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Java - DataInputStream readUTF() method

Description

The Java DataInputStream readUTF() method reads in a string that has been encoded using a modified UTF-8 format. The string of character is decoded from the UTF and returned as String.

Declaration

Following is the declaration for java.io.DataInputStream.readUTF() method −

public final String readUTF()

Parameters

Return Value

This method returns a unicode string.

Exception

IOException − If the stream is closed or the or any I/O error occurs.
EOFException − If the input stream has reached the ends.
UTFDataFormatException − If the bytes do not represent a valid modified UTF-8 encoding.

Example 1

The following example shows the usage of Java DataInputStream readUTF() method. We've created InputStream, DataInputStream, FileOutputStream and DataOutputStream reference. A String[] buf is initialized with some string values. A FileOutputStream object is created with a File. Then DataOutputStream is initialized with FileOutputStream object created before. Then string array is iterated to write string values to the dataoutputstream.

Once string arrays is fully written into the stream, we've flush the stream to store the values in the file. Now using FileInputStream and DataInputStream, we're reading the file written earlier. Now we're checking if DataInputStream object has data using available() method. Then using readUTF() method, we're reading every value as String. Finally we're closing all the streams.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
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;
      FileOutputStream fos = null;
      DataOutputStream dos = null;
      String[] buf = {"Hello", "World!!"};
      
      try {
         // create file output stream
         fos = new FileOutputStream("F:\\test.txt");
         
         // create data output stream
         dos = new DataOutputStream(fos);
         
         // for each string in the buffer
         for (String j:buf) {
         
            // write string encoded as modified UTF-8
            dos.writeUTF(j);        
         }
         
         // force data to the underlying stream
         dos.flush();
         
         // create file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);
         
         // read till end of the stream
         while(dis.available()>0) {
         
            // reads characters encoded with modified UTF-8
            String k = dis.readUTF();
            
            // print
            System.out.print(k+" ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dos!=null)
            is.close();
         if(dis!=null)
            dis.close();
         if(fos!=null)
            fos.close();
      }
   }
}

Output

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

Hello World!!

Example 2

The following example shows the usage of Java DataInputStream readUTF() method. We've created InputStream, DataInputStream, FileOutputStream and DataOutputStream reference. A String[] buf is initialized with some String values. A FileOutputStream object is created with a File. Then DataOutputStream is initialized with FileOutputStream object created before. Then String array is iterated to write String values to the dataoutputstream.

Once String arrays is fully written into the stream, we've flush the stream to store the values in the file. Now using FileInputStream and DataInputStream, we're reading the file written earlier. Now we're checking if DataInputStream object has data using available() method. Then using readUTF() method, we're reading every value as String. Now as a special case, we're closing the stream before reading the values to see if this method throw exception or not. As a result, we can see the available() method throws the exception.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
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;
      FileOutputStream fos = null;
      DataOutputStream dos = null;
      String[] buf = {"Hello", "World!!"};
      
      try {
         // create file output stream
         fos = new FileOutputStream("F:\\test.txt");
         
         // create data output stream
         dos = new DataOutputStream(fos);
         
         // for each String in the buffer
         for (String j:buf) {
         
            // write string encoded as modified UTF-8
            dos.writeUTF(j);         
         }
         
         // force Strings to the underlying stream
         dos.flush();
         
         // create file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);

         // close the streams
         is.close();
         dis.close();
         
         // read till end of the stream
         while(dis.available()>0) {
         
            // reads characters encoded with modified UTF-8
            String k = dis.readUTF();
            
            // print
            System.out.print(k+" ");
         }
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dos!=null)
            is.close();
         if(dis!=null)
            dis.close();
         if(fos!=null)
            fos.close();
      }
   }
}

Output

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

java.io.IOException: Stream Closed
	at java.base/java.io.FileInputStream.available0(Native Method)
	at java.base/java.io.FileInputStream.available(FileInputStream.java:330)
	at java.base/java.io.FilterInputStream.available(FilterInputStream.java:167)
	at DataInputStreamDemo.main(DataInputStreamDemo.java:44)

Example 3

The following example shows the usage of Java DataInputStream readUTF() method. We've created InputStream, DataInputStream, FileOutputStream and DataOutputStream reference. A String[] buf is initialized with some String values. A FileOutputStream object is created with a File. Then DataOutputStream is initialized with FileOutputStream object created before. Then String array is iterated to write String values to the dataoutputstream.

Once String arrays is fully written into the stream, we've flush the stream to store the values in the file. Now using FileInputStream and DataInputStream, we're reading the file written earlier. Now we're checking if DataInputStream object has data using available() method. Then using readUTF() method, we're reading every value as String. Now as a special case, we're reading Strings after all Strings are read using readUTF() method. As a result, we can see the readUTF() throws an EOFException.

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
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;
      FileOutputStream fos = null;
      DataOutputStream dos = null;
      String[] buf = {"Hello", "World!!"};
      
      try {
         // create file output stream
         fos = new FileOutputStream("F:\\test.txt");
         
         // create data output stream
         dos = new DataOutputStream(fos);
         
         // for each String in the buffer
         for (String j:buf) {
         
            // write string encoded as modified UTF-8
            dos.writeUTF(j);
         }
         
         // force Strings to the underlying stream
         dos.flush();
         
         // create file input stream
         is = new FileInputStream("F:\\test.txt");
         
         // create new data input stream
         dis = new DataInputStream(is);
         
         // read till end of the stream
         while(dis.available()>0) {
         
            // reads characters encoded with modified UTF-8
            String k = dis.readUTF();
            
            // print
            System.out.print(k+" ");
         }
		 System.out.print(dis.readUTF());
         
      } catch(Exception e) {
         // if any I/O error occurs
         e.printStackTrace();
      } finally {
         // releases all system resources from the streams
         if(is!=null)
            is.close();
         if(dos!=null)
            is.close();
         if(dis!=null)
            dis.close();
         if(fos!=null)
            fos.close();
      }
   }
}

Output

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

Hello World!! java.io.EOFException
	at java.base/java.io.DataInputStream.readUnsignedShort(DataInputStream.java:345)
	at java.base/java.io.DataInputStream.readUTF(DataInputStream.java:594)
	at java.base/java.io.DataInputStream.readUTF(DataInputStream.java:569)
	at DataInputStreamDemo.main(DataInputStreamDemo.java:48)

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