theotherian/ Handlebars Helper Functions with Jersey

## Handlebars Helper Functions with Jersey
A way to map Handlebars helper functions on the server side within a Jersey resource

## DesktopView.java
import java.io.IOException;
import java.util.concurrent.ExecutionException;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.Response;

import com.github.jknack.handlebars.Template;

@Path("desktop")
public class DesktopView {

  @GET
  @Produces(MediaType.TEXT_HTML)
  public Response get() throws IOException, InterruptedException, ExecutionException {
    Template template = HandlebarsManager.get().compile("home");
    return Response.ok(template.apply(new Args("Ian", "Denny", "Chris"))).build();
  }

}

## HandlebarsResourceFeature.java
import javax.ws.rs.Path;
import javax.ws.rs.container.DynamicFeature;
import javax.ws.rs.container.ResourceInfo;
import javax.ws.rs.core.FeatureContext;

import org.apache.log4j.Logger;

import com.github.jknack.handlebars.Handlebars;
import com.github.jknack.handlebars.Helper;

public class HandlebarsResourceFeature implements DynamicFeature {

  private final Logger logger = Logger.getLogger(getClass());

  @Override
  public void configure(ResourceInfo resourceInfo, FeatureContext context) {
    if (Helper.class.isAssignableFrom(resourceInfo.getResourceClass())) {
      Class<?> resourceClass = resourceInfo.getResourceClass();
      String helperName = resourceClass.getAnnotation(Path.class).value();
      // HandlebarsManager exists in the project linked at the end of this post.
      Handlebars handlebars = HandlebarsManager.get();
      if (handlebars.helper(helperName) == null) {
        Helper<?> helper = null;
        try {
          helper = resourceInfo.getResourceClass().asSubclass(Helper.class).newInstance();
        } catch (InstantiationException | IllegalAccessException e) {
          logger.fatal("Can't instantiate " + resourceClass.getCanonicalName(), e);
        }
        if (helper != null) {
          handlebars.registerHelper(helperName, helper);
        }
        else {
          logger.info("Not registering " + helperName + " a second time; already registered previously");
        }
      }
    }
  }

}

## home.html
<html>
  <head>
    <title>Home Page</title>
  </head>
  <body>
    <h1>Welcome to the site!</h1>
    <p>Here are the latest messages:</p>
    {{#each names}}
      <ul>
        <li>
          <h2>Messages from {{this}}</h2>
          {{#latestmessages this}}
            {{> messages this}}
          {{/latestmessages}}
        </li>
      </ul>
    {{/each}}
  </body>
</html>

## home.mobile.html
<html>
  <head>
    <title>Mobile Home Page</title>
    <script src="/handlebars.js"></script>
    <script src="//ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
    <script type="text/javascript">
      {{#precompile "messages"}}{{/precompile}}
    </script>
  </head>
  <body>
    <h1>Welcome to the mobile site!</h1>
    <h4>Click on a name to see messages</h4>
    {{#each names}}
      <div class="message-container-{{this}}">
        <p><a class="message-link" id="{{this}}" href="#">{{this}}</a></p>
      </div>
    {{/each}}
    <script type="text/javascript">
      $(document).ready(function bindAll() {
        $('.message-link').bind('click', event, function showMessages() {
          var name = event.target.id;
          var messageList = '#message-list-' + name;
          if ($(messageList).length) {
            if ($(messageList).is(':visible')) {
              return;
            }
            else {
              $('.message-list').hide();
              $(messageList).show();
              return;
            }
          }
          else {
            $('.message-list').hide();
          }
          // here's the important bit involving calling the resource
          var messageTemplate = Handlebars.templates['messages'];
          $.get('latestmessages/' + name).done( function(data) {
            var html = messageTemplate(data);
            $('.message-container-' + name).append('<div id="message-list-' + name + '" class="message-list">');
            $(messageList).append(html);
          });
        });

      });
    </script>
  </body>
</html>

## MessageResource.java
import java.io.IOException;
import java.util.List;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.PathParam;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import com.github.jknack.handlebars.Helper;
import com.github.jknack.handlebars.Options;

@Path("latestmessages")
public class MessageResource implements Helper<String> {

  @GET
  @Path("{name}")
  @Produces(MediaType.APPLICATION_JSON)
  public List<Message> get(@PathParam("name") String name) {
    return getMessages(name);
  }

  private List<Message> getMessages(String name) {
    // MessageDatastore exists in the project linked at the end of this post
    return MessageDatastore.getMessagesByName(name);
  }

  @Override
  public CharSequence apply(String context, Options options) throws IOException {
    return options.fn(getMessages(context));
  }

}

## messages.html
<ul>
{{#each this}}
  <li>{{text}} <span style="font-size: x-small;">{{when}}</span></li>
{{/each}}
</ul>
	import java.io.IOException;
	import java.util.concurrent.ExecutionException;

	import javax.ws.rs.GET;
	import javax.ws.rs.Path;
	import javax.ws.rs.Produces;
	import javax.ws.rs.core.MediaType;
	import javax.ws.rs.core.Response;

	import com.github.jknack.handlebars.Template;

	@Path("desktop")
	public class DesktopView {

	@GET
	@Produces(MediaType.TEXT_HTML)
	public Response get() throws IOException, InterruptedException, ExecutionException {
	Template template = HandlebarsManager.get().compile("home");
	return Response.ok(template.apply(new Args("Ian", "Denny", "Chris"))).build();
	}

	}
	import javax.ws.rs.Path;
	import javax.ws.rs.container.DynamicFeature;
	import javax.ws.rs.container.ResourceInfo;
	import javax.ws.rs.core.FeatureContext;

	import org.apache.log4j.Logger;

	import com.github.jknack.handlebars.Handlebars;
	import com.github.jknack.handlebars.Helper;

	public class HandlebarsResourceFeature implements DynamicFeature {

	private final Logger logger = Logger.getLogger(getClass());

	@Override
	public void configure(ResourceInfo resourceInfo, FeatureContext context) {
	if (Helper.class.isAssignableFrom(resourceInfo.getResourceClass())) {
	Class<?> resourceClass = resourceInfo.getResourceClass();
	String helperName = resourceClass.getAnnotation(Path.class).value();
	// HandlebarsManager exists in the project linked at the end of this post.
	Handlebars handlebars = HandlebarsManager.get();
	if (handlebars.helper(helperName) == null) {
	Helper<?> helper = null;
	try {
	helper = resourceInfo.getResourceClass().asSubclass(Helper.class).newInstance();
	} catch (InstantiationException \| IllegalAccessException e) {
	logger.fatal("Can't instantiate " + resourceClass.getCanonicalName(), e);
	}
	if (helper != null) {
	handlebars.registerHelper(helperName, helper);
	}
	else {
	logger.info("Not registering " + helperName + " a second time; already registered previously");
	}
	}
	}
	}

	}
	<html>
	<head>
	<title>Home Page</title>
	</head>
	<body>
	<h1>Welcome to the site!</h1>
	<p>Here are the latest messages:</p>
	{{#each names}}
	<ul>
	<li>
	<h2>Messages from {{this}}</h2>
	{{#latestmessages this}}
	{{> messages this}}
	{{/latestmessages}}
	</li>
	</ul>
	{{/each}}
	</body>
	</html>
	<html>
	<head>
	<title>Mobile Home Page</title>
	<script src="/handlebars.js"></script>
	<script src="//ajax.googleapis.com/ajax/libs/jquery/2.0.3/jquery.min.js"></script>
	<script type="text/javascript">
	{{#precompile "messages"}}{{/precompile}}
	</script>
	</head>
	<body>
	<h1>Welcome to the mobile site!</h1>
	<h4>Click on a name to see messages</h4>
	{{#each names}}
	<div class="message-container-{{this}}">
	<p><a class="message-link" id="{{this}}" href="#">{{this}}</a></p>
	</div>
	{{/each}}
	<script type="text/javascript">
	$(document).ready(function bindAll() {
	$('.message-link').bind('click', event, function showMessages() {
	var name = event.target.id;
	var messageList = '#message-list-' + name;
	if ($(messageList).length) {
	if ($(messageList).is(':visible')) {
	return;
	}
	else {
	$('.message-list').hide();
	$(messageList).show();
	return;
	}
	}
	else {
	$('.message-list').hide();
	}
	// here's the important bit involving calling the resource
	var messageTemplate = Handlebars.templates['messages'];
	$.get('latestmessages/' + name).done( function(data) {
	var html = messageTemplate(data);
	$('.message-container-' + name).append('<div id="message-list-' + name + '" class="message-list">');
	$(messageList).append(html);
	});
	});

	});
	</script>
	</body>
	</html>
	import java.io.IOException;
	import java.util.List;

	import javax.ws.rs.GET;
	import javax.ws.rs.Path;
	import javax.ws.rs.PathParam;
	import javax.ws.rs.Produces;
	import javax.ws.rs.core.MediaType;

	import com.github.jknack.handlebars.Helper;
	import com.github.jknack.handlebars.Options;

	@Path("latestmessages")
	public class MessageResource implements Helper<String> {

	@GET
	@Path("{name}")
	@Produces(MediaType.APPLICATION_JSON)
	public List<Message> get(@PathParam("name") String name) {
	return getMessages(name);
	}

	private List<Message> getMessages(String name) {
	// MessageDatastore exists in the project linked at the end of this post
	return MessageDatastore.getMessagesByName(name);
	}

	@Override
	public CharSequence apply(String context, Options options) throws IOException {
	return options.fn(getMessages(context));
	}

	}
	<ul>
	{{#each this}}
	<li>{{text}} <span style="font-size: x-small;">{{when}}</span></li>
	{{/each}}
	</ul>