With the continuous development of Internet technology, real-time communication has become an indispensable part of many application systems. In the field of Web applications, WebSocket technology has become one of the main means of real-time communication. On the Java platform, the Java API also provides a set of WebSocket APIs, which can facilitate WebSocket development.

This article will focus on how to use WebSocket API for real-time communication in Java API development. In the process of implementing WebSocket communication, we will explain it in the following aspects:

1. Introduction to WebSocket protocol
2. Basic use of WebSocket API
3. WebSocket API thread model
4. Advanced usage scenarios of WebSocket API

1. Introduction to WebSocket protocol

The WebSocket protocol is a new protocol in HTML5, which implements full-duplex communication between the browser and the server. Before the emergence of the WebSocket protocol, the communication between the browser and the server was based on the HTTP protocol. The HTTP protocol was a half-duplex communication, that is, it could only communicate in one way, and the server could not actively send messages to the client. The WebSocket protocol allows true two-way communication between the server and the client.

An important feature of the WebSocket protocol is that it is based on the TCP protocol. When establishing a WebSocket connection, the client and server will first perform a TCP handshake, and then encapsulate the WebSocket protocol data in an HTTP protocol data frame to achieve two-way communication.

2. Basic use of WebSocket API

The WebSocket API in Java API is included in the javax.websocket package, which provides a set of WebSocket standard API interfaces and related class libraries, which can be used Used to implement various operations of WebSocket communication.

The following is the basic usage process of WebSocket API:

1. Creating a WebSocket server

You need to define a server endpoint through which a WebSocket connection can be established. and receive and send messages. This endpoint needs to inherit the javax.websocket.Endpoint class and implement key methods such as onOpen, onClose, onMessage, and onError.

2. Creating a WebSocket client

You need to specify the address of the WebSocket server and use the WebSocket client object to connect to the server.

3. Send a message

WebSocket communication is based on messages. You can use the send method provided by the javax.websocket.Session interface to send messages.

4. Receive messages

The logic of message reception needs to be implemented in both the server and the client. You can override the onMessage method to implement the corresponding logic.

The following is an example of using the WebSocket API:

Server-side code:

@ServerEndpoint("/server")
public class WebSocketServer {

    @OnOpen
    public void onOpen(Session session) {
        System.out.println("WebSocket opened: " + session.getId());
    }

    @OnClose
    public void onClose(Session session) {
        System.out.println("WebSocket closed: " + session.getId());
    }

    @OnMessage
    public void onMessage(String message, Session session) {
        System.out.println("WebSocket received message: " + message);
        try {
            session.getBasicRemote().sendText("Server received message: " + message);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }

    @OnError
    public void onError(Session session, Throwable throwable) {
        System.out.println("WebSocket error: " + throwable.getMessage());
    }
}

Client-side code:

URI uri = new URI("ws://localhost:8080/server");

WebSocketContainer container = ContainerProvider.getWebSocketContainer();
Session session = container.connectToServer(MyClient.class, uri);

session.getBasicRemote().sendText("Hello Server!");

Note: In the client, MyClient .class needs to implement the javax.websocket.ClientEndpoint interface and override the onMessage method.

3. WebSocket API thread model

The thread model in WebSocket API is quite special. WebSocket communication is built on Web containers (such as Tomcat, Jetty, etc.), so the thread model in the WebSocket API also depends on the thread model of the Web container. Since WebSocket creates some fixed thread pools in the Web container, special attention needs to be paid to thread safety issues.

WebSocket API provides two annotations: @OnOpen and @OnClose, which can be used to perform related logical operations when establishing and disconnecting WebSocket connections. In these two callback methods, if database operations or other time-consuming operations are required, the connection should be released immediately, otherwise the performance of the web container may be affected.

4. Advanced usage scenarios of WebSocket API

In addition to the above basic usage scenarios, WebSocket API also provides some advanced usage scenarios, such as using annotations to write endpoints and using interceptors to write Endpoints, writing endpoints programmatically, and more.

Due to space limitations, this article cannot introduce these advanced usage scenarios in detail. Readers can study it in combination with official documents.

Summary

This article mainly introduces how to use WebSocket API for real-time communication in Java API development, including an introduction to the WebSocket protocol, the basic use of WebSocket API, and the threading model of WebSocket API and advanced usage scenarios for the WebSocket API. By studying this article, readers can have a preliminary understanding of the programming ideas and implementation methods of WebSocket API, and then better cope with the development needs of real-time communication.

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