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NOTICE: This library is no longer supported by Vaadin

Vaadin transfers the ownership of this library, thus Vaadin no longer provides support or does active development on it.

We took this decision because once demonstrated that polymer elements could be easily be integrated in GWT, we want to invest our team’s time in adding valuable user benefits to Vaadin Core Elements, and pass the baton to the community to do integrations with other frameworks.

In addition, we are happy to announce that ownership of the repository will be transferred by 20 Apr 2017 to @manolo, who will continue to maintain it.

If you are willing to participate as a collaborator, please leave a comment in #151. The collaborators will be granted access after transferring. We encourage contribution in any form and shape.


  • Polymer: is a JavaScript library for building web applications with Web Components.
  • Polymer-Elements: is a collection of widgets built in Polymer. The collection is divided in sections: Iron, Paper, Gold, Neon, Platinum, Vaadin, etc.
  • GWT-Polymer-Elements: is a Java wrapper enabling Polymer Elements to be used in GWT projects. Right now it includes wrappers for Iron, Paper, App, Platinum and Vaadin collections, but more might be added in the future.

The library has been generated using the Vaadin gwt-api-generator, an utility able to inspect polymer webcomponents and emit GWT Java code.

Because Polymer differentiates between collections, gwt-polymer-elements classes are prefixed with the same prefixes (Iron, Paper, Vaadin), in order to easily refer to the original web component, and to easily find the documentation related with it.


Visit our show case to see how components look like, and to take a look to the example code using each component.


When we parse the original components code to generate the Java API, we copy all the existing JS documentation so as it's available in the javadoc. Note that sometimes descriptions would refer to JS, but we consider that it's better to maintain the info.

Using the GWT library

You need at least GWT-2.8.0 to use the library.

Add vaadin-gwt-polymer-elements to your CLASSPATH

The .jar file includes all the java code and web components of Polymer Iron and Paper collections, so as you don't have to deal with the process of downloading and deploying all js wrapped libraries and components.

Using maven
  • If your project uses maven add the following dependency to your pom.xml
  • otherwise you can download the vaadin-gwt-polymer-elements- archive and put it in your gwt project classpath.

Update your module configuration

  • Add this line to your *.gwt.xml module file:
 <inherits name="com.vaadin.polymer.Elements"/>

Add the Web Components Polyfill (Optional).

  • Only Chrome has full native support for Web Components nowadays, therefore, to make your project work with all modern browsers, you have to include the WebComponents Polyfill.

    If you use the polymer components as Widgets, the library will lazy load it when needed. Otherwise load it very early in your .html host page as it is shown in the following code.

    <script src="myapp/bower_components/webcomponentsjs/webcomponents.js"></script>
    <script src="myapp/myapp.nocache.js"></script>

Consuming Web Components in GWT

Vaadin gwt-polymer-elements bundles classes to build your application using either Widgets or JsInterop Elements. The former is the classic approach, while the latter will become the new tendency.

But Right now, Elements is the most difficult way because GWT lacks of a complete Elemental-2.0 API relying on JsInterop. We provide a very small set of elemental interfaces limited to those needed for our implementation, they will be replaced by Elemental-2.0 when it was available.

In summary, for classic and production GWT projects it would be easier to use the Widget since the API would not have important changes. Otherwise, if you want to get rid of the widget hierarchy we recommend to start using the Element API mixing it with some DOM manipulation library like gwtquery or just the methods included in the elemental API.

  • Using the classic Widget API in Java.
PaperButton button = new PaperButton();

button.addClickHandler(new ClickHandler() {
  public void onClick(ClickEvent event) {
    // ...


Note: Widget constructors accept any HTML content as argument which is appended to the web component rendered DOM

  • Using the Element API in Java.
// Create a new instance of PaperButton
PaperButtonElement button = Polymer.createElement(PaperButtonElement.TAG);
// Set some properties

// Add event listeners
button.addEventListener("click", new EventListener() {
    public void onBrowserEvent(Event event) {
    // ...

// Append to the html document
  • Using Widgets or Elements in UiBinder
 <ui:UiBinder xmlns:ui=''

   .container paper-button.colored {
     background: #4285f4;
     color: #fff;

   <!-- As Widget -->
   <p:PaperButton toggles="true" raised="true" active="true" addStyleNames="{style.colored}">active</p:PaperButton>

   <!-- As Element -->
   <paper-button raised="" noink="">Click me</paper-button>

Styling your application.

Polymer uses Shadow DOM styling rules for providing scoped styling of the element’s local DOM. It supports some extra syntax which is not understable by the GWT GSS parser.

Polymer takes care of its syntax parsing any <style> block you might have in your host page, but if you want to specify some styling rules in UiBinder, you have to add your style blocks to any panel.

<ui:UiBinder xmlns:ui=''

<style is="custom-style">
   paper-toolbar paper-icon-button {
      --paper-icon-button-ink-color: var(--paper-indigo-500);
   <p:PaperIconButton icon="menu"/>
   <span class="title">Toolbar</span>

For more information about polymer styling syntax visit their documentation


Java Sources

If you want to dive into .java sources, we don't maintain generated files, thus you need to download the vaadin-gwt-polymer-elements-x.x.x-sources.jar bundle. Otherwise you might take a look java helper classes and templates look in the gwt-api-generator project.

Importing Web Components

Before using any component, you have to import the appropriate files. But gwt-polymer-elements comes with some utilities so as you it would be done automatically.

  • Widgets : When you use a widget, the import happens automatically
    PaperButton button = new PapperButton();
  • Elements : Create new components through the Polymer helper class
    PaperButtonElement button = Polymer.createElement(PaperButtonElement.TAG);
  • Dynamic imports : Polymer has a couple of methods to do the import dynamically
  • Static imports : Adding tags to the hosted page head is the traditional way to make webcomponents available if you want them in a mixed application (DOM, JS, or GWT) or if you want to be sure that web components are available from the beginning.
   <link rel='import' href='application_context/bower_components/paper-button/paper-button.html'></link>

Asynchronous issues

Web Components could be registered and initialised asynchronously. Thus gwt-polymer-elements comes with some methods which helps to run callbacks when the component is actually ready.

  PaperButtonElement button = Polymer.createElement(PaperButtonElement.TAG);
  Polymer.ready(button, new Function() {
     public Object call(Object args) {
        // Set button properties here

  PolymerButton button = new PolymerButton();
  // You could set methods here

  button.ready(new Function() {
     public Object call(Object args) {
       // But you have to enclose in a callback calls to element methods

  Polymer.importHref(Arrays.asList("paper-tabs", "paper-tab-element"), new Function() {
     public Object call(Object args) {
        // Create your elements here and call their methods

Using latest snapshot

Add the following repo to your pom.xml, and change the version using the latest listed at in this url



Building the project

To compile the vaadin-gwt-polymer-elements library by yourself.

  1. Clone the repository with $ git checkout
  2. Change to the project folder $ cd gwt-polymer-elements
  3. Run $ npm install to download all components to the src/main/resources folder, to create all java files needed for GWT in the src/main/java/ folder and to compile and install the components library in you local maven repo.

Running the demo locally

  1. To run and debug the demo, go to the demo folder $ cd demo
  2. Run $ mvn gwt:devmode to run the demo in SuperDevMode, otherwise run $ mvn clean package to build the demo application under target directory.
  3. You can serve the demo directly from the target/gwt-polymer-demo or you can deploy the generated target/gwt-polymer-demo.war in a servlet container.