How to use Java to develop Websocket file transfer function

With the development of the Internet, file transfer has become an indispensable part of daily work and life. As a communication protocol that establishes a persistent connection between the browser and the server, Websocket has the characteristics of real-time and two-way transmission, making it an ideal choice for file transfer. This article will introduce how to use Java to develop Websocket file transfer function and provide specific code examples.

1. Create a Websocket server

To implement the file transfer function, you first need to create a Websocket server to receive and process client requests. The following is a sample code for creating a Websocket server using Java's Tomcat framework:

@ServerEndpoint("/upload")
public class FileUploadServer {

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

    @OnMessage
    public void onMessage(ByteBuffer byteBuffer, Session session) throws IOException {
        Path path = Paths.get("uploads", session.getId() + ".jpg");
        Files.write(path, byteBuffer.array());
        System.out.println("File uploaded: " + path.toString());
    }

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

    @OnError
    public void onError(Throwable e) {
        e.printStackTrace();
    }
}

In the above code, we use the @ServerEndpoint annotation to annotate a Websocket server and specify client access The URL is /upload. The server side provides four methods to handle client connections, receive file data, disconnect and handle exceptions respectively. Among them, the onMessage method is called when receiving file data, saves the file to the uploads folder, and uses the client's ID as the file name.

2. Create a Websocket client

Next, we need to create a Websocket client to send file data to the server. Below is the sample code for creating a Websocket client using Java's JavaFX framework:

public class FileUploadClient extends Application {

    private static final String SERVER_URI = "ws://localhost:8080/upload";

    private WebSocketClient client;

    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) {
        try {
            URI uri = new URI(SERVER_URI);
            client = new WebSocketClient(uri) {
                @Override
                public void onOpen(ServerHandshake handshakedata) {
                    System.out.println("Connected to server");
                }

                @Override
                public void onMessage(String message) {
                    System.out.println("Received message: " + message);
                }

                @Override
                public void onClose(int code, String reason, boolean remote) {
                    System.out.println("Disconnected from server");
                }

                @Override
                public void onError(Exception ex) {
                    ex.printStackTrace();
                }
            };
            client.connect();
        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
    }

    public void uploadFile(Path path) throws IOException {
        byte[] bytes = Files.readAllBytes(path);
        client.send(bytes);
        System.out.println("File uploaded: " + path.toString());
    }
}

In the above code, we have created a simple interface using JavaFX by connecting to the server-side URL ws://localhost :8080/upload, and implements four methods of the client to handle various stages of communication with the server. The uploadFile method is used to read the specified file into a byte array and send it to the server through the client.

3. Start the server and client

After completing the server and client code, we need to start them to test the file transfer function. First, you need to deploy the server-side code to Tomcat or other server that supports Java web applications, and start the server. You can then run the client code directly, launching the JavaFX application.

After the program runs, the client will establish a connection with the server, and the "Connected to server" prompt message will be printed on the console. Then, we can select the file to upload through the file selector on the interface and click the "Upload" button. The client will send the selected file to the server and print out the "File uploaded: file path" prompt message on the console.

4. Summary

This article introduces how to use Java to develop the Websocket file transfer function, and provides specific code examples for the server and client. Through the two-way communication and real-time nature of the Websocket protocol, we are able to achieve fast, efficient, and secure file transfer. I believe readers can further explore and apply Websocket file transfer technology based on the sample code provided in this article.

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