目录

• Java Websocket 01: 原生模式 Websocket 基础通信
• Java Websocket 02: 原生模式通过 Websocket 传输文件

Websocket 原生模式

原生模式下

• 服务端通过 @ServerEndpoint 实现其对应的 @OnOpen, @OnClose, @OnMessage, @OnError 方法
• 客户端创建 WebSocketClient 实现对应的 onOpen(), onClose(), onMessage(), onError()

演示项目

完整示例代码 https://github.com/MiltonLai/websocket-demos/tree/main/ws-demo01

目录结构

│   pom.xml
└───src
    ├───main
    │   ├───java
    │   │   └───com
    │   │       └───rockbb
    │   │           └───test
    │   │               └───wsdemo
    │   │                       SocketServer.java
    │   │                       WebSocketConfig.java
    │   │                       WsDemo01App.java
    │   └───resources
    │           application.yml
    └───test
        └───java
            └───com
                └───rockbb
                    └───test
                        └───wsdemo
                                SocketClient.java

pom.xml

• 可以用 JDK11, 也可以用 JDK17
• 通过 Spring Boot plugin repackage, 生成 fat jar
• 用 Java-WebSocket 作为 client 的 websocket 实现库, 当前最新版本为 1.5.3

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.rockbb.test</groupId>
    <artifactId>ws-demo01</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>

    <name>WS: Demo 01</name>

    <properties>
        <!-- Global encoding -->
        <project.jdk.version>17</project.jdk.version>
        <project.source.encoding>UTF-8</project.source.encoding>
        <!-- Global dependency versions -->
        <spring-boot.version>2.7.11</spring-boot.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <!-- Spring Boot Dependencies -->
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-dependencies</artifactId>
                <version>${spring-boot.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

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

        <dependency>
            <groupId>org.java-websocket</groupId>
            <artifactId>Java-WebSocket</artifactId>
            <version>1.5.3</version>
        </dependency>

    </dependencies>

    <build>
        <finalName>ws-demo01</finalName>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.10.1</version>
                <configuration>
                    <source>${project.jdk.version}</source>
                    <target>${project.jdk.version}</target>
                    <encoding>${project.source.encoding}</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-resources-plugin</artifactId>
                <version>3.3.0</version>
                <configuration>
                    <encoding>${project.source.encoding}</encoding>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <version>${spring-boot.version}</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>repackage</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

application.yml

设置服务端口为 8763

server:
  port: 8763
  tomcat:
    uri-encoding: UTF-8

spring:
  application:
    name: ws-demo01

WsDemo01App.java

• 将 @RestController 也合并到应用入口了. 和单独拆开做一个 Controller 类是一样的
• '/msg' 路径用于从 server 往 client 发送消息

@RestController
@SpringBootApplication
public class WsDemo01App {

    public static void main(String[] args) {
        SpringApplication.run(WsDemo01App.class, args);
    }

    @RequestMapping("/msg")
    public String sendMsg(String sessionId, String msg) throws IOException {
        Session session = SocketServer.getSession(sessionId);
        SocketServer.sendMessage(session, msg);
        return "send " + sessionId + " : " + msg;
    }
}

WebSocketConfig.java

必须显式声明 ServerEndpointExporter 这个 Bean 才能提供 websocket 服务

@Configuration
public class WebSocketConfig {

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

SocketServer.java

提供 websocket 服务的关键类. @ServerEndpoint 的作用类似于 RestController, 这里指定 client 访问的路径格式为 ws://host:port/websocket/server/[id],
当 client 访问使用不同的 id 时, 会对应产生不同的 SocketServer 实例

@Component
@ServerEndpoint("/websocket/server/{sessionId}")
public class SocketServer {
    private static final org.slf4j.Logger log = LoggerFactory.getLogger(SocketServer.class);
    private static final Map<String, Session> sessionMap = new ConcurrentHashMap<>();

    private String sessionId = "";

    @OnOpen
    public void onOpen(Session session, @PathParam("sessionId") String sessionId) {
        this.sessionId = sessionId;
        /* Old connection will be kicked by new connection */
        sessionMap.put(sessionId, session);
        /*
         * this: instance id. New instances will be created for each sessionId
         * sessionId: assigned from path variable
         * session.getId(): the actual session id (start from 0)
         */
        log.info("On open: this{} sessionId {}, actual {}", this, sessionId, session.getId());
    }

    @OnClose
    public void onClose() {
        sessionMap.remove(sessionId);
        log.info("On close: sessionId {}", sessionId);
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        log.info("On message: sessionId {}, {}", session.getId(), message);
    }

    @OnError
    public void onError(Session session, Throwable error) {
        log.error("On error: sessionId {}, {}", session.getId(), error.getMessage());
    }

    public static void sendMessage(Session session, String message) throws IOException {
        session.getBasicRemote().sendText(message);
    }

    public static Session getSession(String sessionId){
        return sessionMap.get(sessionId);
    }
}

关于会话对象 Session

OnOpen 会注入一个 Session 参数, 这个是实际的 Websocket Session, 其 ID 是全局唯一的, 可以唯一确定一个客户端连接. 在当前版本的实现中, 这是一个从0开始自增的整数. 如果你需要实现例如单个用户登录多个会话, 在通信中, 将消息转发给同一个用户的多个会话, 就要小心记录这些 Session 的 ID.

@OnOpen
public void onOpen(Session session, @PathParam("sessionId") String sessionId)

关于会话意外关闭

在客户端意外停止后, 服务端会收到 OnError 消息, 可以通过这个消息管理已经关闭的会话

SocketClient.java

client 测试类, 连接后可以通过命令行向 server 发送消息

public class SocketClient {

    private static final org.slf4j.Logger log = LoggerFactory.getLogger(SocketClient.class);

    public static void main(String[] args) throws URISyntaxException {

        WebSocketClient wsClient = new WebSocketClient(
                new URI("ws://127.0.0.1:8763/websocket/server/10001")) {

            @Override
            public void onOpen(ServerHandshake serverHandshake) {
                log.info("On open: {}, {}", serverHandshake.getHttpStatus(), serverHandshake.getHttpStatusMessage());
            }

            @Override
            public void onMessage(String s) {
                log.info("On message: {}", s);
            }

            @Override
            public void onClose(int i, String s, boolean b) {
                log.info("On close: {}, {}, {}", i, s, b);
            }

            @Override
            public void onError(Exception e) {
                log.info("On error: {}", e.getMessage());
            }
        };

        wsClient.connect();
        log.info("Connecting...");
        while (!ReadyState.OPEN.equals(wsClient.getReadyState())) {
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                log.error(e.getMessage(), e);
            }
        }
        log.info("Connected");

        wsClient.send("hello");

        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            String line = scanner.next();
            wsClient.send(line);
        }
        wsClient.close();
    }
}

代码的执行过程就是新建一个 WebSocketClient 并实现其处理消息的接口方法, 使用 10001 作为 sessionId 进行连接, 在连接成功后, 不断读取键盘输入 (System.in), 将输入的字符串发送给服务端.

运行示例

示例是一个普通的 Spring Boot jar项目, 可以通过mvn clean package进行编译, 再通过java -jar ws-demo01.jar运行, 启动后工作在8763端口

然后运行 SocketClient.java, 可以观察到服务端接收到的消息.

服务端可以通过浏览器访问 http://127.0.0.1:8763/msg?sessionId=10001&msg=123 向客户端发送消息.

结论

以上说明并演示了原生的 Websocket 实现方式, 可以尝试运行多个 SocketClient, 使用相同或不同的 server sessionId 路径, 观察通信的变化情况.