import java.util.HashMap;

import java.util.Map;

import java.util.logging.Logger;

public class QueryStringValidator {

private static final Logger logger = Logger.getLogger(QueryStringValidator.class.getName());

public static String validateQueryString(String queryString, Map<String, String> allowedParameters) {

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

logger.warning("Query string is null or empty.");

return ""; // Or handle as appropriate for your use case

}

Map<String, String> parsedParams = parseQueryString(queryString);

for (Map.Entry<String, String> entry : parsedParams.entrySet()) {

String paramName = entry.getKey();

String paramValue = entry.getValue();

if (!allowedParameters.containsKey(paramName)) {

logger.error("Invalid query parameter: " + paramName + " with value: " + paramValue);

return ""; // Or handle as appropriate. Could return null, throw exception, etc.

}

// Optionally add validation logic for the parameter value here

// Example: if (paramName.equals("age") && !isValidAge(paramValue)) { ... }

}

return queryString; // Return the original query string if all parameters are valid.

}

private static Map<String, String> parseQueryString(String queryString) {

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

if (queryString != null && !queryString.isEmpty()) {

String[] pairs = queryString.split("&");

for (String pair : pairs) {

String[] parts = pair.split("=");

if (parts.length == 2) {

String paramName = parts[0];

String paramValue = parts[1];

params.put(paramName, paramValue);

}

}

}

return params;

}

public static void main(String[] args) {

// Example usage

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

allowedParams.put("id", "true");

allowedParams.put("name", "test");

String queryString1 = "id=true&name=test&extra=value";

String queryString2 = "id=true&name=test";

String queryString3 = "id=true&name=test&age=30"; //age is not allowed

String validatedQueryString1 = validateQueryString(queryString1, allowedParams);

String validatedQueryString2 = validateQueryString(queryString2, allowedParams);

String validatedQueryString3 = validateQueryString(queryString3, allowedParams);

System.out.println("Validated Query String 1: " + validatedQueryString1);

System.out.println("Validated Query String 2: " + validatedQueryString2);

System.out.println("Validated Query String 3: " + validatedQueryString3);

}

}