How to Extract a Specific Text from URL Parameters in Java

What is the method to retrieve and extract a specific part of a URL parameter in Java?

String url = "http://example.com?name=JohnDoe&age=30"; 
String parameterValue = getParameter(url, "name"); // returns "JohnDoe"

In Java, you can retrieve and extract specific text from URL parameters using the built-in classes from the java.net package. By parsing the URL, you can access the query string and obtain desired parameter values efficiently.

import java.net.URI;
import java.net.URISyntaxException;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class URLParameterExtractor {
    public static String getParameter(String url, String param) throws URISyntaxException {
        URI uri = new URI(url);
        String query = uri.getQuery();
        Map<String, List<String>> queryPairs = 
                Arrays.stream(query.split("&"))
                      .map(pair -> pair.split("="))
                      .collect(Collectors.toMap(
                          pair -> pair[0],
                          pair -> Arrays.asList(pair[1])));
        return queryPairs.getOrDefault(param, Collections.emptyList()).get(0);
    }
}

Causes

• Improper URL formation leading to failure in parameter extraction.
• Using incorrect methods for parsing URL strings.
• Not handling exceptions when working with URL objects.

Solutions

• Use the `URI` and `URL` classes to parse and construct your URLs.
• Implement a method that extracts query parameters from a URL string.
• Utilize libraries like Apache Commons or Google Guava for easy parsing.

Mistake: Not URL-encoding parameters, leading to incorrect retrieval of values.

Solution: Always encode your URL parameters using `URLEncoder.encode(value, "UTF-8")` before appending.

Mistake: Failing to handle multiple parameters with the same name, which may lead to loss of data.

Solution: Use a List to collect all values for parameters that may appear multiple times.