Java.lang.SecurityManager.checkWrite() Method

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Description

The java.lang.SecurityManager.checkWrite(FileDescriptor fd) method throws a SecurityException if the calling thread is not allowed to write to the specified file descriptor. This method calls checkPermission with the RuntimePermission("writeFileDescriptor") permission.

If you override this method, then you should make a call to super.checkWrite at the point the overridden method would normally throw an exception.

Declaration

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

public void checkWrite(FileDescriptor fd)

Parameters

fd − the system-dependent file descriptor.

Return Value

This method does not return a value.

Exception

• SecurityException − if the calling thread does not have permission to access the specified file descriptor.

• NullPointerException − if the file descriptor argument is null.

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.checkWrite() method.

package com.tutorialspoint;

import java.io.FileDescriptor;


public class SecurityManagerDemo extends SecurityManager {

   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
      FileDescriptor fd=new FileDescriptor();
      sm.checkWrite(fd);

      // 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.security.AccessControlException: access denied (java.lang.RuntimePermission writeFileDescriptor)