MemCached缓存操作

　　Web项目在运行时，通常需要从数据库中进行读写。随着操作数据量的增大，以及访问量的集中，数据库的负载增加，数据库响应变慢，网站访问速度变慢的情况。Memcached就是用来解决这些问题的。

　　Memcached是一个开源的高性能的分布式缓存系统。主要用于减轻数据库负载，加速Web应用访问。它是基于内存的Key-Value存储系统，主要存储Value较小的数据，Value大小不能超过1M。总的来说，Memcached支持的数据结构是键值对，在支持的数据结构上要比Redis简单。

　　Memcached的使用场景有：

　　访问频度极高的业务，如社交网络，电子商务，游戏，广告等，可以将频繁访问的数据存储到Memcached中，从而减少对数据库的访问。

　　促销类业务，秒杀类业务，这些业务访问压力非常大，一般数据库根本无法承载这么大的业务量。

　　计数器，如点赞人数，文章阅读人数等。

　　存储小图片，减轻硬盘存储系统的访问压力。

　　那么，我们为什么要基于内存来存储呢？我们先来看一张比较计算机中各种存储介质处理数据速率的图片：　　

　　内存，磁盘，CPU的运行方式不同。磁盘是毫秒级，内存是微妙级，CPU是纳秒级。可以说，比较内存和磁盘的速度差异，内存比磁盘快10万~100万倍。传输速度和总线的速度差异，虽然有SSD（Solid State Drives，固态硬盘），但是其速度还是无法和内存相比。

　　在操作中，如果无法在内存中计算的话，就必须搜索磁盘上的数据，但是磁盘I/O输入输出非常耗时。一般网站的一个请求响应时间要控制在1秒内。

　　我们来看MemCached的物理架构：

　　使用Memcached时的数据读取流程是：先从Memcached中取数据，如果取不到再从数据库中取数据，然后把数据保存到Memcached中。

　　使用Memcached时的数据更新流程是：先更新数据库，然后再更新Memcached缓存，或者删除数据缓存。

　　我们接下来看Memcached的应用：

　　首先，要安装Memcached服务器。我们以win7系统为例，切换到Memcached路径，在DOS窗口的命令行中执行安装与启动命令：

#安装Memcached服务器
memcached -d install
#启动Memcached服务
net strat "memcached server"

　　安装与启动Memcached服务后，我们接下来在idea开发工具中创建一个maven项目，在里面通过代码查看Memcached的基本操作：

package com.itszt.DemoMC.domain;
/**
 *  订单实体类,id,名称,下订单时间
 */
public class OrderRequest {
    private int orderId;
    private String orderName,orderTime;

    public OrderRequest() {
    }

    public OrderRequest(int orderId, String orderName, String orderTime) {
        this.orderId = orderId;
        this.orderName = orderName;
        this.orderTime = orderTime;
    }

    public int getOrderId() {
        return orderId;
    }

    @Override
    public String toString() {
        return "OrderRequest{" +
                "orderId=" + orderId +
                ", orderName='" + orderName + '\'' +
                ", orderTime='" + orderTime + '\'' +
                '}';
    }

    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }

    public String getOrderName() {
        return orderName;
    }

    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }

    public String getOrderTime() {
        return orderTime;
    }

    public void setOrderTime(String orderTime) {
        this.orderTime = orderTime;
    }
}
********************************************
package com.itszt.DemoMC;

import com.alibaba.fastjson.JSON;
import com.itszt.DemoMC.domain.OrderRequest;
import net.rubyeye.xmemcached.MemcachedClient;
import net.rubyeye.xmemcached.XMemcachedClientBuilder;
import net.rubyeye.xmemcached.exception.MemcachedException;
import net.rubyeye.xmemcached.utils.AddrUtil;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.Map;
import java.util.concurrent.TimeoutException;

/**
 * MemCached的基本操作
 */
public class App {
    public static void main(String[] args) {
        //创建操作MemCached的客户端
        XMemcachedClientBuilder memcachedClientBuilder = new XMemcachedClientBuilder(AddrUtil.getAddresses("192.168.1.160:11211"));
        MemcachedClient memcachedClient =null;
        try {
            memcachedClient = memcachedClientBuilder.build();
            System.out.println("memcachedClient = " + memcachedClient);

            boolean booDel = memcachedClient.delete("data1");
            if(booDel){
                System.out.println("删除成功");
            }else{
                System.out.println("无此数据");
            }

            //向MemCached中插入字符串数据
            /*memcachedClient.add("data1",0,"测试数据1");
            memcachedClient.add("data2",0,"测试数据2");*/

            /*memcachedClient.set("data1",0,"测试数据1");
            memcachedClient.set("data2",0,"测试数据2");*/
        } catch (IOException e) {
            e.printStackTrace();
        } /*catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
            e.printStackTrace();
        }*/ catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        } catch (TimeoutException e) {
            e.printStackTrace();
        }

        //从MemCached中取单个数据
        /*try {
            Object data1 = memcachedClient.get("data1");
            System.out.println("data1 = " + data1);
        } catch (TimeoutException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        }*/

        //取出一批数据
        List<String> keys=new ArrayList<>();
        keys.add("data1");
        keys.add("data2");
        try {
            //从memcached中读取字符串
            Map<String, Object> objectMap = memcachedClient.get(keys);
            System.out.println("objectMap = " + objectMap);
        } catch (TimeoutException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        }

        //存储对象
        OrderRequest orderRequest = new OrderRequest(1, "大黄", new Date().toString());
        System.out.println(JSON.toJSON(orderRequest).toString());
        try {
            memcachedClient.set("order_"+orderRequest.getOrderId(),0, JSON.toJSON(orderRequest).toString());
        } catch (TimeoutException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        }

        try {
            String obj = memcachedClient.get("order_" + orderRequest.getOrderId());
            OrderRequest orderFromJson = JSON.parseObject(obj, OrderRequest.class);
            System.out.println("orderFromJson = " + orderFromJson);
        } catch (TimeoutException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        }
    }
}

　　上面代码是MemCached的基本操作，我们在工作中是要结合数据库来使用的，为此，我们在maven中配置mybatis环境，同时在数据库中建一张测试表user（int uid，varchar username，varchar userpwd）。在maven项目的pom.xml文件中的配置如下：

<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/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.itszt.DemoMC</groupId>
  <artifactId>DemoMC</artifactId>
  <version>1.0</version>
  <packaging>jar</packaging>

  <name>DemoMC</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>

    <dependency>
      <groupId>com.googlecode.xmemcached</groupId>
      <artifactId>xmemcached</artifactId>
      <version>2.3.2</version>
    </dependency>

    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.44</version>
    </dependency>

    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.2.8</version>
    </dependency>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>5.1.39</version>
    </dependency>

    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-simple</artifactId>
      <version>1.7.25</version>
    </dependency>

    <dependency>
      <groupId>log4j</groupId>
      <artifactId>log4j</artifactId>
      <version>1.2.17</version>
    </dependency>

  </dependencies>

  <build>
    <finalName>DemoMC</finalName>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.7</source>
          <target>1.7</target>
        </configuration>
      </plugin>
    </plugins>
  </build>

</project>

　　接下来，我们再看mybatis-config.xml配置文件：

<?xml version="1.0" encoding="UTF-8" ?>
<!--DTD约束引入-->
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">

<!--全局配置开始-->
<configuration>

    <!-- 运行环境设置  1.连接  2.事务-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/a0314?useUnicode=true&CharsetEncodig=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="2018"/>
            </dataSource>
        </environment>
    </environments>

    <!--  引入配置文件2-->
    <mappers>
        <package name="com.itszt.DemoMC.demo"></package>
    </mappers>
</configuration>

　　在将上述配置文件完毕后，我们接下来写一个小案例，其文件体系如下图所示：

　　我们接下来看代码：　　

package com.itszt.DemoMC.util;

import net.rubyeye.xmemcached.MemcachedClient;
import net.rubyeye.xmemcached.XMemcachedClientBuilder;
import net.rubyeye.xmemcached.exception.MemcachedException;
import net.rubyeye.xmemcached.utils.AddrUtil;

import java.io.IOException;
import java.util.concurrent.TimeoutException;

/**
 * memcached工具类
 */
public class MCUtil {

    private static MemcachedClient memcachedClient =null;

    static {
        XMemcachedClientBuilder memcachedClientBuilder = new XMemcachedClientBuilder(AddrUtil.getAddresses("192.168.1.160:11211"));
        try {
            memcachedClient = memcachedClientBuilder.build();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static boolean setData(String key,int expire,Object obj){
        try {
            memcachedClient.set(key,expire,obj);
            return true;
        } catch (TimeoutException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        }
        return false;
    }

    public static <T> T getData(String key){
        try {
            return memcachedClient.get(key);
        } catch (TimeoutException e) {
            e.printStackTrace();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (MemcachedException e) {
            e.printStackTrace();
        }
        return null;
    }

}
*********************************************
package com.itszt.DemoMC.demo;

import java.io.Serializable;

/**
 * 实体类,映射数据库a0314中的user表
 */
public class User implements Serializable{
    private int uid;
    private String username,userpwd;

    public User() {
    }

    @Override
    public String toString() {
        return "User{" +
                "uid=" + uid +
                ", username='" + username + '\'' +
                ", userpwd='" + userpwd + '\'' +
                '}';
    }

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getUserpwd() {
        return userpwd;
    }

    public void setUserpwd(String userpwd) {
        this.userpwd = userpwd;
    }
}
************************************************
package com.itszt.DemoMC.demo;

/**
 * 接口,操作数据库
 */
public interface UserDao {
    //根据用户名和密码查询用户
    public User findUserByNameAndPwd(String username,String userpwd);
    //根据uid修改用户名
    public boolean resetUsername(int uid,String username);
}
*************************************************
package com.itszt.DemoMC.demo;

import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

/**
 * 操作数据库用
 */
public interface UserDaoDB extends UserDao{
    @Override
    @Select("select * from user where username=#{username} and userpwd=#{userpwd}")
    User findUserByNameAndPwd(@Param("username") String username,@Param("userpwd") String userpwd);

    @Override
    @Update("update user set username=#{username} where uid=#{uid}")
    boolean resetUsername(@Param("uid") int uid,@Param("username") String username);
}
************************************************
UserDaoDB.xml配置内容：
<?xml version="1.0" encoding="UTF-8" ?>
<!--引入DTD约束-->
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.itszt.DemoMC.demo.UserDaoDB">
</mapper>
************************************************
package com.itszt.DemoMC.demo;

import com.itszt.DemoMC.util.MCUtil;

/**
 * 操作MemCached缓存
 */
public class UserDaoCached implements UserDao{
    @Override
    public User findUserByNameAndPwd(String username, String userpwd) {
        return MCUtil.getData("user_"+username+"_"+userpwd);
    }

    @Override
    public boolean resetUsername(int uid, String username) {
        boolean boo = MCUtil.setData("user_" + uid, 0, username);
        return boo;
    }
}
************************************************
package com.itszt.DemoMC.demo;

import com.itszt.DemoMC.util.MCUtil;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.InputStream;

/**
 * UserDao的实现类
 */
public class UserDaoImpl implements UserDao{
    private UserDaoCached userDaoCached;
    private UserDaoDB userDaoDB;
    SqlSession sqlSession;

    public UserDaoImpl(){
        userDaoCached=new UserDaoCached();
        String resource="mybatis-config.xml";
        InputStream inputStream=null;
        try {
            inputStream=Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            e.printStackTrace();
        }
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        sqlSession = sqlSessionFactory.openSession();
        userDaoDB= sqlSession.getMapper(UserDaoDB.class);
    }

    @Override
    public User findUserByNameAndPwd(String username, String userpwd) {
        User userByNameAndPwd=null;
        //先从缓存查找,若缓存没有,则再从数据库查找
        userByNameAndPwd=userDaoCached.findUserByNameAndPwd(username,userpwd);
        if(userByNameAndPwd==null){
            System.out.println("缓存里没有,从数据库中查找");
            userByNameAndPwd=userDaoDB.findUserByNameAndPwd(username,userpwd);
            if(userByNameAndPwd==null){
                System.out.println("数据库无匹配项");
                return null;
            }
            //从数据库查找到后,再添加入缓存
            MCUtil.setData("user_"+username+"_"+userpwd,0,userByNameAndPwd);
            System.out.println("成功保存到缓存");
        }
        System.out.println("从缓存获取");
        return userByNameAndPwd;
    }

    @Override
    public boolean resetUsername(int uid, String username) {
        //先更新数据库,再更新缓存
        try {
            boolean boo = userDaoDB.resetUsername(uid, username);
            if(boo){
                sqlSession.commit();
                userDaoCached.resetUsername(uid,username);
                return true;
            }else{
                System.out.println("数据更新失败");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }
}
***********************************************
package com.itszt.DemoMC.demo;

/**
 * 测试类
 */
public class Test {
    public static void main(String[] args) {
        //操作UserDaoImpl实现类
        UserDaoImpl userDao=new UserDaoImpl();
        User userByNameAndPwd = userDao.findUserByNameAndPwd("admin", "123456");
        System.out.println("userByNameAndPwd = " + userByNameAndPwd);

        //更新数据库中的数据,并更新到缓存中
        boolean boo = userDao.resetUsername(userByNameAndPwd.getUid(), "admin123");
        if(boo){
            System.out.println("数据更新完毕");
            User user = userDao.findUserByNameAndPwd("admin123", "123456");
            System.out.println("user = " + user);
        }else{
            System.out.println("数据更新失败");
        }
    }
}

　　运行上述代码中的测试类Test后，显示结果如下：

从缓存获取
userByNameAndPwd = User{uid=1, username='admin', userpwd='123456'}
数据更新完毕
缓存里没有,从数据库中查找
成功保存到缓存
从缓存获取
user = User{uid=1, username='admin123', userpwd='123456'}

　　此时已功地实现了操作MemCached缓存和数据库。