Java FileInputStream class

In this tutorial, we will learn Java FileInputStream and its methods with the help of examples.

The java.io package's FileInputStream class can be used to read data from a file (in bytes).

It inherits the InputStream abstract class.

Before learning FileInputStream, make sure you understandJava File (file).

Create a FileInputStream

To create a file input stream, we must first import the java.io.FileInputStream package. After importing the package, we can use Java to create a file input stream.

1Using the file path

FileInputStream input = new FileInputStream(stringPath);

Here, we create an input stream that will be linked to the specified file path.

2Using the file object

FileInputStream input = new FileInputStream(File fileObject);

Here, we create an input stream that will be linked to the file specified by fileObject.

FileInputStream methods

The FileInputStream class provides implementations for different methods that appear in the InputStream class.

The read() method

• read() - Reads a byte from the file

• read(byte[] array) - Reads bytes from the file and stores them in the specified array

• read(byte[] array, int start, int length) - Reads a number of bytes equal to length from the file and stores them in the specified array starting from position start

Suppose we have a file namedinput.txtThe file contains the following content.

This is a line of text inside the file.

Let's try to read this file using FileInputStream.

import java.io.FileInputStream;
public class Main {
　　public static void main(String args[]) {
　　　　　try {
　　　　　　　　FileInputStream input = new FileInputStream("input.txt");
　　　　　　　　System.out.println("File data: ");
　　　　　　　　//Read the first byte
　　　　　　　　int i = input.read();
　　　　　　　while(i !=　-1) {
　　　　　　　　　　　System.out.print((char)i);
　　　　　　　　　　　//Read the next byte from the file
　　　　　　　　　　　i = input.read();
　　　　　　　　}
　　　　　　　　input.close();
　　　　　}
　　　　　catch(Exception e) {
　　　　　　　　e.getStackTrace();
　　　　　}
　　}
}

Output Result

Data in the file:
This is a line of text inside the file.

In the above example, we created a file input stream named input. The input stream is associated withinput.txtfile link.

FileInputStream input = new FileInputStream("input.txt");

To read data from the file, we used the read() method in the while loop.

available() method

To get the number of available bytes, we can use the available() method. For example,

import java.io.FileInputStream;
public class Main {
　　　public static void main(String args[]) {
　　　　　　try {
　　　　　　　　//Assuming the input.txt file contains the following text
　　　　　　　　//This is a line of text in the file.
　　　　　　　　　FileInputStream input = new FileInputStream("input.txt");
　　　　　　　　　//Returns the number of available bytes
　　　　　　　　　System.out.println("Available bytes at the beginning: ");　+　input.available());
　　　　　　　　　//Read from the file3bytes
　　　　　　　　　input.read();
　　　　　　　　　input.read();
　　　　　　　　　input.read();
　　　　　　　　　//Returns the number of available bytes
　　　　　　　　　System.out.println("Available bytes at the end: ");　+　input.available());
　　　　　　　　　input.close();
　　　　　　}
　　　　　　catch (Exception e) {
　　　　　　　　　e.getStackTrace();
　　　　　　}
　　　}
}

Output Result

Available bytes at the beginning:　39
Available bytes at the end:　36

In the above example,

1. We first use the available() method to check the number of available bytes in the file input stream.

2. Then, we have used the read() method3time from the file input stream3bytes.

3. Now, after reading the bytes, we have checked the available bytes again. This time, the available bytes have decreased by3.

skip() method

To discard and skip a specified number of bytes, you can use the skip() method. For example

import java.io.FileInputStream;
public class Main {
　　　public static void main(String args[]) {
　　　　　　try {
　　　　　　　　//Assuming the input.txt file contains the following text
　　　　　　　　//This is a line of text in the file.
　　　　　　　　　FileInputStream input = new FileInputStream("input.txt");
　　　　　　　　　//skip5bytes
　　　　　　　　　input.skip(5);
　　　　　　　　　System.out.println("Input stream skips5bytes: ");
　　　　　　　　　//Read the first byte
　　　　　　　　　int i = input.read();
　　　　　　　　　while (i !=　-1) {
　　　　　　　　　　　　System.out.print((char) i);
　　　　　　　　　　　　//Read the next byte from the file
　　　　　　　　　　　　i = input.read();
　　　　　　　　　}
　　　　　　　　　//　close() method
　　　　　　　　　input.close();
　　　　　　}
　　　　　　catch (Exception e) {
　　　　　　　　　e.getStackTrace();
　　　　　　}
　　　}
}

Output Result

Input Stream Skip5bytes:
is a line of text inside the file.

In the above example, we used the skip() method to skip5bytes of data. Therefore, text representation will not be read from the input stream“This”bytes.

close() method

To close the file input stream, you can use the close() method. Once the close() method is called, we cannot use the input stream to read data.

In all the above examples, we have used the close() method to close the file input stream.

Other Methods of FileInputStream