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Java SecurityManager checkWrite() method with example

SecurityManager Class checkWrite() method: Here, we are going to learn about the checkWrite() method of SecurityManager Class with its syntax and example.
Submitted by Preeti Jain, on December 14, 2019

Syntax:

    public void checkWrite(FileDescriptor  file_des);
    public void checkWrite(String fi);

SecurityManager Class checkWrite() method

• checkWrite() method is available in java.lang package.
• checkWrite(FileDescriptor file_des) method invokes checkPermission with the RuntimePermission("writeFileDescriptor") to write the given file descriptor.
• checkWrite(String fi) method invokes checkPermission with the FilePermission(fi,"write") to write to the file by the given fi parameter.
• checkWrite(FileDescriptor file_des), checkWrite(String fi) methods may throw an exception at the time of writing the file from different media.
• checkWrite(FileDescriptor file_des):
  • SecurityException – This exception may throw when the calling thread is not allowed to write the given file descriptor.
  • NullPointerException – This exception may throw when the given parameter is null.
• checkWrite(String fi):
  • SecurityException – This exception may throw when the calling thread is not allowed to write the given file.
  • NullPointerException – This exception may throw when the given parameter is null.
• These are non-static methods, it is accessible with the class object only and, if we try to access these methods with the class name then we will get an error.

Parameter(s):

• In the first case, FileDescriptor file_des - This parameter represents the system-specific file descriptor.
• In the second case, String fi - This parameter represents the system-specific file name.

Return value:

The return type of this method is void, it returns nothing.

Example:

// Java program to demonstrate the example 
// of checkWrite() method of SecurityManager class

import java.security.*;
import java.io.*;

public class CheckWrite extends SecurityManager {
    public static void main(String[] args) {
        FileDescriptor file_desc = new FileDescriptor();
        String fi = "getProperties().doc";

        // By using setProperty() method is to set the policy property 
        // with security manager
        System.setProperty("java.security.policy", "file:/C:/java.policy");

        // Instantiating a CheckWrite object
        CheckWrite cw = new CheckWrite();

        // By using setSecurityManager() method is to set the
        // security manager
        System.setSecurityManager(cw);

        // By using CheckWrite(FileDescriptor) method is to
        // check that write file by using file descriptor
        cw.checkWrite(file_desc);

        // By using CheckWrite(String) method is to
        // check that write file by using String 
        cw.checkWrite(fi);

        // Display the message 
        System.out.println("Accepted..");
    }
}

Output

Exception in thread "main" java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "writeFileDescriptor")
	at java.base/java.security.AccessControlContext.checkPermission(AccessControlContext.java:472)
	at java.base/java.security.AccessController.checkPermission(AccessController.java:897)
	at java.base/java.lang.SecurityManager.checkPermission(SecurityManager.java:322)
	at java.base/java.lang.SecurityManager.checkWrite(SecurityManager.java:727)
	at CheckWrite.main(CheckWrite.java:25)