Question

我可以使用下面的代码将任何类型的文件上传到服务器。但是，在上传完成后，我在服务器上收到一条错误消息

java.net.SocketException: Socket is closed Exception in thread "Thread-0" java.lang.NullPointerException at Server2Connection.run(server1.java:407) at java.lang.Thread.run(Unknown Source)

server1.java: 407指的是服务器代码中的行switch (clientMsg)。该文件确实上传正确。但似乎我没有用.close指令做正确的事情。此后服务器不会断开连接，但客户端只会再次循环断开连接。任何人都可以告诉我在哪里弄乱吗？感谢。

服务器端：

public BufferedReader msgFromClient() throws IOException {
    BufferedReader receiveClientmsg = null;

    try {
        receiveClientmsg = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    } catch (IOException e) {
        System.out.println(e);
    }
    return receiveClientmsg;
}

public DataOutputStream outToClient() throws IOException {
    DataOutputStream sendClientmsg = null;

    try {
        sendClientmsg = new DataOutputStream(clientSocket.getOutputStream());
    } catch (IOException e) {
        System.out.println(e);
    }
    return sendClientmsg;
}

public void upload() throws IOException {
    byte[] mybytearray = new byte[8192];
    InputStream is = clientSocket.getInputStream();
    String file_name = msgFromClient().readLine();
    File rqstd_upld_file = new File(SERVER_FILE_LOCATION + file_name);

    if (rqstd_upld_file.exists()){
        outToClient().writeBytes("yes\n");
        outToClient().writeBytes("A file with the name " + file_name + " already exists on server\n");
        System.out.println("A file with the name " + file_name + " already exists");
    }
    else {
        outToClient().writeBytes("no\n");
        FileOutputStream fos = new FileOutputStream(SERVER_FILE_LOCATION +"\\"+ file_name);
        BufferedOutputStream bos = new BufferedOutputStream(fos);

        int count;
        System.out.println("Downloading " + file_name + " ...");
        outToClient().writeBytes("Uploading. Please wait...\n");
        while ((count = is.read(mybytearray)) > 0){
            bos.write(mybytearray, 0, count);
        }
        System.out.println("Download Successful");
        is.close();
        bos.close();
    }
}
try {
        while (true) {
            //Message sent by the client
            String clientMsg = server.msgFromClient().readLine();               

            switch (clientMsg) {
            case "1":
                //'Upload file' command from client
                System.out.print("\nCommand from " + clientSocket.getInetAddress() + ":"+ clientSocket.getPort()+" : ");
                System.out.println("Upload file");
                server.upload();
                break;

            case "1fail":
                //In case client fails to find the file it wants to upload
                System.out.print("\nCommand from " + clientSocket.getInetAddress() + ":"+ clientSocket.getPort()+" : ");
                System.out.println("Upload file");
                System.out.println("Client could not upload: File did not exist on client machine\n");
                break;
}
catch(IOException e){
        System.out.println(e);
    }

客户方：

while (true) {
try{
Scanner scan0 = new Scanner(System.in);
String command = scan0.nextLine();

switch (command) {
case "1":
    //Upload file
    File file_to_upload = null;
    System.out.print("Enter file path: ");
    Scanner scan = new Scanner(System.in);
    String pathname = scan.nextLine();
    System.out.print("Enter file name: ");
    Scanner scan1 = new Scanner(System.in);
    String file = scan1.nextLine();
    Path path = Paths.get(pathname, file);
    file_to_upload = new File(path.toString());

    if (file_to_upload.exists()){   
        outToServer.writeBytes(command + '\n');
        outToServer.writeBytes(file + '\n');
        String existsOnServer = msgFromServer.readLine();

        switch (existsOnServer) {
        case "yes":
            System.out.println('\n'+ msgFromServer.readLine() + '\n');
            break;
        case "no":
            int count;
            System.out.println('\n'+ msgFromServer.readLine() + '\n');
            byte[] bytearray = new byte[8192];
            InputStream in = new FileInputStream(file_to_upload);
            BufferedInputStream bis = new BufferedInputStream(in);
            OutputStream os = client1.getOutputStream();
                while ((count = bis.read(bytearray)) > 0){
                os.write(bytearray, 0, count);
            }
            System.out.println("Done Uploading");
            os.close();
            in.close();
            bis.close();
            break;
        }
    }
    else{
        System.out.println("File " + path + " does not exist\n");
        outToServer.writeBytes("1fail" + '\n');
    }
    break;

    case "2":
//...
}
                catch(IOException e){
                    System.out.println(e);
                    break;
                }
}

Answer 1

只需添加一个新命令即可关闭与服务器的连接。

switch (clientMsg) {
        case "1":
            //'Upload file' command from client
            System.out.print("\nCommand from " + clientSocket.getInetAddress() + ":"+ clientSocket.getPort()+" : ");
            System.out.println("Upload file");
            server.upload();
            break;

        case "1fail":
            //In case client fails to find the file it wants to upload
            System.out.print("\nCommand from " + clientSocket.getInetAddress() + ":"+ clientSocket.getPort()+" : ");
            System.out.println("Upload file");
            System.out.println("Client could not upload: File did not exist on client machine\n");
            break;
        case "-1":
            is.close();

            break;

Answer 2

您正在为每笔交易创建新流并关闭它们。这会关闭套接字，导致下次发生的异常。

但该技术无论如何都无效。您应该在套接字的生命周期中使用相同的流。您还需要安排对等方知道您正在发送的文件中有多少数据，通常是事先通过发送它并让对等体读取多少字节，而不是像现在一样读取到流的末尾。

Answer 3

您可能过早关闭客户端strem，不允许服务器完成读取。在关闭客户端的straem和socket之前尝试放一个计时器。如果它有效，你应该考虑一种更好的同步方式，以允许服务器读取整个文件。

使用套接字上传文件

3 个答案: