Java.lang.SecurityManager.checkRead() Method

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Description

The java.lang.SecurityManager.checkRead(String file, Object context) method throws a SecurityException if the specified security context is not allowed to read the file specified by the string argument. The context must be a security context returned by a previous call to getSecurityContext.

If context is an instance of AccessControlContext then the AccessControlContext.checkPermission method will be invoked with the FilePermission(file,"read") permission. If context is not an instance of AccessControlContext then a SecurityException is thrown. If you override this method, then you should make a call to super.checkRead at the point the overridden method would normally throw an exception.

Declaration

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

public void checkRead(String file, Object context)

Parameters

• file − the system-dependent file name.

• context − a system-dependent security context.

Return Value

This method does not return a value.

Exception

• SecurityException − if the specified security context is not an instance of AccessControlContext (e.g., is null), or does not have permission to read the specified file.

• NullPointerException − if the file 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.checkRead() method.

package com.tutorialspoint;

import java.security.AccessControlContext;
import java.security.AccessController;

public class SecurityManagerDemo extends SecurityManager {

   public static void main(String[] args) {

      // get current context
      AccessControlContext con = AccessController.getContext();

      // 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.checkRead("test.txt", con);

      // 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 −

Allowed!