Java - FileInputStream getFD() method

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Description

The Java FileInputStream getFD() method returns the FileDescriptor object associated with the input stream. A FileDescriptor represents a handle to an open file, which can be used for lower-level file operations.

Declaration

Following is the declaration for java.io.FileInputStream.getFD() method −

public final FileDescriptor getFD()

Parameters

NA

Return Value

The methods returns the file descriptor object associated with this file input stream.

Exception

IOException− If any I/O error occurs.

Example - Usage of FileInputStream getFD() method

The following example shows the usage of Java FileInputStream getFD() method.

FileInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileDescriptor;
import java.io.IOException;
import java.io.FileInputStream;

public class FileInputStreamDemo {
   public static void main(String[] args) throws IOException {
      FileDescriptor fd = null;
      FileInputStream fis = null;
      boolean bool = false;
      
      try {
         // create new file input stream
         fis = new FileInputStream("test.txt");
         
         // get file descriptor
         fd = fis.getFD();
         
         // tests if the file is valid
         bool = fd.valid();
         
         // prints
         System.out.println("Valid file: "+bool);
         
      } catch(Exception ex) {
         // if an I/O error occurs
         ex.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(fis!=null)
            fis.close();
      }
   }
}

Output

Assumption

Assuming we have a text file test.txt in current directory, which has the following content. This file will be used as an input for our example program.

ABCDEF

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

Valid file: true

Example - Checking if a File Descriptor is Valid

The following example shows the usage of Java FileInputStream getFD() method.

FileInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.IOException;

public class FileInputStreamDemo {
   public static void main(String[] args) {
      try (FileInputStream fis = new FileInputStream("example.txt")) {
         FileDescriptor fd = fis.getFD(); // Get file descriptor

         if (fd.valid()) {
            System.out.println("The file descriptor is valid.");
         } else {
            System.out.println("The file descriptor is not valid.");
         }

      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output(if example.txt exists and opens correctly)

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

The file descriptor is valid.

Explanation

• Open FileInputStream for "example.txt".

• Retrieve the file descriptor using getFD().

• Check if the file descriptor is valid using fd.valid().

• Print whether the file descriptor is valid or not.

Example - Forcing a File to be Written to Disk

The following example shows the usage of Java FileInputStream getFD() method.

FileInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileDescriptor;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileInputStreamDemo {
   public static void main(String[] args) {
      try (FileOutputStream fos = new FileOutputStream("example.txt")) {
         fos.write("Hello, FileDescriptor!".getBytes()); // Write data

         FileDescriptor fd = fos.getFD(); // Get file descriptor
         fd.sync(); // Force write data to disk

         System.out.println("Data written and synchronized to disk.");

      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Data written and synchronized to disk.

Explanation

• Open FileOutputStream for "example.txt".

• Write data to the file using write().

• Retrieve the file descriptor using getFD().

• Call fd.sync() to forcefully flush all written data to disk (ensuring no data loss in case of a system crash).