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第三章：Kafka，构建TB级异步消息系统

一、阻塞队列

BlockingQueue
- 解决线程通信的问题。
- 阻塞方法：put、take。
生产者消费者模式
- 生产者：产生数据的线程。
- 消费者：使用数据的线程。
实现类
- ArrayBlockingQueue
- LinkedBlockingQueue
- PriorityBlockingQueue、SynchronousQueue、DelayQueue等。

1. 阻塞队列测试方法

在 test 中添加 BlockingQueueTests类，来表示阻塞队列的测试方法，代码如下：

public class BlockingQueueTests {
    public static void main(String[] args) {
        BlockingQueue queue = new ArrayBlockingQueue(10);
        new Thread(new Producer(queue)).start();
        new Thread(new Consumer(queue)).start();
        new Thread(new Consumer(queue)).start();
        new Thread(new Consumer(queue)).start();
    }
}

class Producer implements Runnable{
    private BlockingQueue<Integer> queue;

    public Producer(BlockingQueue<Integer> queue) {
        this.queue = queue;
    }
    @Override
    public void run(){
        try{
            for(int i = 0; i < 20; i ++ ) {
                Thread.sleep(20);
                queue.put(i);
                System.out.println(Thread.currentThread().getName()+"生产："+ queue.size());
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

class Consumer implements Runnable{
    private BlockingQueue<Integer> queue;

    public Consumer(BlockingQueue<Integer> queue) {
        this.queue = queue;
    }

    @Override
    public void run() {
        try {
            while (true){
                Thread.sleep(new Random().nextInt(1000));
                queue.take();
                System.out.println(Thread.currentThread().getName()+"消费："+ queue.size());
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

2. 测试结果

Thread-0生产：1
Thread-0生产：2
Thread-0生产：3
Thread-0生产：4
Thread-0生产：5
Thread-0生产：6
Thread-0生产：7
Thread-0生产：8
Thread-0生产：9
Thread-0生产：10
Thread-3消费：9
Thread-0生产：10
Thread-1消费：9
Thread-0生产：10
Thread-2消费：9
Thread-0生产：10
Thread-3消费：9
Thread-0生产：10
Thread-1消费：9
Thread-0生产：10
Thread-2消费：9
Thread-0生产：10
Thread-1消费：9
Thread-0生产：10
Thread-1消费：9
Thread-0生产：10
Thread-3消费：9
Thread-0生产：10
Thread-1消费：9
Thread-0生产：10
Thread-1消费：9
Thread-1消费：8
Thread-2消费：7
Thread-1消费：6
Thread-2消费：5
Thread-1消费：4
Thread-3消费：3
Thread-3消费：2
Thread-2消费：1
Thread-3消费：0

二、Kafka入门

Kafka简介
- Kafka是一个分布式的流媒体平台。
- 应用：消息系统、日志收集、用户行为追踪、流式处理。
Kafka特点
- 高吞吐量、消息持久化、高可靠性、高扩展性。
Kafka术语
- Broker、Zookeeper
- Topic、Partition、Offset
- Leader Replica 、Follower Replica

1. Kafka下载

Kafka官网: https://kafka.apache.org/
在这里插入图片描述

2. Kafka安装与配置

下载Kafka的安装包后进行解压，就相当于安装成功了。
需要进行以下配置：
修改 config包下的 zookeeper.properties:
在这里插入图片描述
修改 config包下的 server.properties:

3. Kafka的启动

首先在命令行中启动 Zookeeper:

C:\Users\Andrew> d:
D:\> cd d:\kafka_2.13-3.2.3
d:\kafka_2.13-3.2.3>bin\windows\zookeeper-server-start.bat config\zookeeper.properties

启动成功后不关闭此窗口，重新打开一个新的命令窗口，用于启动 kafka：

C:\Users\Andrew> d:
D:\> cd d:\kafka_2.13-3.2.3
d:\kafka_2.13-3.2.3>bin\windows\kafka-server-start.bat config\server.properties

注意： 当遇到“‘wmic’不是内部或外部命令，也不是可运行程序”。
在C盘下找到wbem文件夹，且里面包含WMIC.exe，将其添加到系统变量path中去。
比如我的路径是：C:\Windows\System32\wbem，在系统变量path中新建该路径。就可以正常启动Kafka了。

4. Kafka使用

创建主题

cd到 …\kafka_2.13-2.8.0\bin\windows这里，然后输入 kafka-topics.bat --create --bootstrap-server localhost:9092 --replication-factor 1 --partitions 1 --topic test
创建服务器端口号为9092（Kafka默认端口号）的topic，指生产者发布消息存储的位置在该服务器上localhost:9092。--replication-factor 1 指1个副本。--partitions 1 指1个分区。--topic test 指该主题名为 test。
在这里插入图片描述

以生产者身份发送消息

输入：kafka-console-producer.bat --broker-list localhost:9092 --topic test
生产者身份打开服务器列表中为localhost:9092的服务器上的test主题。--broker-list 指服务器列表。
并且输入要发送的消息：
在这里插入图片描述

以消费者身份读取消息

新打开一个命令行窗口，且cd到…\kafka_2.13-2.8.0\bin\windows，并输入：kafka-console-consumer.bat --bootstrap-server localhost:9092 --topic test --from-beginning
可以看到生产者发送的消息。并且这个消息队列中可以实时传送消息。
比如在生产者的命令行中继续输入信息，很快在消费者这边也能得到消息。
在这里插入图片描述

三、Spring整合Kafka

引入依赖
```
- `spring-kafka`
```
- 配置Kafka
  - 配置 server、consumer
- 访问Kafka
  - 生产者:
  kafkaTemplate.send(topic, data);
  - 消费者:
  @KafkaListener(topics = {"test"}
  public void handleMessage(ConsumerRecord record) {}

1. 引入依赖

在 pom.xml 添加相关的依赖：

        <dependency>
            <groupId>org.springframework.kafka</groupId>
            <artifactId>spring-kafka</artifactId>
            <version>2.8.6</version>
        </dependency>

2. 配置Kafka

#KafkaProperties
spring.kafka.bootstrap-servers=localhost:9092
spring.kafka.consumer.group-id=test-consumer-group
spring.kafka.consumer.enable-auto-commit=true
spring.kafka.consumer.auto-commit-interval=3000

3. 测试

在 test 包下添加 KafkaTests 类，代码如下：

@RunWith(SpringRunner.class)
@SpringBootTest
@ContextConfiguration(classes = CommunityApplication.class)
public class KafkaTests {

    @Autowired
    private KafkaProducer kafkaProducer;

    @Test
    public void testKafka() {
        kafkaProducer.sendMessage("test", "你好");
        kafkaProducer.sendMessage("test", "在吗");

        try {
            Thread.sleep(1000 * 20);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

}

@Component
class KafkaProducer {

    @Autowired
    private KafkaTemplate kafkaTemplate;

    public void sendMessage(String topic, String content) {
        kafkaTemplate.send(topic, content);
    }

}

@Component
class KafkaConsumer {

    @KafkaListener(topics = {"test"})
    public void handleMessage(ConsumerRecord record) {
        System.out.println(record.value());
    }
}

4. 测试结果

在这里插入图片描述

四、发送系统消息

触发事件
- 评论后，发布通知
- 点赞后，发布通知
- 关注后，发布通知
处理事件
- 封装事件对象
- 开发事件的生产者
- 开发事件的消费者

在这里插入图片描述

1. 实体类

在 entity 包中添加 Event 实体类，代码如下：

public class Event {

    private String topic;
    private int userId;      //用户Id
    private int entityType;  //实体类型
    private int entityId;    //实体Id
    private int entityUserId;  //实体作者Id
    private Map<String,Object> data = new HashMap<>();


    public String getTopic() {
        return topic;
    }

    public Event setTopic(String topic) {
        this.topic = topic;
        return this;
    }

    public int getUserId() {
        return userId;
    }

    public Event setUserId(int userId) {
        this.userId = userId;
        return this;
    }

    public int getEntityType() {
        return entityType;
    }

    public Event setEntityType(int entityType) {
        this.entityType = entityType;
        return this;
    }

    public int getEntityId() {
        return entityId;
    }

    public Event setEntityId(int entityId) {
        this.entityId = entityId;
        return this;
    }

    public int getEntityUserId() {
        return entityUserId;
    }

    public Event setEntityUserId(int entityUserId) {
        this.entityUserId = entityUserId;
        return this;
    }

    public Map<String, Object> getData() {
        return data;
    }

    public Event setData(String key,Object value) {
        this.data.put(key,value);
        return this;
    }
}

创建 event 包，添加 EventProducer 类和 EventConsumer 类，代码如下：

@Component
public class EventProducer {

    @Autowired
    private KafkaTemplate kafkaTemplate;

    //处理事件
    public void fireEvent(Event event){
        //将事件发布到指定的主题
        kafkaTemplate.send(event.getTopic(), JSONObject.toJSONString(event));
    }
}

@Component
public class EventConsumer implements CommunityConstant {

    private static final Logger logger = LoggerFactory.getLogger(EventConsumer.class);

    @Autowired
    private MessageService messageService;

    @KafkaListener(topics = {TOPIC_COMMENT, TOPIC_LIKE, TOPIC_FOLLOW})
    public void handleCommentMessage(ConsumerRecord record) {
        if (record == null || record.value() == null) {
            logger.error("消息的内容为空!");
            return;
        }

        Event event = JSONObject.parseObject(record.value().toString(), Event.class);
        if (event == null) {
            logger.error("消息格式错误!");
            return;
        }

        // 发送站内通知
        Message message = new Message();
        message.setFromId(SYSTEM_USER_ID);
        message.setToId(event.getEntityUserId());
        message.setConversationId(event.getTopic());
        message.setCreateTime(new Date());

        Map<String, Object> content = new HashMap<>();
        content.put("userId", event.getUserId());
        content.put("entityType", event.getEntityType());
        content.put("entityId", event.getEntityId());

        //这里代码要再盘一下 额外数据，比如postId
        if (!event.getData().isEmpty()) {
            for (Map.Entry<String, Object> entry : event.getData().entrySet()) {
                content.put(entry.getKey(), entry.getValue());
            }
        }

        message.setContent(JSONObject.toJSONString(content));
        messageService.addMessage(message);
    }
}

2. util包

在 CommunityConstant 类中添加新的字段，代码如下：

public interface CommunityConstant {

    /**
     * 激活成功
     */
    int ACTIVATION_SUCCESS = 0;

    /**
     * 重复激活
     */
    int ACTIVATION_REPEAT = 1;

    /**
     * 激活失败
     */
    int ACTIVATION_FAILURE = 2;

    /**
     * 默认状态的登录凭证的超时时间
     */
    int DEFAULT_EXPIRED_SECONDS = 3600 * 12;

    /**
     * 记住状态的登录凭证超时时间
     */
    int REMEMBER_EXPIRED_SECONDS = 3600 * 24 * 100;

    /**
     * 实体类型: 帖子
     */
    int ENTITY_TYPE_POST = 1;

    /**
     * 实体类型: 评论
     */
    int ENTITY_TYPE_COMMENT = 2;

    /**
     * 实体类型：用户
     */
    int ENTITY_TYPE_USER = 3;

    /**
     * 主题: 评论
     */
    String TOPIC_COMMENT = "comment";

    /**
     * 主题: 点赞
     */
    String TOPIC_LIKE = "like";

    /**
     * 主题: 关注
     */
    String TOPIC_FOLLOW = "follow";

    /**
     * 系统用户ID
     */
    int SYSTEM_USER_ID = 1;

}

3. dao层

CommentMapper类中添加 selectCommentById 方法，代码如下：

@Mapper
public interface CommentMapper {
        List<Comment> selectCommentsByEntity(int entityType, int entityId, int offset, int limit);

        int selectCountByEntity(int entityType, int entityId);

        int insertComment(Comment comment);

        Comment selectCommentById(int id);
        
}

对应的 comment-mapper.xml代码如下：

<?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.nowcoder.community.dao.CommentMapper">

    <sql id="selectFields">
        id, user_id, entity_type, entity_id, target_id, content, status, create_time
    </sql>

    <sql id="insertFields">
        user_id, entity_type, entity_id, target_id, content, status, create_time
    </sql>

    <select id="selectCommentsByEntity" resultType="com.nowcoder.community.entity.Comment">
        select <include refid="selectFields"></include>
        from comment
        where status = 0
        and entity_type = #{entityType}
        and entity_id = #{entityId}
        order by create_time asc
        limit #{offset}, #{limit}
    </select>

    <select id="selectCountByEntity" resultType="int">
        select count(id)
        from comment
        where status = 0
        and entity_type = #{entityType}
        and entity_id = #{entityId}
    </select>


    <insert id="insertComment" parameterType="com.nowcoder.community.entity.Comment">
        insert into comment(<include refid="insertFields"></include>)
        values(#{userId},#{entityType},#{entityId},#{targetId},#{content},#{status},#{createTime})
    </insert>

    <select id = "selectCommentById" resultType="com.nowcoder.community.entity.Comment">
        select <include refid="selectFields"></include>
        from comment
        where id = #{id}
    </select>

</mapper>

4. service包

在 CommentService 类中添加 findCommentById 方法，代码如下：

@Service
public class CommentService implements CommunityConstant {

    @Autowired
    private CommentMapper commentMapper;

    @Autowired
    private SensitiveFilter sensitiveFilter;

    @Autowired
    private DiscussPostService discussPostService;


    public List<Comment> findCommentsByEntity(int entityType, int entityId, int offset, int limit) {
        return commentMapper.selectCommentsByEntity(entityType, entityId, offset, limit);
    }

    public int findCommentCount(int entityType, int entityId) {
        return commentMapper.selectCountByEntity(entityType, entityId);
    }

    @Transactional(isolation = Isolation.READ_COMMITTED, propagation = Propagation.REQUIRED)
    public int addComment(Comment comment) {
        if (comment == null) {
            throw new IllegalArgumentException("参数不能为空！");
        }
        // 添加评论
        comment.setContent(HtmlUtils.htmlEscape(comment.getContent()));
        comment.setContent(sensitiveFilter.filter(comment.getContent()));
        int rows = commentMapper.insertComment(comment);

        // 更新帖子评论数量
        if (comment.getEntityType() == ENTITY_TYPE_POST) {
            int count = commentMapper.selectCountByEntity(comment.getEntityType(), comment.getEntityId());
            discussPostService.updateCommentCount(comment.getEntityId(), count);
        }
        return  rows;
    }

    public Comment findCommentById(int id) {
        return commentMapper.selectCommentById(id);
    }
}

## 5.controller层
在 commentcontroller 类中添加触发评论事件，代码如下：

@Controller
@RequestMapping("/comment")
public class CommentController implements CommunityConstant {

   @Autowired
   private CommentService commentService;

   @Autowired
   private HostHolder hostHolder;

   @Autowired
   private EventProducer eventProducer;

   @Autowired
   private DiscussPostService discussPostService;

   @RequestMapping(value = "/add/{discussPostId}", method = RequestMethod.POST)
   public String addComment(@PathVariable("discussPostId") int discussPostId, Comment comment) {
       comment.setUserId(hostHolder.getUser().getId());
       comment.setStatus(0);
       comment.setCreateTime(new Date());
       commentService.addComment(comment);

       // 触发评论事件
       Event event = new Event()
               .setTopic(TOPIC_COMMENT)
               .setUserId(hostHolder.getUser().getId())
               .setEntityType(comment.getEntityType())
               .setEntityId(comment.getEntityId())
               .setData("postId", discussPostId);
       if (comment.getEntityType() == ENTITY_TYPE_POST) {
           DiscussPost target = discussPostService.findDiscussPostById(comment.getEntityId());
           event.setEntityUserId(target.getUserId());
       } else if (comment.getEntityType() == ENTITY_TYPE_COMMENT) {
           Comment target = commentService.findCommentById(comment.getEntityId());
           event.setEntityUserId(target.getUserId());
       }
       eventProducer.fireEvent(event);

       return "redirect:/discuss/detail/" + discussPostId;
   }
}

在 likecontroller 类中添加触发点赞事件，代码如下：

@Controller
public class LikeController implements CommunityConstant {

    @Autowired
    private LikeService likeService;

    @Autowired
    private HostHolder hostHolder;

    @Autowired
    private EventProducer eventProducer;


    @RequestMapping(path = "/like", method = RequestMethod.POST)
    @ResponseBody
    public String like(int entityType, int entityId, int entityUserId, int postId) {
        User user = hostHolder.getUser();

        // 点赞
        likeService.like(user.getId(), entityType, entityId, entityUserId);

        // 数量
        long likeCount = likeService.findEntityLikeCount(entityType, entityId);
        // 状态
        int likeStatus = likeService.findEntityLikeStatus(user.getId(), entityType, entityId);
        // 返回的结果
        Map<String, Object> map = new HashMap<>();
        map.put("likeCount", likeCount);
        map.put("likeStatus", likeStatus);

        // 触发点赞事件
        if (likeStatus == 1) {
            Event event = new Event()
                    .setTopic(TOPIC_LIKE)
                    .setUserId(hostHolder.getUser().getId())
                    .setEntityType(entityType)
                    .setEntityId(entityId)
                    .setEntityUserId(entityUserId)
                    .setData("postId", postId);  //postId对于点赞的是帖子而言，这个数据是冗余的
            eventProducer.fireEvent(event);
        }


        return CommunityUtil.getJSONString(0, null, map);
    }
}

在 followeController 中添加触发关注事件，代码如下：

@Controller
public class FollowController implements CommunityConstant {

    @Autowired
    private FollowService followService;

    @Autowired
    private HostHolder hostHolder;

    @Autowired
    private UserService userService;

    @Autowired
    private EventProducer eventProducer;



    @RequestMapping(path = "/follow", method = RequestMethod.POST)
    @ResponseBody
    public String follow(int entityType, int entityId) {
        User user = hostHolder.getUser();

        followService.follow(user.getId(), entityType, entityId);

        // 触发关注事件
        Event event = new Event()
                .setTopic(TOPIC_FOLLOW)
                .setUserId(hostHolder.getUser().getId())
                .setEntityType(entityType)
                .setEntityId(entityId)
                .setEntityUserId(entityId);
        eventProducer.fireEvent(event);


        return CommunityUtil.getJSONString(0, "已关注！");
    }

    @RequestMapping(path = "/unfollow", method = RequestMethod.POST)
    @ResponseBody
    public String unfollow(int entityType, int entityId) {
        User user = hostHolder.getUser();

        followService.unfollow(user.getId(), entityType, entityId);

        return CommunityUtil.getJSONString(0, "已取消关注!");
    }


    @RequestMapping(path = "/followees/{userId}", method = RequestMethod.GET)
    public String getFollowees(@PathVariable("userId") int userId, Page page, Model model) {
        User user = userService.findUserById(userId);
        if (user == null) {
            throw new RuntimeException("该用户不存在!");
        }
        model.addAttribute("user", user);

        page.setLimit(5);
        page.setPath("/followees/" + userId);
        page.setRows((int) followService.findFolloweeCount(userId, ENTITY_TYPE_USER));

        List<Map<String, Object>> userList = followService.findFollowees(userId, page.getOffset(), page.getLimit());
        if (userList != null) {
            for (Map<String, Object> map : userList) {
                User u = (User) map.get("user");
                map.put("hasFollowed", hasFollowed(u.getId()));
            }
        }
        model.addAttribute("users", userList);

        return "/site/followee";
    }

    @RequestMapping(path = "/followers/{userId}", method = RequestMethod.GET)
    public String getFollowers(@PathVariable("userId") int userId, Page page, Model model) {
        User user = userService.findUserById(userId);
        if (user == null) {
            throw new RuntimeException("该用户不存在!");
        }
        model.addAttribute("user", user);

        page.setLimit(5);
        page.setPath("/followers/" + userId);
        page.setRows((int) followService.findFollowerCount(ENTITY_TYPE_USER, userId));

        List<Map<String, Object>> userList = followService.findFollowers(userId, page.getOffset(), page.getLimit());
        if (userList != null) {
            for (Map<String, Object> map : userList) {
                User u = (User) map.get("user");
                map.put("hasFollowed", hasFollowed(u.getId()));
            }
        }
        model.addAttribute("users", userList);

        return "/site/follower";
    }


    private boolean hasFollowed(int userId) {
        if (hostHolder.getUser() == null) {
            return false;
        }

        return followService.hasFollowed(hostHolder.getUser().getId(), ENTITY_TYPE_USER, userId);
    }


}

6. view层

对 discudd-detail.html 中的like 方法进行重构。
discuss.js：

function like(btn, entityType, entityId, entityUserId, postId) {
    $.post(
        CONTEXT_PATH + "/like",
        {"entityType":entityType,"entityId":entityId,"entityUserId":entityUserId,"postId":postId},
        function(data) {
            data = $.parseJSON(data);
            if(data.code == 0) {
                $(btn).children("i").text(data.likeCount);
                $(btn).children("b").text(data.likeStatus==1?'已赞':"赞");
            } else {
                alert(data.msg);
            }
        }
    );
}

在这里插入图片描述

五、显示系统通知

通知列表
- 显示评论、点赞、关注三种类型的通知
通知详情
- 分页显示某一类主题所包含的通知
未读消息
- 在页面头部显示所有的未读消息数量

1. dao层

在 MessageMapper 类中添加 selectLatestNotice、selectNoticeCount、selectNoticeUnreadCount、selectNotices 方法，代码如下：

@Mapper
public interface MessageMapper {

    // 查询当前用户的会话列表,针对每个会话只返回一条最新的私信.
    List<Message> selectConversations(int userId, int offset, int limit);

    // 查询当前用户的会话数量.
    int selectConversationCount(int userId);

    // 查询某个会话所包含的私信列表.
    List<Message> selectLetters(String conversationId, int offset, int limit);

    // 查询某个会话所包含的私信数量.
    int selectLetterCount(String conversationId);

    // 查询未读私信的数量
    int selectLetterUnreadCount(int userId, String conversationId);

    // 新增消息
    int insertMessage(Message message);

    // 修改消息的状态
    int updateStatus(List<Integer> ids, int status);

    // 查询某个主题下最新的通知
    Message selectLatestNotice(int userId, String topic);

    // 查询某个主题所包含的通知数量
    int selectNoticeCount(int userId, String topic);

    // 查询未读的通知的数量
    int selectNoticeUnreadCount(int userId, String topic);

    // 查询某个主题所包含的通知列表
    List<Message> selectNotices(int userId, String topic, int offset, int limit);

}

对应的 message-mapper.xml 代码如下：

<?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.gerrard.community.dao.MessageMapper">

    <sql id="selectFields">
        id, from_id, to_id, conversation_id, content, status, create_time
    </sql>

    <sql id="insertFields">
        from_id, to_id, conversation_id, content, status, create_time
    </sql>

    <select id="selectConversations" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where id in (
            select max(id) from message
            where status != 2
            and from_id != 1
            and (from_id = #{userId} or to_id = #{userId})
            group by conversation_id
        )
        order by id desc
        limit #{offset}, #{limit}
    </select>

    <select id="selectConversationCount" resultType="int">
        select count(m.maxid) from (
            select max(id) as maxid from message
            where status != 2
            and from_id != 1
            and (from_id = #{userId} or to_id = #{userId})
            group by conversation_id
        ) as m
    </select>

    <select id="selectLetters" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where status != 2
        and from_id != 1
        and conversation_id = #{conversationId}
        order by id desc
        limit #{offset}, #{limit}
    </select>

    <select id="selectLetterCount" resultType="int">
        select count(id)
        from message
        where status != 2
        and from_id != 1
        and conversation_id = #{conversationId}
    </select>

    <select id="selectLetterUnreadCount" resultType="int">
        select count(id)
        from message
        where status = 0
        and from_id != 1
        and to_id = #{userId}
        <if test="conversationId!=null">
            and conversation_id = #{conversationId}
        </if>
    </select>

    <insert id="insertMessage" parameterType="Message" keyProperty="id">
        insert into message(<include refid="insertFields"></include>)
        values(#{fromId},#{toId},#{conversationId},#{content},#{status},#{createTime})
    </insert>

    <update id="updateStatus">
        update message set status = #{status}
        where id in
        <foreach collection="ids" item="id" open="(" separator="," close=")">
            #{id}
        </foreach>
    </update>

    <select id="selectLatestNotice" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where id in (
            select max(id) from message
            where status != 2
            and from_id = 1
            and to_id = #{userId}
            and conversation_id = #{topic}
        )
    </select>

    <select id="selectNoticeCount" resultType="int">
        select count(id) from message
        where status != 2
        and from_id = 1
        and to_id = #{userId}
        and conversation_id = #{topic}
    </select>

    <select id="selectNoticeUnreadCount" resultType="int">
        select count(id) from message
        where status = 0
        and from_id = 1
        and to_id = #{userId}
        <if test="topic!=null">
            and conversation_id = #{topic}
        </if>
    </select>

    <select id="selectNotices" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where status != 2
        and from_id = 1
        and to_id = #{userId}
        and conversation_id = #{topic}
        order by create_time desc
        limit #{offset}, #{limit}
    </select>

</mapper>

2. service层

在 MessageService 类中添加 findLatesNotice、findNoticeCount 、findNoticeUnreadCount、findNotices方法，代码如下：

<?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.gerrard.community.dao.MessageMapper">

    <sql id="selectFields">
        id, from_id, to_id, conversation_id, content, status, create_time
    </sql>

    <sql id="insertFields">
        from_id, to_id, conversation_id, content, status, create_time
    </sql>

    <select id="selectConversations" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where id in (
            select max(id) from message
            where status != 2
            and from_id != 1
            and (from_id = #{userId} or to_id = #{userId})
            group by conversation_id
        )
        order by id desc
        limit #{offset}, #{limit}
    </select>

    <select id="selectConversationCount" resultType="int">
        select count(m.maxid) from (
            select max(id) as maxid from message
            where status != 2
            and from_id != 1
            and (from_id = #{userId} or to_id = #{userId})
            group by conversation_id
        ) as m
    </select>

    <select id="selectLetters" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where status != 2
        and from_id != 1
        and conversation_id = #{conversationId}
        order by id desc
        limit #{offset}, #{limit}
    </select>

    <select id="selectLetterCount" resultType="int">
        select count(id)
        from message
        where status != 2
        and from_id != 1
        and conversation_id = #{conversationId}
    </select>

    <select id="selectLetterUnreadCount" resultType="int">
        select count(id)
        from message
        where status = 0
        and from_id != 1
        and to_id = #{userId}
        <if test="conversationId!=null">
            and conversation_id = #{conversationId}
        </if>
    </select>

    <insert id="insertMessage" parameterType="Message" keyProperty="id">
        insert into message(<include refid="insertFields"></include>)
        values(#{fromId},#{toId},#{conversationId},#{content},#{status},#{createTime})
    </insert>

    <update id="updateStatus">
        update message set status = #{status}
        where id in
        <foreach collection="ids" item="id" open="(" separator="," close=")">
            #{id}
        </foreach>
    </update>

    <select id="selectLatestNotice" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where id in (
            select max(id) from message
            where status != 2
            and from_id = 1
            and to_id = #{userId}
            and conversation_id = #{topic}
        )
    </select>

    <select id="selectNoticeCount" resultType="int">
        select count(id) from message
        where status != 2
        and from_id = 1
        and to_id = #{userId}
        and conversation_id = #{topic}
    </select>

    <select id="selectNoticeUnreadCount" resultType="int">
        select count(id) from message
        where status = 0
        and from_id = 1
        and to_id = #{userId}
        <if test="topic!=null">
            and conversation_id = #{topic}
        </if>
    </select>

    <select id="selectNotices" resultType="Message">
        select <include refid="selectFields"></include>
        from message
        where status != 2
        and from_id = 1
        and to_id = #{userId}
        and conversation_id = #{topic}
        order by create_time desc
        limit #{offset}, #{limit}
    </select>

</mapper>

3. controller层

在 MessageController 类中添加 getNoticeList、getNoticerDetail 方法，代码如下：

@Controller
public class MessageController implements CommunityConstant {

    @Autowired
    private MessageService messageService;

    @Autowired
    private HostHolder hostHolder;

    @Autowired
    private UserService userService;

    // 私信列表
    @RequestMapping(path = "/letter/list", method = RequestMethod.GET)
    public String getLetterList(Model model, Page page) {
        User user = hostHolder.getUser();
        // 分页信息
        page.setLimit(5);
        page.setPath("/letter/list");
        page.setRows(messageService.findConversationCount(user.getId()));

        // 会话列表
        List<Message> conversationList = messageService.findConversations(
                user.getId(), page.getOffset(), page.getLimit());
        List<Map<String, Object>> conversations = new ArrayList<>();
        if (conversationList != null) {
            for (Message message : conversationList) {
                Map<String, Object> map = new HashMap<>();
                map.put("conversation", message);
                map.put("letterCount", messageService.findLetterCount(message.getConversationId()));
                map.put("unreadCount", messageService.findLetterUnreadCount(user.getId(), message.getConversationId()));
                int targetId = user.getId() == message.getFromId() ? message.getToId() : message.getFromId();
                map.put("target", userService.findUserById(targetId));

                conversations.add(map);
            }
        }
        model.addAttribute("conversations", conversations);

        // 查询未读消息数量
        int letterUnreadCount = messageService.findLetterUnreadCount(user.getId(), null);
        model.addAttribute("letterUnreadCount", letterUnreadCount);
        int noticeUnreadCount = messageService.findNoticeUnreadCount(user.getId(), null);
        model.addAttribute("noticeUnreadCount", noticeUnreadCount);

        return "/site/letter";
    }

    @RequestMapping(path = "/letter/detail/{conversationId}", method = RequestMethod.GET)
    public String getLetterDetail(@PathVariable("conversationId") String conversationId, Page page, Model model) {
        // 分页信息
        page.setLimit(5);
        page.setPath("/letter/detail/" + conversationId);
        page.setRows(messageService.findLetterCount(conversationId));

        // 私信列表
        List<Message> letterList = messageService.findLetters(conversationId, page.getOffset(), page.getLimit());
        List<Map<String, Object>> letters = new ArrayList<>();
        if (letterList != null) {
            for (Message message : letterList) {
                Map<String, Object> map = new HashMap<>();
                map.put("letter", message);
                map.put("fromUser", userService.findUserById(message.getFromId()));
                letters.add(map);
            }
        }
        model.addAttribute("letters", letters);

        // 私信目标
        model.addAttribute("target", getLetterTarget(conversationId));

        // 设置已读
        List<Integer> ids = getLetterIds(letterList);
        if (!ids.isEmpty()) {
            messageService.readMessage(ids);
        }

        return "/site/letter-detail";
    }

    private User getLetterTarget(String conversationId) {
        String[] ids = conversationId.split("_");
        int id0 = Integer.parseInt(ids[0]);
        int id1 = Integer.parseInt(ids[1]);

        if (hostHolder.getUser().getId() == id0) {
            return userService.findUserById(id1);
        } else {
            return userService.findUserById(id0);
        }
    }

    private List<Integer> getLetterIds(List<Message> letterList) {
        List<Integer> ids = new ArrayList<>();

        if (letterList != null) {
            for (Message message : letterList) {
                if (hostHolder.getUser().getId() == message.getToId() && message.getStatus() == 0) {
                    ids.add(message.getId());
                }
            }
        }

        return ids;
    }

    @RequestMapping(path = "/letter/send", method = RequestMethod.POST)
    @ResponseBody
    public String sendLetter(String toName, String content) {
        User target = userService.findUserByName(toName);
        if (target == null) {
            return CommunityUtil.getJSONString(1, "目标用户不存在!");
        }

        Message message = new Message();
        message.setFromId(hostHolder.getUser().getId());
        message.setToId(target.getId());
        if (message.getFromId() < message.getToId()) {
            message.setConversationId(message.getFromId() + "_" + message.getToId());
        } else {
            message.setConversationId(message.getToId() + "_" + message.getFromId());
        }
        message.setContent(content);
        message.setCreateTime(new Date());
        messageService.addMessage(message);

        return CommunityUtil.getJSONString(0);
    }

    @RequestMapping(path = "/notice/list", method = RequestMethod.GET)
    public String getNoticeList(Model model) {
        User user = hostHolder.getUser();

        // 查询评论类通知
        Message message = messageService.findLatestNotice(user.getId(), TOPIC_COMMENT);
        Map<String, Object> messageVO = new HashMap<>();
        if (message != null) {
            messageVO.put("message", message);

            String content = HtmlUtils.htmlUnescape(message.getContent());
            Map<String, Object> data = JSONObject.parseObject(content, HashMap.class);

            messageVO.put("user", userService.findUserById((Integer) data.get("userId")));
            messageVO.put("entityType", data.get("entityType"));
            messageVO.put("entityId", data.get("entityId"));
            messageVO.put("postId", data.get("postId"));

            int count = messageService.findNoticeCount(user.getId(), TOPIC_COMMENT);
            messageVO.put("count", count);

            int unread = messageService.findNoticeUnreadCount(user.getId(), TOPIC_COMMENT);
            messageVO.put("unread", unread);
        }
        model.addAttribute("commentNotice", messageVO);

        // 查询点赞类通知
        message = messageService.findLatestNotice(user.getId(), TOPIC_LIKE);
        messageVO = new HashMap<>();
        if (message != null) {
            messageVO.put("message", message);

            String content = HtmlUtils.htmlUnescape(message.getContent());
            Map<String, Object> data = JSONObject.parseObject(content, HashMap.class);

            messageVO.put("user", userService.findUserById((Integer) data.get("userId")));
            messageVO.put("entityType", data.get("entityType"));
            messageVO.put("entityId", data.get("entityId"));
            messageVO.put("postId", data.get("postId"));

            int count = messageService.findNoticeCount(user.getId(), TOPIC_LIKE);
            messageVO.put("count", count);

            int unread = messageService.findNoticeUnreadCount(user.getId(), TOPIC_LIKE);
            messageVO.put("unread", unread);
        }
        model.addAttribute("likeNotice", messageVO);

        // 查询关注类通知
        message = messageService.findLatestNotice(user.getId(), TOPIC_FOLLOW);
        messageVO = new HashMap<>();
        if (message != null) {
            messageVO.put("message", message);

            String content = HtmlUtils.htmlUnescape(message.getContent());
            Map<String, Object> data = JSONObject.parseObject(content, HashMap.class);

            messageVO.put("user", userService.findUserById((Integer) data.get("userId")));
            messageVO.put("entityType", data.get("entityType"));
            messageVO.put("entityId", data.get("entityId"));

            int count = messageService.findNoticeCount(user.getId(), TOPIC_FOLLOW);
            messageVO.put("count", count);

            int unread = messageService.findNoticeUnreadCount(user.getId(), TOPIC_FOLLOW);
            messageVO.put("unread", unread);
        }
        model.addAttribute("followNotice", messageVO);

        // 查询未读消息数量
        int letterUnreadCount = messageService.findLetterUnreadCount(user.getId(), null);
        model.addAttribute("letterUnreadCount", letterUnreadCount);
        int noticeUnreadCount = messageService.findNoticeUnreadCount(user.getId(), null);
        model.addAttribute("noticeUnreadCount", noticeUnreadCount);

        return "/site/notice";
    }

    @RequestMapping(path = "/notice/detail/{topic}", method = RequestMethod.GET)
    public String getNoticeDetail(@PathVariable("topic") String topic, Page page, Model model) {
        User user = hostHolder.getUser();

        page.setLimit(5);
        page.setPath("/notice/detail/" + topic);
        page.setRows(messageService.findNoticeCount(user.getId(), topic));

        List<Message> noticeList = messageService.findNotices(user.getId(), topic, page.getOffset(), page.getLimit());
        List<Map<String, Object>> noticeVoList = new ArrayList<>();
        if (noticeList != null) {
            for (Message notice : noticeList) {
                Map<String, Object> map = new HashMap<>();
                // 通知
                map.put("notice", notice);
                // 内容
                String content = HtmlUtils.htmlUnescape(notice.getContent());
                Map<String, Object> data = JSONObject.parseObject(content, HashMap.class);
                map.put("user", userService.findUserById((Integer) data.get("userId")));
                map.put("entityType", data.get("entityType"));
                map.put("entityId", data.get("entityId"));
                map.put("postId", data.get("postId"));
                // 通知作者
                map.put("fromUser", userService.findUserById(notice.getFromId()));

                noticeVoList.add(map);
            }
        }
        model.addAttribute("notices", noticeVoList);

        // 设置已读
        List<Integer> ids = getLetterIds(noticeList);
        if (!ids.isEmpty()) {
            messageService.readMessage(ids);
        }

        return "/site/notice-detail";
    }

}

旧版：新建 MessageInterceptor 类拦截器。
新版：在 LoginTicketinterceptor 中对 posthandle 方法进行修改，代码如下：

@Component
public class LoginTicketInterceptor implements HandlerInterceptor {
    @Autowired
    private UserService userService;

    @Autowired
    private HostHolder hostHolder;

    @Autowired
    private MessageService messageService;

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //从cookie中获取凭证
        String ticket= CookieUtil.getValue(request,"ticket");
        if(ticket!=null){
            //查询凭证
            LoginTicket loginTicket=userService.findLoginTicket(ticket);

            //检查凭证是否有效
            //一般不会检测到过期，因为时间一到，cookie自动被销毁了？？？？？
            if(loginTicket!=null && loginTicket.getStatus()==0 && loginTicket.getExpired().after(new Date())){
                //根据凭证查询用户
                User user=userService.findUserById(loginTicket.getUserId());
                //在本次请求中持有用户
                hostHolder.setUser(user);

                //构建用户认证的结果，并存入SecurityContext，以便于Security进行授权
                Authentication authentication=new UsernamePasswordAuthenticationToken(
                        user,user.getPassword(),userService.getAuthorities(user.getId()));

                SecurityContextHolder.setContext(new SecurityContextImpl(authentication));
            }
        }
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        User user=hostHolder.getUser();

        if(user!=null && modelAndView !=null){
            int unReadLetterCount=messageService.findLetterUnreadCount(user.getId(),null);
            int unReadNoticeCount=messageService.findNoticeUnreadCount(user.getId(),null);
            modelAndView.addObject("loginUser",user);
            modelAndView.addObject("messageUnRead",unReadLetterCount+unReadNoticeCount);
        }
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        hostHolder.clear();

       // SecurityContextHolder.clearContext();
    }
}