What is the use of FileInputStream and FileOutputStream in classes in Java?

Java provides I/O Streams to read and write data where, a Stream represents an input source or an output destination which could be a file, i/o devise, other program etc.

There are two types of streams available −

• InputStream − This is used to read (sequential) data from a source.
• OutputStream − This is used to write data to a destination.

FileInputStream

This class reads the data from a specific file (byte by byte). It is usually used to read the contents of a file with raw bytes, such as images.

To read the contents of a file using this class −

• First of all, you need to instantiate this class by passing a String variable or a File object, representing the path of the file to be read.

FileInputStream inputStream = new FileInputStream("file_path");
or,
File file = new File("file_path");
FileInputStream inputStream = new FileInputStream(file);

• Then read the contents of the specified file using either of the variants of read() method −

  • int read() − This simply reads data from the current InputStream and returns the read data byte by byte (in integer format).

    This method returns -1 if the end of the file is reached.

  • int read(byte[] b) − This method accepts a byte array as parameter and reads the contents of the current InputStream, to the given array

    This method returns an integer representing the total number of bytes or, -1 if the end of the file is reached.

  • int read(byte[] b, int off, int len) − This method accepts a byte array, its offset (int) and, its length (int) as parameters and reads the contents of the current InputStream, to the given array.

  • This method returns an integer representing the total number of bytes or, -1 if the end of the file is reached.

Example

Assume we have the following image in the directory D:/images

Following program reads contents of the above image using the FileInputStream.

Example

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
public class FileInputStreamExample {
   public static void main(String args[]) throws IOException {
      //Creating a File object
      File file = new File("D:/images/javafx.jpg");
      //Creating a FileInputStream object
      FileInputStream inputStream = new FileInputStream(file);
      //Creating a byte array
      byte bytes[] = new byte[(int) file.length()];
      //Reading data into the byte array
      int numOfBytes = inputStream.read(bytes);
      System.out.println("Data copied successfully...");
   }
}

Output

Data copied successfully...

FileOutputStream

This writes data into a specific file or, file descriptor (byte by byte). It is usually used to write the contents of a file with raw bytes, such as images.

To write the contents of a file using this class −

• First of all, you need to instantiate this class by passing a String variable or a File object, representing the path of the file to be read.

FileOutputStream outputStream = new FileOutputStream("file_path");
or,
File file = new File("file_path");
FileOutputStream outputStream = new FileOutputStream (file);

You can also instantiate a FileOutputStream class by passing a FileDescriptor object.

FileDescriptor descriptor = new FileDescriptor();
FileOutputStream outputStream = new FileOutputStream(descriptor);

• Then write the data to a specified file using either of the variants of write() method −
  • int write(int b) − This method accepts a single byte and writes it to the current OutputStream.
  • int write(byte[] b) − This method accepts a byte array as parameter and writes data from it to the current OutputStream.
  • int write(byte[] b, int off, int len) − This method accepts a byte array, its offset (int) and, its length (int) as parameters and writes its contents to the current OutputStream.

Example

Assume we have the following image in the directory D:/images

Following program reads contents of the above image and writes it back to another file using the FileOutputStream class.

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
public class FileInputStreamExample {
   public static void main(String args[]) throws IOException {
      //Creating a File object
      File file = new File("D:/images/javafx.jpg");
      //Creating a FileInputStream object
      FileInputStream inputStream = new FileInputStream(file);
      //Creating a byte array
      byte bytes[] = new byte[(int) file.length()];
      //Reading data into the byte array
      int numOfBytes = inputStream.read(bytes);
      System.out.println("Data copied successfully...");
      //Creating a FileInputStream object
      FileOutputStream outputStream = new FileOutputStream("D:/images/output.jpg");
      //Writing the contents of the Output Stream to a file
      outputStream.write(bytes);
      System.out.println("Data written successfully...");
   }
}

Output

Data copied successfully...
Data written successfully...

If you verify the given path you can observe the generated image as −