🧠 What is URL Encoding?

✅ URL encoding is the process of translating special characters in a URL into a format that can be safely transmitted over the Internet.

In URLs:

• Only letters, digits, and a few special characters (-, _, ., ~) are allowed as-is.
• Spaces, symbols (@, #, ?, =, /, etc.) must be encoded.

🔵 Encoding replaces unsafe characters with a % followed by two hexadecimal digits.

✅ Example:

Character	Encoded as
Space ()	%20
@	%40
:	%3A
/	%2F
?	%3F
&	%26

🎯 Why do we need URL encoding?

• To safely pass data inside URLs without confusion.
• To avoid breaking the URL structure.
• To transmit non-ASCII characters (like ü, ç, 你好) safely over HTTP.

If you don’t encode properly:

• URLs can get corrupted.
• Parameters might be misinterpreted.

⚙️ How to Do URL Encoding in Java

✅ Java provides a built-in class: java.net.URLEncoder

Example:

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

public class UrlEncodeExample {
    public static void main(String[] args) {
        String original = "Hello World! @2024";
        String encoded = URLEncoder.encode(original, StandardCharsets.UTF_8);
        System.out.println(encoded);
    }
}

✅ Output:

Hello+World%21+%402024

🔵 Note:

• Spaces become + (in application/x-www-form-urlencoded).
• Special characters are encoded as %XX.

🛠️ Important:

• Always specify the character encoding (usually UTF-8).
• Don’t forget to decode later if needed using URLDecoder.decode()!

import java.net.URLDecoder;

String decoded = URLDecoder.decode(encoded, StandardCharsets.UTF_8);
System.out.println(decoded); // back to "Hello World! @2024"

🔥 Example: Sending data safely in a query parameter

Suppose you want to create a link like:

https://example.com/search?query=Hello World! @2024

✅ Correct way:

String query = "Hello World! @2024";
String encodedQuery = URLEncoder.encode(query, StandardCharsets.UTF_8);

String url = "https://example.com/search?query=" + encodedQuery;
System.out.println(url);

Result:

https://example.com/search?query=Hello+World%21+%402024

🛡️ Warning:

Situation	Correct Approach
Encoding full URL	❌ Don’t encode the whole URL blindly (only parameters!)
Encoding query parameters	✅ Always encode values (key/value parts)
Encoding path segments	✅ Encode separately if needed

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🚀 Quick Summary

Concept	Meaning
URL Encoding	Convert unsafe characters in a URL into safe %XX format
Java class	URLEncoder.encode(String, Charset)
Common encoding	UTF-8
Also decode	Use URLDecoder.decode() when needed