Question

我正在尝试为相当复杂的Java服务器编写上传系统。我在下面列出的两个小程序中重现了这个错误。基本上，我使用ObjectOutputStream / ObjectInputStream通过客户端/服务器进行通信。这是一项要求;我有数千行代码在这个ObjectOutputStream / ObjectInputStream设置下运行得非常好，所以我必须能够在上传完成后仍然使用这些流。

要访问文件（在客户端上读取的文件和正在服务器上写入的文件），使用FileInputStream和FileOutputStream。我的客户出现以完美运行;它读入文件并在每次迭代时发送一个不同的字节数组（它一次读取1MB，因此可以处理大型文件而不会溢出堆）。但是，在服务器上，似乎字节数组总是只发送第一个数组（文件的前1MB）。这不符合我对ObjectInputStream / ObjectOutputStream的理解。我正在寻求解决这个问题的工作方法，或者就此问题进行足够的教育，以形成我自己的解决方案。

以下是客户端代码：

import java.net.*;
import java.io.*;

public class stupidClient
{
  public static void main(String[] args)
  {
    new stupidClient();
  }

  public stupidClient()
  {
    try
    {
      Socket s = new Socket("127.0.0.1",2013);//connect
      ObjectOutputStream output = new ObjectOutputStream(s.getOutputStream());//init stream

      //file to be uploaded
      File file = new File("C:\\Work\\radio\\upload\\(Op. 9) Nocturne No. 1 in  Bb Minor.mp3");
      long fileSize = file.length();
      output.writeObject(file.getName() + "|" + fileSize);//send name and size to server

      FileInputStream fis = new FileInputStream(file);//open file
      byte[] buffer = new byte[1024*1024];//prepare 1MB buffer
      int retVal = fis.read(buffer);//grab first MB of file
      int counter = 0;//used to track progress through upload

      while (retVal!=-1)//until EOF is reached
      {
        System.out.println(Math.round(100*counter/fileSize)+"%");//show current progress to system.out
        counter += retVal;//track progress

        output.writeObject("UPACK "+retVal);//alert server upload packet is incoming, with size of packet read

        System.out.println(""+buffer[0]+" "+buffer[1]+" "+buffer[2]);//preview first 3 bytes being sent
        output.writeObject(buffer);//send bytes
        output.flush();//make sure all bytes read are gone

        retVal = fis.read(buffer);//get next MB of file
      }
      System.out.println(Math.round(100*counter/fileSize)+"%");//show progress at end of file
      output.writeObject("UPLOAD_COMPLETE");//let server know protocol is finished
      output.close();
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
  }
}

以下是我的服务器代码：

import java.net.*;
import java.io.*;

public class stupidServer
{
  Socket s;
  ServerSocket server;

  public static void main(String[] args)
  {
    new stupidServer();
  }

  public stupidServer()
  {
    try 
    {
      //establish connection and stream
      server = new ServerSocket(2013);
      s = server.accept();
      ObjectInputStream input = new ObjectInputStream(s.getInputStream());
      String[] args = ((String)input.readObject()).split("\\|");//args[0] will be file name, args[1] will be file size
      String fileName = args[0];
      long filesize = Long.parseLong(args[1]);

      String upack = (String)input.readObject();//get upload packet(string reading UPACK [bytes read])
      FileOutputStream outStream = new FileOutputStream("C:\\"+fileName.trim());

      while (!upack.equalsIgnoreCase("UPLOAD_COMPLETE"))//until protocol is complete
      {
        int bytes = Integer.parseInt(upack.split(" ")[1]);//get number of bytes being written
        byte[] buffer = new byte[bytes];
        buffer = (byte[])input.readObject();//get bytes sent from client

        outStream.write(buffer,0,bytes);//go ahead and write them bad boys to file
        System.out.println(buffer[0]+" "+buffer[1]+" "+buffer[2]);//peek at first 3 bytes received
        upack = (String)input.readObject();//get next 'packet' - either another UPACK or a UPLOAD_COMPLETE
      }
      outStream.flush();
      outStream.close();//make sure all bytes are in file
      input.close();//sign off
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
  } 
}

一如既往，非常感谢您的时间！

Answer 1

您当前的问题是ObjectOutputStream使用ID机制来避免多次在流上发送相同的对象。客户端将为buffer的第二次和后续写入发送此ID，服务器将使用其缓存值。

这个直接问题的解决方案是添加对reset()的调用：

output.writeObject(buffer);//send bytes
output.reset(); // force buffer to be fully written on next pass through loop

除此之外，您通过在它们之上分层自己的协议来滥用对象流。例如，将文件名和文件大小写为由“|”分隔的单个字符串;只需将它们写为两个独立的值。同上每个写入的字节数。

发出在java中的objectoutputstream上发送字节数组的问题

1 个答案: