Java BufferedInputStream Class

The BufferedInputStream class of the java.io package is used with other input streams to read the data (in bytes) more efficiently.

It extends the InputStream abstract class.

Working of BufferedInputStream

The BufferedInputStream maintains an internal buffer of 8192 bytes.

During the read operation in BufferedInputStream, a chunk of bytes is read from the disk and stored in the internal buffer. And from the internal buffer bytes are read individually.

Hence, the number of communication to the disk is reduced. This is why reading bytes is faster using the BufferedInputStream.

Create a BufferedInputStream

In order to create a BufferedInputStream, we must import the java.io.BufferedInputStream package first. Once we import the package here is how we can create the input stream.

// Creates a FileInputStream
FileInputStream file = new FileInputStream(String path);

// Creates a BufferedInputStream
BufferedInputStream buffer = new BufferInputStream(file);

In the above example, we have created a BufferdInputStream named buffer with the FileInputStream named file.

Here, the internal buffer has the default size of 8192 bytes. However, we can specify the size of the internal buffer as well.

// Creates a BufferedInputStream with specified size internal buffer
BufferedInputStream buffer = new BufferInputStream(file, int size);

The buffer will help to read bytes from the files more quickly.

Methods of BufferedInputStream

The BufferedInputStream class provides implementations for different methods present in the InputStream class.

read() Method

• read() - reads a single byte from the input stream
• read(byte[] arr) - reads bytes from the stream and stores in the specified array
• read(byte[] arr, int start, int length) - reads the number of bytes equal to the length from the stream and stores in the specified array starting from the position start

Suppose we have a file named input.txt with the following content.

This is a line of text inside the file.

Let's try to read the file using BufferedInputStream.

import java.io.BufferedInputStream;
import java.io.FileInputStream;

class Main {
    public static void main(String[] args) {
        try {

            // Creates a FileInputStream
            FileInputStream file = new FileInputStream("input.txt");

            // Creates a BufferedInputStream
            BufferedInputStream input = new BufferedInputStream(file);

            // Reads first byte from file
            int i = input .read();

            while (i != -1) {
                System.out.print((char) i);

                // Reads next byte from the file
                i = input.read();
            }
            input.close();
        }

        catch (Exception e) {
            e.getStackTrace();
        }
    }
}

Output

This is a line of text inside the file.

In the above example, we have created a buffered input stream named buffer along with FileInputStream. The input stream is linked with the file input.txt.

FileInputStream file = new FileInputStream("input.txt");
BufferedInputStream buffer = new BufferedInputStream(file);

Here, we have used the read() method to read an array of bytes from the internal buffer of the buffered reader.

available() Method

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

import java.io.FileInputStream;
import java.io.BufferedInputStream;

public class Main {

   public static void main(String args[]) {

      try {

         // Suppose, the input.txt file contains the following text
         // This is a line of text inside the file.
         FileInputStream file = new FileInputStream("input.txt");
         
         // Creates a BufferedInputStream
         BufferedInputStream buffer = new BufferedInputStream(file);

         // Returns the available number of bytes
         System.out.println("Available bytes at the beginning: " + buffer.available());

         // Reads bytes from the file
         buffer.read();
         buffer.read();
         buffer.read();

         // Returns the available number of bytes
         System.out.println("Available bytes at the end: " + buffer.available());

         buffer.close();
      }

      catch (Exception e) {
         e.getStackTrace();
      }
   }
}

Output

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 input stream.
2. Then, we have used the read() method 3 times to read 3 bytes from the input stream.
3. Now, after reading the bytes we again have checked the available bytes. This time the available bytes decreased by 3.

skip() Method

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

import java.io.FileInputStream;
import java.io.BufferedInputStream;

public class Main {

   public static void main(String args[]) {

      try {
         // Suppose, the input.txt file contains the following text
         // This is a line of text inside the file.
         FileInputStream file = new FileInputStream("input.txt");

         // Creates a BufferedInputStream
         BufferedInputStream buffer = new BufferedInputStream(file);

         // Skips the 5 bytes
         buffer.skip(5);
         System.out.println("Input stream after skipping 5 bytes:");

         // Reads the first byte from input stream
         int i = buffer.read();
         while (i != -1) {
            System.out.print((char) i);

            // Reads next byte from the input stream
            i = buffer.read();
         }

         // Closes the input stream
         buffer.close();
      }

      catch (Exception e) {
         e.getStackTrace();
      }
   }
}

Output

Input stream after skipping 5 bytes: is a line of text inside the file.

In the above example, we have used the skip() method to skip 5 bytes from the file input stream. Hence, the bytes 'T', 'h', 'i', 's' and ' ' are skipped from the input stream.

close() Method

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

Other Methods Of BufferedInputStream

To learn more, visit Java BufferdInputStream (official Java documentation).