在程序中创建一个简单的websocket，其中onOpen方法被调用

Question

我找到了一个代码来创建一个简单的websocket连接。在主函数中，只有WebsocketClientEndpoint的构造函数被调用，我没有看到在构造函数中调用onOpen函数。输出结果中"opening websocket"按照onOpen函数的设置打印。谁能告诉我onOpen函数的调用发生在哪里?

TestApp.java:

package testapp;
import java.net.URI;
import java.net.URISyntaxException;
public class TestApp {
public static void main(String[] args) {
    try {
        // open websocket
        final WebsocketClientEndpoint clientEndPoint = new WebsocketClientEndpoint(new URI("wss://real.okcoin.cn:10440/websocket/okcoinapi"));
        // add listener
        clientEndPoint.addMessageHandler(new WebsocketClientEndpoint.MessageHandler() {
            public void handleMessage(String message) {
                System.out.println(message);
            }
        });
        // send message to websocket
        clientEndPoint.sendMessage("{'event':'addChannel','channel':'ok_btccny_ticker'}");
        // wait 5 seconds for messages from websocket
        Thread.sleep(5000);
    } catch (InterruptedException ex) {
        System.err.println("InterruptedException exception: " + ex.getMessage());
    } catch (URISyntaxException ex) {
        System.err.println("URISyntaxException exception: " + ex.getMessage());
    }
}

}

WebsocketClientEndpoint.java

package testapp;
import java.net.URI;
import javax.websocket.ClientEndpoint;
import javax.websocket.CloseReason;
import javax.websocket.ContainerProvider;
import javax.websocket.OnClose;
import javax.websocket.OnMessage;
import javax.websocket.OnOpen;
import javax.websocket.Session;
import javax.websocket.WebSocketContainer;
 /**
 * ChatServer Client
 *
 * @author Jiji_Sasidharan
 */
@ClientEndpoint
public class WebsocketClientEndpoint {
Session userSession = null;
private MessageHandler messageHandler;
public WebsocketClientEndpoint(URI endpointURI) {
    try {
        WebSocketContainer container = ContainerProvider.getWebSocketContainer();
        container.connectToServer(this, endpointURI);
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}
/**
 * Callback hook for Connection open events.
 *
 * @param userSession the userSession which is opened.
 */
@OnOpen
public void onOpen(Session userSession) {
    System.out.println("opening websocket");
    this.userSession = userSession;
}
/**
 * Callback hook for Connection close events.
 *
 * @param userSession the userSession which is getting closed.
 * @param reason the reason for connection close
 */
@OnClose
public void onClose(Session userSession, CloseReason reason) {
    System.out.println("closing websocket");
    this.userSession = null;
}
/**
 * Callback hook for Message Events. This method will be invoked when a client send a message.
 *
 * @param message The text message
 */
@OnMessage
public void onMessage(String message) {
    if (this.messageHandler != null) {
        this.messageHandler.handleMessage(message);
    }
}
/**
 * register message handler
 *
 * @param message
 */
public void addMessageHandler(MessageHandler msgHandler) {
    this.messageHandler = msgHandler;
}
/**
 * Send a message.
 *
 * @param user
 * @param message
 */
public void sendMessage(String message) {
    this.userSession.getAsyncRemote().sendText(message);
}
/**
 * Message handler.
 *
 * @author Jiji_Sasidharan
 */
public static interface MessageHandler {
    public void handleMessage(String message);
}
}

Answer 1

您必须阅读注释的工作原理才能理解这一点。@OnOpen是一个注释。@OnOpen允许我们拦截新会话的创建。

注释类型OnOpen

@Retention(值=运行时)
@Target (value =方法)
public @interface OnOpen

这个方法级注释可以用来修饰Java方法当一个新的web套接字会话打开时，它希望被调用。

方法只能接受以下参数:-

可选会话参数
可选EndpointConfig参数
0 ~ n用PathParam注释的字符串参数。

参数可以按任意顺序出现。

Answer 2

当你的WebsocketClientEndpoint的构造函数被调用时，它将尝试打开一个连接到位于endPointURI的websocket服务器，并通过编写@clientEndPoint注释来扩展EndPoint类。因此，所有的注释，如@OnOpen, @OnMessage, OnClose将根据从服务器接收到的信号被调用。因此，当连接自动打开时，将调用带有@OnOpen注释的函数