Java - Socket setKeepAlive() Method

Description

The Java Socket setKeepAlive() enables/disables SO_KEEPALIVE.

Declaration

Following is the declaration for java.net.Socket.setKeepAlive() method.

public void setKeepAlive(boolean on) throws SocketException

Parameters

on − whether or not to have socket keep alive turned on.

Return Value

NA

Exception

SocketException − if there is an error in the underlying protocol, such as a TCP error.

Example 1

The following example shows the usage of Java Socket setKeepAlive() method to enable the status of SO_KEEPALIVE flag of socket instance. As first step, we've created a Socket instance using no argument constructor. Then in order to create a SocketAddress object, we've initialized an InetAddress instance of localhost address. Using InetSocketAddress object, we've created a SocketAddress object and then using bind() method, we bind the address to the socket. Now we're enabling the SO_KEEPALIVE flag using setKeepAlive() method call. Once done, we're printing the keep alive flag using getKeepAlive() method, local port and inetaddress as shown. In the end, we closed the socket using close() method.

package com.tutorialspoint;

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketAddress;

public class SocketDemo {
   public static void main(String[] args) throws IOException {
      Socket socket = new Socket();  
      InetAddress inetAddress=InetAddress.getByName("localhost");  
      SocketAddress socketAddress=new InetSocketAddress(inetAddress, 6066);  
      socket.bind(socketAddress); 
      socket.setKeepAlive(true);
      System.out.println("Is Keep Alive: "+socket.getKeepAlive()); 
      System.out.println("Port number: "+socket.getLocalPort()); 
      System.out.println("Inet Address: "+socket.getInetAddress()); 
      socket.close();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Is Keep Alive: true
Port number: 6066
Inet Address: null

Example 2

The following example shows the usage of Java Socket setKeepAlive() method to set the status of SO_KEEPALIVE flag of socket instance. As first step, we've created a Socket instance using no argument constructor. Now, we're printing the keep alive flag using getKeepAlive() method. Then we're setting the keep alive flag as true using setKeepAlive() method and print the same. In the end, we closed the socket using close() method.

package com.tutorialspoint;

import java.io.IOException;
import java.net.Socket;

public class SocketDemo {
   public static void main(String[] args) throws IOException {
      Socket socket = new Socket();  

      System.out.println("Is Keep Alive: "+socket.getKeepAlive());
      socket.setKeepAlive(true);  
      System.out.println("Is Keep Alive: "+socket.getKeepAlive());
      socket.close();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Is Keep Alive: false
Is Keep Alive: true

Example 3

The following example shows the usage of Java Socket setKeepAlive() method to set the status of SO_KEEPALIVE flag of socket instance, if socket is already closed. As first step, we've created a Socket instance using no argument constructor. Using socket.close(), we're closing the socket. Then we're setting the keep alive flag as true using setKeepAlive() method and print the same. In the end, we closed the socket using close() method. As socket is already closed, setKeepAlive() method call throws an exception as shown below −

package com.tutorialspoint;

import java.io.IOException;
import java.net.Socket;

public class SocketDemo {
   public static void main(String[] args) throws IOException {
      Socket socket = new Socket();  
      socket.close();	  

      //System.out.println("Is Keep Alive: "+socket.getKeepAlive());
      socket.setKeepAlive(true);  
      System.out.println("Is Keep Alive: "+socket.getKeepAlive());
      socket.close();
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Exception in thread "main" java.net.SocketException: Socket is closed
	at java.base/java.net.Socket.setKeepAlive(Socket.java:1326)
	at com.tutorialspoint.SocketDemo.main(SocketDemo.java:12)