DataInputStream read() 总是 return -1

Question

我在 java 中有一个客户端-服务器程序，其中客户端向服务器发送请求，服务器通过发送文件进行响应。与服务器的连接正确，客户端发送的第一个请求被服务器正确解释。

此时服务器读入一个特定的文件，该文件似乎读得很好，因为写入发送了正确的字节数和字符串（通过打印字节数和字符串进行了测试）。

发送第一条消息后，客户端等待接收文件，但是一旦收到消息，读取 returns -1 就好像读取了 EOF 一样，我无法理解原因，如何解决？

发送文件时服务器上的方法

private void sendFile(Socket client, String path, DataOutputStream writer) {
        File file = new File(path);
        byte[] bytes = new byte[1024];
        InputStream in = null;
        try {
            in = new FileInputStream(file);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        int count;
        try {
            while ((count = in.read(bytes)) > 0) {
                System.out.println("nBytes " + count);
                String tmp = new String(bytes);
                System.out.println(tmp);

                //i'm reading from a json file this string
                //[{"username":"user"},{"score":0},{"friendList":["us1","us2"]},{"password":"password"}]
                //and it is printed correctly

                writer.write(bytes, 0, count);
            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        try {
            in.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

客户端方法

public void getFile (String username) {
        // first of all connects correctly with the server and sends a message, the message is received correctly by the server, after it waits for a reply message

        Socket socket = connect2server();
        DataInputStream reader = null;
        BufferedWriter writer = null;


        try {
            reader = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
            writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        //send message to the server using writer 

        OutputStream out = null;
        String file = username+".json";
        try {
            out = new FileOutputStream(file);
        } catch (FileNotFoundException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

        byte[] bytes = new byte[1024];

        int count;
        try {
            while ((count = reader.read(bytes)) >= 0) {
                System.out.println("nByte " + count);
                out.write(bytes, 0, count);
            }

            // the client is waiting correctly on the read but as soon as it receives a message, the read returns -1 as if it had only read an EOF and not the whole message

            System.out.println(count);
        } catch (IOException e2) {
            // TODO Auto-generated catch block
            e2.printStackTrace();
        }

        try {
            out.close();
            reader.close();
            writer.close();
            socket.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }   
    }

Answer 1

在你的sendFile() writer没有关闭。您需要 flush() 然后 close() 作者以保证创建输出。也许这会解决您的问题

Answer 2

关于 write，您不是 closing/flushing 输出流，输出流又不会释放与该流关联的任何资源。您有两个选择：

关闭调用其 flush 方法的输出流，并然后调用其底层输出流的关闭方法。
刷新输出流缓冲区。缓冲主要是为了提高 I/O 性能。

来自doc，read()

的总合同

Reads the next byte of data from the input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown. A subclass must provide an implementation of this method.

Returns: 下一个数据字节，如果到达流的末尾则为 -1。

DataInputStream read() 总是 return -1

DataInputStream read() always return -1

java

client

file

datainputstream

server