Java - ObjectInputStream readUTF() method

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Description

The Java ObjectInputStream readUTF() method reads a UTF-8 encoded string from the input stream. It is useful when dealing with serialized text data in a binary format.

Declaration

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

public String readUTF()

Parameters

NA

Return Value

This method returns the String.

Exception

• UTFDataFormatException − If read bytes do not represent a valid modified UTF-8 encoding of a string.

• IOException − If there are I/O errors while reading from the underlying InputStream.

Example - Usage of ObjectInputStream readUTF() method

The following example shows the usage of Java ObjectInputStream readUTF() method.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      String s = "Hello World!";
      
      try {
         // create a new file with an ObjectOutputStream
         FileOutputStream out = new FileOutputStream("test.txt");
         ObjectOutputStream oout = new ObjectOutputStream(out);

         // write something in the file
         oout.writeUTF(s);
         oout.writeUTF("This is an example");
         oout.flush();

         // create an ObjectInputStream for the file we created before
         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));

         // read and print the string
         System.out.println("" + ois.readUTF());

         // read and print the string
         System.out.println("" + ois.readUTF());
      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }
}

Output

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

Hello World!
This is an example

Example - Reading a Single UTF String

The following example shows the usage of Java ObjectInputStream readUTF() method. This example writes a single UTF-8 string to a file and reads it back using readUTF().

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      String filename = "utfData.bin";

      // Writing a UTF string to a file
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         oos.writeUTF("Hello, World!"); // Writing a UTF-8 encoded string
         System.out.println("UTF string written to file.");
      } catch (IOException e) {
         e.printStackTrace();
      }

      // Reading the UTF string using ObjectInputStream
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         String message = ois.readUTF(); // Reads the UTF-8 string
         System.out.println("Read UTF string: " + message);
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

UTF string written to file.
Read UTF string: Hello, World!

Explanation

• Writes a UTF-8 encoded string ("Hello, World!") to a binary file using writeUTF().

• readUTF() reads the string correctly without character corruption.

• This is useful for cross-platform compatibility since UTF-8 supports international characters.

Example - Reading Multiple UTF Strings from a File

The following example shows the usage of Java ObjectInputStream readUTF() method. This example writes multiple UTF-8 strings to a file and reads them back.

ObjectInputStreamDemo.java

package com.tutorialspoint;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputStreamDemo {
   public static void main(String[] args) {
      String filename = "multiUtfData.bin";

      // Writing multiple UTF strings to a file
      try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(filename))) {
         oos.writeUTF("Java Programming");
         oos.writeUTF("こんにちは (Hello in Japanese)");
         oos.writeUTF("Hola, ¿cómo estás? (Spanish)");
         System.out.println("Multiple UTF strings written to file.");
      } catch (IOException e) {
         e.printStackTrace();
      }

      // Reading the UTF strings using ObjectInputStream
      try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(filename))) {
         System.out.println("Reading UTF strings:");
         for (int i = 0; i < 3; i++) {
            String message = ois.readUTF(); // Reads each UTF-8 string
            System.out.println("String " + (i + 1) + ": " + message);
         }
      } catch (IOException e) {
         e.printStackTrace();
      }
   }
}

Output

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

Multiple UTF strings written to file.
Reading UTF strings:
String 1: Java Programming
String 2: こんにちは (Hello in Japanese)
String 3: Hola, ¿cómo estás? (Spanish)

Explanation

• Writes three UTF-8 encoded strings: "Java Programming" , "こんにちは (Hello in Japanese)" , "Hola, ¿cómo estás? (Spanish)".

• readUTF() reads each string in the correct order.

• This ensures correct character encoding for international text.