Reading file part-by-part at client side and sendi

问题:

I wanted to send a part of file to server where it will be printed on server screen...however dos reads entire input...kindly suggest what i can do....is there any other way to read stream from socket into parts and copy those parts in file or print tem on screen

Server side:

/*Aim:to read file in parts...send part to server...write part in the file..*/
import java.io.*;
import java.net.*;
public class Tser {

    public static void main(String a[])throws IOException{

        ServerSocket sock=new ServerSocket(6000);
        Socket csock=sock.accept();
        DataInputStream dis=new DataInputStream(csock.getInputStream());
        FileWriter fw=new FileWriter("elephant");
        BufferedWriter bw=new BufferedWriter(fw);
        BufferedInputStream br=new BufferedInputStream(dis);
        String mess="";int c;
        byte b[]=new byte[20];
        while(br.read(b,0,20)!=-1)
        {
            for(int i=0;i<20;i++)
                mess+=(char)b[i];
            System.out.println(mess);
            System.out.println("XX");
        }

        //bw.write(mess);
        //System.out.print(mess);
        br.close();
        bw.close();
        dis.close();
        sock.close();
        csock.close();
    }

}

Client side:

import java.io.*;
import java.net.*;
public class Tcle {

    public static void main(String a[])throws IOException{
        Socket soc=new Socket("localhost",6000);

        FileReader fr=new FileReader("samp1");
        BufferedReader br=new BufferedReader(fr);
        DataOutputStream dos=new DataOutputStream(soc.getOutputStream());
        String hi="";int c;
        char ch[]=new char[20];

        while(br.read(ch,0,20)!=-1)
        {
            hi=String.valueOf(ch);
            dos.writeBytes(hi);
            //System.out.println(ch);
        }


        //br.flush();
        fr.close();
        br.close();
        dos.close();
        soc.close();

    }}

回答1:

As @EJP says, an easy way for doing it is using InputStream.skip()

The solution could be to create a new method,

readBlock(int offset, byte[] buffer, BufferedInputStream bis)

Which reads buffer.length bytes at the specified offset from bis

public static int readBlock(int offset, byte[] buffer,
            BufferedInputStream bis) throws IOException {

        bis.skip(offset);
        int numberOfBytesRead = bis.read(buffer);

        return numberOfBytesRead;
    }

So, your new Tser class will look like

public class Tser {
    static int BLOCK_SIZE = 20; // only for this example

    public static void main(String a[]) throws IOException {

        ServerSocket sock = new ServerSocket(6000);
        Socket csock = sock.accept();
        DataInputStream dis = new DataInputStream(csock.getInputStream());
        FileWriter fw = new FileWriter("elephant");
        BufferedWriter bw = new BufferedWriter(fw);
        BufferedInputStream br = new BufferedInputStream(dis);
        String mess = "";
        int c;

        byte b[] = new byte[BLOCK_SIZE];
        // we want to read the part contained from byte 10 to 30. (20 bytes)
        readBlock(10, b, br);
        // beware of the encoding!
        System.out.println(new String(b, "UTF-8"));
        System.out.println("XX");

        // bw.write(mess);
        // System.out.print(mess);
        br.close();
        bw.close();
        dis.close();
        sock.close();
        csock.close();
    }    
}

And, you can do the same in the client:

public class Tcle {

    public static void main(String a[]) throws IOException {
        Socket soc = new Socket("localhost", 6000);

        FileInputStream fis = new FileInputStream("sample");
        BufferedInputStream bis = new BufferedInputStream(fis);
        DataOutputStream dos = new DataOutputStream(soc.getOutputStream());

        // 64 bytes, starting at 2nd byte, for example.
        byte[] b = new byte[64];
        readBlock(2, b, bis);
        dos.write(b);

        bis.close();
        dos.close();
        soc.close();

    }



}

In this example, we do the splitting in parts in both sides (client and server).

Let's suppose that the file sample contains the following characters:

---

12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890

---

1.(Client side): we take 64 bytes starting at byte 2. So, we are sending:

---

3456789012345678901234567890123456789012345678901234567890123456

---

2.(Server side): we read 20 bytes starting at byte 10. (That's it, it will be the byte 74 of the original file). So, the output will be:

34567890123456789012
XX

回答2:

Use InputStream.skip() to get to where you want to start sending.

And if you're using an InputStream to read, you should be writing with an OutputStream, not a Reader. Conversely, if you're using a Writer you should be reading with a Reader, but only if you know the data is text.