A Simple Java TCP Server and TCP Client

Posted: June 15, 2011 in Java

A Simple Java TCP Server and TCP Client

Following up on my previous post, we also had to demonstrate a sample Java TCP Server and TCP Client. The code footprint pretty small and it gives you a good idea about how a TDP Server opens up a port, and then the TCP Client sends or receives data from that port.

This is a good page on the differences between TCP and UDP.

To compile these, install Java JDK to your system. Then compile the program with javac TCPClient.java – this will create a TCPClient.class. Execute the file with java TCPClient – leave off the .class, or you will get the error: “Exception in thread “main” java.lang.NoClassDefFoundError”.

Here is sample code for a simple Java TCP Server/Client, originally from the excellent Computer Networking: A Top Down Approach, by Kurose and Ross:

TCPServer.java

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

class TCPServer
{
public static void main(String argv[]) throws Exception
{
String clientSentence;
String capitalizedSentence;
ServerSocket welcomeSocket = new ServerSocket(6789);

while(true)
{
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient =
new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
clientSentence = inFromClient.readLine();
System.out.println(“Received: ” + clientSentence);
capitalizedSentence = clientSentence.toUpperCase() + ‘\n’;
outToClient.writeBytes(capitalizedSentence);
}
}
}

and the client:

TCPClient.java

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

class TCPClient
{
public static void main(String argv[]) throws Exception
{
String sentence;
String modifiedSentence;
BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
Socket clientSocket = new Socket(“localhost”, 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
sentence = inFromUser.readLine();
outToServer.writeBytes(sentence + ‘\n’);
modifiedSentence = inFromServer.readLine();
System.out.println(“FROM SERVER: ” + modifiedSentence);
clientSocket.close();
}
}

Reference
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