SSE长连接（ SpringBoot整合SSE（Server-Sent Events）可以实现后端主动向前端推送数据）

Demo代码分享

依赖

<?xml version="1.0" encoding="UTF-8"?>
<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.7</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
        <mybatis-plus.version>3.5.2</mybatis-plus.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>

        <!-- test -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

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

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

后端接收sse连接

@Controller
@RequestMapping("/sse")
public class IndexController {
    /**
     * 创建SSE连接
     *
     * @return
     */
    @GetMapping(path = "/connect")
    public SseEmitter sse() {
        SseEmitter sseEmitter = new SseEmitter();

        // 发送一个注释，响应前端请求
        sseEmitter.send(SseEmitter.event().comment("welcome"));
        return sseEmitter;
    }
}

前端浏览器代码

// 连接服务器
var sseSource = new EventSource("http://localhost:8080/sse/connect");

// 连接打开
sseSource.onopen = function () {
    console.log("连接打开");
}

// 连接错误
sseSource.onerror = function (err) {
    console.log("连接错误:", err);
}

// 接收到数据
sseSource.onmessage = function (event) {
    console.log("接收到数据:", event);
    handleReceiveData(JSON.parse(event.data))
}

定义一个返回数据 Message.java

package com.example.demo.entity;

import lombok.Data;

@Data
public class Message {
    private String data;
    private Integer total;
}

定义sse接口 SseService.java

package com.example.demo.service;

import com.example.demo.entity.Message;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

public interface SseService {
    SseEmitter connect(String uuid);

    void sendMessage(Message message);
}

实现sse接口 SseServiceImpl.java

package com.example.demo.service.impl;

import com.example.demo.entity.Message;
import com.example.demo.service.SseService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Service;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

@Slf4j
@Service
public class SseServiceImpl implements SseService {
    /**
     * messageId的 SseEmitter对象映射集
     */
    private static Map<String, SseEmitter> sseEmitterMap = new ConcurrentHashMap<>();

    /**
     * 连接sse
     * @param uuid
     * @return
     */
    @Override
    public SseEmitter connect(String uuid) {
        SseEmitter sseEmitter = new SseEmitter();

        // 连接成功需要返回数据，否则会出现待处理状态
        try {
            sseEmitter.send(SseEmitter.event().comment("welcome"));
        } catch (IOException e) {
            e.printStackTrace();
        }

        // 连接断开
        sseEmitter.onCompletion(() -> {
            sseEmitterMap.remove(uuid);
        });

        // 连接超时
        sseEmitter.onTimeout(() -> {
            sseEmitterMap.remove(uuid);
        });

        // 连接报错
        sseEmitter.onError((throwable) -> {
            sseEmitterMap.remove(uuid);
        });

        sseEmitterMap.put(uuid, sseEmitter);

        return sseEmitter;
    }

    /**
     * 发送消息
     * @param message
     */
    @Override
    public void sendMessage(Message message) {
        message.setTotal(sseEmitterMap.size());

        sseEmitterMap.forEach((uuid, sseEmitter) -> {
            try {
                sseEmitter.send(message, MediaType.APPLICATION_JSON);
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
    }
}

定时任务 SendMessageTask.java

package com.example.demo.task;


import com.example.demo.entity.Message;
import com.example.demo.service.SseService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.Scheduled;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

@Configuration
public class SendMessageTask {
    @Autowired
    private SseService sseService;

    /**
     * 定时执行 秒 分 时 日 月 周
     */
    @Scheduled(cron = "*/5 * * * * *")  // 间隔5秒
    public void sendMessageTask() {
        Message message = new Message();
        DateTimeFormatter format = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        message.setData(LocalDateTime.now().format(format));
        sseService.sendMessage(message);
    }
}

前端路由 IndexController.java

package com.example.demo.controller;

import com.example.demo.entity.Message;
import com.example.demo.service.SseService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.servlet.mvc.method.annotation.SseEmitter;

import java.util.UUID;

@Slf4j
@Controller
@RequestMapping("/sse")
public class IndexController {

    @Autowired
    private SseService sseService;

    /**
     * 首页
     *
     * @return
     */
    @GetMapping("/")
    public String index() {
        return "index";
    }

    /**
     * 创建SSE连接
     *
     * @return
     */
    @GetMapping(path = "/connect", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public SseEmitter sse() {
        String uuid = UUID.randomUUID().toString();
        log.info("新用户连接：{}", uuid);
        return sseService.connect(uuid);
    }

    /**
     * 广播消息
     *
     * @param message
     */
    @PostMapping("/sendMessage")
    @ResponseBody
    public void sendMessage(@RequestBody Message message) {
        sseService.sendMessage(message);
    }
}