如何使用Java正确地从套接字流式传输数据

Question

I am attempting stream data over a socket with Java in an attempt to write a Kafka producer. I've written a class to pull the data in but I'm not getting the results I'd expect. I've got it set up so the data is being streamed from a Linux box. The source of the data is a csv file that I'm using the nc utility to stream. The class is running on a Windows 10 machine from Eclipse. When I run the class I see two weird things.

1. The column headers don't get transmitted.
2. I can only run the class once. If I want to run it again, I have to stop nc and restart it.

Below is my code. Am I missing anything? At this point I'm just trying to connect to the socket and pull the data over.

I run nc with the following command: $ nc -kl 9999 < uber_data.csv

Below is my class

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

public class Client 
{
static String userInput;

public static void main(String [] args)
{

    try
    {
        InetAddress serverAddress = InetAddress.getByName("servername");
        Socket socket = new Socket(serverAddress, 9999);
        BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        while ((userInput = input.readLine()) != null) {
            System.out.println(input.readLine());
        }

        input.close();
        socket.close();

    }
    catch(UnknownHostException e1)
    {
        System.out.println("Unknown host exception " + e1.toString());
    }
    catch(IOException e2)
    {
        System.out.println("IOException " + e2.toString());
    }
    catch(IllegalArgumentException e3)
    {
        System.out.println("Illegal Argument Exception " + e3.toString());
    }
    catch(Exception e4)
    {
        System.out.println("Other exceptions " + e4.toString());
    }
}
}

Answer 1

First, each call readLine() tries to read line from input stream. In userInput = input.readLine() you read header, but println(input.readLine()) read body and print in console.

while ((userInput = input.readLine()) != null) { 
     System.out.println(userInput); //instead input.readLine()
}

Second, I didn't use nc, but I think problem will solve if you will close socket (and reader) in finally statement.

Answer 2

I hope it would be helpful.

For the first question: you were trying to print userInput string. But it's printing the result of another readline() call.

For the second: after the file has been transferred, you have to stop and restart nc ; no matter what you do from your side. It's from nc side.

See the nc documentation .

Answer 3

You're throwing away every odd-numbered line. It should be:

while ((userInput = input.readLine()) != null) {
    System.out.println(userInput);
}

Secondly, you aren't closing the socket. Use a try-with-resources:

try
{
    InetAddress serverAddress = InetAddress.getByName("servername");
    try (
        Socket socket = new Socket(serverAddress, 9999);
        BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    ) {
        while ((userInput = input.readLine()) != null) {
            System.out.println(input.readLine());
        }
    }
}
catch (...)