无法使用JAVA中的网络将文件从一台电脑传输到另一台电脑

Question

I am trying to send file from one client 1 to another Client 2 using an intermediate server. Both Client 1 and Client 2 are connected to server through network.For this, I have given IP-address of server to both clients. But I am unable to transfer the file properly due to some mistake in my code. I am using the following code and its not working and at the Client 2 (receiver's) end, the file which is created is empty. Kindly find the possible error in my code.

Server code

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

public class S1 {


public static void main(String[] args) {

try{

ServerSocket sc1=new ServerSocket(6988);
Socket c1=sc1.accept();
Socket c2=sc1.accept();



DataInputStream dis=new DataInputStream(c1.getInputStream());
int m=c1.getInputStream().available();
byte b2[]=new byte[m];
dis.read(b2);

DataOutputStream dos=new DataOutputStream(c2.getOutputStream());
dos.write(b2);
dos.flush();
dos.close();


}
catch(Exception e){}
}
}

---

Client 1 (Sender)

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

public class C11 {


public static void main(String[] args) {
    try{
        Socket c2=new Socket("127.0.0.1",6988);
        FileInputStream fis=new FileInputStream("f:/abc.jpg");
        File f1=new File("f:/abc.jpg");
        long l1=f1.length();
        int a=(int)l1;
        byte b1[]=new byte[a];
        DataInputStream dis=new DataInputStream(fis);
        dis.read(b1);
        DataOutputStream dout=new DataOutputStream(c2.getOutputStream());
        dout.write(b1);

    }
    catch(Exception e){}
    }

}

---

Client 2 (Receiver)

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

public class C22 {


public static void main(String[] args) {
    try{
        Socket c2=new Socket("127.0.0.1",6988);
        DataInputStream dis=new DataInputStream(c2.getInputStream());
        int m=c2.getInputStream().available();
        byte b2[]=new byte[m];
        dis.read(b2);
        FileOutputStream fout=new FileOutputStream("E:\\PRACTICE\\xyz.txt");
        DataOutputStream dos=new DataOutputStream(fout);
        dos.write(b2);
        dos.close();
    }
    catch(Exception e){}
    }
}

Answer 1

Usual problems.

nt m=c1.getInputStream().available();
byte b2[]=new byte[m];

From the Javadoc : "It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream."

dis.read(b2);

The read() method returns a value. You are ignoring it. The value can be -1, or a postive number between 1 and the buffer size. You're assuming the read filled the buffer. It isn't obliged to do that.

dout.write(b1);

That should be

dout.write(b1, 0, count);

where count was the length returned by read(), and it should be in a loop:

while ((count = in.read(buffer)) > 0)
{
    out.write(buffer, 0, count);
}

Use this at both ends, with any buffer size greater than zero. I usually use 8192.

Answer 2

The most obvious mistake is here:

 int m=c2.getInputStream().available();

The available method only tells you how much data can be read without blocking , not how much data could potentially be read from the socket. To read all of the data that was sent you need to write a loop that reads from the socket until read returns -1.