事件驱动的方式
1 需求分析
需求：当用户评论帖子，点赞或关注其他用户时，系统给对应的用户发送通知。
思路：封装好一个通用的事件类，保存事件的发送者，接受者、事件主题（评论、点赞、关注）和事件内容。当用户有评论点赞等行为时，构造事件类。通过Kafaka，生产者将事件发布不同的主题，同时消费者监听不同的主题并作出相应的处理（这里为了简单起见将不同的主题一起监听）。
2 处理事件
- 封装事件对象
event.java
set方法返回this，方便连续调用set方法
import java.util.HashMap;
import java.util.Map;
public class Event {
private String topic;
// 发送者
private int userId;
private int entityType;
private int entityId;
// 接收者
private int entityUserId;
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;
}
}
- 开发事件的生产者
主动触发
import com.alibaba.fastjson.JSONObject;
import com.nowcoder.community.entity.Event;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.stereotype.Component;
@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));
}
}
- 开发事件的消费者
被动触发
主题定义CommunityConstant.java
public interface CommunityConstant {
/**
* 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;
}
事件消费者EventConsumer.java
import com.alibaba.fastjson.JSONObject;
import com.nowcoder.community.entity.Event;
import com.nowcoder.community.entity.Message;
import com.nowcoder.community.service.MessageService;
import com.nowcoder.community.util.CommunityConstant;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;
import java.util.Date;
import java.util.HashMap;
import java.util.Map;
@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());
// 构造消息内容
Map<String, Object> content = new HashMap<>();
content.put("userId", event.getUserId());
content.put("entityType", event.getEntityType());
content.put("entityId", event.getEntityId());
// 存放额外内容
if (!event.getData().isEmpty()) {
for (Map.Entry<String, Object> entry : event.getData().entrySet()) {
content.put(entry.getKey(), entry.getValue());
}
}
// 将数据存到message表
message.setContent(JSONObject.toJSONString(content));
messageService.addMessage(message);
}
}
3 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
以评论为例CommentController.java
import com.nowcoder.community.entity.Comment;
import com.nowcoder.community.entity.DiscussPost;
import com.nowcoder.community.entity.Event;
import com.nowcoder.community.event.EventProducer;
import com.nowcoder.community.service.CommentService;
import com.nowcoder.community.service.DiscussPostService;
import com.nowcoder.community.util.CommunityConstant;
import com.nowcoder.community.util.HostHolder;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import java.util.Date;
@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(path = "/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;
}
}
4 显示通知
用户进入个人通知页面时，查询该用户的各种通知消息，封装到Map中提供模板使用。具体步骤略。
Message.java
// ...
// 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);
message-mapper.xml
<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>