Question

今天下午我写了这个课程，其目的是通过TCP Socket交换发送文件的简单方法问题是，尽管最终文件大小正确，但内容错误：目标文件恰好由通过Socket发送的第一个缓冲区的各种副本组成。我的类很简单：它根据缓冲区大小计算Q和R，并将此数字与原始文件名一起发送给客户端。我使用字节数组通过Socket发送数据。

package it.s4sytems.java;  
import java.io.*;  
import java.net.*;  

public class FileOverObjectStream
{
    private File file;
    private int bufferSize = 4*1024*1024; //4MB default, comunque è stabilito dal sender

    private static class Info implements Serializable
    {
        public String fileName;
        public long q;
        public int r;
        public int bufferSize;
    }

    public FileOverObjectStream(File file)
    {
        this.file = file;
    }

    public FileOverObjectStream(File file, int bufferSize)
    {
        this(file);
        this.bufferSize = bufferSize;
    }

    public void sendFile(Socket socket) throws IOException
    {
        socket.getInputStream();
        sendFile( socket.getOutputStream() );
    }

    public void sendFile(OutputStream outStream)throws IOException
    {
        sendFile( new ObjectOutputStream(outStream) );
    }

    public void sendFile(ObjectOutputStream objOutStream) throws IOException
    {
        BufferedInputStream in = new BufferedInputStream( new FileInputStream(file) );
        byte[] buffer = new byte[bufferSize];

        Info info = new Info();
            info.fileName = file.getName();
            info.bufferSize = bufferSize;
            info.q = file.length() / bufferSize;
            info.r = (int) file.length() % bufferSize;
        objOutStream.writeObject(info);

        for(long i=0; i<info.q; i++)
        {
            in.read(buffer);
            objOutStream.writeObject(buffer);
            objOutStream.flush();
        }
        in.read( buffer = new byte[info.r]);
        objOutStream.writeObject(buffer);

        objOutStream.flush();
        in.close();
    }

    public String receiveFile(Socket socket) throws IOException, ClassNotFoundException
    {
        socket.getOutputStream();
        return receiveFile( socket.getInputStream() );
    }

    public String receiveFile(InputStream inStream) throws IOException, ClassNotFoundException
    {
        return receiveFile( new ObjectInputStream(inStream) );
    }

    public String receiveFile(ObjectInputStream objInStream) throws IOException, ClassNotFoundException
    {
        BufferedOutputStream out = new BufferedOutputStream( new FileOutputStream(file) );

        Info info = (Info) objInStream.readObject();
        for(long i=0; i<info.q+1; i++)
        {
            byte[] buffer = (byte[]) objInStream.readObject();
            out.write( buffer );
        }

        out.close();
        return info.fileName;
    }
}

我创建了两个类来尝试...

import it.s4sytems.java.*;
import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;

public class Server
{
    public static void main(String arg[]) throws IOException
    {
        ServerSocket ss = new ServerSocket(18000);

        while(true)
        {
            Socket s = ss.accept();

            File file = new File("G:\\HCHCK_72_5.38.part04.rar");
            FileOverObjectStream sender = new FileOverObjectStream(file);
            sender.sendFile(s);
            s.close();
        }
    }
}

和客户......

import it.s4sytems.java.*;
import java.io.*;
import java.net.*;

public class Client
{
    public static void main(String arg[]) throws IOException, ClassNotFoundException
    {
        Socket s = new Socket("localhost", 18000);

        String matricola = "616002424";

        File directory = new File(System.getProperty("user.dir") + "\\" + matricola);
        directory.mkdir();

        File file = File.createTempFile("7897_", null, directory);

        String originalName = new FileOverObjectStream(file).receiveFile(s);

        System.out.println(originalName);

        s.close();


        File file2 = new File(directory, originalName);
        System.out.println( file.renameTo( file2 ) );
        System.out.println( file.getAbsoluteFile());
        System.out.println( file2.getAbsoluteFile());
    }
}

可能这是一个愚蠢的事情，但我看不到它，所以我需要你的帮助。

谢谢

Answer 1

我认为ObjectOutputStream不适合您的用例。除非我错过了什么。通常，尝试为IO使用一些好的库，例如Apache Commons IO。它的方法总能做正确的事情。例如，请查看IOUtils。

要强调的一些错误（好的库不会发生这种情况）

in.read(buffer)无法保证读取确切的字节数。您必须检查其结果并只写出正确的数字。
使用writeObject将缓冲区对象写入ObjectOutputStream。它写入序列化字节缓冲区而不是原始字节序列。

Answer 2

您的ObjectInput / OutputStream代码在Alex注意到的所有方面都存在缺陷。我根本不会使用它，我只会使用原始I / O.在Java中复制流的规范方法如下：

int count;
byte[] buffer = new byte[8192]; // or more, but megabytes is pointless as the network will packetize anyway
while ((count = in.read(buffer)) > 0)
{
  out.write(buffer, 0, count);
}

在发送和接收文件时使用相同的代码。如果你想发送＆gt;每个连接1个文件，你需要通过发送文件名和长度来为所有这些添加前缀，你可以在接收器上使用DataOutputStream.writeUTF()/writeLong()和DataInputStream.readUTF()/readLong()，并修改循环控制以准确读取多个字节数：

long remaining = size; // the file size read from the network
while ((count = in.read(buffer, 0, remaining > buffer.length ? buffer.length : (int)remaining)) > 0)
{
    out.write(buffer, 0, count);
    remaining -= count;
}

通过java Socket错误的文件传输

2 个答案: