Java知识点梳理——读写分离

1、读写分离：可以通过Spring提供的AbstractRoutingDataSource类，重写determineCurrentLookupKey方法，实现动态切换数据源的功能；读写分离可以有效减轻写库的压力，又可以把查询数据的请求分发到不同读库；MySql主从同步传送门

2、写数据库：当调用insert、update、delete及一些实时数据用到的库；

3、读数据库：当调用select查询数据用到的库；

4、JaveWeb工程通过AbstractRoutingDataSource类实现读写分离；

a、jdbc.properties文件配置读写数据源

datasource.type=mysql
datasource.driverClassName=com.mysql.jdbc.Driver
datasource.username=root
#写库
w.datasource.url=jdbc\:mysql\://127.0.0.1\:3306/ddt?characterEncoding\=utf-8
w.datasource.password=write123
#读库
r.datasource.url=jdbc\:mysql\://IP\:3306/ddt?characterEncoding\=utf-8
r.datasource.password=read123

#连接池配置
c3p0.acquireIncrement=3
c3p0.acquireRetryAttempts=10
c3p0.acquireRetryDelay=1000
c3p0.initialPoolSize=20
c3p0.idleConnectionTestPeriod=3600
c3p0.testConnectionOnCheckout=true
c3p0.minPoolSize=10
c3p0.maxPoolSize=80
c3p0.maxStatements=100
c3p0.numHelperThreads=10
c3p0.maxIdleTime=10800

b、application.xml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:jee="http://www.springframework.org/schema/jee"
    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop" xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:task="http://www.springframework.org/schema/task"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
                        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
                        http://www.springframework.org/schema/tx
                        http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
                        http://www.springframework.org/schema/jee
                        http://www.springframework.org/schema/jee/spring-jee-3.0.xsd
                        http://www.springframework.org/schema/context
                        http://www.springframework.org/schema/context/spring-context-3.0.xsd
                        http://www.springframework.org/schema/aop
                        http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
                        http://www.springframework.org/schema/task
                        http://www.springframework.org/schema/task/spring-task-3.0.xsd">
    <!-- 使用annotation 自动注册bean,并保证@Required,@Autowired的属性被注入    -->
    <context:component-scan base-package="com.eb3">
        <context:include-filter type="annotation"            expression="org.springframework.stereotype.Service" />
        <context:exclude-filter type="annotation"            expression="org.springframework.stereotype.Controller" />
    </context:component-scan>
    <bean class="org.springframework.beans.factory.config.PreferencesPlaceholderConfigurer" >
        <property name="ignoreResourceNotFound" value="true" />
        <property name="properties" ref="configProperties" />
    </bean>
    <bean id="configProperties" class="org.springframework.beans.factory.config.PropertiesFactoryBean">
        <property name="locations">
            <list>
                <value>classpath*:jdbc.properties</value>
            </list>
        </property>
    </bean>

    <context:property-placeholder location="classpath:jdbc.properties"/>
    <!-- 定义Hibernate读数据源 -->
    <bean id="dataSourceRead" class="com.mchange.v2.c3p0.ComboPooledDataSource"
        destroy-method="close">
        <property name="driverClass">
            <value>${datasource.driverClassName}</value>
        </property>
        <property name="jdbcUrl">
            <value>${r.datasource.url}</value>
        </property>
        <property name="user">
            <value>${datasource.username}</value>
        </property>
        <property name="password">
            <value>${r.datasource.password}</value>
        </property>
        <!--当连接池中的连接耗尽的时候c3p0一次同时获取的连接数。-->
        <property name="acquireIncrement">
            <value>${c3p0.acquireIncrement}</value>
        </property>
        <!--定义在从数据库获取新连接失败后重复尝试的次数。-->
        <property name="acquireRetryAttempts">
            <value>${c3p0.acquireRetryAttempts}</value>
        </property>
        <!--两次连接中间隔时间，单位毫秒。-->
        <property name="acquireRetryDelay">
            <value>${c3p0.acquireRetryDelay}</value>
        </property>
        <property name="initialPoolSize">
            <value>${c3p0.initialPoolSize}</value>
        </property>
        <property name="testConnectionOnCheckout">
            <value>${c3p0.testConnectionOnCheckout}</value>
        </property>
        <property name="minPoolSize">
            <value>${c3p0.minPoolSize}</value>
        </property>
        <property name="maxPoolSize">
            <value>${c3p0.maxPoolSize}</value>
        </property>
        <property name="maxIdleTime">
            <value>${c3p0.maxIdleTime}</value>
        </property>
        <property name="idleConnectionTestPeriod">
            <value>${c3p0.idleConnectionTestPeriod}</value>
        </property>
        <property name="maxStatements">
            <value>${c3p0.maxStatements}</value>
        </property>
        <property name="numHelperThreads">
            <value>${c3p0.numHelperThreads}</value>
        </property>
    </bean>
    <!-- 定义Hibernate写数据源 -->
    <bean id="dataSourceWrite" class="com.mchange.v2.c3p0.ComboPooledDataSource"
        destroy-method="close">
        <property name="driverClass">
            <value>${datasource.driverClassName}</value>
        </property>
        <property name="jdbcUrl">
            <value>${w.datasource.url}</value>
        </property>
        <property name="user">
            <value>${datasource.username}</value>
        </property>
        <property name="password">
            <value>${w.datasource.password}</value>
        </property>
        <!--当连接池中的连接耗尽的时候c3p0一次同时获取的连接数。-->
        <property name="acquireIncrement">
            <value>${c3p0.acquireIncrement}</value>
        </property>
        <!--定义在从数据库获取新连接失败后重复尝试的次数。-->
        <property name="acquireRetryAttempts">
            <value>${c3p0.acquireRetryAttempts}</value>
        </property>
        <!--两次连接中间隔时间，单位毫秒。-->
        <property name="acquireRetryDelay">
            <value>${c3p0.acquireRetryDelay}</value>
        </property>
        <property name="initialPoolSize">
            <value>${c3p0.initialPoolSize}</value>
        </property>
        <property name="testConnectionOnCheckout">
            <value>${c3p0.testConnectionOnCheckout}</value>
        </property>
        <property name="minPoolSize">
            <value>${c3p0.minPoolSize}</value>
        </property>
        <property name="maxPoolSize">
            <value>${c3p0.maxPoolSize}</value>
        </property>
        <property name="maxIdleTime">
            <value>${c3p0.maxIdleTime}</value>
        </property>
        <property name="idleConnectionTestPeriod">
            <value>${c3p0.idleConnectionTestPeriod}</value>
        </property>
        <property name="maxStatements">
            <value>${c3p0.maxStatements}</value>
        </property>
        <property name="numHelperThreads">
            <value>${c3p0.numHelperThreads}</value>
        </property>
    </bean>
    <!-- 动态数据源 -->
    <bean id="dynamicDataSource" class="com.eb3.ddt.DynamicDataSource">
       <!-- 通过key-value关联数据源 -->
       <property name="targetDataSources">
           <map>
               <entry value-ref="dataSourceWrite" key="dataSourceWrite"></entry>
               <entry value-ref="dataSourceRead" key="dataSourceRead"></entry>
           </map>
       </property>
       <property name="defaultTargetDataSource" ref="dataSourceWrite" />
    </bean>

    <!-- 设置sessionFactory -->
    <bean id="sessionFactory"
        class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
        <!--  依赖注入数据源，注入正是上文定义的dataSource -->
        <property name="dataSource" ref="dynamicDataSource" />
        <property name="packagesToScan" value="com.eb3.ddt.pojo,com.eb3.loan.pojo"/>
        <!--定义Hibernate的SessionFactory的属性 -->
        <property name="hibernateProperties">
            <props>
                <!--  指定Hibernate的连接方言-->
                <prop key="hibernate.dialect">
                    ${hibernate.dialect}
                </prop>
                <prop key="hibernate.connection.autocommit">${hibernate.connection.autocommit}</prop>
                <!-- 制定Hibernate是否打印SQL语句 -->
                <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>
                <prop key="hibernate.format_sql">${hibernate.format_sql}</prop>
                <!-- 设create(启动创建),create-drop(启动创建,退出删除),update(启动更新),validate(启动验证) -->
                <prop key="hibernate.hbm2ddl.auto">${hibernate.hbm2ddl.auto}</prop>
                <prop key="connection.characterEncoding">utf-8</prop>
                <!-- 设置二级缓存 -->
                <prop key="hibernate.cache.user_query_cache">${hibernate.cache.user_query_cache}</prop>
                <prop key="hibernate.user_second_level_cache">${hibernate.user_second_level_cache}</prop>
                <prop key="hibernate.cache.provider_class">${hibernate.cache.class}</prop>
                <prop key="hibernate.cache.provider_configuration_file_resource_path">${hibernate.ehcache_config_file}</prop>
            </props>
        </property>
    </bean>
    <!-- 事务管理器配置,单数据源事务 -->
    <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory"/>
    </bean>  

    <tx:advice id="txAdvice" transaction-manager="transactionManager">
        <tx:attributes>
            <tx:method name="save*"  propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="add*"   propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="delete*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="update*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="merge*"  isolation="READ_COMMITTED" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="get*" read-only="true"/>
            <tx:method name="find*" read-only="true"/>
            <tx:method name="list*" read-only="true"/>
            <tx:method name="select*" read-only="true"/>
            <tx:method name="*" propagation="REQUIRED"  />
        </tx:attributes>
    </tx:advice>
    <aop:config>
        <aop:pointcut id="interceptorPointCuts"       expression="execution(* com.eb3.*.service.*.*(..))" />
        <aop:advisor advice-ref="txAdvice"            pointcut-ref="interceptorPointCuts" />
    </aop:config>     

    <aop:aspectj-autoproxy proxy-target-class="true" />

    <!-- 定时器配置 task:scheduler@pool-size调度线程池的大小，调度线程在被调度任务完成前不会空闲 task:executor/@pool-size：可以指定执行线程池的初始大小、最大大小
        task:executor/@queue-capacity：等待执行的任务队列的容量 task:executor/@rejection-policy：当等待队已满时的策略，分为丢弃、由任务执行器直接运行等方式
        @Async 异步任务时 task任务执行线程数 task:scheduler 和 task:executor 两个线程池同样起作用 没有异步注解时
        task任务执行线程数只受task:scheduler的线程池大小影响 -->
    <!-- 声明一个具有10个线程的池，每一个对象将获取同样的运行机会 -->
    <task:scheduler id="scheduler" pool-size="10" />
    <task:executor id="executor" keep-alive="3600" pool-size="100-300" queue-capacity="500" rejection-policy="CALLER_RUNS" />
    <task:annotation-driven executor="executor" scheduler="scheduler" />

</beans>

c、继承AbstractRoutingDataSource类的动态数据源类DynamicDataSource

package com.eb3.ddt;

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

public class DynamicDataSource extends AbstractRoutingDataSource {
    /**
     * 重写determineCurrentLookupKey方法
     */
    @Override
    protected Object determineCurrentLookupKey() {
        Object obj = DBHelper.getDbType();
        return obj;
    }
}

d、DBHelper工具类

package com.eb3.ddt;

import org.apache.commons.lang.StringUtils;

public class DBHelper {
    private static ThreadLocal<String> dbContext = new ThreadLocal<String>();

    // 写数据源标识
    public final static String DB_WRITE = "dataSourceWrite";
    // 读数据源标识
    public final static String DB_READ = "dataSourceRead";

    /**
     * 获取数据源类型，即是写数据源，还是读数据源
     *
     * @return
     */
    public static String getDbType() {
        String db_type = dbContext.get();
        if (StringUtils.isEmpty(db_type)) {
            // 默认是写数据源
            db_type = DB_WRITE;
        }
        return db_type;
    }

    /**
     * 设置该线程的数据源类型
     *
     * @param str
     */
    public static void setDbType(String str) {
        dbContext.set(str);
    }
}

e、服务层调用

/*@Aspect 此注解会影响数据源切换，运行代码得知不加的话会先执行DynamicDataSource里的determineCurrentLookupKey方法，后执行Service层里DBHelper.setDbType()方法，导致数据源切换失败！
*/
@Aspect
@Component("userService")
public class UserServiceImpl extends BaseServiceImpl<User, User, Integer> implements UserService {
    @Resource
    private UserDao userDao;

    @Override
    protected BaseDao<User, Integer> getDao() {
        return this.userDao;
    }

    @Override
    public void save(User user) {
        DBHelper.setDbType(DBHelper.DB_WRITE); // 写库
        this.userDao.save(user);
    }

    @Override
    public User findByUserName(String username) {
        DBHelper.setDbType(DBHelper.DB_READ); // 读库
        List<User> userList = this.userDao.findBy("username", username);
        return CollectionUtils.isNotEmpty(userList) ? userList.get(0) : null;
    }
}