A Simple Java TCP Server and TCP Client

Dave — Thu, 18 Sep 2008 13:01:30 +0000

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

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

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

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();
}
}

If you have any questions, please leave a comment!

A Simple Java UDP Server and UDP Client

Dave — Wed, 17 Sep 2008 10:58:29 +0000

For a class I am taking, we are testing out a simple UDP Server and UDP Client to demonstrate what each one does and how sockets work. The code size is very small and give you a good idea about how a UDP Server opens up a port, and then the UDP Client sends or receives data from that port.

To compile these, install Java JDK to your system. Then compile the program with javac UDPClient.java – this will create a UDPClient.class. Execute the file with java UDPClass – 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 UCP Server and Client, originally from Computer Networking: A Top Down Approach, by Kurose and Ross:

UDPServer.java:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

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

class UDPServer
{
public static void main(String args[]) throws Exception
{
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
while(true)
{
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
String sentence = new String( receivePacket.getData());
System.out.println("RECEIVED: " + sentence);
InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();
String capitalizedSentence = sentence.toUpperCase();
sendData = capitalizedSentence.getBytes();
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, port);
serverSocket.send(sendPacket);
}
}
}

UDPClient.java:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

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

class UDPClient
{
public static void main(String args[]) throws Exception
{
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
DatagramSocket clientSocket = new DatagramSocket();
InetAddress IPAddress = InetAddress.getByName("localhost");
byte[] sendData = new byte[1024];
byte[] receiveData = new byte[1024];
String sentence = inFromUser.readLine();
sendData = sentence.getBytes();
DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
clientSocket.send(sendPacket);
DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
clientSocket.receive(receivePacket);
String modifiedSentence = new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}

systemBash » Java

A Simple Java TCP Server and TCP Client

A Simple Java UDP Server and UDP Client

UDPServer.java:

UDPClient.java: