import java.util.HashMap;

import java.util.Map;

public class UrlParameterTransformer {

public static Map<String, String> transformUrlParams(String url) {

Map<String, String> params = new HashMap<>();

if (url == null || url.isEmpty()) {

return params; // Return empty map for null or empty URL

}

String[] pairs = url.split("&"); // Split URL into key-value pairs

for (String pair : pairs) {

if (pair == null || pair.isEmpty()) {

continue; // Skip empty pairs

}

int equalsIndex = pair.indexOf("=");

if (equalsIndex == -1) {

continue; // Skip pairs without equals sign

}

String key = pair.substring(0, equalsIndex);

String value = pair.substring(equalsIndex + 1);

if (key == null || key.isEmpty()) {

continue; // Skip pairs with empty key

}

if (value == null || value.isEmpty()) {

value = "null"; //Handle empty values as "null"

}

params.put(key, value);

}

return params;

}

public static void main(String[] args) {

//Example usage and testing

String url1 = "param1=value1&param2=value2";

String url2 = "param1=value1&param2";

String url3 = "param1=&param2=value2";

String url4 = "";

String url5 = null;

String url6 = "param1=value1&param2=value2&param1=value3";

String url7 = "param1=value1&param2=value2&param1=value3&param1=";

String url8 = "param1=value1&param2=value2&param1=value3&";

String url9 = "param1=value1&param2=value2&param1=value3&param1=value3";

System.out.println(transformUrlParams(url1));

System.out.println(transformUrlParams(url2));

System.out.println(transformUrlParams(url3));

System.out.println(transformUrlParams(url4));

System.out.println(transformUrlParams(url5));

System.out.println(transformUrlParams(url6));

System.out.println(transformUrlParams(url7));

System.out.println(transformUrlParams(url8));

System.out.println(transformUrlParams(url9));

}

}