How can a Java server proactively push data?

2 years ago
Olivia Parker
2 minutes

Java server can utilize WebSocket for pushing data actively. WebSocket is a protocol that enables full-duplex communication over a single TCP connection, allowing real-time data exchange between clients and servers.

Firstly, you need to create a WebSocket server on a Java server. You can use the Java WebSocket API in the Java library to achieve this. Below is a simple example:

import javax.websocket.*;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;

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

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

    @OnMessage
    public void onMessage(String message, Session session) throws IOException {
        System.out.println("Received message from client: " + message);
        session.getBasicRemote().sendText("Hello client!");
    }

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

    @OnError
    public void onError(Throwable error) {
        System.err.println("WebSocket error: " + error.getMessage());
    }
}

You can then communicate with the server using the WebSocket API in JavaScript or other languages in the client. Send messages to the server via WebSocket and receive messages from the server.

Here is a simple example using JavaScript:

var socket = new WebSocket("ws://localhost:8080/websocket");

socket.onopen = function() {
    console.log("WebSocket opened");
    socket.send("Hello server!");
};

socket.onmessage = function(event) {
    console.log("Received message from server: " + event.data);
};

socket.onclose = function() {
    console.log("WebSocket closed");
};

socket.onerror = function(error) {
    console.error("WebSocket error: " + error);
};

In the examples mentioned above, a message is sent to the server when the WebSocket connection is successfully established. Upon receiving the message, the server will send a reply back to the client.

In this way, the server can actively push data to the client. You can use session.getBasicRemote().sendText() method to send messages to the client from anywhere on the server side.

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