Java套接字在写入字节数组后仅获得NUL字符

Posted 2023-02-25

【中文标题】Java套接字在写入字节数组后仅获得NUL字符

【英文标题】：Java socket getting only NUL characters after writing byte array

【发布时间】：2022-01-03 11:33:59

【问题描述】：

我正在尝试通过byte 数组将文件以块的形式从客户端发送到服务器。我正在使用ObjectInputStream。写入有效并且文件大小匹配，但是当我打开文件时，我只得到一个空白文本文件（在 IDE 中打开时，显示 NUL,NUL,NUL...）。

服务器代码：

try(
    FileOutputStream fileOut = new FileOutputStream(file);
    ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
    ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
)
byte[] arr = new byte[chunkSize];
try 
    int len = 0;
    long bytesRead = 0;

    byte[] bytes = new byte[chunkSize];
    int chunkNo = 1;


    while(true)
    
        len = in.read(bytes,0, chunkSize);
        System.out.println();
        if(len < 0)
            break;

        fileOut.write(arr, 0, len);

        bytesRead += len;

        out.writeObject(Server.CHUNK_ACKNOWLEDGE_MSG);
        String ackReply = (String) in.readObject();

        if(ackReply.equalsIgnoreCase((Server.UPLOAD_ACKNOWLEDGE_RECEIVE_TIMEOUT_MSG)))
            if(Server.DEBUG)
                System.out.println(fileName + " send timeout.");

            deleteFile();
            break;
        else if (ackReply.equalsIgnoreCase(Server.UPLOAD_COMPLETE_MSG))
            if(bytesRead != fileSize)

                System.out.println(fileName + " File size mismatch");
                deleteFile();
                break;
            else
                System.out.println( fileName + " File written");
                break;
            
        
    
    
catch (IOException ioe)
    if(Server.DEBUG)
        ioe.printStackTrace();

客户端代码：

 try(
        FileInputStream fileInput = new FileInputStream(file);
        ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
        ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
    )
        byte[] arr = new byte[chunkSize];
        try 
            int len = 0;
            int bytesRead = 0;
            int chunkCount = 1;
            while((len = fileInput.read(arr, 0, chunkSize)) != -1)
            
                out.write(arr, 0, len);
                out.flush();

                bytesRead += len;

                
                    try 
                        System.out.println("wait ack");

                        socket.setSoTimeout(timeout);
                        String ack = (String) in.readObject();
                        System.out.println(ack);

                        if(bytesRead >= fileSize)
                            out.writeObject(Server.UPLOAD_COMPLETE_MSG);
                            System.out.println(Server.UPLOAD_COMPLETE_MSG);
                            break;
                        else
                            out.writeObject(Server.CHUNK_ACKNOWLEDGE_MSG);
                        
                    catch (SocketTimeoutException e)
                        out.writeObject(Server.UPLOAD_ACKNOWLEDGE_RECEIVE_TIMEOUT_MSG);
                        System.out.println(Server.UPLOAD_ACKNOWLEDGE_RECEIVE_TIMEOUT_MSG);

                        break;
                    finally 
                        socket.setSoTimeout(0);
                    
                
            

        catch (IOException ioe)
            ioe.printStackTrace();
        
    catch (FileNotFoundException fnfe)
        System.out.println("No such file: " + fileName);
    catch (Exception e)
        e.printStackTrace();
    
    finally 
        try 
            socket.close();
        catch (Exception ex)
            ex.printStackTrace();
        
    

我尝试将byte 数组写入客户端的另一个文件，副本是相同的。所以问题一定是在通过套接字发送数据期间。

Server.X_MSG 只是一个常量字符串。我不知道在同一个ObjectInputStream 上混合readobject() 和read(bytearray) 是否会导致任何问题。

【问题讨论】：

我不懂try( 的语法，没见过。您使用的是哪个 Java 版本？

@kiner_shah 这是资源语法的正常尝试。它应该相当于用 finally 语句关闭它们。

【参考方案1】：

也许是因为fileOut.write(arr, 0, len); 使用arr 和len = in.read(bytes,0, chunkSize); 使用bytes？它们不是同一个数组。