线程和 FileOutputStream ：虽然同步

编程问答 2022-05-28

问题描述

我有一个简单的服务器类，它在套接字中接收数据片段，例如：WRITE#filename.txt#data

服务器必须将它接收到的数据写入同一个文件中。 当我测试它时，每个片段的“写作：”行都正确显示，“确定”也是如此：

Connection established
WRITE#file.txt#frag1\nthis is a fragment of text

writing : frag1\nthis is a fragment of text
ok

Connection established
WRITE#file.txt#fragment2\nthis is another fragment

writing : fragment2\nthis is another fragment
ok

Connection established
WRITE#file.txt#fragment3

writing : fragment3
ok

...但最后，我只看到服务器上文件中的第一个片段。但是第二个和第三个应该也写了，如上所示。

FileOutputStream 和 FileWriter 都会发生这种情况。

代码如下：

import java.io.*;
import java.net.ServerSocket;
import java.net.socket;

public class MyServer extends Thread {
    private Socket socket;
    public static Object mutex = new Object();  

    public MyServer(final Socket socket) {
        this.socket = socket;
    }

    public static void main(final String[] args) throws IOException {
        final ServerSocket serverSocket = new ServerSocket(8080);
        
    while (true) {
            MyServer h = new MyServer(serverSocket.accept());
            h.start();      
        }
    }

    @Override
    public void run() {
        
        try {
            System.out.println("Connection established");

            // get data from client
            final InputStream is = this.socket.getInputStream();
            
            synchronized(mutex){
            
                byte[] data = new byte[1024];
                is.read(data);
            
                String s = new String(data);
                System.out.println(s);
                
                // command: WRITE#filename#content 
                final String[] split_command = s.split("#");
    
                final String commandtype = split_command[0];
                final String filename = split_command[1];
                final String data_frag = split_command[2]

                switch (commandtype) {
                case "WRITE":
                    // Write data_frag on the server
                                
                    FileOutputStream fos = new FileOutputStream(PATH_SERVER + filename,true);
                            
                    
                    try {
                        System.out.println("writing : "+ data_frag);
                        fos.write(data_frag.getBytes());
                        System.out.println("ok");

                    }
                    catch (IOException e) {
                        System.out.println("exception!");
                    }
                
            
                    is.close();
                    this.socket.close();
                    fos.close();
                    break;
                
                
                case "CMD_READ":
                    // Something else
                    break;
                
                default:
                    System.out.println(commandtype + " : unkNown");
                }
            
            } // end of synchronization
        } catch (Exception ex) {
            ex.printstacktrace();
        }
    }
}

谢谢，

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