gumdrop.web

Gumdrop-Web

A library for handling HTTP requests and building dynamic HTML documents.

Setup

At application startup, we register our Controllers with a single Dispatcher, associating each Controller with a request pattern.

For example, if we have a Controller to show messages by id, and we want our server to respond to requests to /messages/<message-id>, we'd tell our Dispatcher how to create new instances of our controller and bind that to the request pattern, /messages/#.

Dispatcher dispatcher = new Dispatcher();
dispatcher.register(GET, "/messages/#", () -> new ShowMessageController());

The # is a numeric wildcard. Using a numeric wildcard in /messages/# means that GET requests to, for example /messages/42, will match, with the matching number passed to the Controller instance.

We then pass our dispatcher to NioServer along with a port number and call run to start the Gumdrop Server.

new NioServer(dispatcher, 8080).run();

HTML Generation

Gumdrop provides a convenient library for generating HTML. Instead of using a template language, we create nested HTML-like tags in Java with its attendant compile-time safety, refactoring capability, and performance.

An anchor Widget might look like this:

import gumdrop.web.html.Buildable;
import gumdrop.web.html.Widget;

import static gumdrop.web.html.TagLib.a;

public class AnchorWidget extends Widget {

  private final String text, url;

  public LinkWidget(String text, String url) {
    this.text = text;
    this.url = url;
  }

  @Override
  protected Buildable getBuildable() {
    return a(text).attr("href", url);
  }

}

That static a method returns a Tag, for which we set the href value to the url attribute of our AnchorWidget instance.

A slightly more complex Widget -- one that uses a section, and nested header and main tags -- might look this this:

import gumdrop.web.html.Buildable;
import gumdrop.web.html.Widget;

import static gumdrop.web.html.TagLib.*;

public class TitledPanelWidget extends Widget {

  private final Buildable titleBar;
  private final Buildable contents;

  public TitledPanelWidget(String title, Buildable contents) {
    titleBar = span(title);
    this.contents = contents;
  }

  public TitledPanelWidget(Buildable titleBar, Buildable contents) {
    this.titleBar = titleBar;
    this.contents = contents;
  }

  @Override
  protected Buildable getBuildable() {
    return section(
      header(titleBar),
      main(contents)
    );
  }

}

In this case, we create header and main tags as children of our section tag and end up with an HTML structure that looks like our method call structure:

<section>
  <header>titleBar stuff</header>
  <main>content stuff</main>
</section>