使用Java实现类似Comet风格的web app

针对使用Java实现类似Comet风格的web app，我可以给您提供以下的攻略：

一、了解Comet

Comet是一种Web服务器向浏览器发送异步数据的技术。在传统的Web应用程序中，客户端通过HTTP协议发起请求，服务器收到请求后即时返回响应。而Comet则是一种在Web服务器与浏览器之间建立持久连接的技术，使得服务端可以在有数据更新时主动向客户端推送数据。

二、使用CometD

CometD是一个开源的Comet框架，支持数万个客户端在线，支持通过多种方式（如WebSocket、LongPolling）与客户端通信。下面我们演示如何使用CometD构建一个Comet风格的web app。

1. 添加CometD依赖

首先，需要在项目中添加CometD的maven依赖：

<dependency>
    <groupId>org.cometd.java</groupId>
    <artifactId>cometd-java-server</artifactId>
    <version>4.0.6</version>
</dependency>

2. 编写CometD服务

接下来，我们编写一个CometD服务，用于向所有连接的客户端推送消息。该服务继承自org.cometd.bayeux.server.AbstractService，并实现了一个publish方法，用于将消息推送给所有客户端：

import org.cometd.bayeux.server.AbstractService;
import org.cometd.bayeux.server.LocalSession;
import org.cometd.bayeux.server.ServerMessage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class MyCometDService extends AbstractService {

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

    public MyCometDService(String name) {
        super(name);
    }

    @Override
    public void init() {
        super.init();
        addService("/chat", "chatMessage");
    }

    public void chatMessage(ServerSession remote, ServerMessage message) {
        String user = (String) message.get("user");
        String text = (String) message.get("text");
        // 推送消息给所有客户端
        for (LocalSession session : getSessions()) {
            if (session.isConnected()) {
                session.deliver(getServerSession(), "/chat", text, null);
            }
        }
        logger.debug("Received chat message from user '{}' with text: '{}'", user, text);
    }
}

3. 启动CometD服务

下面是一个使用Jetty启动CometD服务的示例：

import org.cometd.bayeux.server.BayeuxServer;
import org.cometd.server.BayeuxServerImpl;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;

public class CometDServer {

    public static void main(String[] args) throws Exception {
        int port = 8080;
        Server server = new Server(port);

        ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
        context.setContextPath("/");
        server.setHandler(context);

        BayeuxServerImpl bayeuxServer = new BayeuxServerImpl();
        bayeuxServer.setOption(BayeuxServerImpl.LOG_LEVEL, "debug");

        MyCometDService cometDService = new MyCometDService("chat");
        cometDService.setBayeux(bayeuxServer);
        cometDService.init();

        bayeuxServer.addService(cometDService);

        ServletHolder cometdServletHolder = new ServletHolder("cometd", org.cometd.server.CometDServlet.class);
        cometdServletHolder.setInitParameter("transports", "websocket, long-polling");
        cometdServletHolder.setInitParameter("ws.cometdURLMapping", "/cometd/*");
        cometdServletHolder.setInitParameter("timeout", "240000");
        cometdServletHolder.setInitParameter("interval", "100");
        context.addServlet(cometdServletHolder, "/cometd/*");

        server.start();
        server.join();
    }
}

4. 编写客户端

我们可以使用CometD提供的JavaScript库，编写一个简单的客户端，用于实时接收服务端推送的消息，并将消息显示在页面上：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <script src="/cometd/javascript/jquery/jquery-3.4.1.min.js"></script>
    <script src="/cometd/javascript/cometd.js"></script>
    <script src="/cometd/javascript/jquery/jquery.cometd.js"></script>
</head>
<body>
    <script>
        // 连接CometD服务
        var cometd = new $.Cometd();
        cometd.configure({
            url: location.protocol + "//" + location.hostname + (location.port ? ":" + location.port : "") + "/cometd",
            logLevel: "debug"
        });
        cometd.handshake();
        cometd.subscribe("/chat", function(message) {
            console.log("Received chat message: " + message.data);
            var li = document.createElement("li");
            li.textContent = message.data;
            document.getElementById("chatList").appendChild(li);
        });

        // 发送聊天消息
        var input = document.getElementById("input");
        var button = document.getElementById("button");
        button.onclick = function() {
            var text = input.value;
            input.value = "";
            cometd.publish("/chat", {user: "guest", text: text});
        }
    </script>

    <input type="text" id="input">
    <button id="button">发送</button>
    <ul id="chatList"></ul>
</body>
</html>

三、另一种实现方式

除了使用CometD，我们还可以使用Spring WebFlux + WebSocket来实现Comet风格的web app。下面是一个使用Spring WebFlux + WebSocket实现的demo：

1. 添加依赖

首先，需要在项目中添加spring-webflux和spring-boot-starter-webflux依赖：

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

2. 编写WebSocketHandler

接下来，我们编写一个WebSocketHandler，通过WebSocket向所有连接的客户端推送消息：

import org.springframework.http.codec.websocket.WebSocketHandler;
import org.springframework.http.codec.websocket.WebSocketSession;
import org.springframework.stereotype.Component;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

@Component
public class MyWebSocketHandler implements WebSocketHandler {

    private final Flux<String> chatMessages = createChatMessages();

    private Flux<String> createChatMessages() {
        // 模拟从数据库或者其他地方获取聊天消息
        return Flux.interval(Duration.ofSeconds(1))
                .zipWith(Flux.just("张三", "李四", "王五", "赵六"))
                .map(t -> String.format("%s 说：%s", t.getT2(), UUID.randomUUID().toString()));
    }

    @Override
    public Mono<Void> handle(WebSocketSession session) {
        return session.send(chatMessages.map(session::textMessage))
                .and(session.receive()
                        .map(webSocketMessage -> webSocketMessage.getPayloadAsText() + " - from server")
                        .map(session::textMessage)
                        .flatMap(session::send));
    }
}

3. 配置WebSocket

下面是配置WebSocket的代码：

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.http.server.reactive.WebSocketHandler;
import org.springframework.http.server.reactive.WebSocketService;
import org.springframework.http.server.reactive.WebSocketSession;
import org.springframework.web.reactive.config.EnableWebFlux;
import org.springframework.web.reactive.config.WebFluxConfigurer;
import org.springframework.web.reactive.handler.SimpleUrlHandlerMapping;
import reactor.core.publisher.Mono;

import java.util.HashMap;
import java.util.Map;

@Configuration
@EnableWebFlux
public class WebConfig implements WebFluxConfigurer {

    @Bean
    public WebSocketService myWebSocketService() {
        return new MyWebSocketService();
    }

    @Bean
    public MyWebSocketHandler myWebSocketHandler() {
        return new MyWebSocketHandler();
    }

    @Bean
    public SimpleUrlHandlerMapping myWebSocketHandlerMapping() {
        Map<String, WebSocketHandler> map = new HashMap<>();
        map.put("/ws", myWebSocketHandler());
        SimpleUrlHandlerMapping handlerMapping = new SimpleUrlHandlerMapping();
        handlerMapping.setUrlMap(map);
        handlerMapping.setOrder(-1);
        return handlerMapping;
    }

    private static class MyWebSocketService implements WebSocketService {
        @Override
        public Mono<Void> handleRequest(WebSocketSession session, WebSocketHandler handler) {
            return handler.handle(session);
        }

        @Override
        public void setWebSocketFactory(WebSocketListenerFactory factory) {
        }

        @Override
        public void afterConnectionEstablished(WebSocketSession session) {
        }

        @Override
        public void afterConnectionClosed(WebSocketSession session, CloseStatus closeStatus) {
        }

        @Override
        public void handleTransportError(WebSocketSession session, Throwable exception) {
        }

        @Override
        public List<String> getSubProtocols() {
            return Collections.emptyList();
        }

        @Override
        public void setHandshakeTimeout(Duration handshakeTimeout) {
        }

        @Override
        public void setSendTimeLimit(Duration timeLimit) {
        }

        @Override
        public void setSendBufferSizeLimit(int bufferSizeLimit) {
        }

        @Override
        public boolean supportsPartialMessages() {
            return false;
        }
    }
}

4. 编写客户端

我们可以使用JavaScript编写一个简单的客户端，用于实时接收服务端推送的消息，并将消息显示在页面上：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <script src="/webjars/jquery/3.4.1/jquery.min.js"></script>
    <script>
        // 建立WebSocket连接
        var webSocket = new WebSocket("ws://" + location.hostname + (location.port ? ":" + location.port : "") + "/ws");
        webSocket.onmessage = function(event) {
            console.log("Received chat message: " + event.data);
            var li = document.createElement("li");
            li.textContent = event.data;
            document.getElementById("chatList").appendChild(li);
        };

        // 发送聊天消息
        var input = document.getElementById("input");
        var button = document.getElementById("button");
        button.onclick = function() {
            var text = input.value;
            input.value = "";
            webSocket.send(text);
        }
    </script>
</head>
<body>
    <input type="text" id="input">
    <button id="button">发送</button>
    <ul id="chatList"></ul>
</body>
</html>

以上就是使用Java实现类似Comet风格的web app的详细攻略了，希望能对您有所帮助。

本站文章如无特殊说明，均为本站原创，如若转载，请注明出处：使用Java实现类似Comet风格的web app - Python技术站

使用Java实现类似Comet风格的web app

一、了解Comet

二、使用CometD

1. 添加CometD依赖

2. 编写CometD服务

3. 启动CometD服务

4. 编写客户端

三、另一种实现方式

1. 添加依赖

2. 编写WebSocketHandler

3. 配置WebSocket

4. 编写客户端

相关文章