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Java.io - Discussion

Java - DataInputStream read(byte[] b, int off, int len) method

Description

The Java DataInputStream read(byte[] b, int off, int len) method reads len bytes from the contained input stream and allocate them in the buffer b starting at b[off]. The method is blocked until input data is available, an exception is thrown or end of file is detected.

Declaration

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

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

Parameters

b − The byte[] into which the data is read from the input stream.
off − The start offset in the b[].
len − The maximum number of bytes read.

Return Value

Total number of bytes read, else -1 if the stream has reached the end.

Exception

IOException − If an I/O error occurs, the first byte cannot be read, or close() is invoked before this method.
NullPointerException − If b is null.
IndexOutOfBoundsException − If len is greater than b.length - off, off is negative, or len is negative

Example 1

The following example shows the usage of Java DataInputStream read(byte[] b, int offset, int len) method. We've created InputStream and DataInputStream references and then initialized them with FileInputStream and DataInputStream objects. In order to initialize DataInputStream(), we requires FileInputStream object. Once objects are created, we're checking if inputStream has content using available() method. Then a bytearray of available bytes is created which is then used in DataInputStream read() method, which populates the bytearray as per given input. Then this bytearray is iterated and printed.

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class DataInputStreamDemo {
   public static void main(String[] args) throws IOException {
      InputStream is = null;
      DataInputStream dis = null;
      
      try {
         // create input stream from file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create data input stream
         dis = new DataInputStream(is);
         
         // count the available bytes form the input stream
         int count = is.available();
         
         // create buffer
         byte[] bs = new byte[count];
         
         // read data into buffer
         dis.read(bs, 4, 3);
         
         // for each byte in the buffer
         for (byte b:bs) {

            // print the byte
            System.out.print(b+" ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases any associated system files with this stream
         if(is!=null)
            is.close();
         if(dis!=null)
            dis.close();
      }   
   }
}

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

ABCDEFGH

Output

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

0 0 0 0 65 66 67 0

Example 2

The following example shows the usage of Java DataInputStream read(byte[] b, int offset, int len) method. We've created InputStream and DataInputStream references and then initialized them with FileInputStream and DataInputStream objects. In order to initialize DataInputStream(), we requires FileInputStream object. Once objects are created, we're checking if inputStream has content using available() method. Then a bytearray of available bytes is created which is then used in DataInputStream read() method, which populates the bytearray with an invalid length required as input. Then this bytearray is iterated and printed.

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class DataInputStreamDemo {
   public static void main(String[] args) throws IOException {
      InputStream is = null;
      DataInputStream dis = null;
      
      try {
         // create input stream from file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create data input stream
         dis = new DataInputStream(is);
         
         // count the available bytes form the input stream
         int count = is.available();
         
         // create buffer
         byte[] bs = new byte[count];
         
         // read data into buffer with an invalid length
         dis.read(bs, 4, 10);
         
         // for each byte in the buffer
         for (byte b:bs) {

            // print the byte
            System.out.print(b+" ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases any associated system files with this stream
         if(is!=null)
            is.close();
         if(dis!=null)
            dis.close();
      }   
   }
}

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

ABCDEFGH

Output

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

java.lang.IndexOutOfBoundsException
	at java.base/java.io.FileInputStream.readBytes(Native Method)
	at java.base/java.io.FileInputStream.read(FileInputStream.java:279)
	at java.base/java.io.DataInputStream.read(DataInputStream.java:149)
	at DataInputStreamDemo.main(DataInputStreamDemo.java:25)

Example 3

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
public class DataInputStreamDemo {
   public static void main(String[] args) throws IOException {
      InputStream is = null;
      DataInputStream dis = null;
      
      try {
         // create input stream from file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create data input stream
         dis = new DataInputStream(is);
         
         // count the available bytes form the input stream
         int count = is.available();
         
         // create buffer
         byte[] bs = new byte[count];
         
         // read data into buffer
         dis.read(bs, 0, count);
         
         // for each byte in the buffer
         for (byte b:bs) {

            // print the byte
            System.out.print(b+" ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases any associated system files with this stream
         if(is!=null)
            is.close();
         if(dis!=null)
            dis.close();
      }   
   }
}

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

ABCDEFGH

Output

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

65 66 67 68 69 70 71 72

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