Java API实现WebSocket客户端

迷南。 2022-08-18 13:16 203阅读 0赞

上一篇是说浏览器与服务器建立WebSocket通信，而这篇来通过WebSocket-api提供的接口来实现客户端的功能。

客户端主要也是通过注解的方式来实现，但是创建的方式会用到其他类，注解为@ClientEndpoint，其他注解一样，WebSocketClient.java具体代码如下：

@ClientEndpoint
    public class WebSocketClient {
        
    
        private Logger logger = Logger.getLogger(WebSocketServer.class);
        private Session session;
    
        @OnOpen
        public void open(Session session){
            logger.info("Client WebSocket is opening...");
            this.session = session;
        }
    
        @OnMessage
        public void onMessage(String message){
            logger.info("Server send message: " + message);
        }
    
        @OnClose
        public void onClose(){
            logger.info("Websocket closed");
        }
    
    
        @OnError
        public void onError(Session session, Throwable t) {
            t.printStackTrace();
        }
    
        public void send(String message){
            this.session.getAsyncRemote().sendText(message);
        }
    
        public void close() throws IOException{
            if(this.session.isOpen()){
                this.session.close();
            }
        }
    }

另外添加两个方法`send`和`close`，可以主动发送消息和关闭连接。只要可以获取到建立连接的`session`，就可以进行相关的操作，如消息发送、状态判断等等。  
以上为客户端的简单实现，接下来，来看看`@ClientEndpoint`注解的代码：

@Retention(RetentionPolicy.RUNTIME)
    @Target({java.lang.annotation.ElementType.TYPE})
    public @interface ClientEndpoint
    {
        
      String[] subprotocols() default {};
    
      Class<? extends Decoder>[] decoders() default {};
    
      Class<? extends Encoder>[] encoders() default {};
    
      Class<? extends ClientEndpointConfig.Configurator> configurator() default ClientEndpointConfig.Configurator.class;
    }

可以看见，有四个配置参数，接下来分别对这些配置进行实现：

> subprotocols: 为字符串数组，表示支持的子协议名称列表

无特别

> Decoder的实现：

public class SampleDecoder implements Decoder.Text<String>{
        
    
        public void init(EndpointConfig paramEndpointConfig) {
            // Auto-generated method stub
        }
    
        public void destroy() {
            // Auto-generated method stub
        }
    
        public String decode(String paramString) throws DecodeException {
            // Auto-generated method stub
            return paramString.toLowerCase();
        }
    
        public boolean willDecode(String paramString) {
            // Auto-generated method stub
            return true;
        }
    
    }

> Encoder实现

public class SimpleEncoder implements javax.websocket.Encoder.Text<String> {
        
    
        public void init(EndpointConfig paramEndpointConfig) {
            //Auto-generated method stub
            System.out.println("Encoder init: " + paramEndpointConfig.getUserProperties());
        }
    
        public void destroy() {
            //Auto-generated method stub
        }
    
        public String encode(String paramT) throws EncodeException {
            //Auto-generated method stub
            return paramT.toUpperCase();
        }
    
    }

`encode`方法是接收到数据进行解码操作，如对字符串解码，对json格式转换为对象等等；

> Configurator实现

public class SampleConfigurator extends Configurator {
        
    
        @Override
        public void beforeRequest(Map<String, List<String>> headers) {
            //Auto-generated method stub
            System.out.println(headers);
        }
    
        @Override
        public void afterResponse(HandshakeResponse handshakeResponse) {
            //Auto-generated method stub
            System.out.println(handshakeResponse);
        }
    
    }

可以通过打印来查看这些参数是什么，我们通过函数名称就可以知道，`beforeRequest`是在请求之前调用，可以对请求头进行修改或者查看；`afterResponse`是在握手成功后调用的，`handshakeResponse`为握手响应头；

而现在的客户端配置如下：

@ClientEndpoint(
            configurator=SampleConfigurator.class,
            decoders={SampleDecoder.class},
            encoders={SimpleEncoder.class},
            subprotocols={
       "subprotocol1"})
    public class WebSocketClient {
        
    
        private Logger logger = Logger.getLogger(WebSocketServer.class);
        private Session session;
    
        ......
    }

添加主程序AppMain.java:

public class AppMain {
        
    
        public static void main(String[] args) 
                throws DeploymentException, IOException, URISyntaxException, InterruptedException {
            // Auto-generated method stub
            WebSocketContainer conmtainer = ContainerProvider.getWebSocketContainer();
            WebSocketClient client = new WebSocketClient();
            conmtainer.connectToServer(client, 
                    new URI("ws://localhost:8080/websocket/chat?query=Picasso"));
    
            int turn = 0;
            while(turn++ < 10){
                client.send("send text: " + turn);
                Thread.sleep(1000);
            }
            client.close();
        }
    
    }

先启动服务器，之后启动客户端的应用程序，查看控制台

服务端控制台：

2015-12-21 23:28:10,673  INFO (cc.eabour.websocket.filter.DispatcherFilter:30) - Request URL: http://localhost:8080/websocket/chat
    2015-12-21 23:28:10,684  INFO (cc.eabour.websocket.WebSocketServer:23) - WebSocket is opening...
    2015-12-21 23:28:10,685  INFO (cc.eabour.websocket.WebSocketServer:25) - Sesson id: 1a
    2015-12-21 23:28:10,685  INFO (cc.eabour.websocket.WebSocketServer:26) - Query string: query=Picasso
    2015-12-21 23:28:10,731  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: B
    2015-12-21 23:28:11,734  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: C
    2015-12-21 23:28:12,739  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: D
    2015-12-21 23:28:13,743  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: E
    2015-12-21 23:28:14,746  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: F
    2015-12-21 23:28:15,751  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: G
    2015-12-21 23:28:16,753  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: H
    2015-12-21 23:28:17,756  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: I
    2015-12-21 23:28:18,758  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: J
    2015-12-21 23:28:19,761  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: send text: K
    2015-12-21 23:28:20,764  INFO (cc.eabour.websocket.WebSocketServer:42) - Websocket closed

客户端控制台：

{
       Sec-WebSocket-Version=[13], Upgrade=[websocket], Host=[localhost:8080], Sec-WebSocket-Key=[Wwy8SvU9vSmJClaLPw+z1w==], Connection=[upgrade]}
    org.apache.tomcat.websocket.WsHandshakeResponse@dd550c
    Encoder init: {}
    2015-12-21 23:28:10,700  INFO (cc.eabour.websocket.WebSocketServer:31) - Client WebSocket is opening...
    2015-12-21 23:28:10,731  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:11,735  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:12,740  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:13,744  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:14,748  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:15,752  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:16,754  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:17,757  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:18,759  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    2015-12-21 23:28:19,762  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server

仔细一看，在注解中配置的Encoder和Decoder没有起作用，分别在encode和decode方法中添加打印语句，都没有生效：

public String decode(String paramString) throws DecodeException {
            // Auto-generated method stub
            return "MESS:" + paramString.toLowerCase();
        }
    
        .....
    
        public String encode(String paramT) throws EncodeException {
            //Auto-generated method stub
            System.out.println("encode: " + paramT);
            return "mess:" + paramT.toUpperCase();
        }

最后通过查看encode和decode方法的调用堆栈，而得知调用这些方法的方法为sendObject，这时才恍然大悟，当客户端发送的为Object类型的时候，才会去调用Encoder和Decoder，所以修改方法：

//WebSocketClient.java
    
        public void send(Object message){
            this.session.getAsyncRemote().sendObject(message);
        }

到此，大功告成：

--服务器
    2015-12-21 23:37:47,637  INFO (cc.eabour.websocket.WebSocketServer:23) - WebSocket is opening...
    2015-12-21 23:37:47,638  INFO (cc.eabour.websocket.WebSocketServer:25) - Sesson id: 1b
    2015-12-21 23:37:47,638  INFO (cc.eabour.websocket.WebSocketServer:26) - Query string: query=Picasso
    2015-12-21 23:37:47,670  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: mess:SEND TEXT: B
    2015-12-21 23:37:48,671  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: mess:SEND TEXT: C
    2015-12-21 23:37:49,673  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: mess:SEND TEXT: D
    2015-12-21 23:37:50,683  INFO (cc.eabour.websocket.WebSocketServer:32) - Client send message: mess:SEND TEXT: E
    ......
    --客户端
    {
       Sec-WebSocket-Version=[13], Upgrade=[websocket], Host=[localhost:8080], Sec-WebSocket-Key=[NGvTXYipeBUGuMn9SpwZWg==], Connection=[upgrade]}
    org.apache.tomcat.websocket.WsHandshakeResponse@1d28d39
    Encoder init: {}
    2015-12-21 23:37:47,639  INFO (cc.eabour.websocket.WebSocketServer:31) - Client WebSocket is opening...
    encode: send text: B
    2015-12-21 23:37:47,670  INFO (cc.eabour.websocket.WebSocketServer:37) - Server send message: Server message form Websocket server
    encode: send text: C
    ......

Java API WebSocket客户端基本实现，可以参照，实现更复杂的功能。

**不吝赐教**

项目Github地址：[https://github.com/FlowerBirds/WebSocketExplorer][https_github.com_FlowerBirds_WebSocketExplorer]

参考资料：

*  [https://tools.ietf.org/html/rfc6455\#section-11.5][https_tools.ietf.org_html_rfc6455_section-11.5]
 *  [https://tyrus.java.net/documentation/1.12/index/websocket-api.html][https_tyrus.java.net_documentation_1.12_index_websocket-api.html]

[https_github.com_FlowerBirds_WebSocketExplorer]: https://github.com/FlowerBirds/WebSocketExplorer
[https_tools.ietf.org_html_rfc6455_section-11.5]: https://tools.ietf.org/html/rfc6455#section-11.5
[https_tyrus.java.net_documentation_1.12_index_websocket-api.html]: https://tyrus.java.net/documentation/1.12/index/websocket-api.html