springboot整合websocket遇到的小问题

今天尝试了通过springboot整合websocket来初步学习使用websocket，然后发现启动的时候报错了，发这篇文章分享一下。

springboot整合websocket的步骤很简单：

第一步：创建一个springboot项目，在这里命名为websocket

在IntelliJ IDEA里创建一个springboot项目，创建过程中只需要修改项目名和选择java的版本为8，然后点击Next等待片刻就创建好了。

第二步：pom.xml中添加websocket的依赖

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

不需要指定版本，默认和springboot版本一致，修改springboot版本为2.5.9，完整的配置文件如下

<?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>2.5.9</version>
        <relativePath/>
    </parent>

    <groupId>com.example</groupId>
    <artifactId>websocket</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <properties>
        <java.version>1.8</java.version>
        <lombok.version>1.18.22</lombok.version>
        <fastjson.version>2.0.8</fastjson.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-test</artifactId>
            <scope>test</scope>
        </dependency>

        <!--lombok-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${lombok.version}</version>
        </dependency>

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

        <!--fastjson-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>${fastjson.version}</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

第三步：添加websocket的配置类

在项目的根目录下创建config包，在config包下创建一个配置类WebSocketConfig

package com.example.websocket.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.socket.server.standard.ServerEndpointExporter;

/**
 * @author heyunlin
 * @version 1.0
 */
@Configuration
public class WebSocketConfig {

    @Bean
    public ServerEndpointExporter serverEndpointExporter() {
        return new ServerEndpointExporter();
    }

}

第四步：使用websocket

在项目根目录下创建一个endpoint包，在endpoint包下创建一个WebSocket类，在类上添加@Component和@ServerEndpoint注解，并通过@ServerEndpoint的value属性指定请求路径，用法类似于@RequestMapping。

package com.example.websocket.endpoint;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.PathVariable;

import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * websocket访问路径：ws://localhost:8082/websocket/用户ID
 * @author heyunlin
 * @version 1.0
 */
@Slf4j
@Component
@ServerEndpoint("/websocket/{userId}")
public class WebSocket {
    private Session session;
    private String userId;

    private final CopyOnWriteArraySet<WebSocket> webSockets = new CopyOnWriteArraySet<>();
    private final ConcurrentHashMap<String, Session> hashMap = new ConcurrentHashMap<>();

    /**
     * 链接成功调用的方法
     */
    @OnOpen
    public void onOpen(Session session, @PathVariable String userId) {
        this.session = session;
        this.userId = userId;

        webSockets.add(this);
        hashMap.put(userId, session);

        log.debug("和用户{}创建连接。", this.userId);
    }

    /**
     * 链接关闭调用的方法
     */
    @OnClose
    public void onClose() {
        webSockets.remove(this);
        hashMap.remove(this.userId);

        log.debug("用户{}关闭了websocket连接。", this.userId);
    }

    /**
     * 收到客户端消息后调用的方法
     */
    @OnMessage
    public void onMessage(String message) {
        log.debug("收到用户{}发送的消息：", this.userId);
    }

    /**
     * 发送错误时的处理
     * @param error Throwable
     */
    @OnError
    public void onError(Throwable error) {
        error.printStackTrace();
    }

    /**
     * 发送单条消息
     * @param userId 用户ID
     * @param message 消息内容
     */
    public void sendMessage(String userId, String message) {
        if (hashMap.containsKey(userId)) {
            Session session = hashMap.get(userId);

            if (session.isOpen()) {
                session.getAsyncRemote().sendText(message);
            }
        }
    }

}

第五步：启动项目

然后启动报错了ovo

java.lang.IllegalStateException: Failed to register @ServerEndpoint class: class com.example.websocket.endpoint.WebSocket
	at org.springframework.web.socket.server.standard.ServerEndpointExporter.registerEndpoint(ServerEndpointExporter.java:159) ~[spring-websocket-5.3.15.jar:5.3.15]
	at org.springframework.web.socket.server.standard.ServerEndpointExporter.registerEndpoints(ServerEndpointExporter.java:134) ~[spring-websocket-5.3.15.jar:5.3.15]
	at org.springframework.web.socket.server.standard.ServerEndpointExporter.afterSingletonsInstantiated(ServerEndpointExporter.java:112) ~[spring-websocket-5.3.15.jar:5.3.15]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:972) ~[spring-beans-5.3.15.jar:5.3.15]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.15.jar:5.3.15]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.15.jar:5.3.15]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:145) ~[spring-boot-2.5.9.jar:2.5.9]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:767) [spring-boot-2.5.9.jar:2.5.9]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:447) [spring-boot-2.5.9.jar:2.5.9]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:338) [spring-boot-2.5.9.jar:2.5.9]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1356) [spring-boot-2.5.9.jar:2.5.9]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1345) [spring-boot-2.5.9.jar:2.5.9]
	at com.example.websocket.WebsocketApplication.main(WebsocketApplication.java:10) [classes/:na]
Caused by: javax.websocket.DeploymentException: A parameter of type [class java.lang.String] was found on method[onOpen] of class [java.lang.reflect.Method] that did not have a @PathParam annotation
	at org.apache.tomcat.websocket.pojo.PojoMethodMapping.getPathParams(PojoMethodMapping.java:347) ~[tomcat-embed-websocket-9.0.56.jar:9.0.56]
	at org.apache.tomcat.websocket.pojo.PojoMethodMapping.<init>(PojoMethodMapping.java:221) ~[tomcat-embed-websocket-9.0.56.jar:9.0.56]
	at org.apache.tomcat.websocket.server.WsServerContainer.addEndpoint(WsServerContainer.java:155) ~[tomcat-embed-websocket-9.0.56.jar:9.0.56]
	at org.apache.tomcat.websocket.server.WsServerContainer.addEndpoint(WsServerContainer.java:279) ~[tomcat-embed-websocket-9.0.56.jar:9.0.56]
	at org.apache.tomcat.websocket.server.WsServerContainer.addEndpoint(WsServerContainer.java:229) ~[tomcat-embed-websocket-9.0.56.jar:9.0.56]
	at org.springframework.web.socket.server.standard.ServerEndpointExporter.registerEndpoint(ServerEndpointExporter.java:156) ~[spring-websocket-5.3.15.jar:5.3.15]
	... 12 common frames omitted

Disconnected from the target VM, address: '127.0.0.1:53445', transport: 'socket'

Process finished with exit code 1

重点看这行

Caused by: javax.websocket.DeploymentException: A parameter of type [class java.lang.String] was found on method[onOpen] of class [java.lang.reflect.Method] that did not have a @PathParam annotation

意思是onOpen()方法上的一个String类型的参数上没有用@PathParam注解，检查了一下，确实没有用这个注解，用的是@PathVariable，这两个注解的作用是类似的，都是获取rest风格请求的参数。修改一下onOpen()方法

package com.example.websocket.endpoint;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import javax.websocket.*;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArraySet;

/**
 * websocket访问路径：ws://localhost:8082/websocket/用户ID
 * @author heyunlin
 * @version 1.0
 */
@Slf4j
@Component
@ServerEndpoint("/websocket/{userId}")
public class WebSocket {
    private Session session;
    private String userId;

    private final CopyOnWriteArraySet<WebSocket> webSockets = new CopyOnWriteArraySet<>();
    private final ConcurrentHashMap<String, Session> hashMap = new ConcurrentHashMap<>();

    /**
     * 链接成功调用的方法
     */
    @OnOpen
    public void onOpen(Session session, @PathParam("userId") String userId) {
        this.session = session;
        this.userId = userId;

        webSockets.add(this);
        hashMap.put(userId, session);

        log.debug("和用户{}创建连接。", this.userId);
    }

    /**
     * 链接关闭调用的方法
     */
    @OnClose
    public void onClose() {
        webSockets.remove(this);
        hashMap.remove(this.userId);

        log.debug("用户{}关闭了websocket连接。", this.userId);
    }

    /**
     * 收到客户端消息后调用的方法
     */
    @OnMessage
    public void onMessage(String message) {
        log.debug("收到用户{}发送的消息：", this.userId);
    }

    /**
     * 发送错误时的处理
     * @param error Throwable
     */
    @OnError
    public void onError(Throwable error) {
        error.printStackTrace();
    }

    /**
     * 发送单条消息
     * @param userId 用户ID
     * @param message 消息内容
     */
    public void sendMessage(String userId, String message) {
        if (hashMap.containsKey(userId)) {
            Session session = hashMap.get(userId);

            if (session.isOpen()) {
                session.getAsyncRemote().sendText(message);
            }
        }
    }

}

修改之后能正常启动了。