CREATE TABLE `user` (
   `id` int(10) NOT NULL AUTO_INCREMENT COMMENT 'id',
   `name` varchar(20) NOT NULL COMMENT '姓名',
   `age` int(3) NOT NULL COMMENT '年龄',
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8

初始数据都为：

---

代码：

工程结构如下：

代码如下：

package com.light.domain;

import java.io.Serializable;

public class User implements Serializable{

    private static final long serialVersionUID = 6102526449700267066L;

    private int id;
    private String name;
    private int age;

    public User() {
        super();
    }

    public User(int id, String name, int age) {
        super();
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + ", age=" + age + "]";
    }

}

package com.light.dynamicdatasource;
import org.apache.commons.lang3.StringUtils;
import org.aspectj.lang.JoinPoint;

/**
 * 定义数据源的AOP切面，通过该Service的方法名判断是应该走读库还是写库
 *
 */
public class DataSourceAspect {

    /**
     * 在进入Service方法之前执行
     *
     * @param point 切面对象
     */
    public void before(JoinPoint point) {
        // 获取到当前执行的方法名
        String methodName = point.getSignature().getName();
        if (isSlave(methodName)) {
            // 标记为读库
            DynamicDataSourceHolder.markSlave();
        } else {
            // 标记为写库
            DynamicDataSourceHolder.markMaster();
        }
    }

    /**
     * 判断是否为读库
     * @param methodName
     * @return
     */
    private Boolean isSlave(String methodName) {
        // 方法名以query、find、get开头的方法名走从库
        return StringUtils.startsWithAny(methodName, "query", "find", "get");
    }

}

package com.light.dynamicdatasource;
import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

/**
 * 定义动态数据源，实现通过集成Spring提供的AbstractRoutingDataSource，
 * 只需要实现determineCurrentLookupKey方法即可
 *
 * 由于DynamicDataSource是单例的，线程不安全的，所以采用ThreadLocal保证线程安全，
 * 由DynamicDataSourceHolder完成。
 *
 */
public class DynamicDataSource extends AbstractRoutingDataSource{

    @Override
    protected Object determineCurrentLookupKey() {
        // 使用DynamicDataSourceHolder保证线程安全，并且得到当前线程中的数据源key
        String dataSourceKey = DynamicDataSourceHolder.getDataSourceKey();
        System.out.println("dataSourceKey ======> "+dataSourceKey);
        return dataSourceKey;
    }

}

package com.light.dynamicdatasource;
/**
 *
 * 使用ThreadLocal技术来记录当前线程中的数据源的key
 *
 */
public class DynamicDataSourceHolder {

    //写库对应的数据源key
    private static final String MASTER = "master";

    //读库对应的数据源key
    private static final String SLAVE = "slave";

    //使用ThreadLocal记录当前线程的数据源key
    private static final ThreadLocal<String> holder = new ThreadLocal<String>();

    /**
     * 设置数据源key
     * @param key
     */
    public static void putDataSourceKey(String key) {
        holder.set(key);
    }

    /**
     * 获取数据源key
     * @return
     */
    public static String getDataSourceKey() {
        return holder.get();
    }

    /**
     * 标记写库
     */
    public static void markMaster(){
        putDataSourceKey(MASTER);
    }

    /**
     * 标记读库
     */
    public static void markSlave(){
        putDataSourceKey(SLAVE);
    }

}

package com.light.mapper;

import com.light.domain.User;

public interface UserMapper {

    public User getById(int id);

    public void deleteById(int id);

    public void insertUserCacheId(User user);

}

package com.light.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.light.domain.User;
import com.light.mapper.UserMapper;

@Service
public class UserService {

    @Autowired
    private UserMapper userMapper;

    public User getUser(int id) {
        return this.userMapper.getById(id);
    }

    public void delete(int id) {
        this.userMapper.deleteById(id);
    }

    public void insert(User user) {
        this.userMapper.insertUserCacheId(user);
    }
}

package com.light.web;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import com.light.domain.User;
import com.light.service.UserService;

@RestController
@RequestMapping("user")
public class UserController {

    @Autowired
    private UserService userService;

    @RequestMapping("get/{id}")
    public User get(@PathVariable("id") int id) {
        System.out.println("查询的id是: "+ id);
        System.out.println("id: " + this.userService.getUser(id));
        return this.userService.getUser(id);
    }

    @RequestMapping("delete/{id}")
    public String delete(@PathVariable("id") int id) {
        System.out.println("删除用户id: " + id);
        this.userService.delete(id);
        return "success";
    }

    @RequestMapping("insert")
    public void insert() {
        System.out.println("增加用户信息记录");
        User user = new User(4, "小黑", 19);
        this.userService.insert(user);
        System.out.println("增加用户成功：" + user);
    }
}

配置文件：

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.light.mapper.UserMapper">

    <select id="getById" parameterType="java.lang.Integer" resultType="com.light.domain.User">
        select id, name, age from user where id = #{id}
    </select>

    <delete id="deleteById" parameterType="java.lang.Integer">
        delete from user where id = #{id}
    </delete>

    <insert id="insertUserCacheId" parameterType="com.light.domain.User">
         insert into user(id,name,age) values(#{id},#{name},#{age})
     </insert>
</mapper>

SqlMapConfig.xml

<?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>

     <settings>
        <!-- 获取数据库自增主键值 -->
        <setting name="useGeneratedKeys" value="true"/>
        <!-- 使用列别名替换列名，默认为 true -->
        <setting name="useColumnLabel" value="true"/>
        <!-- 开启驼峰命名转换：Table(create_time) => Entity(createTime) -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
        <!-- 开启懒加载 -->
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>

</configuration>

applicationContext-mybatis.xml

<?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: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-4.0.xsd
                    http://www.springframework.org/schema/context
                    http://www.springframework.org/schema/context/spring-context-4.0.xsd
                    http://www.springframework.org/schema/tx
                    http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
                    http://www.springframework.org/schema/aop
                    http://www.springframework.org/schema/aop/spring-aop-4.0.xsd">

    <context:component-scan base-package="com.light.*">
        <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
    </context:component-scan>

    <context:property-placeholder location="classpath:*.properties"/>

    <!-- 数据源 -->
    <bean id="dataSource" class="com.light.dynamicdatasource.DynamicDataSource">
        <property name="targetDataSources">
            <map key-type="java.lang.String">
                <entry key="master" value-ref="masterDataSource"></entry>
                <entry key="slave" value-ref="slave01DataSource"></entry>
            </map>
        </property>
        <!-- 默认数据源 -->
        <property name="defaultTargetDataSource" ref="masterDataSource"/>
    </bean>

    <!-- 主库数据源 -->
    <bean id="masterDataSource" class="com.alibaba.druid.pool.DruidDataSource" destroy-method="close">
        <property name="url" value="${jdbc.master.url}"/>
        <property name="username" value="${jdbc.master.username}"/>
        <property name="password" value="${jdbc.master.password}"/>
        <property name="driverClassName" value="${jdbc.driver}"/>
        <property name="initialSize" value="5"/>
        <property name="minIdle" value="5"/>
        <property name="maxActive" value="50"/>
    </bean>

    <!-- 从库数据源 -->
    <bean id="slave01DataSource" class="com.alibaba.druid.pool.DruidDataSource" destroy-method="close">
        <property name="url" value="${jdbc.slave01.url}"/>
        <property name="username" value="${jdbc.slave01.username}"/>
        <property name="password" value="${jdbc.slave01.password}"/>
        <property name="driverClassName" value="${jdbc.driver}"/>
        <property name="initialSize" value="5"/>
        <property name="minIdle" value="5"/>
        <property name="maxActive" value="50"/>
    </bean>

    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        <!-- 引入 mybatis 配置文件 -->
        <property name="configLocation" value="classpath:mybatis/SqlMapConfig.xml"></property>
         <property name="typeAliasesPackage" value="com.light.domain"></property>
        <!-- sql配置文件 -->
         <property name="mapperLocations" value="classpath:mybatis/mapper/*.xml"></property>
    </bean>

    <!-- 扫描Mapper -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.light.mapper"></property>
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
    </bean>

    <!-- 事务管理器 -->
    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <!-- 通知 -->
    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <!-- 传播行为 -->
            <tx:method name="save*" propagation="REQUIRED"/>
            <tx:method name="insert*" propagation="REQUIRED"/>
            <tx:method name="delete*" propagation="REQUIRED"/>
            <tx:method name="update*" propagation="REQUIRED"/>
            <tx:method name="find*" propagation="SUPPORTS" read-only="true"/>
            <tx:method name="get*" propagation="SUPPORTS" read-only="true"/>
            <tx:method name="query*" propagation="SUPPORTS" read-only="true"/>
        </tx:attributes>
    </tx:advice>

    <!-- 切面 -->
    <bean id="dataSourceAspect" class="com.light.dynamicdatasource.DataSourceAspect"></bean>

    <aop:config proxy-target-class="true">
        <aop:pointcut id="myPointcut" expression="execution(* com.light.service.*.*(..))" />
        <!-- 事务切面 -->
        <aop:advisor advice-ref="txAdvice" pointcut-ref="myPointcut"/>
        <!-- 自定义切面 -->
        <aop:aspect ref="dataSourceAspect" order="-9999">
            <aop:before method="before" pointcut-ref="myPointcut" />
        </aop:aspect>
    </aop:config>

    <tx:annotation-driven transaction-manager="transactionManager"/>

</beans>

jdbc.properties

jdbc.driver=com.mysql.jdbc.Driver

jdbc.master.url=jdbc:mysql://localhost:3306/masterDB
jdbc.master.username=root
jdbc.master.password=123456

jdbc.slave01.url=jdbc:mysql://localhost:3306/slaverDB
jdbc.slave01.username=root
jdbc.slave01.password=123456

log4j.properties

# Global logging configuration
#\u5728\u5f00\u53d1\u73af\u5883\u4e0b\u65e5\u5fd7\u7ea7\u522b\u8981\u8bbe\u7f6e\u6210DEBUG\uff0c\u751f\u4ea7\u73af\u5883\u8bbe\u7f6e\u6210info\u6216error
log4j.rootLogger=debug, stdout
# Console
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d [%t] %-5p [%c] - %m%n 

springmvc.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
                        http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
                        http://www.springframework.org/schema/mvc
                        http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd
                        http://www.springframework.org/schema/context
                           http://www.springframework.org/schema/context/spring-context-4.0.xsd">

    <!-- 只扫描含有@Controller注解 -->
    <context:component-scan base-package="com.light.web">
        <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
    </context:component-scan>

    <!-- 加载解析 @rquestMapping等注解的解析器 -->
    <mvc:annotation-driven>
        <!-- 处理responseBody 里面日期类型 -->
        <mvc:message-converters>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="objectMapper">
                    <bean class="com.fasterxml.jackson.databind.ObjectMapper">
                        <property name="dateFormat">
                            <bean class="java.text.SimpleDateFormat">
                                <constructor-arg type="java.lang.String" value="yyyy-MM-dd HH:mm:ss" />
                            </bean>
                        </property>
                    </bean>
                </property>
            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

</beans>

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.light</groupId>
  <artifactId>dynamicdatasource</artifactId>
  <packaging>war</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>dynamicdatasource Maven Webapp</name>
  <url>http://maven.apache.org</url>

  <properties>
        <spring.version>4.3.7.RELEASE</spring.version>
        <mybatis.version>3.4.2</mybatis.version>
        <mybatis.spring.version>1.3.0</mybatis.spring.version>
        <slf4j.version>1.7.12</slf4j.version>
        <druid.version>1.0.28</druid.version>
        <commons-lang3.version>3.4</commons-lang3.version>
        <commons-io.version>2.4</commons-io.version>
        <commons-codec.version>1.10</commons-codec.version>
        <jackson.version>2.8.8</jackson.version>
        <fastjson.version>1.2.32</fastjson.version>
        <spring.redis.version>1.7.2.RELEASE</spring.redis.version>
        <mapper.version>3.4.5</mapper.version>
        <pagehelper.version>4.1.6</pagehelper.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>${commons-lang3.version}</version>
        </dependency>
        <dependency>
            <groupId>commons-io</groupId>
            <artifactId>commons-io</artifactId>
            <version>${commons-io.version}</version>
        </dependency>
        <dependency>
            <groupId>commons-codec</groupId>
            <artifactId>commons-codec</artifactId>
            <version>${commons-codec.version}</version>
        </dependency>
        <!-- 日志处理 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>${slf4j.version}</version>
        </dependency>
        <!-- Mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>${mybatis.version}</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>${mybatis.spring.version}</version>
        </dependency>
        <!-- MySql -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.8</version>
        </dependency>
        <!-- 连接池 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>${druid.version}</version>
        </dependency>
        <!-- Spring -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-aspects</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <!-- Jackson Json处理工具包 -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <!-- fastjson -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>${fastjson.version}</version>
        </dependency>

        <!-- servlet API -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>4.0.0</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.1</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>dynamicdatasource</finalName>

        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.7.0</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>2.2</version>
                <configuration>
                    <port>8080</port>
                    <path>/</path>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>
  

---

测试结果：

查询：

增加：http://localhost:8080/dynamicdatasource/user/insert

masterdb库的user表数据增加了，slaverdb库的user表没有增加记录

删除：

结果：masterdb库的user表的id=4的记录删除了。