How to Convert String to Hex in Java

1. Convert String to Hex by Using Array of char and Integer.toHexString()
2. Convert String to Hex Using an Array of byte and String Formatter
3. Convert String to Hex in Java Using Apache Commons Codec
4. Convert String to Hex in Java Using BigInteger
5. Conclusion

In programming, there are various scenarios where you might need to convert a string into its hexadecimal representation. This task is particularly important in fields like data encoding, cryptography, and data storage.

Java, being a versatile language, provides multiple methods to achieve this goal. In this article, we will explore four distinct approaches to converting a string into its hexadecimal form in Java.

Convert String to Hex by Using Array of char and Integer.toHexString()

The Integer.toHexString() method in Java is a straightforward way to convert integers to their hexadecimal string representation. You can pass an integer value to this method, and it will return a string representing the hexadecimal value of that integer.

However, converting a string to hexadecimal requires working with individual characters in the string.

Here’s the basic idea of how we can convert a string to hexadecimal using Integer.toHexString():

Let’s break down the process into code snippets and explanations:

public static String stringToHex(String input) {
  char[] characters = input.toCharArray();
  StringBuilder hexString = new StringBuilder();

  for (char c : characters) {
    int intValue = (int) c;
    String hexValue = Integer.toHexString(intValue);
    hexString.append(hexValue);
  }

  return hexString.toString();
}

Now, let’s discuss each step in detail.

First, the toCharArray() method is used to convert the input string into an array of characters. This step is necessary to process each character in the string individually.

Using (int) c, we cast each character to an integer to obtain its Unicode code point. This step allows us to convert characters to their corresponding integer values.

Then, by using the Integer.toHexString() method, we convert the integer value to its hexadecimal representation as a string.

Next, we append the hexadecimal value to a StringBuilder using hexString.append(hexValue). Utilizing a StringBuilder is more efficient for concatenating strings repeatedly in a loop, as it reduces memory overhead.

Finally, we convert the StringBuilder to a string using the toString() method and return the result.

Here’s how you can use the stringToHex method to convert a string to its hexadecimal representation:

public class StringToHexExample {
  public static String stringToHex(String input) {
    char[] characters = input.toCharArray(); // Convert the input string to an array of characters
    StringBuilder hexString =
        new StringBuilder(); // Create a StringBuilder to store the hexadecimal representation

    for (char c : characters) {
      int intValue = (int) c; // Convert the character to its integer value
      String hexValue =
          Integer.toHexString(intValue); // Convert the integer to its hexadecimal representation
      hexString.append(hexValue); // Append the hexadecimal value to the StringBuilder
    }

    return hexString.toString(); // Convert the StringBuilder to a string and return the result
  }

  public static void main(String[] args) {
    String input = "Hello, World!";
    String hexadecimalString = stringToHex(input);
    System.out.println("Original String: " + input);
    System.out.println("Hexadecimal String: " + hexadecimalString);
  }
}

When you run this code, it will output:

Original String: Hello, World!
Hexadecimal String: 48656c6c6f2c20576f726c6421

As you can see, the stringToHex method effectively converts the input string into its hexadecimal representation.

Convert String to Hex Using an Array of byte and String Formatter

Java’s String.format() method provides a versatile way to format and create strings. It allows you to specify a format string, which includes placeholders for various data types, such as integers and floating-point numbers.

In the context of converting a string to hexadecimal, we can use the %02X format specifier to represent each byte as a two-character uppercase hexadecimal value.

Here’s the basic approach for converting a string to hexadecimal using String.format():

Let’s break down the process into code snippets and explanations:

public static String stringToHex(String input) {
  byte[] bytes = input.getBytes(); // Convert the input string to an array of bytes
  StringBuilder hexString =
      new StringBuilder(); // Create a StringBuilder to store the hexadecimal representation

  for (byte b : bytes) {
    hexString.append(String.format("%02X",
        b)); // Format the byte as a two-character hexadecimal value and append to the StringBuilder
  }

  return hexString.toString(); // Convert the StringBuilder to a string and return the result
}

Now, let’s discuss each step in detail.

We convert the input string into an array of bytes using the getBytes() method. This step is necessary to process each byte of the string individually.

Next, the %02X format specifier within String.format() is used to format each byte as a two-character uppercase hexadecimal value. It ensures that each hexadecimal value is represented as two characters and is in uppercase.

We then use hexString.append(...) to append the formatted hexadecimal value to a StringBuilder. Using a StringBuilder is more memory-efficient when concatenating strings in a loop.

Finally, we convert the StringBuilder to a string using the toString() method and return the result.

Here’s how you can use the stringToHex method to convert a string to its hexadecimal representation:

public class StringToHexExample {
  public static String stringToHex(String input) {
    byte[] bytes = input.getBytes();
    StringBuilder hexString = new StringBuilder();

    for (byte b : bytes) {
      hexString.append(String.format("%02X", b));
    }

    return hexString.toString();
  }

  public static void main(String[] args) {
    String input = "Hello, World!";
    String hexadecimalString = stringToHex(input);
    System.out.println("Original String: " + input);
    System.out.println("Hexadecimal String: " + hexadecimalString);
  }
}

When you run this code, it will output:

Original String: Hello, World!
Hexadecimal String: 48656C6C6F2C20576F726C6421

As you can see, the stringToHex method effectively converts the input string into its hexadecimal representation using the %02X format specifier and the String.format() method.

Convert String to Hex in Java Using Apache Commons Codec

Apache Commons Codec is a part of the Apache Commons project, which provides open-source, reusable libraries for various programming tasks. The Codec library focuses on encoding and decoding data in various formats, including Base64, hexadecimal, URL encoding, and more.

It simplifies data manipulation and is widely used in Java development for encoding and decoding operations.

Before you can use Apache Commons Codec, you need to add it to your Java project. You can do this using a build tool like Apache Maven or Gradle or by manually downloading and including the library.

If you’re using Apache Maven, you can include Apache Commons Codec as a dependency in your project’s pom.xml file:

<dependency>
    <groupId>commons-codec</groupId>
    <artifactId>commons-codec</artifactId>
    <version>1.15</version> <!-- Replace with the latest version -->
</dependency>

For Gradle users, add the following to your build.gradle file:

implementation group: 'commons-codec', name: 'commons-codec', version: '1.15' // Replace with the latest version

After adding the dependency, make sure to update your project so that Gradle or Maven downloads the library.

To use Apache Commons Codec for hexadecimal encoding, you need to import the Hex class from the library:

import org.apache.commons.codec.binary.Hex;

Now, you can create a method that takes a string as input and returns its hexadecimal representation. The core of the conversion is done by the Hex.encodeHex method provided by Apache Commons Codec:

public static String stringToHex(String input) {
  byte[] bytes = input.getBytes(); // Convert the input string to an array of bytes
  char[] hexChars = Hex.encodeHex(bytes); // Encode the byte array as hexadecimal
  return new String(hexChars); // Convert the char array back to a string and return the result
}

This method accepts an input string, converts it to a byte array, encodes the bytes as hexadecimal, and finally converts the hexadecimal bytes back to a string.

You can now use the stringToHex method to convert a string to its hexadecimal representation.

Here’s a complete working example of how to use it:

import org.apache.commons.codec.binary.Hex;

public class StringToHexExample {
  public static String stringToHex(String input) {
    byte[] bytes = input.getBytes(); // Convert the input string to an array of bytes
    char[] hexChars = Hex.encodeHex(bytes); // Encode the byte array as hexadecimal
    return new String(hexChars); // Convert the char array back to a string and return the result
  }

  public static void main(String[] args) {
    String input = "Hello, World!";
    String hexadecimalString = stringToHex(input);
    System.out.println("Original String: " + input);
    System.out.println("Hexadecimal String: " + hexadecimalString);
  }
}

When you run this code, it will output:

Original String: Hello, World!
Hexadecimal String: 48656c6c6f2c20576f726c6421

This output demonstrates the successful conversion of the input string to its hexadecimal representation using Apache Commons Codec.

Convert String to Hex in Java Using BigInteger

The BigInteger class in Java provides a way to represent integers of arbitrary precision. This class includes a method, toString(int radix), which allows us to convert numbers to a specified radix, such as hexadecimal (base 16).

Here are the steps to convert a string to its hexadecimal representation using BigInteger:

Take a look at the example below:

import java.math.BigInteger;

public class StringToHexUsingBigInteger {
  public static String stringToHex(String input) {
    byte[] bytes = input.getBytes();

    BigInteger bigInt = new BigInteger(1, bytes);

    String hexadecimalString = bigInt.toString(16);

    return hexadecimalString;
  }

  public static void main(String[] args) {
    String input = "Hello, World!";
    String hexadecimalString = stringToHex(input);

    System.out.println("Original String: " + input);
    System.out.println("Hexadecimal String: " + hexadecimalString);
  }
}

Here’s how the code works:

The stringToHex method takes an input string as its argument. Then, it converts the input string into a byte array using getBytes().

Next, it creates a BigInteger instance named bigInt from the byte array. The 1 passed as the first argument signifies that the byte array is positive.

Once that is done, it converts the BigInteger to a hexadecimal string using the toString(16) method. Finally, it returns the hexadecimal string.

The main method is the entry point of the program. It defines the input string as Hello, World! (you can change this string to any text you want to convert).

Then, it calls the stringToHex method to obtain the hexadecimal representation of the input string. Lastly, it displays both the original string and its hexadecimal representation in the console using System.out.println.

When you run the provided Java code, it will output:

Original String: Hello, World!
Hexadecimal String: 48656c6c6f2c20576f726c6421

This output demonstrates the successful conversion of the input string to its hexadecimal representation using the BigInteger class in Java.

Conclusion

Converting a string to its hexadecimal representation is a common operation in Java, and it’s important to understand the various methods available to achieve this task. Depending on your specific use case and requirements, you can choose the approach that best suits your needs.

Whether you opt for the simplicity of using arrays of characters, the versatility of BigInteger, the efficiency of byte arrays with a StringBuilder, or the convenience of Apache Commons Codec, you’ll be well-equipped to handle this essential operation in your Java projects.