Java - 下载后开始上传

Question

我的程序只能执行 1 笔交易，即 下载或上传 但不能 先下载后上传

服务器:

    ServerSocket serverSocket = new ServerSocket(4444);
    Socket socket = serverSocket.accept();

    /* GET */
    InputStream is = socket.getInputStream();        
    BufferedOutputStream bos =  new BufferedOutputStream(new FileOutputStream("E:\\23c-dl.mkv"));


    int count;
    byte[] bytes = new byte[8192];

    while ((count = is.read(bytes)) > 0) {
        bos.write(bytes, 0, count);
        System.out.println("-->" + count);
    }

    System.out.println("DONE DOWNLOADING");


    /* SEND */
    BufferedInputStream fileInput = new BufferedInputStream(new FileInputStream(new File("E:\\23s.mkv")));
    BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());

    int count2;
    byte[] bytes2 = new byte[8192];

    while ((count2 = fileInput.read(bytes2)) > 0) {
        out.write(bytes2, 0, count2);
        System.out.println("--> " + count2);
    }

    /* CLOSE */
    socket.close();
    serverSocket.close();

客户

    Socket socket = new Socket("127.0.0.1", 4444);

    /* SEND */
    BufferedInputStream fileInput = new BufferedInputStream(new FileInputStream(new File("E:\\23c.mkv")));
    BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());

    int count;        
    byte[] bytes = new byte[8192];

    while ((count = fileInput.read(bytes)) > 0) {
        out.write(bytes, 0, count);
        System.out.println("-->" + count);
    }
    System.out.println("DONE UPLOADING");

    /* GET */
    InputStream is = socket.getInputStream();        
    BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("E:\\23s-dl.mkv"));

    int count2; 
    byte[] bytes2 = new byte[8192];

    while ((count2 = is.read(bytes2)) > 0) {
        bos.write(bytes2, 0, count2);
        System.out.println("-->" + count2);
    }

    /* CLOSE */
    socket.close();

如果我注释掉服务器的获取和客户端的发送:程序可以正常工作。服务器可以下载该文件。

如果我注释掉服务器的发送和客户端的获取:程序可以正常工作。 客户端可以下载该文件。

不注释任何内容:只有服务器可以下载该文件。 有什么问题吗？

Answer 1

这是因为一旦您开始从输入流(在服务器端)读取，您的代码将被阻止(直到客户端关闭其自己的输出流)。要调查这种情况，请运行您的服务器，然后使用 telnet 连接到它，如下所示:

telnet 127.0.0.1 4444

键入多行，每行后按 Enter 键。并看到您的服务器将为每个字符串打印 -->，并且在您关闭 telnet session 之前，服务器不会继续进行。

所以你的客户端应该向服务器发送一些数据。然后它应该关闭输出流并重新连接到服务器。同时服务器应该等待新的连接。然后客户端就可以从服务器下载文件了。

更一般地，您可以在单独的线程中读取套接字，这样您的主代码就不会挂起。

代码(我还稍微更改了文件名):

服务器

    ServerSocket serverSocket = new ServerSocket(4444);
    Socket socket = serverSocket.accept();

    /* GET */
    InputStream is = socket.getInputStream();        
    BufferedOutputStream bos =  new BufferedOutputStream(new FileOutputStream("serverlog.txt"));


    int count;
    byte[] bytes = new byte[8192];

    while ((count = is.read(bytes)) > 0) {
        bos.write(bytes, 0, count);
        System.out.println("-->" + count);
    }

    System.out.println("DONE DOWNLOADING");
    bos.close();
    socket.close();


    /* SEND */
    socket = serverSocket.accept();
    BufferedInputStream fileInput = new BufferedInputStream(new FileInputStream(new File("server.txt")));
    BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());

    int count2;
    byte[] bytes2 = new byte[8192];

    while ((count2 = fileInput.read(bytes2)) > 0) {
        out.write(bytes2, 0, count2);
        System.out.println("--> " + count2);
    }
    out.close();

    /* CLOSE */
    socket.close();
    serverSocket.close();

客户端

    Socket socket = new Socket("127.0.0.1", 4444);

    /* SEND */
    BufferedInputStream fileInput = new BufferedInputStream(new FileInputStream(new File("client.txt")));
    BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());
    int count;        
    byte[] bytes = new byte[8192];
    while ((count = fileInput.read(bytes)) > 0) {
    out.write(bytes, 0, count);
        System.out.println("-->" + count);
    }
    System.out.println("DONE UPLOADING");
    out.close();
    socket.close();

    /* GET */
    socket = new Socket("127.0.0.1", 4444);
    InputStream is = socket.getInputStream();        
    BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream("clientlog.txt"));

    int count2; 
    byte[] bytes2 = new byte[8192];

    while ((count2 = is.read(bytes2)) > 0) {
        bos.write(bytes2, 0, count2);
        System.out.println("-->" + count2);
    }
    bos.close();

    /* CLOSE */
    socket.close();
}