Java.io.InputStream.read() Method

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Description

The java.io.InputStream.read(byte[] b, int off, int len) method reads upto len bytes of data from the input stream into an array of bytes. If the parameter len is zero, then no bytes are read and 0 is returned; else there is an attempt to read atleast one byte. If the stream is at the end of the file, the value returned is -1.

Declaration

Following is the declaration for java.io.InputStream.read(byte[] b, int off, int len) method −

public int read(byte[] b, int off, int len)

Parameters

• b − The destination byte array.

• off − The start offset in array b at which the data is written.

• len − The number of bytes to read.

Return Value

The method returns the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.

Exception

• IOException − If an I/O error occurs.

• NullPointerException − If b is null.

• IndexOutOfBoundsException − If off is negative, len is negative, or len is greater than b.length - off.

Example

The following example shows the usage of java.io.InputStream.read(byte[] b, int off, int len) method.

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.InputStream;

public class InputStreamDemo {
   public static void main(String[] args) throws Exception {
      InputStream is = null;
      byte[] buffer = new byte[5];
      char c;
      
      try {
         // new input stream created
         is = new FileInputStream("C://test.txt");
         
         System.out.println("Characters printed:");
         
         // read stream data into buffer
         is.read(buffer, 2, 3);
         
         // for each byte in the buffer
         for(byte b:buffer) {
         
            // convert byte to character
            if(b == 0)
               
               // if b is empty
               c = '-';
            else
               
               // if b is read
               c = (char)b;
            
            // prints character
            System.out.print(c);
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases system resources associated with this stream
         if(is!=null)
            is.close();
      }
   }
}

Assuming we have a text file c:/test.txt, which has the following content. This file will be used as an input for our example program −

ABCDE

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

Characters printed:
--ABC