JavaAPI.java

import j2html.tags.DomContent;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.lang.reflect.Member;
import java.util.stream.Stream;

import static j2html.TagCreator.*;

public class JavaAPI extends HttpServlet {
    public static void main(String[] args) throws Exception {
        ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
        context.setContextPath("/");
        context.addServlet(new ServletHolder(new JavaAPI()), "/api");

        Server server = new Server(4000);
        server.setHandler(context);
        server.start();
        server.join();
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String clazz = request.getParameter("class");
        response.setContentType("text/html");
        response.setStatus(HttpServletResponse.SC_OK);

        try {
            response.getWriter().println(content(Class.forName(clazz)));
        } catch (ClassNotFoundException e) {
            response.getWriter().println("Class not found: " + e.getMessage());
        }

    }

    private static String content(Class<?> clazz) {
        return html(
                head(
                        title(clazz.getCanonicalName()),
                        link().withRel("stylesheet").withHref("https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css")
                ),
                body(attrs(".container"),
                        h2(attrs(".text-center"), clazz.getCanonicalName()),
                        membersList("Fields", clazz.getDeclaredFields()),
                        membersList("Constructors", clazz.getDeclaredConstructors()),
                        membersList("Methods", clazz.getDeclaredMethods())
                )
        ).render();
    }

    private static DomContent membersList(String header, Member[] members) {
        return div(
                    h5(header),
                    ul(
                        Stream.of(members)
                                .map(member -> li(member.toString()))
                                .toArray(DomContent[]::new)
                    )
            );
    }
}