In Java, you can use the URLEncoder and URLDecoder classes to handle URL encoding and decoding. These classes are part of the java.net package and are often used to ensure that special characters in URLs are properly encoded so they can be safely transmitted over the web. For decoding, you can convert encoded URLs back to their original form.

Here’s how you can implement URL encoding and decoding:

1. Encoding a URL using URLEncoder

Encoding a URL involves replacing unsafe characters or special characters with a % followed by hexadecimal digits. For instance, a space will be replaced by %20.

package org.kodejava.net;

import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;

public class UrlEncodingExample {
   public static void main(String[] args) {
      try {
         String url = "https://example.com/query?name=John Doe&city=New York";

         // Encode the URL
         String encodedUrl = URLEncoder.encode(url, StandardCharsets.UTF_8);

         System.out.println("Original URL: " + url);
         System.out.println("Encoded URL: " + encodedUrl);
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}

2. Decoding a URL using URLDecoder

Decoding a URL transforms it back to its original, human-readable form by replacing encoded sequences with their respective characters.

package org.kodejava.net;

import java.net.URLDecoder;
import java.nio.charset.StandardCharsets;

public class UrlDecodingExample {
   public static void main(String[] args) {
      try {
         String encodedUrl = "https%3A%2F%2Fexample.com%2Fquery%3Fname%3DJohn%2BDoe%26city%3DNew%2BYork";

         // Decode the URL
         String decodedUrl = URLDecoder.decode(encodedUrl, StandardCharsets.UTF_8);

         System.out.println("Encoded URL: " + encodedUrl);
         System.out.println("Decoded URL: " + decodedUrl);
      } catch (Exception e) {
         e.printStackTrace();
      }
   }
}

Explanation of the Parameters:

1. URLEncoder.encode(String, String):
   • First argument: The string (URL or part of it) to encode.
   • Second argument: The character encoding (e.g., UTF-8).
2. URLDecoder.decode(String, String):
   • First argument: The encoded string to decode.
   • Second argument: The character encoding.

Both URLEncoder.encode and URLDecoder.decode require a character encoding parameter, which specifies how characters are encoded/decoded. It’s common to use UTF-8 as it is the standard encoding for the web.

Output Example:

Encoding Example:

• Input: https://example.com/query?name=John Doe&city=New York
• Encoded: https%3A%2F%2Fexample.com%2Fquery%3Fname%3DJohn%2BDoe%26city%3DNew%2BYork

Decoding Example:

• Input: https%3A%2F%2Fexample.com%2Fquery%3Fname%3DJohn%2BDoe%26city%3DNew%2BYork
• Decoded: https://example.com/query?name=John Doe&city=New York

Important Notes

• Be sure to use the appropriate character encoding (e.g., UTF-8), as using the wrong one might result in garbled data.
• URLEncoder encodes spaces as + (plus sign), conforming to application/x-www-form-urlencoded (often used in HTML form submissions). If you need to encode spaces as %20 (used in URLs), additional handling may be required.

This is how you can use URLEncoder and URLDecoder effectively for URL encoding and decoding in Java.