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Showing content from https://www.tutorialspoint.com/java/io/datainputstream_readfully.htm below:

Java - DataInputStream readFully(byte[] b) method

The Java DataInputStream readFully(byte[] b) method reads bytes from an input stream and allocates those into the buffer array b.

It blocks until the one of the below conditions occurs −

• b.length bytes of input data are available.

• End of file detected.

• If any I/O error occurs.

Following is the declaration for java.io.DataInputStream.readFully(byte[] b) method −

public final void readFully(byte[] b)

NA

This method does not return any value.

• IOException − If any I/O error occurs or the stream has been closed.

• EOFException − If this input stream reaches the end before.

The following example shows the usage of Java DataInputStream readFully(byte[] b) 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 readFully() method, which populates the bytearray completely. Then this bytearray is iterated and printed.

package com.tutorialspoint;

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 file input stream
         is = new FileInputStream("test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);
         
         // available stream to be read
         int length = dis.available();
         
         // create buffer
         byte[] buf = new byte[length];
         
         // read the full data into the buffer
         dis.readFully(buf);
         
         // for each byte in the buffer
         for (byte b:buf) {
         
            // convert byte to char
            char c = (char)b; 
            
            // prints character
            System.out.print(c);
         }
         
      } catch(Exception e) {
         // if any error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dis!=null)
            dis.close();
      }
   }
}

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

Hello World!

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

Hello World!

The following example shows the usage of Java DataInputStream readFully(byte[] b) 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. In this example, we're using a non-existing file and see if readFully() method is throwing exception.

package com.tutorialspoint;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
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("test1.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.readFully(bs);
         
         // for each byte in the buffer
         for (byte b:bs) {
         
            // convert byte into character
            char c = (char)b;
            
            // print the character
            System.out.print(c+" ");
         }
         
      } 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 are not having a text file test1.txt. This file will be used as an input for our example program −

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

java.io.FileNotFoundException: test1.txt (The system cannot find the file specified)
	at java.base/java.io.FileInputStream.open0(Native Method)
	at java.base/java.io.FileInputStream.open(FileInputStream.java:219)
	at java.base/java.io.FileInputStream.<init&t;(FileInputStream.java:157)
	at java.base/java.io.FileInputStream.<init&t;(FileInputStream.java:112)
	at DataInputStreamDemo.main(DataInputStreamDemo.java:14)

The following example shows the usage of Java DataInputStream readFully(byte[] b) 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. In this example, we're using an empty file and see if readFully() method is throwing exception or able to read an empty file successfully.

package com.tutorialspoint;

import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
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("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.readFully(bs);
         
         // for each byte in the buffer
         for (byte b:bs) {
         
            // convert byte into character
            char c = (char)b;
            
            // print the character
            System.out.print(c+" ");
         }
         
      } 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 test.txt, which has no content.

Let us compile and run the above program, this will produce the result as empty content

java_io_datainputstream.htm

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