Url Parsing in Mercury

Here’s the translation of the Go URL parsing example to Java, formatted in Markdown suitable for Hugo:

import java.net.URI;
import java.net.URISyntaxException;
import java.util.Map;

public class URLParsing {
    public static void main(String[] args) {
        // We'll parse this example URL, which includes a
        // scheme, authentication info, host, port, path,
        // query params, and query fragment.
        String s = "postgres://user:pass@host.com:5432/path?k=v#f";

        try {
            // Parse the URL and ensure there are no errors.
            URI uri = new URI(s);

            // Accessing the scheme is straightforward.
            System.out.println(uri.getScheme());

            // UserInfo contains all authentication info; we need to split it
            // to get individual username and password.
            System.out.println(uri.getUserInfo());
            String[] userInfo = uri.getUserInfo().split(":");
            System.out.println(userInfo[0]);
            System.out.println(userInfo[1]);

            // The Host contains both the hostname and the port,
            // if present. We can access them separately.
            System.out.println(uri.getHost());
            System.out.println(uri.getPort());

            // Here we extract the path and the fragment after
            // the #.
            System.out.println(uri.getPath());
            System.out.println(uri.getFragment());

            // To get query params in a string of k=v format,
            // use getRawQuery(). You can also parse query params
            // into a map using a custom method (not provided by URI).
            System.out.println(uri.getRawQuery());
            Map<String, String> queryParams = parseQuery(uri.getQuery());
            System.out.println(queryParams);
            System.out.println(queryParams.get("k"));

        } catch (URISyntaxException e) {
            e.printStackTrace();
        }
    }

    // A simple method to parse query parameters into a map.
    // In a real application, you might want to use a library like Apache HttpClient.
    private static Map<String, String> parseQuery(String query) {
        Map<String, String> queryPairs = new LinkedHashMap<>();
        String[] pairs = query.split("&");
        for (String pair : pairs) {
            int idx = pair.indexOf("=");
            queryPairs.put(URLDecoder.decode(pair.substring(0, idx), "UTF-8"), 
                           URLDecoder.decode(pair.substring(idx + 1), "UTF-8"));
        }
        return queryPairs;
    }
}

This Java program demonstrates URL parsing using the java.net.URI class. Here’s a breakdown of the code:

We start by importing necessary classes from java.net package.
In the main method, we define our example URL string.
We create a URI object by parsing the URL string. This is wrapped in a try-catch block to handle potential URISyntaxException.
We then access various components of the URI:
- Scheme using getScheme()
- User info using getUserInfo()
- Host using getHost()
- Port using getPort()
- Path using getPath()
- Fragment using getFragment()
- Raw query using getRawQuery()
For parsing query parameters, we’ve included a simple parseQuery method. In a real-world application, you might want to use a more robust solution or a library.
We print out each component to see the parsed results.

To run this program:

Save it as URLParsing.java
Compile it: javac URLParsing.java
Run it: java URLParsing

The output will show all the different pieces that we extracted from the URL.

Note that Java’s URI class doesn’t provide as straightforward access to username and password separately as Go’s url.URL does. In this example, we’ve split the user info string manually. Also, Java doesn’t have a built-in method to parse query parameters into a map, so we’ve provided a simple implementation. In practice, you might want to use a more robust solution or a library for this.

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