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

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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
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b、application.xml文件

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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">;



classpath*:jdbc.properties





    
        ${datasource.driverClassName}
    
    
        ${r.datasource.url}
    
    
        ${datasource.username}
    
    
        ${r.datasource.password}
    
     
    
        ${c3p0.acquireIncrement}
        
     
    
        ${c3p0.acquireRetryAttempts}
    
     
    
        ${c3p0.acquireRetryDelay}
    
    
        ${c3p0.initialPoolSize}
    
    
        ${c3p0.testConnectionOnCheckout}
    
    
        ${c3p0.minPoolSize}
    
    
        ${c3p0.maxPoolSize}
    
    
        ${c3p0.maxIdleTime}
     
    
        ${c3p0.idleConnectionTestPeriod}
    
    
        ${c3p0.maxStatements}
    
    
        ${c3p0.numHelperThreads}
    



    
        ${datasource.driverClassName}
    
    
        ${w.datasource.url}
    
    
        ${datasource.username}
    
    
        ${w.datasource.password}
    
     
    
        ${c3p0.acquireIncrement}
        
     
    
        ${c3p0.acquireRetryAttempts}
    
     
    
        ${c3p0.acquireRetryDelay}
    
    
        ${c3p0.initialPoolSize}
    
    
        ${c3p0.testConnectionOnCheckout}
    
    
        ${c3p0.minPoolSize}
    
    
        ${c3p0.maxPoolSize}
    
    
        ${c3p0.maxIdleTime}
     
    
        ${c3p0.idleConnectionTestPeriod}
    
    
        ${c3p0.maxStatements}
    
    
        ${c3p0.numHelperThreads}
    

  
  
     
     
         
             
             
         
     
         




    
    
    
    
    
        
            
            
                ${hibernate.dialect}
            
            ${hibernate.connection.autocommit}
            
            ${hibernate.show_sql}
            ${hibernate.format_sql}
            
            ${hibernate.hbm2ddl.auto}
            utf-8              
            
            ${hibernate.cache.user_query_cache}
            ${hibernate.user_second_level_cache}
            ${hibernate.cache.class}
            ${hibernate.ehcache_config_file}


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

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package com.eb3.ddt;

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

public class DynamicDataSource extends AbstractRoutingDataSource {
/**

  • 重写determineCurrentLookupKey方法br/>*/
    @Override
    protected Object determineCurrentLookupKey() {
    Object obj = DBHelper.getDbType();
    return obj;
    }
    }
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    d、DBHelper工具类

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package com.eb3.ddt;

import org.apache.commons.lang.StringUtils;

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

// 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);
}

}
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e、服务层调用

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/@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！
/br/>@Aspect
@Component("userService")
public class UserServiceImpl extends BaseServiceImpl implements UserService {br/>@Resource
private UserDao userDao;

@Override
protected BaseDao 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 userList = this.userDao.findBy("username", username);
    return CollectionUtils.isNotEmpty(userList) ? userList.get(0) : null;
}

}
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