Java Networking
### Java Networking
Java provides a powerful networking API that makes it easy to communicate over networks. The `java.net` package provides the classes for implementing networking applications. Here are the key concepts and classes used in Java networking:
#### Key Concepts
1. **IP Address**: A unique address that identifies a device on the internet or a local network.
2. **Port Number**: A numerical identifier in networking used to identify a specific process or service.
3. **Socket**: An endpoint for communication between two machines.
4. **Client-Server Architecture**: A model where the server provides resources or services, and the client accesses them.
#### Key Classes
1. **InetAddress**: Represents an IP address.
2. **URL**: Represents a Uniform Resource Locator, which is a reference to a web resource.
3. **URLConnection**: Represents a communication link between the application and a URL.
4. **HttpURLConnection**: A subclass of `URLConnection` that handles HTTP-specific communication.
5. **Socket**: Represents a client socket.
6. **ServerSocket**: Represents a server socket.
7. **DatagramSocket** and **DatagramPacket**: Used for sending and receiving datagram packets, which are used for connectionless communication.
#### 1. InetAddress
The `InetAddress` class represents an IP address, both IPv4 and IPv6. It provides methods to get the IP address of a host.
Example:
```java
import java.net.*;
public class InetAddressExample {
public static void main(String[] args) {
try {
InetAddress ip = InetAddress.getByName("www.example.com");
System.out.println("Host Name: " + ip.getHostName());
System.out.println("IP Address: " + ip.getHostAddress());
InetAddress local = InetAddress.getLocalHost();
System.out.println("Local Host Name: " + local.getHostName());
System.out.println("Local IP Address: " + local.getHostAddress());
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
}
```
#### 2. URL and URLConnection
The `URL` class represents a URL, and the `URLConnection` class represents a connection to a URL.
Example of accessing a webpage:
```java
import java.net.*;
import java.io.*;
public class URLConnectionExample {
public static void main(String[] args) {
try {
URL url = new URL("http://www.example.com");
URLConnection urlConnection = url.openConnection();
BufferedReader in = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
String inputLine;
while ((inputLine = in.readLine()) != null) {
System.out.println(inputLine);
}
in.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
```
#### 3. Socket and ServerSocket
Sockets are used for client-server communication. The `Socket` class represents a client socket, and the `ServerSocket` class represents a server socket.
##### Client-Side
```java
import java.io.*;
import java.net.*;
public class Client {
public static void main(String[] args) {
try {
Socket socket = new Socket("localhost", 6666);
DataOutputStream dout = new DataOutputStream(socket.getOutputStream());
dout.writeUTF("Hello Server");
dout.flush();
dout.close();
socket.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
```
##### Server-Side
```java
import java.io.*;
import java.net.*;
public class Server {
public static void main(String[] args) {
try {
ServerSocket serverSocket = new ServerSocket(6666);
Socket socket = serverSocket.accept();
DataInputStream dis = new DataInputStream(socket.getInputStream());
String str = dis.readUTF();
System.out.println("Message from client: " + str);
serverSocket.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
```
#### 4. DatagramSocket and DatagramPacket
Datagram sockets are used for connectionless communication. The `DatagramSocket` class represents a socket for sending and receiving datagram packets, and the `DatagramPacket` class represents a datagram packet.
##### Sender
```java
import java.net.*;
public class DatagramSender {
public static void main(String[] args) {
try {
DatagramSocket ds = new DatagramSocket();
String str = "Hello";
InetAddress ip = InetAddress.getByName("localhost");
DatagramPacket dp = new DatagramPacket(str.getBytes(), str.length(), ip, 3000);
ds.send(dp);
ds.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
```
##### Receiver
```java
import java.net.*;
public class DatagramReceiver {
public static void main(String[] args) {
try {
DatagramSocket ds = new DatagramSocket(3000);
byte[] buf = new byte[1024];
DatagramPacket dp = new DatagramPacket(buf, 1024);
ds.receive(dp);
String str = new String(dp.getData(), 0, dp.getLength());
System.out.println("Message from sender: " + str);
ds.close();
} catch (Exception e) {
System.out.println(e);
}
}
}
```
#### Conclusion
Java networking provides a robust framework for network communication. By understanding and utilizing classes like `InetAddress`, `URL`, `URLConnection`, `Socket`, `ServerSocket`, `DatagramSocket`, and `DatagramPacket`, you can develop a wide range of networked applications, from simple client-server models to more complex protocols and services.
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