how to achieve transfer file between client and server using java socket

Question

I have implement the simple TCP server and TCP client classes which can send the message from client to server and the message will be converted to upper case on the server side, but how can I achieve transfer files from server to client and upload files from client to server. the following codes are what I have got.

TCPClient.java

        import java.io.*;
        import java.net.*;
        import java.util.Scanner;

 class TCPClient {

public static void main(String args[]) throws Exception {
        int filesize=6022386;
        int bytesRead;
        int current = 0;
    String ipAdd="";
    int portNum=0;
    boolean goes=false;
    if(goes==false){
    System.out.println("please input the ip address of the file server");
    Scanner scan=new Scanner(System.in);
    ipAdd=scan.nextLine();
    System.out.println("please input the port number of the file server");
    Scanner scan1=new Scanner(System.in);
    portNum=scan1.nextInt();
    goes=true;
    }
    System.out.println("input done");
    int timeCount=1;
    while(goes==true){
    //System.out.println("connection establishing");

    String sentence="";
    String modifiedSentence;

    BufferedReader inFromUser = new BufferedReader(new InputStreamReader(
            System.in));

    Socket clientSocket = new Socket(ipAdd, portNum);
    //System.out.println("connecting");
    //System.out.println(timeCount);
    if(timeCount==1){
    sentence="set";
    //System.out.println(sentence);


    }
    if(timeCount!=1)
        sentence = inFromUser.readLine();
            if(sentence.equals("close"))
                clientSocket.close();
            if(sentence.equals("download"))
            {
                byte [] mybytearray  = new byte [filesize];
                InputStream is = clientSocket.getInputStream();
                FileOutputStream fos = new FileOutputStream("C:\\users\\cguo\\kk.lsp");
                BufferedOutputStream bos = new BufferedOutputStream(fos);
                bytesRead = is.read(mybytearray,0,mybytearray.length);
                current = bytesRead;
                do {
   bytesRead =
      is.read(mybytearray, current, (mybytearray.length-current));
   if(bytesRead >= 0) current += bytesRead;
} while(bytesRead > -1);

bos.write(mybytearray, 0 , current);
bos.flush();
long end = System.currentTimeMillis();
//System.out.println(end-start);
bos.close();
clientSocket.close();
            }
           // if(sentence.equals("send"))
               // clientSocket.
    timeCount--;
    //System.out.println("connecting1");
    DataOutputStream outToServer = new DataOutputStream(clientSocket
            .getOutputStream());

    BufferedReader inFromServer = new BufferedReader(new InputStreamReader(
            clientSocket.getInputStream()));


    //System.out.println("connecting2");
    //System.out.println(sentence);
    outToServer.writeBytes(sentence + "\n");

    modifiedSentence = inFromServer.readLine();

    System.out.println("FROM SERVER:" + modifiedSentence);

    clientSocket.close();

}
}

}

---

TCPServer.java

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

     class TCPServer {
public static void main(String args[]) throws Exception {

    Socket s = null;

    int firsttime=1;


    while (true) {
        String clientSentence;
    String capitalizedSentence="";

        ServerSocket welcomeSocket = new ServerSocket(3248);
        Socket connectionSocket = welcomeSocket.accept();

             //Socket sock = welcomeSocket.accept();


        BufferedReader inFromClient = new BufferedReader(
                new InputStreamReader(connectionSocket.getInputStream()));

        DataOutputStream outToClient = new DataOutputStream(
                connectionSocket.getOutputStream());

        clientSentence = inFromClient.readLine();
        //System.out.println(clientSentence);
                    if(clientSentence.equals("download"))
                    {
                         File myFile = new File ("C:\\Users\\cguo\\11.lsp");
  byte [] mybytearray  = new byte [(int)myFile.length()];
  FileInputStream fis = new FileInputStream(myFile);
  BufferedInputStream bis = new BufferedInputStream(fis);
  bis.read(mybytearray,0,mybytearray.length);
  OutputStream os = connectionSocket.getOutputStream();
  System.out.println("Sending...");
  os.write(mybytearray,0,mybytearray.length);
  os.flush();
  connectionSocket.close();
                    }
        if(clientSentence.equals("set"))
            {outToClient.writeBytes("connection is ");
            System.out.println("running here");
            //welcomeSocket.close();
             //outToClient.writeBytes(capitalizedSentence);
            }



        capitalizedSentence = clientSentence.toUpperCase() + "\n";


    //if(!clientSentence.equals("quit"))
           outToClient.writeBytes(capitalizedSentence+"enter the message or command: ");


        System.out.println("passed");
        //outToClient.writeBytes("enter the message or command: ");
        welcomeSocket.close();
    System.out.println("connection terminated");
    }
}

}

So, the TCPServer.java will be executed first, and then execute the TCPClient.java, and I try to use the if clause in the TCPServer.java to test what is user's input,now I really want to implement how to transfer files from both side(download and upload).Thanks.

Answer 1

Reading quickly through the source it seems that you're not far off. The following link should help (I did something similar but for FTP). For a file send from server to client, you start off with a file instance and an array of bytes. You then read the File into the byte array and write the byte array to the OutputStream which corresponds with the InputStream on the client's side.

http://www.rgagnon.com/javadetails/java-0542.html

Edit: Here's a working ultra-minimalistic file sender and receiver. Make sure you understand what the code is doing on both sides.

package filesendtest;

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

class TCPServer {

    private final static String fileToSend = "C:\\test1.pdf";

    public static void main(String args[]) {

        while (true) {
            ServerSocket welcomeSocket = null;
            Socket connectionSocket = null;
            BufferedOutputStream outToClient = null;

            try {
                welcomeSocket = new ServerSocket(3248);
                connectionSocket = welcomeSocket.accept();
                outToClient = new BufferedOutputStream(connectionSocket.getOutputStream());
            } catch (IOException ex) {
                // Do exception handling
            }

            if (outToClient != null) {
                File myFile = new File( fileToSend );
                byte[] mybytearray = new byte[(int) myFile.length()];

                FileInputStream fis = null;

                try {
                    fis = new FileInputStream(myFile);
                } catch (FileNotFoundException ex) {
                    // Do exception handling
                }
                BufferedInputStream bis = new BufferedInputStream(fis);

                try {
                    bis.read(mybytearray, 0, mybytearray.length);
                    outToClient.write(mybytearray, 0, mybytearray.length);
                    outToClient.flush();
                    outToClient.close();
                    connectionSocket.close();

                    // File sent, exit the main method
                    return;
                } catch (IOException ex) {
                    // Do exception handling
                }
            }
        }
    }
}

---

package filesendtest;

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

class TCPClient {

    private final static String serverIP = "127.0.0.1";
    private final static int serverPort = 3248;
    private final static String fileOutput = "C:\\testout.pdf";

    public static void main(String args[]) {
        byte[] aByte = new byte[1];
        int bytesRead;

        Socket clientSocket = null;
        InputStream is = null;

        try {
            clientSocket = new Socket( serverIP , serverPort );
            is = clientSocket.getInputStream();
        } catch (IOException ex) {
            // Do exception handling
        }

        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        if (is != null) {

            FileOutputStream fos = null;
            BufferedOutputStream bos = null;
            try {
                fos = new FileOutputStream( fileOutput );
                bos = new BufferedOutputStream(fos);
                bytesRead = is.read(aByte, 0, aByte.length);

                do {
                        baos.write(aByte);
                        bytesRead = is.read(aByte);
                } while (bytesRead != -1);

                bos.write(baos.toByteArray());
                bos.flush();
                bos.close();
                clientSocket.close();
            } catch (IOException ex) {
                // Do exception handling
            }
        }
    }
}

Related

Byte array of unknown length in java

Edit: The following could be used to fingerprint small files before and after transfer (use SHA if you feel it's necessary):

public static String md5String(File file) {
    try {
        InputStream fin = new FileInputStream(file);
        java.security.MessageDigest md5er = MessageDigest.getInstance("MD5");
        byte[] buffer = new byte[1024];
        int read;
        do {
            read = fin.read(buffer);
            if (read > 0) {
                md5er.update(buffer, 0, read);
            }
        } while (read != -1);
        fin.close();
        byte[] digest = md5er.digest();
        if (digest == null) {
            return null;
        }
        String strDigest = "0x";
        for (int i = 0; i < digest.length; i++) {
            strDigest += Integer.toString((digest[i] & 0xff)
                    + 0x100, 16).substring(1).toUpperCase();
        }
        return strDigest;
    } catch (Exception e) {
        return null;
    }
}