Java/Security/File Read Write

Authenticate and login context

   <source lang="java">

import java.io.File; import java.io.FileWriter; import java.io.IOException; import java.security.PrivilegedAction; import javax.security.auth.Subject; import javax.security.auth.login.LoginContext; import javax.security.auth.login.LoginException; public class AuthenticateNT {

 public static void main(String[] args) {
   try {
     LoginContext loginContext = new LoginContext("AuthenticateNT");
     loginContext.login();
     System.out.println("Login Successful");
     Subject subject = loginContext.getSubject();
     System.out.println(subject);
     Subject.doAs(subject, new WriteFileAction());
     loginContext.logout();
     System.exit(0);
   } catch (LoginException loginException) {
     loginException.printStackTrace();
     System.exit(-1);
   }
 }

}

class WriteFileAction implements PrivilegedAction {

 public Object run() 
 {
    try {
       File file = new File( "D:/", "privilegedFile.txt" );
       FileWriter fileWriter = new FileWriter( file );
       
       fileWriter.write( "Welcome to JAAS!" );
       fileWriter.close();
    }    
    catch ( IOException ioException ) {
       ioException.printStackTrace();
    }
    
    return null;
    
 } 

} /* // java.policy // Policy file that grants AllPermission to JAAS modules and specific permissions to the D:\Projects\Java codebase. grant codebase "file:/D:/jdk1.3.1/jre/lib/ext/jaas.jar" {

  permission java.security.AllPermission;

}; grant codebase "file:/D:/JavaProjects/src/-" {

  permission javax.security.auth.AuthPermission 
     "createLoginContext";
  permission javax.security.auth.AuthPermission "doAs";
  permission java.io.FilePermission "D:/privilegedFile.txt", 
     "write";
  permission java.io.FilePermission "D:/privilegedFile.txt", 
     "read";

};

• /

/* // jaas.policy // Policy file defining the permissions for the named Principal grant codeBase "file:D:/",

  Principal com.sun.security.auth.NTUserPrincipal "santry" {
  permission java.io.FilePermission "D:/privilegedFile.txt", 
     "write";
  permission java.io.FilePermission "D:/privilegedFile.txt", 
     "read";

};

• /

/* // jaas.config // Configures JAAS to use NTLoginModule // for authentication. AuthenticateNT {

  com.sun.security.auth.module.NTLoginModule required debug=false;

};

• /

      </source>
   
  
 
  

Checking permissions

   <source lang="java">

import java.io.File; public class Permissions {

 public static void main(String[] args) {
   if (args.length != 1) {
     System.err.println("usage: java Permissions filespec");
     return;
   }
   File file = new File(args[0]);
   System.out.println("Checking permissions for " + args[0]);
   System.out.println("  Execute = " + file.canExecute());
   System.out.println("  Read = " + file.canRead());
   System.out.println("  Write = " + file.canWrite());
 }

}

</source>
   
  
 
  

Writable, read only file

   <source lang="java">

import java.io.File; public class ROW {

 public static void main(String[] args) {
   File filespec = new File("c:\text.txt");
   if (filespec.setWritable(false))
     System.out.println(filespec + " made read-only");
   else
     System.out.println("Permission denied");
   if (filespec.setWritable(true))
     System.out.println(filespec + " made writable");
   else
     System.out.println("Permission denied");
   System.out.println(filespec + " is currently "
       + (filespec.canWrite() ? "writable" : "read-only"));
 }

}

</source>