Java.lang.SecurityManager.checkListen() Method

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Description

The java.lang.SecurityManager.checkListen(int port) method throws a SecurityException if the calling thread is not allowed to wait for a connection request on the specified local port number.

If port is not 0, this method calls checkPermission with the SocketPermission ("localhost:"+port,"listen"). If port is zero, this method calls checkPermission with SocketPermission("localhost:1024-","listen"). If you override this method, then you should make a call to super.checkListen at the point the overridden method would normally throw an exception.

Declaration

Following is the declaration for java.lang.SecurityManager.checkListen() method

public void checkListen(int port)

Parameters

port − the local port.

Return Value

This method does not return a value.

Exception

SecurityException − if the calling thread does not have permission to listen on the specified port.

Example

Our examples require that the permissions for each command is blocked. A new policy file was set that allows only the creating and setting of our Security Manager. The file is in C:/java.policy and contains the following text −

grant {
   permission java.lang.RuntimePermission "setSecurityManager";
   permission java.lang.RuntimePermission "createSecurityManager";
   permission java.lang.RuntimePermission "usePolicy";
};

The following example shows the usage of lang.SecurityManager.checkListen() method.

package com.tutorialspoint;

public class SecurityManagerDemo extends SecurityManager {

   // checkListen needs to be overriden
   @Override
   public void checkListen(int port) {
      throw new SecurityException();
   }

   public static void main(String[] args) {

      // set the policy file as the system securuty policy
      System.setProperty("java.security.policy", "file:/C:/java.policy");

      // create a security manager
      SecurityManagerDemo sm = new SecurityManagerDemo();

      // set the system security manager
      System.setSecurityManager(sm);

      // perform the check
      sm.checkListen(8080);

      // print a message if we passed the check
      System.out.println("Allowed!");
   }
}

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

Exception in thread "main" java.lang.SecurityException