How to Properly Encode URI Parameter Values According to RFC 2396

How do I properly encode URI parameter values in Java according to RFC 2396?

String originalUri = "http://google.com/resource?key=value1 & value2";

Encoding URI parameter values correctly is crucial for making sure your requests are properly interpreted by servers and clients. RFC 2396 outlines specific rules for encoding characters in URI components, ensuring that query parameters are correctly formatted and interpreted. In Java, the usual tools may not suffice. Here's how to correctly handle URI encoding.

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.net.URI;
import java.net.URISyntaxException;

public class URIEncodingExample {
    public static String encodeUri(String uriString) throws UnsupportedEncodingException, URISyntaxException {
        URI uri = new URI(uriString);
        return URLEncoder.encode(uri.toString(), "UTF-8")
               .replaceAll("%3A", ":")
               .replaceAll("%2F", "/")
               .replaceAll("%3F", "?")
               .replaceAll("%3D", "=")
               .replaceAll("%26", "&");
    }

    public static void main(String[] args) throws Exception {
        String originalUri = "http://google.com/resource?key=value1 & value2";
        String encodedUri = encodeUri(originalUri);
        System.out.println(encodedUri);
    }
}

Causes

• Common libraries like `java.net.URLEncoder` are designed for application/x-www-form-urlencoded, which is different from URI encoding as defined in RFC 2396.
• The special characters such as '&' and '=' need specific encoding to ensure they are interpreted correctly as part of parameters, rather than delimiters.

Solutions

• To encode a URI parameter value correctly, you can use `java.net.URI` alongside manual string replacements to achieve the required output.
• Firstly, replace problematic characters in your URI string with their percent-encoded counterparts manually as per RFC 2396 guidelines.
• Use the following approach to encode your entire URI including the query components: ```java import java.io.UnsupportedEncodingException; import java.net.URLEncoder; import java.net.URI; import java.net.URISyntaxException; public class URIEncodingExample { public static String encodeUri(String uriString) throws UnsupportedEncodingException, URISyntaxException { URI uri = new URI(uriString); return URLEncoder.encode(uri.toString(), "UTF-8") .replaceAll("%3A", ":") .replaceAll("%2F", "/") .replaceAll("%3F", "?") .replaceAll("%3D", "=") .replaceAll("%26", "&"); } public static void main(String[] args) throws Exception { String originalUri = "http://google.com/resource?key=value1 & value2"; String encodedUri = encodeUri(originalUri); System.out.println(encodedUri); } } ```
• This code first encodes the full URI and replaces reserved characters that are pertinent to RFC 2396.
• Be careful to retain the integrity of the query parameters while encoding.

Mistake: Not encoding spaces and special characters properly.

Solution: Always ensure to replace spaces with '%20' or '+'. For other special characters, refer to the requested encoding specification.

Mistake: Assuming all encodings performed are the same for form and URI encoding.

Solution: Understand the distinction between application/x-www-form-urlencoded and URI encoding as per RFC 2396.