Check out example codes for "Java use Base64". It will help you in understanding the concepts better.

Code Example 1

//For Strings:
  
  //Encode:
  public static String encode(String input) {

      return Base64.getEncoder().encodeToString(input.getBytes());

  }

  //Decode:
  public static String decode(String input) {

      byte[] decodedBytes = Base64.getDecoder().decode(input);
      return new String(decodedBytes);

  }
  
//For Urls
  //Encode:
  public static String encodeURL(String input) {

      return Base64.getUrlEncoder().encodeToString(input.getBytes());

  }

  //Decode:
  public static String decodeURL(String input) {

      byte[] decodedBytes = Base64.getUrlDecoder().decode(input);
      return new String(decodedBytes);

  }

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