Java Socket Programming and Streams

Question

I have written the following code for sending a text file from Client to Server using Sockets. I am new to both JAVA and Socket Programming. I feel I have got the socket concepts but Java Streams are quite confusing. Any help with the following code will be really helpful. PLEASE mention the mistake and Solution with reasoning.

The data seems to be sent just fine. But it is not received on the other end.

Server Code:

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

public class Server {
    public static void main(String[] args) throws Exception {
        ServerSocket serverSocket = new ServerSocket(3000);
        while(true)
        {
            Socket convSocket = serverSocket.accept();
            System.out.println("connection accepted");

            BufferedReader in = new BufferedReader(new InputStreamReader(convSocket.getInputStream()));
            FileWriter fileOut = new FileWriter("/Users/aakashmalhotra/a.txt");

            int c;
            while( (c = in.read()) != -1){
                fileOut.write(c);
            }
            System.out.println("Transfer Done");
        }


    }
}

Client Code:

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

public class Client {
    public static void main(String[] argv) throws Exception {
        Socket clientSocket = new Socket("localhost", 3000); // create a socket

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));

        BufferedReader fileIn = new BufferedReader(new FileReader("/Users/aakashmalhotra/s.txt"));

        int c;
        while ((c = fileIn.read()) != -1) {
            out.write(c);
        }

    }
}

For one, you don't appear to be closing your readers or writers. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Sep 29, 2016 at 20:35
... and for another throws Exception while not the cause of your problems, just shouldn't be done. In the least, catch exceptions and print stacktraces. — Hovercraft Full Of Eels
– Hovercraft Full Of Eels, Commented Sep 29, 2016 at 20:36
it will be more efficient, and more generalized, if you don't use readers, but use Streams. there's no need to go thru the hassle of converting bytes to characters if you are just copying them — MeBigFatGuy
– MeBigFatGuy, Commented Sep 29, 2016 at 20:36
Note: even with Sockets you have to remember the basic of closing any resources which need to be closed when you are done with them. — Peter Lawrey
– Peter Lawrey, Commented Sep 29, 2016 at 20:40

MeBigFatGuy · Accepted Answer · 2016-09-29 20:37:24Z

2

You need to .flush() or .close() the out writer on the client side.

answered Sep 29, 2016 at 20:37

MeBigFatGuy

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3 Comments

flakes Over a year ago

Or better yet use a try-with resources statement.

Hovercraft Full Of Eels Over a year ago

@flkes: there's a danger to that if you use threading and helper classes to do handle your streams.

flakes Over a year ago

@HovercraftFullOfEels For sure; In that case close it manually later to not kill the stream prematurely

Jazzwave06 · Accepted Answer · 2016-09-29 20:40:58Z

IO objects, and especially streams, always need to be closed. This is because the OS is optimized for these type of operations, and it decides when the data should be sent on the pipe. Closing the resource make sure that the remainder of the data is sent. Example for the server side:

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

public class Server {
    public static void main(String[] args) throws Exception {
        ServerSocket serverSocket = new ServerSocket(3000);
        while (true) {
            Socket convSocket = serverSocket.accept();
            System.out.println("connection accepted");

            try (BufferedReader in = new BufferedReader(new InputStreamReader(convSocket.getInputStream()))) {
                try (FileWriter fileOut = new FileWriter("/Users/aakashmalhotra/a.txt")) {
                    int c;
                    while ((c = in.read()) != -1) {
                        fileOut.write(c);
                    }
                    System.out.println("Transfer Done");
                }
            }
        }
    }
}

It is important to note the usage of a try-with-resource statement, which ensures that the streams will be closed regardless of the outcome of your application. This guarantees that your stream will always be closed and that no resource will leak.

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