Mastering Base64 Encoding and Decoding in Java

Introduction

In this lab, we will learn how to encode and decode Base64 data in Java using the java.util.Base64 class and the Apache Commons library.

Create a new Java file

In this step, you will create a new Java file. Open the terminal and execute the following command to create a new Java file:

touch ~/project/Base64Encoding.java

This command will create a new file named Base64Encoding.java inside the ~/project directory. You can use any preferred name, but ensure it ends with .java.

Basic Encoding and Decoding

In this step, we will learn about Basic Encoding and Decoding.

The Basic encoder uses the Base64 Alphabet for encoding and decoding.
It will not add any line separators to the encoded string.
We will use the getEncoder() method that returns a simple Base64.Encoder.
Then, we will use the encodeToString() method to encode the string.

For decoding an encoded string, we will use the Base64.Decoder returned by the getDecoder() method.

We will use the decode() method of the decoder.

Use the code block below for encoding and decoding a string:

import java.util.Base64;

public class Base64Encoding {
    public static void main(String[] args) {
        String strToEncode = "Hello World";
        byte[] bytesToEncode = strToEncode.getBytes(); // convert the string to a byte array

        // Encoding
        String encodedStr = Base64.getEncoder().encodeToString(bytesToEncode);
        System.out.println("Encoded String: " + encodedStr);

        // Decoding
        byte[] decodedByteArr = Base64.getDecoder().decode(encodedStr);
        String decodedStr = new String(decodedByteArr);
        System.out.println("Decoded String: " + decodedStr);
    }
}

Execute the following command in the terminal to compile and run the code:

javac Base64Encoding.java && java Base64Encoding

Base64 Encoding Without Padding

In the previous step, we saw that encoding adds padding characters ( = ) at the end of the encoded string. In this step, we will learn how to encode without padding characters.

Use the following code block for encoding the string without padding:

import java.util.Base64;

public class Base64Encoding {
    public static void main(String[] args) {
        String strToEncode = "Java";
        byte[] bytesToEncode = strToEncode.getBytes(); // convert the string to a byte array

        // Encoding without padding
        String encodedStr = Base64.getEncoder().withoutPadding().encodeToString(bytesToEncode);
        System.out.println("Encoded String: " + encodedStr);
    }
}

Execute the following command in the terminal to compile and run the code:

javac Base64Encoding.java && java Base64Encoding

URL and Filename Safe Encoding and Decoding

In this step, we will learn about URL and Filename Safe Encoding and Decoding.

The Base64 class handles URL encoding and decoding by using the URL and Filename safe Base64 Alphabet.

We will use the getUrlEncoder() method to obtain a Base64 URL encoder.
Then, we will use the encodeToString() method as we did in the previous section.

Similarly, we have a getUrlDecoder() method that returns a URL decoder.

We can use the decode() method with this decoder for decoding.

Use the code block below to encode and decode a URL:

import java.util.Base64;

public class Base64Encoding {
    public static void main(String[] args) {
        String urlToEncode = "https://go.java/?intcmp=gojava-banner-java-com";

        // Encoding
        String encodedUrl = Base64.getUrlEncoder().encodeToString(urlToEncode.getBytes());
        System.out.println("Encoded URL: " + encodedUrl);

        // Decoding
        byte[] decodedUrlBytes = Base64.getUrlDecoder().decode(encodedUrl);
        String decodedUrl = new String(decodedUrlBytes);
        System.out.print("Decoded URL: " + decodedUrl);
    }
}

Execute the following command in the terminal to compile and run the code:

javac Base64Encoding.java && java Base64Encoding

MIME Encoding and Decoding

In this step, we will learn about MIME Encoding and Decoding.

The Base64 class uses the Base64 Alphabet for its encoding and decoding operations.
In the encoded output, each line contains a maximum of 76 characters.
Each line ends with a carriage return( \r ) followed by a linefeed( \n ) as the line separator.

We can use the getMimeEncoder() and the encodeToString() methods for the encoding. To decode, we will use the getMimeDecoder() method to obtain a decoder, and then we will use the decode() method.

Use the following code block for encoding and decoding MIME data:

import java.util.Base64;
import java.util.UUID;

public class Base64Encoding {
    public static void main(String[] args) {
        // Creating a MIME input for encoding
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 10; ++i) {
            sb.append(UUID.randomUUID().toString());
        }
        // Encoding
        byte[] bytes = sb.toString().getBytes();
        String mimeEncodedStr = Base64.getMimeEncoder().encodeToString(bytes);
        System.out.println("Encoded String: " + mimeEncodedStr);

        // Decoding
        byte[] mimeDecodedBytes = Base64.getMimeDecoder().decode(mimeEncodedStr);
        String mimeDecodedStr = new String(mimeDecodedBytes);
    }
}

Execute the following command in the terminal to compile and run the code:

javac Base64Encoding.java && java Base64Encoding

Using Apache Commons Library

In this step, we will learn how to use the Apache Commons library for encoding and decoding Base64 data.

The Apache Commons library provides a Base64 class inside its org.apache.commons.codec.binary package.

This class contains five different constructors for different encoding schemes.
After creating a Base64 instance, we can use the encode() and decode() methods on the string bytes to perform encoding and decoding.

Use the following code block to encode and decode a string using the Apache Commons Base64 class:

import org.apache.commons.codec.binary.Base64;

public class Base64Encoding {
    public static void main(String[] args) {

        Base64 base64 = new Base64();

        // Encoding
        String strToEncode = "Hello World";
        byte[] encodedBytes = base64.encode(strToEncode.getBytes());
        String encodedStr = new String(encodedBytes);
        System.out.println("Encoded String: " + encodedStr);

        // Decoding
        byte[] decodedByteArr = base64.decode(encodedStr.getBytes());
        String decodedStr = new String(decodedByteArr);
        System.out.println("Decoded String: " + decodedStr);

        // Directly access the API by using the static methods encodeBase64() and decodeBase64()
        String strToEncode2 = "Hello World";
        String encodedStr2 = new String(Base64.encodeBase64(strToEncode.getBytes()));
        String decodedStr2 = new String(Base64.decodeBase64(encodedStr.getBytes()));
    }
}

Execute the following command in the terminal to compile and run the code:

javac -cp commons-codec-1.15.jar Base64Encoding.java && java -cp commons-codec-1.15.jar:. Base64Encoding

Note: To run this code, you need to download and import the Apache Commons Codec library's .jar file into the classpath. In the command above, we added -cp commons-codec-1.15.jar to specify the classpath of the library.

Summary

In this lab, we learned how to encode and decode Base64 data in Java using the java.util.Base64 class and the Apache Commons library. We covered three different Base64 encoding and decoding schemes - Basic, URL, and Filename safe, and MIME.