Java Spring mvc 操作 Redis 及 Redis 集群

 本文原创，转载请注明：http://www.cnblogs.com/fengzheng/p/5941953.html

关于 Redis 集群搭建可以参考我的另一篇文章 Redis集群搭建与简单使用

Redis 是什么，能做什么

Redis 是一个开源（BSD许可），内存存储的数据结构服务器，可用作数据库，高速缓存和消息队列代理。它支持字符串、哈希表、列表、集合、有序集合，位图，hyperloglogs等数据类型。内置复制、Lua脚本、LRU收回、事务以及不同级别磁盘持久化功能，同时通过Redis Sentinel 提供高可用，通过 Redis Cluster 提供自动分区。(摘自 Redis 官网)

作为内存数据库，在现代互联网 web 系统中，还是主要将 Redis 作为缓存使用。大型互联网 Web 系统对性能要求很高，而在前端和数据层之间增加数据缓存已成为必不可少的手段之一，当前比较流行的两个技术就是 Redis 和 Memcached，至于两者有什么区别，不是本文要说的内容。本文主要讲 Java web 如何操作 Redis 及 Redis 集群。

一般 Java 程序操作Redis

Redis 提供了多种语言的客户端，在 Java 中最流行的是 Jedis 。访问可查看源码及使用方式。目前 Jedis 最新版本是2.9.0。无论是单机还是集群，Jedis 都有很详细的说明和实例代码，这里只做简单说明。如果用 Maven 做包管理，需要引用  jedis 包，本例使用最新的2.9.0版本，如下：

<dependency>
      <groupId>redis.clients</groupId>
      <artifactId>jedis</artifactId>
      <version>2.9.0</version>
</dependency>　　

操作 Redis 单机

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

/**
 * Created by fengdezitai on 2016/10/9.
 */
public class JedisClient {

    private static final String host= "192.168.31.121";

    private static final JedisClient jedisClient = new JedisClient();

    private Jedis jedis = null;
    /**
     * 私有构造函数
     */
    private JedisClient(){}

    public static JedisClient getInstance(){
        return jedisClient;
    }

    private JedisPoolConfig getPoolConfig(){
        JedisPoolConfig jedisPoolConfig = new JedisPoolConfig();
        jedisPoolConfig.setMaxIdle(10);
        jedisPoolConfig.setMaxTotal(100);
        jedisPoolConfig.setMaxWaitMillis(3000);
        return jedisPoolConfig;
    }

    /**
     * 添加
     * @param key
     * @param value
     * @return
     * @throws Exception
     */
    public Boolean add(String key,String value) throws Exception{
        JedisPool pool = new JedisPool(getPoolConfig(),host);
        Jedis jedis = null;
        try {
            jedis = pool.getResource();
            if(jedis.exists(key)){
                throw new Exception(String.format("key (%s) 已存在 ",key));
            }
            jedis.set(key,value);

        }catch (Exception e){
            throw e;
        }
        finally {
            if(jedis!=null){
                jedis.close();
            }
        }
        pool.destroy();
        return true;
    }

    /**
     * 获取值
     * @param key
     * @return
     * @throws Exception
     */
    public String get(String key) throws Exception{
        JedisPool pool = new JedisPool(getPoolConfig(),host);
        Jedis jedis = null;
        String result = "";
        try {
            jedis = pool.getResource();
            result = jedis.get(key);
        }catch (Exception e){
            throw e;
        }
        finally {
            if(jedis!=null){
                jedis.close();
            }
        }
        pool.destroy();
        return result;
    }

    public static void main(String[] args) {
        JedisClient jedisClient = JedisClient.getInstance();
        try {
            /*Boolean result = jedisClient.add("hello", "redis1");
            if(result){
                System.out.println("success");
            }*/

            System.out.println(jedisClient.get("hello"));
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

操作 redis 集群

import redis.clients.jedis.*;
import java.util.HashSet;
import java.util.Set;

/**
 * Created by fengdezitai on 2016/10/13.
 */
public class JedisClusterClient {

    private static int count = 0;

    private static final JedisClusterClient redisClusterClient = new JedisClusterClient();

    /**
     * 私有构造函数
     */
    private JedisClusterClient() {}

    public static JedisClusterClient getInstance() {
        return redisClusterClient;
    }

    private JedisPoolConfig getPoolConfig(){
        JedisPoolConfig config = new JedisPoolConfig();
        config.setMaxTotal(1000);
        config.setMaxIdle(100);
        config.setTestOnBorrow(true);
        return config;
    }

    public void SaveRedisCluster() {
        Set<HostAndPort> jedisClusterNodes = new HashSet<HostAndPort>();
        jedisClusterNodes.add(new HostAndPort("192.168.31.245", 7000));
        jedisClusterNodes.add(new HostAndPort("192.168.31.245", 7001));
        jedisClusterNodes.add(new HostAndPort("192.168.31.245", 7002));
        jedisClusterNodes.add(new HostAndPort("192.168.31.210", 7003));
        jedisClusterNodes.add(new HostAndPort("192.168.31.210", 7004));
        jedisClusterNodes.add(new HostAndPort("192.168.31.210", 7005));

        JedisCluster jc = new JedisCluster(jedisClusterNodes,getPoolConfig());
        jc.set("cluster", "this is a redis cluster");
        String result = jc.get("cluster");
        System.out.println(result);
    }

    public static void main(String[] args) {
        JedisClusterClient jedisClusterClient = JedisClusterClient.getInstance();
        jedisClusterClient.SaveRedisCluster();
    }
}　　

Spring mvc 操作 Redis

在 Spring mvc 中操作 Redis ，首先当然要搭好 Spring mvc 框架了。以下是在假设 Spring mvc 环境已经架好的情况下。本例中 Spring 版本为 4.3.2 RELEASE。关于 Spring 的 maven 引用如下：

<!-- spring版本号 -->
<spring.version>4.3.2.RELEASE</spring.version>

<!-- spring核心包 -->
    <!-- springframe start -->
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>${spring.version}</version>
      <exclusions>
        <exclusion>
          <groupId>commons-logging</groupId>
          <artifactId>commons-logging</artifactId>
        </exclusion>
      </exclusions>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-web</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-oxm</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</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-webmvc</artifactId>
      <version>${spring.version}</version>
      <exclusions>
        <exclusion>
          <groupId>commons-logging</groupId>
          <artifactId>commons-logging</artifactId>
        </exclusion>
      </exclusions>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-aop</artifactId>
      <version>${spring.version}</version>
    </dependency>

    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context-support</artifactId>
      <version>${spring.version}</version>
    </dependency>


    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-test</artifactId>
      <version>${spring.version}</version>
    </dependency>
    <!-- springframe end -->

操作 Redis 单机

只用 Jedis 自己实现注入（区别于下面的引用spring-data-redis） 

把前面的 JedisClient 代码拿过来引用即可，只需实现一个访问 Redis 的 Service ，就可以集成到 Spring mvc 。Service 代码如下：

import org.springframework.stereotype.Service;
import util.JedisClient;

/**
 * Created by fengdezitai on 2016/10/9.
 */
@Service
public class RedisService {

    public String get(String key) throws Exception{
        JedisClient jedisClient = JedisClient.getInstance(); //上面实现的JedisClient
        String result = "";
        try {
            result = jedisClient.get("hello");
        }catch (Exception e){
            throw e;
        }
        return result;
    }
}

Controller 实现如下：

@Controller
@RequestMapping(value = "redisAllInOne")
public class RedisAllInOneController {

    @Autowired
    private RedisService redisService;

    @RequestMapping(value = "get",method = RequestMethod.GET)
    @ResponseBody
    public Object getByMyService(String key){
        try {
            String result = redisService.get(key);
            return result;
        }catch (Exception e){
            e.printStackTrace();
        }
        return null;
    }
}　　

用 spring-data-redis 包做集成

上面是自己实现的注入，这里用 spring-data-redis 进行集成，只需简单配置即可，需要引用 maven 包如下，版本为目前最新版 1.7.2.RELEASE：

<dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-redis</artifactId>
      <version>1.7.2.RELEASE</version>
    </dependency>

使用 spring-data-redis ，即省去了自己实现注入的过程，通过它提供的一些配置，即可实现连接池配置、RedisTemplate 配置、JedisConnectionFactory 配置；通过 JedisConnectionFactory 可配置连接池参数、redis 服务器、端口、密码、超时时间、database索引等；RedisTemplate 即注入的bean ，可以使用 RedisTemplate 自动注入的实体进行 redis 的一系列操作，具体看配置；

redis 服务属性配置文件：

redis.maxIdle=300
redis.maxWait=3000
redis.testOnBorrow=true
redis.host=192.168.31.121
redis.port=6379
redis.password=password
redis.timeout=3000

spring-data-redis xml 配置文件 redis-context.xml：

<!-- jedis 连接池 配置 -->
    <bean id="poolConfig" class="redis.clients.jedis.JedisPoolConfig" >
        <property name="maxIdle" value="${redis.maxIdle}" />
        <property name="maxWaitMillis" value="${redis.maxWait}" />
        <property name="testOnBorrow" value="${redis.testOnBorrow}" />
    </bean>
    <!-- redis服务器中心 -->
    <bean id="connectionFactory"  class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory" >
        <property name="poolConfig" ref="poolConfig" />
        <property name="port" value="${redis.port}" />
        <property name="hostName" value="${redis.host}" />
        <!--<property name="password" value="${redis.password}" />-->
        <property name="timeout" value="${redis.timeout}" ></property>
        <property name="database" value="1"></property>
    </bean>

    <bean id="commonRedisTemplate" class="org.springframework.data.redis.core.RedisTemplate" >
        <property name="connectionFactory" ref="connectionFactory" />
        <property name="keySerializer" ref="stringRedisSerializer" />
        <property name="hashKeySerializer" ref="stringRedisSerializer" />
        <property name="valueSerializer" ref="stringRedisSerializer" />
        <property name="hashValueSerializer" ref="stringRedisSerializer" />
    </bean>

    <bean id="connectionFactory1"  class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory" >
        <property name="poolConfig" ref="poolConfig" />
        <property name="port" value="${redis.port}" />
        <property name="hostName" value="${redis.host}" />
        <!--<property name="password" value="${redis.password}" />-->
        <property name="timeout" value="${redis.timeout}" ></property>
        <property name="database" value="2"></property>
    </bean>

    <bean id="stringRedisSerializer" class="org.springframework.data.redis.serializer.StringRedisSerializer" />
    <bean id="cacheRedisTemplate" class="org.springframework.data.redis.core.RedisTemplate" >
        <property name="connectionFactory" ref="connectionFactory1" />
        <property name="keySerializer" ref="stringRedisSerializer" />
        <property name="hashKeySerializer" ref="stringRedisSerializer" />
        <property name="valueSerializer" ref="stringRedisSerializer" />
        <property name="hashValueSerializer" ref="stringRedisSerializer" />
    </bean>

之后在 spring 配置文件中引用以上文件：

<import resource="redis-context.xml" />　　

解释一下上面的配置：

poolConfig 即配置 redis 连接池，之后配置了两个 JedisConnectionFactory 和 RedisTemplate ，一个 RedisTemplate 对应一个 JedisConnectionFactory ，这样可以配置根据场景配置不同的 Redis 连接，比如超时时间要求不一致、database 0-15 可以存储不同的数据等。这里就配置了database 1 和 2 ，调用 commonRedisTemplate 会存到 database1 ，调用 cacheRedisTemplate 会存到 database2。

之后在 Service 层即可注入并引用这两个 RedisTemplate ，如下代码：

import org.apache.commons.lang3.StringUtils;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Repository;

import javax.annotation.Resource;
import java.io.*;

@Repository
public class RedisCache {
　　
    @Resource(name = "cacheRedisTemplate")
    private RedisTemplate<String, String> cacheRedisTemplate;

    public void put(Object key, Object value) {
        if(null == value) {
            return;
        }

        if(value instanceof String) {
            if(StringUtils.isEmpty(value.toString())) {
                return;
            }
        }

        // TODO Auto-generated method stub
        final String keyf = key + "";
        final Object valuef = value;
        final long liveTime = 86400;

        cacheRedisTemplate.execute(new RedisCallback<Long>() {
            public Long doInRedis(RedisConnection connection)
                    throws DataAccessException {
                byte[] keyb = keyf.getBytes();
                byte[] valueb = toByteArray(valuef);
                connection.set(keyb, valueb);
                if (liveTime > 0) {
                    connection.expire(keyb, liveTime);
                }
                return 1L;
            }
        });
    }

    public Object get(Object key) {
        final String keyf = (String) key;
        Object object;
        object = cacheRedisTemplate.execute(new RedisCallback<Object>() {
            public Object doInRedis(RedisConnection connection)
                    throws DataAccessException {

                byte[] key = keyf.getBytes();
                byte[] value = connection.get(key);
                if (value == null) {
                    return null;
                }
                return toObject(value);

            }
        });

        return object;
    }

    /**
     * 描述 : <byte[]转Object>. <br>
     * <p>
     * <使用方法说明>
     * </p>
     *
     * @param bytes
     * @return
     */
    private Object toObject(byte[] bytes) {
        Object obj = null;
        try {
            ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
            ObjectInputStream ois = new ObjectInputStream(bis);
            obj = ois.readObject();
            ois.close();
            bis.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        return obj;
    }

    private byte[] toByteArray(Object obj) {
        byte[] bytes = null;
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            ObjectOutputStream oos = new ObjectOutputStream(bos);
            oos.writeObject(obj);
            oos.flush();
            bytes = bos.toByteArray();
            oos.close();
            bos.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return bytes;
    }
}

最后在 Controller 中调用即可

    @Autowired
    private RedisCache redisCache;


    @RequestMapping(value = "get", method = RequestMethod.GET)
    @ResponseBody
    public Object getByMyService(String key) {
        try {
            String result = redisService.get(key);
            return result;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @RequestMapping(value = "save", method = RequestMethod.GET)
    @ResponseBody
    public Object save() {
        Token token = new Token();
        token.setAccess_token("token");
        token.setExpires_in(1000);
        try {
            redisCache.put("token", token);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "ok";
    }　　

操作 Redis 集群

只用 Jedis 自己实现注入（区别于下面的引用spring-data-redis）

把前面的 JedisClusterClient 代码拿过来引用即可，只需实现一个访问 Redis 的 Service ，就可以集成到 Spring mvc 。Service 代码如下：

import org.springframework.stereotype.Service;
import util.JedisClusterClient;

/**
 * Created by fengdezitai on 2016/10/13.
 */
@Service
public class RedisClusterService {

    public void save() throws Exception{
        //调用 JedisClusterClient 中的方法
        JedisClusterClient jedisClusterClient = JedisClusterClient.getInstance();
        try {
            jedisClusterClient.SaveRedisCluster();
        }catch (Exception e){
            throw e;
        }
    }
}

最后在 Controller 中调用实现的 Service 即可

@Controller
@RequestMapping(value = "redisCluster")
public class RedisClusterController {

    @Autowired
    private RedisClusterService redisClusterService;

    @RequestMapping(value = "save",method = RequestMethod.GET)
    @ResponseBody
    public Object save(){
        try{
            redisClusterService.save();
        }catch (Exception e){
            e.printStackTrace();
            return String.format("error: %s",e.getMessage());
        }
        return "ok";
    }
}　　

用 spring-data-redis 包做集成 

Spring 和 spring-data-redis maven 包引用和前面一致，之所以引用 spring-data-redis 1.7.2.RELEASE，是因为目前只有这个最新版本才支持集群操作。

redis 集群服务属性配置

redis.maxIdle=300
redis.maxWait=3000
redis.testOnBorrow=false
redis.timeout=3000

spring-data-redis xml 集群配置文件 redis-cluster-context.xml

<!-- 连接池 配置 -->
    <bean id="poolConfig" class="redis.clients.jedis.JedisPoolConfig" >
        <property name="maxIdle" value="${redis.maxIdle}" />
        <property name="maxWaitMillis" value="${redis.maxWait}" />
        <property name="testOnBorrow" value="${redis.testOnBorrow}" />
    </bean>


    <bean id="redisClusterConfig" class="org.springframework.data.redis.connection.RedisClusterConfiguration">
        <property name="maxRedirects" value="3"></property>
        <property name="clusterNodes">
            <set>
                <bean class="org.springframework.data.redis.connection.RedisNode">
                    <constructor-arg name="host" value="192.168.31.245"></constructor-arg>
                    <constructor-arg name="port" value="7000"></constructor-arg>
                </bean>
                <bean class="org.springframework.data.redis.connection.RedisNode">
                    <constructor-arg name="host" value="192.168.31.245"></constructor-arg>
                    <constructor-arg name="port" value="7001"></constructor-arg>
                </bean>
                <bean class="org.springframework.data.redis.connection.RedisNode">
                    <constructor-arg name="host" value="192.168.31.245"></constructor-arg>
                    <constructor-arg name="port" value="7002"></constructor-arg>
                </bean>
                 <bean class="org.springframework.data.redis.connection.RedisNode">
                    <constructor-arg name="host" value="192.168.31.210"></constructor-arg>
                    <constructor-arg name="port" value="7003"></constructor-arg>
                </bean>
                <bean class="org.springframework.data.redis.connection.RedisNode">
                    <constructor-arg name="host" value="192.168.31.210"></constructor-arg>
                    <constructor-arg name="port" value="7004"></constructor-arg>
                </bean>
                <bean class="org.springframework.data.redis.connection.RedisNode">
                    <constructor-arg name="host" value="192.168.31.210"></constructor-arg>
                    <constructor-arg name="port" value="7005"></constructor-arg>
                </bean>
            </set>
        </property>
    </bean>

    <bean id="redis4CacheConnectionFactory"
          class="org.springframework.data.redis.connection.jedis.JedisConnectionFactory">
        <constructor-arg name="clusterConfig" ref="redisClusterConfig" />
        <property name="timeout" value="${redis.timeout}" />
        <property name="poolConfig" ref="poolConfig"/>
    </bean>


    <bean name="stringRedisSerializer" class="org.springframework.data.redis.serializer.StringRedisSerializer" />
    <bean id="clusterRedisTemplate" class="org.springframework.data.redis.core.RedisTemplate">
        <property name="connectionFactory" ref="redis4CacheConnectionFactory" />
        <property name="keySerializer" ref="stringRedisSerializer" />
        <property name="hashKeySerializer" ref="stringRedisSerializer" />
        <property name="valueSerializer" ref="stringRedisSerializer" />
        <property name="hashValueSerializer" ref="stringRedisSerializer" />
    </bean>

之后在 Spring 配置文件中引用

<import resource="redis-cluster-context.xml" />

解释以上配置：

poolConfig是连接池配置，redisClusterConfig 配置了 Redis 集群的各个节点（节点 host 和 port 最好写在属性配置文件中），集群搭建可见 我的 另一篇博客 。然后下面和单机配置一样了，一对 JedisConnectionFactory 和 RedisTemplate 。

之后在 Service 层即可注入并引用这个 RedisTemplate，代码如下：

import org.apache.commons.lang3.StringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.stereotype.Repository;

import java.io.*;

/**
 * Created by fengdezitai on 2016/9/29.
 */
@Repository
public class RedisClusterCache {

    @Autowired
    private RedisTemplate clusterRedisTemplate;


    public void put(Object key, Object value) {
        if(null == value) {
            return;
        }

        if(value instanceof String) {
            if(StringUtils.isEmpty(value.toString())) {
                return;
            }
        }

        // TODO Auto-generated method stub
        final String keyf = key + "";
        final Object valuef = value;
        final long liveTime = 86400;

        clusterRedisTemplate.execute(new RedisCallback<Long>() {
            public Long doInRedis(RedisConnection connection)
                    throws DataAccessException {
                byte[] keyb = keyf.getBytes();
                byte[] valueb = toByteArray(valuef);
                connection.set(keyb, valueb);
                if (liveTime > 0) {
                    connection.expire(keyb, liveTime);
                }
                return 1L;
            }
        });
    }

    public Object get(Object key) {
        final String keyf = (String) key;
        Object object;
        object = clusterRedisTemplate.execute(new RedisCallback<Object>() {
            public Object doInRedis(RedisConnection connection)
                    throws DataAccessException {

                byte[] key = keyf.getBytes();
                byte[] value = connection.get(key);
                if (value == null) {
                    return null;
                }
                return toObject(value);

            }
        });

        return object;
    }

    /**
     * 描述 : <byte[]转Object>. <br>
     * <p>
     * <使用方法说明>
     * </p>
     *
     * @param bytes
     * @return
     */
    private Object toObject(byte[] bytes) {
        Object obj = null;
        try {
            ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
            ObjectInputStream ois = new ObjectInputStream(bis);
            obj = ois.readObject();
            ois.close();
            bis.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        return obj;
    }

    private byte[] toByteArray(Object obj) {
        byte[] bytes = null;
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        try {
            ObjectOutputStream oos = new ObjectOutputStream(bos);
            oos.writeObject(obj);
            oos.flush();
            bytes = bos.toByteArray();
            oos.close();
            bos.close();
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return bytes;
    }
}

最后在 Controller 中调用即可

@Controller
@RequestMapping(value = "redisCluster")
public class RedisClusterController {

    @Autowired
    private RedisClusterCache redisClusterCache;

    @RequestMapping(value = "clusterSave",method = {RequestMethod.GET,RequestMethod.POST})
    @ResponseBody
    public Object clusterSave(){
        //redisClusterCache.put("cluster","save cluster");
        Token token = new Token();
        token.setExpires_in(1000);
        token.setAccess_token("hello world");
        redisClusterCache.put("token",token);
        return "ok";
    }

    @RequestMapping(value = "getKey",method = RequestMethod.GET)
    @ResponseBody
    public Object getCluster(String key){
        Object val = redisClusterCache.get(key);
        return val;
    }
}　

注意事项：

• 版本问题，如果用 spring-data-redis 做集成操作 Reids 集群，只有 spring-data-redis 目前最新版本1.7才包含对集群的操作，而最新的 spring-data-redis 中的某些功能对 Spring mvc 的版本也有些限制，所以尽量选择高版本的 Spring mvc 对应。
• 如果存储的value值是一个实体对象，那么一定要实现 Serializable 接口