前言

上一章实现了websocket传输文本信息，实际上网络传输的都是二进制0和1，因而也可以传输文件。

demo

实现websocket传输文件，使用上次的示例，client

package com.feng.socket.client;

import org.java_websocket.client.WebSocketClient;
import org.java_websocket.enums.ReadyState;
import org.java_websocket.handshake.ServerHandshake;

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.OpenOption;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Scanner;

public class SocketClient {

    public static void main(String[] args) throws URISyntaxException, IOException, InterruptedException {
        Object condition = new Object();
        WebSocketClient webSocketClient = new WebSocketClient(new URI("ws://127.0.0.1:8083/websocket/server/10001")) {
            @Override
            public void onOpen(ServerHandshake serverHandshake) {
                System.out.println(serverHandshake.getHttpStatus() + " : " + serverHandshake.getHttpStatusMessage());
            }

            @Override
            public void onMessage(String s) {
                System.out.println("receive msg is " + s);
            }

            @Override
            public void onMessage(ByteBuffer bytes) {
                //To overwrite
                byte mark = bytes.get(0);
                if (mark == 2) {
                    synchronized (condition) {
                        condition.notify();
                    }
                    System.out.println("receive ack for file info");
                } else if (mark == 6){
                    synchronized (condition) {
                        condition.notify();
                    }
                    System.out.println("receive ack for file end");
                }
            }

            @Override
            public void onClose(int i, String s, boolean b) {
                System.out.println(s);
            }

            @Override
            public void onError(Exception e) {
                e.printStackTrace();
            }
        };
        webSocketClient.connect();
        while (!ReadyState.OPEN.equals(webSocketClient.getReadyState())) {
            System.out.println("wait for connecting ...");
        }

//        webSocketClient.send("hello");
//        Scanner scanner = new Scanner(System.in);
//        while (scanner.hasNext()) {
//            String line = scanner.next();
//            webSocketClient.send(line);
//        }
        System.out.println("start websocket client...");



        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            if ("1".equals(scanner.next()))
                sendFile(webSocketClient, condition);
        }
    }

    public static void sendFile(WebSocketClient webSocketClient, Object condition){
        new Thread(() -> {
            try {
                SeekableByteChannel byteChannel = Files.newByteChannel(Path.of("/Users/huahua/IdeaProjects/websocket-demo/websocket-demo/socket-client/src/main/resources/Thunder5.rar"),
                        new StandardOpenOption[]{StandardOpenOption.READ});
                ByteBuffer byteBuffer = ByteBuffer.allocate(4*1024);
                byteBuffer.put((byte)1);
                String info = "{\"fileName\": \"Thunder5.rar\", \"fileSize\":"+byteChannel.size()+"}";
                byteBuffer.put(info.getBytes(StandardCharsets.UTF_8));
                byteBuffer.flip();
                webSocketClient.send(byteBuffer);
                byteBuffer.clear();
                synchronized (condition) {
                    condition.wait();
                }

                byteBuffer.put((byte)3);
                while (byteChannel.read(byteBuffer) > 0) {
                    byteBuffer.flip();
                    webSocketClient.send(byteBuffer);
                    byteBuffer.clear();
                    byteBuffer.put((byte)3);
                }

                byteBuffer.clear();
                byteBuffer.put((byte)5);
                byteBuffer.put("end".getBytes(StandardCharsets.UTF_8));
                byteBuffer.flip();
                webSocketClient.send(byteBuffer);
                synchronized (condition) {
                    condition.wait();
                }

                byteChannel.close();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }).start();
    }
}

Server端使用Tomcat的websocket

package com.feng.socket.admin;

import com.fasterxml.jackson.databind.json.JsonMapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.websocket.*;
import javax.websocket.server.PathParam;
import javax.websocket.server.ServerEndpoint;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.channels.SeekableByteChannel;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.StandardOpenOption;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

@Component
@ServerEndpoint("/websocket/server/{sessionId}")
public class SocketServer {

    private static final Logger LOGGER = LoggerFactory.getLogger(SocketServer.class);
    private static Map<String, Session> sessionMap = new ConcurrentHashMap<>();

    private String sessionId = "";

    private SeekableByteChannel byteChannel;

    @OnOpen
    public void onOpen(Session session, @PathParam("sessionId") String sessionId) {
        this.sessionId = sessionId;
        sessionMap.put(sessionId, session);
        LOGGER.info("new connect， sessionId is " + sessionId);
    }

    @OnClose
    public void onClose() {
        sessionMap.remove(sessionId);
        LOGGER.info("close socket, the sessionId is " + sessionId);

    }

    @OnMessage
    public void onMessage(String message, Session session) {
        LOGGER.info("--------- receive message: " + message);
    }

    @OnMessage
    public void onMessage(ByteBuffer byteBuffer, Session session) throws IOException {
        if (byteBuffer.limit() == 0) {
            return;
        }
        byte mark = byteBuffer.get(0);
        if (mark == 1) {
            byteBuffer.get();
            String info = new String(byteBuffer.array(),
                    byteBuffer.position(),
                    byteBuffer.limit() - byteBuffer.position());
            FileInfo fileInfo = new JsonMapper().readValue(info, FileInfo.class);
            byteChannel = Files.newByteChannel(Path.of("/Users/huahua/"+fileInfo.getFileName()),
                    new StandardOpenOption[]{StandardOpenOption.CREATE, StandardOpenOption.WRITE});
            //ack
            ByteBuffer buffer = ByteBuffer.allocate(4096);
            buffer.put((byte) 2);
            buffer.put("receive fileinfo".getBytes(StandardCharsets.UTF_8));
            buffer.flip();
            session.getBasicRemote().sendBinary(buffer);
        } else if (mark == 3) {
            byteBuffer.get();
            byteChannel.write(byteBuffer);
        } else if (mark == 5) {
            //ack
            ByteBuffer buffer = ByteBuffer.allocate(4096);
            buffer.clear();
            buffer.put((byte) 6);
            buffer.put("receive end".getBytes(StandardCharsets.UTF_8));
            buffer.flip();
            session.getBasicRemote().sendBinary(buffer);
            byteChannel.close();
            byteChannel = null;
        }
    }

    @OnError
    public void onError(Session session, Throwable error) {
        LOGGER.error(error.getMessage(), error);
    }

    public static void sendMessage(Session session, String message) throws IOException {
        session.getBasicRemote().sendText(message);
    }

    public static Session getSession(String sessionId){
        return sessionMap.get(sessionId);
    }
}

实现思路

 

 经验分享

实际在使用过程中有2个问题

1. Tomcat的websocket默认最大只能发送8K的数据

根本原因是

org.apache.tomcat.websocket.WsSession

    // Buffers
    static final int DEFAULT_BUFFER_SIZE = Integer.getInteger(
            "org.apache.tomcat.websocket.DEFAULT_BUFFER_SIZE", 8 * 1024)
            .intValue();

    private volatile int maxBinaryMessageBufferSize = Constants.DEFAULT_BUFFER_SIZE;
    private volatile int maxTextMessageBufferSize = Constants.DEFAULT_BUFFER_SIZE;

通过系统变量，或者JVM -D参数可设置

org.apache.tomcat.websocket.DEFAULT_BUFFER_SIZE

2. json格式化问题，如果对象的属性有byte[]数组

fastjson和Jackson是使用Base64的方式处理的gson是真byte[]数组存储，只是字符串是包括的。

  

总结

实际上websocket是tcp上的双工协议，传输文件是没有问题的，只是需要定义应用层协议才行。如果使用Tomcat的websocket传输，注意传输内容大小。而且HTTP 2.0和HTTP 3.0 并不能使用websocket，尤其是http 3.0 UDP协议。