Java - Socket setReuseAddress() Method

Description

The Java Socket setReuseAddress(boolean on) enables/disables the SO_REUSEADDR socket option. If SO_REUSEADDR is enabled prior to binding the socket using bind(SocketAddress) method, then we can bind the socket even though a previous connection is timedout. Initially SO_REUSEADDR is disabled when a socket is created.

Declaration

Following is the declaration for java.net.Socket.setReuseAddress(boolean on) method.

public void setReuseAddress(boolean on) throws SocketException

Parameters

on whether to enable or disable the socket option.

Return Value

N/A

Exception

SocketException if an error occurs enabling or disabling the SO_REUSEADDR socket option, or the socket is closed.

Example 1

The following example shows the usage of Java Socket setReuseAddress() method to set the status of SO_REUSEADDR 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. Once done, we're enabling the SO_REUSEADDR flag using setReuseAddress() and then we're printing the SO_REUSEADDR flag using getReuseAddress() 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.setReuseAddress(true);  
      System.out.println("Is SO_REUSEADDR: "+socket.getReuseAddress()); 
      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 SO_REUSEADDR: true
Port number: 6066
Inet Address: null

Example 2

The following example shows the usage of Java Socket setReuseAddress() method to set the status of SO_REUSEADDR flag of socket instance. As first step, we've created a Socket instance using no argument constructor. Now, we're printing the SO_REUSEADDR flag using getReuseAddress() method. Then we're setting the SO_REUSEADDR flag as true using setReuseAddress() 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 SO_REUSEADDR: "+socket.getReuseAddress());
      socket.setReuseAddress(true);  
      System.out.println("Is SO_REUSEADDR: "+socket.getReuseAddress());
      socket.close();
   }
}

Output

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

Is SO_REUSEADDR: false
Is SO_REUSEADDR: true

Example 3

The following example shows the usage of Java Socket setReuseAddress() method to set the status of SO_REUSEADDR 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. Now, we're trying to enable the SO_REUSEADDR flag using setReuseAddress() method and then printing the SO_REUSEADDR flag using getReuseAddress() method. In the end, we closed the socket using close() method. As socket is already closed, setReuseAddress() 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();	  
      socket.setReuseAddress(true);  
      System.out.println("Is SO_REUSEADDR: "+socket.getReuseAddress());
      socket.setReuseAddress(false);  
      System.out.println("Is SO_REUSEADDR: "+socket.getReuseAddress());
      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.setReuseAddress(Socket.java:1465)
	at com.tutorialspoint.SocketDemo.main(SocketDemo.java:10)