Going native

A guide to using pure html5 ui and integrating non-gwt javascript with errai 4.0

By Max Barkley, Software Engineer at Red Hat

What is errai?

a web framework built with gwt

```
Dependency Injection
```
```
Client-Side Templating
```
```
Two-Way Data-Binding
```
```
Client-Side JAX-RS Support
```
```
CDI Events over HTTP
```

What is errai?

declarative Good, Boilerplate bad

Annotation-Driven features express intent without boilerplate

Uses CDI APIs (dependency injection and CDI events)

compile-time safety

Leverages the Java type system whenever possible

```
Validate annotation use at compile-time
```

Outline

errai app basics

```
Dependency injection
```
```
Templating
```
```
Data-Binding
```

JS Interop Basics

```
@JsType(isNative=true)
```
```
@JsProperty
```
```
@JsOverlay
```

Errai JS Interop Support

Using JS interop DOM wrappers in Errai templates

Writing/using wrappers for web components

```
Integrating third-party JS libraries
```

errai basics

Declarative Dependency Injection

@ApplicationScoped
public class SingletonService {
    // ...
}

public class FooProducer {
    @Produces static Foo newFoo() {
        // ...
    }
}

Injection points are dependencies of a bean

public class ServiceConsumer {
    @Inject SingletonService service;
    // ...
}

public class FooConsumer {
    @Inject
    public FooConsumer(Foo foo) {
        // ...
    }
}

Beans are objects with managed deps and lifecycles

errai basics

Declarative Dependency Injection

Dependencies are resolved based on type and qualifiers

Qualifiers are annotations for beans and injection points

they remove ambiguity when injecting common supertypes

@Named("Visa")
public class Visa
    implements CreditCard {
    // ...
}

@Named("Amex")
public class Amex
    implements CreditCard {
    // ...
}

```
For example...
```

This is ambgiuous

@Inject CreditCard card;

And this is not

@Inject @Named("Visa") CreditCard card;

errai basics

Declarative Dependency Injection

```
Declaratively define app entrypoints
```

@EntryPoint
public class AppStartup {
    @PostConstruct
    public void start() {
        // Startup logic goes here...
    }
}

@EntryPoint is a scope (like @ApplicationScoped)

```
but it is eagerly instantiated
```

@PostConstruct is a life-cycle method, invoked after the bean is created

errai basics

Client-side Templating

```
Create UI components declaratively
```

A component has two parts:

```
Template (HTML, CSS/LESS)
```
```
@Templated bean (a Java class)
```

errai basics

Client-side Templating

A template consists of:

```
An HTML file (mandatory)
```
```
A CSS or LESS stylesheet (optional)
```

errai basics

Client-side Templating

The HTML file can be a fragment or a full page

<!-- Template as fragment -->
<form class="form">
    <input class="username" type="text">
    <input class="password" type="password">
</form>

<!DOCTYPE html>
<html>
<head></head>
<body>
<!-- Any fragment in the body can be used -->
    <form class="form">
        <input class="username" type="text">
        <input class="password" type="password">
    </form>
</body>
</html>

errai basics

Client-side Templating

A @Templated bean is a Java class that defines behaviour

Is declared with the @Templated annotation

the paths are optional if convention is followed

IsElement allows access to the root element (optional)

@Templated(value = "HomeScreen.html", stylesheet = "HomeScreen.css")
public class HomeScreen implements IsElement {
    // ...
}

If the above compiles, then so does this

@Templated
public class HomeScreen implements IsElement {
    // ...
}

errai basics

Client-side Templating

Use fragment identifiers to replace elements in your template with fields in your @Templated bean

In your template, a fragment identifier is an id, class, or data-field attribute value.

<form id="userForm">
    <input data-field="username" type="text">
    <input class="password" type="password">
</form>

errai basics

Client-side Templating

In your @Templated bean use @DataField to map fields to fragment identifiers

// The "userForm" fragment in "UserForm.html" is the component root
@Templated("#userForm")
public class UserForm {

    // Maps to fragment "username"
    @Inject @DataField TextBox username;

    // Maps to fragment "password"
    @Inject @DataField("password") PasswordTextBox pass;
}

<form id="userForm">
    <input data-field="username" type="text">
    <input class="password" type="password">
</form>

errai basics

Client-side Templating

@EventHandler declares handlers for GWT Widget events and native DOM events

Uses fragment identifiers to declare which UI element the handler is for

errai basics

Client-side Templating

@Templated
public class UserForm {
    // ...

    @Inject @DataField Button submit; // Optional

    @EventHandler("submit")
    public void onClick(@ForEvent("click") MouseEvent event) {
        // ...
    }
}

This declares a listener for a native browser event

```
Listens for the "click" event
```

Listens on the "submit" element in the template

Doesn't require there to be a @DataField for "submit"

errai basics

Client-side Templating

@Templated
public class UserForm {
    // ...

    @Inject @DataField Button submit; // Mandatory

    @EventHandler("submit")
    public void onClick(ClickEvent event) {
        // ...
    }
}

This declares a listener for a GWT widget event

```
Listens for the ClickEvent
```
```
Listens on the "submit" @DataField
```

Requires there to be a @DataField that is a GWT widget

errai basics

Declarative Data-Binding

Data-binding synchronizes state between a data-model and UI elements

Data-binding in Errai is two-way

```
model changes propogate to the UI
```
```
UI changes propogate to the model
```

errai basics

Declarative Data-Binding

Any type annotated with @Bindable can be used as a data-binding model

Properties of a model must be primitives, Strings, or other @Bindable types

Properties are inferred based on getter/setter names

This example has the properties "name" and "address"

@Bindable
public class User {
    private String name;
    private Address address; // Address must be @Bindable
    
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }

    public Address getAddress() { return address; }
    public void setAddress(Address address) { this.address = address; }
}

errai basics

Declarative Data-Binding

Use @Model in UI components to declare a field as a data-binding model

Use @Bound to declare UI fields as being data-bound to model properties

Binds to property with field name by default

Can bind to nested properties using simple notation

@Templated
public class NewUserForm {
    @Inject @Model User user;

    @Inject @Bound @DataField TextBox name;
    @Inject @Bound("address.street") @DataField TextBox street;
    @Inject @Bound("address.number") @DataField IntegerBox number;
}

JS Interop Basics

Declarative JS Interoperability

JS interop is a set of annotations for defining interfaces between GWT-compiled and native JavaScript

Supports two use cases: consuming and publishing

```
In this talk we will focus on consuming
```

JS Interop Basics

@JsType

@JsType declares an API for a JavaScript object

When isNative=false (the default) the usage is for publishing

Preserves names of all public members so they can be called from external JavaScript

package org.errai.example;
@JsType
public class ExportedService {
    private String value;                      // Not exported

    public String getValue() { return value; } // Exported
}

// All good
var service = new org.errai.example.ExportedService();
service.getValue();

// This property is undefined -- the name has been obfuscated
service.value;

JS Interop Basics

@JsType(isNative=true)

A native @JsType is for consuming external JavaScript

Native @JsTypes have no code generated — they are compile-time bindings for external JavaScript objects

This means that methods cannot have implementations (with one exception)

@JsType(isNative=true)
public interface Window {
    void alert(String msg);
    // ...
}

window.alert("Hello World!");

window.alert("Hello World!");

Java

JavaScript

JS Interop Basics

@JsProperty

We can use @JsProperty to compile method invocations to property access

Property name is inferred for getter/setter methods

@JsType(isNative=true)
public interface InputElement {
    @JsProperty String getValue();
    @JsProperty void setValue(String value);
}

String old = input.getValue();
input.setValue("new");

var old = input.value;
input.value = "new";

Java

JavaScript

JS Interop Basics

@JsOverlay

We can use @JsOverlay to add convenience methods on top of native @JsTypes

@JsOverlay methods have lots of restrictions

```
Can only access public members
```
```
Must be effectively final
```

@JsType(isNative=true)
public class NumberInputElement {
    public String value;

    @JsOverlay public final int getValue() {
        return Integer.parseInt(value);
    }
}

errai js interop support

Use Cases

DOM Elements and Web Components

```
@Inject
```
```
@DataField
```
```
@Bound
```

Third-party JS libraries

```
@Inject objects form library APIs
```

errai js interop support

Use Case 1: DOM Elements

As a best practice, prefer the DOM to GWT Widgets

Errai 4 has a collection of JS interop element wrappers

The collection isn't complete but has most common elements (Div, Span, Heading, Input, ...)

errai js interop support

Use Case 1: DOM Elements

```
You can @Inject any of these wrappers
```

@Inject Div div;
@Inject Form form;
@Inject Span span;

Some wrappers are used for multiple elements

```
Use @Named to resolve ambiguity
```

@Inject @Named("h1") Heading title;
@Inject @Named("h2") Heading subtitle;

@Inject @Named("div") HTMLElement div;

Inject a @Named("tagname") HTMLElement to get an instance of any HTMLElement

errai js interop support

Use Case 1: DOM Elements

You can use any of these wrappers as @DataFields

@Templated
public class Example {
    @Inject @DataField Div div;
    @Inject @DataField Form form;
    @Inject @Named("h1") @DataField Heading title;
}

errai js interop support

Use Case 1: DOM Elements

You can use @Bound with any of these wrappers

@Templated
public class Example {
    @Inject @Model User user;

    @Inject @Named("h1")
    @Bound @DataField Heading name;

    @Inject
    @Bound("address.street") @DataField TextInput street;
}

A @Bound Heading, like most other elements, will have its text content synchronized

A @Bound TextInput will have its value property synchronized

TextArea and all other form inputs work similarly

errai js interop support

Use Case 1: DOM Elements

You can easily add your own element definitions

@JsType(isNative = true)
@Element("div")
public interface Div extends HTMLElement {
    // ...
}

@Element makes this type injectable

The container creates instances of TextInput by calling document.createElement("div") and casting

<div></div>

errai js interop support

Use Case 1: DOM Elements

Below is Errai's TextInput wrapper (most of the API is inherited)

@JsType(isNative = true)
@Element("input")
@Property(name = "type", value = "text")
public interface TextInput extends Input {

}

@Property makes the container set the "type" attribute to the value "text"

<input type="text">

@JsType(isNative = true)
@Element("input")
@Property(name = "type", value = "password")
public interface PasswordInput extends Input {

}

<input type="password">

errai js interop support

Use Case 1: DOM Elements

You can define elements, like Heading, with multiple tags

@JsType(isNative = true)
@Element({"h1", "h2", "h3", "h4", "h5", "h6"})
public interface Heading extends HTMLElement {
    // ...
}

This declaration forces use of qualifiers at Heading injection points

@Inject @Named("h1") Heading h1;
@Inject @Named("h2") Heading h2;
@Inject @Named("h3") Heading h3;
@Inject @Named("h4") Heading h4;
@Inject @Named("h5") Heading h5;
@Inject @Named("h6") Heading h6;

@Inject Heading ambiguous;

Valid

Ambiguous

errai js interop support

Use Case 1: Web Components

Wrapping a web component works just like wrapping an element

@Element("paper-input")
@JsType(isNative = true)
public interface PaperInput extends HTMLElement {
    // ...
}

This is a wrapper for the Polymer paper-input element

It uses @Element because you can create web components with document.createElement

After adding Polymer to your host page, you can start injecting PaperInputs

errai js interop support

Use Case 1: Web Components

@Inject @Bound PaperInput input;

But how does binding to a paper-input work?

Recall that data-binding synchronizes element text content for elements that aren't input

But a paper-input behaves like an input element — we'd like to bind to the value property

<paper-input>Content</paper-input>

<paper-input value="Content">

errai js interop support

Use Case 1: Web Components

@Element("paper-input")
@JsType(isNative = true)
public interface PaperInput extends HTMLElement, HasValue<String> {
    // ...
}

```
First we need to extend HasValue<T>
```

```
This is not the HasValue<T> in gwt-user
```

This is an Errai interface used by data-binding

Now data-binding will use the getValue/setValue methods

@JsType(isNative = true)
public interface HasValue<T> {
  T getValue();
  void setValue(T value);
}

errai js interop support

Use Case 1: Web Components

@Element("paper-input")
@JsType(isNative = true)
public interface PaperInput extends HTMLElement, HasValue<String> {
  @Override @JsProperty String getValue();
  @Override @JsProperty void setValue(String value);
}

Declare an element property for binding with @JsProperty

Data-binding will use the setValue/getValue methods

Because of the @JsProperty annotations, these are compiled to property access

String old = input.getValue();
input.setValue("foo");

var old = input.value;
input.value = "foo";

Java

JavaScript

errai js interop support

Use Case 1: Web Components

You can do a similar trick if you'd like data-binding to use a method on the object

String old = input.getValue();
input.setValue("foo");

var old = input.getter();
input.setter("foo");

Java

JavaScript

@Override @JsMethod(name = "getter") String getValue();
@Override @JsMethod(name = "setter") void setValue(String value);

errai js interop support

Use Case 1: Web Components

For more complex bindings, use @JsOverlay method

@Element("a")
@JsType(isNative = true)
public interface BindableEmailAnchor extends Anchor, HasValue<String> {

  @JsOverlay @Override
  default String getValue() {
    return getTextContent();
  }

  @JsOverlay @Override
  default void setValue(final String value) {
    setTextContent(value);
    setHref("mailto:" + value);
  }
}

errai js interop support

Use Case 2: Third-party libraries

Errai's dependency injection makes it easy to define injectors for third-party JavaScript objects

In most cases, the JavaScript object you want is globally scoped or supplied by a factory method

In either case you can declare a @Produces method

errai js interop support

Use Case 2: Third-party libraries

Example: JQuery

JQuery has a globally scoped "$" function

```
$ wraps and enhances HTML elements
```

$(element).children().first().remove();

errai js interop support

Use Case 2: Third-party libraries

Example: JQuery

```
First we need to wrap the API
```

@JsFunction @FunctionalInterface
public static interface JQuery {
  JQueryElement wrap(HTMLElement element);
}

@JsType(isNative = true)
public static interface JQueryElement extends HTMLElement {
  // ...
}

errai js interop support

Use Case 2: Third-party libraries

Example: JQuery

```
Then we need a way to access the object
```
```
A couple options:
```

@JsType(isNative = true)
public abstract class JQueryProducer {
    @JsProperty(namespace = JsPackage.GLOBAL)
    public static JQuery $;
}

@JsType(isNative = true)
public abstract class JQueryProducer {
    @JsProperty(name = "$", namespace = JsPackage.GLOBAL)
    public static native JQuery get();
}

A method makes this read-only from GWT code

errai js interop support

Use Case 2: Third-party libraries

Example: JQuery

With previous definitions, we can write this

JQueryProducer.$
              .wrap(element)
              .remove();

$(element).remove();

Java

JavaScript

```
How can we @Inject the JQuery function?
```

JQueryProducer.get()
              .wrap(element)
              .remove();

or

errai js interop support

Use Case 2: Third-party libraries

Example: JQuery

```
Just add @Produces
```

With either of these we can inject the $ function

@JsType(isNative = true)
public abstract class JQueryProducer {
    @Produces @JsProperty(namespace = JsPackage.GLOBAL)
    public static JQuery $;
}

@JsType(isNative = true)
public abstract class JQueryProducer {
    @Produces
    @JsProperty(name = "$", namespace = JsPackage.GLOBAL)
    public static native JQuery get();
}

@Inject JQuery $;

errai js interop support

Use Case 2: Third-party libraries

Injecting the JQuery function into a constructor makes testing in Java SE easy

@Templated
public class Form {
    @Inject
    public Form(JQuery $) {
        // ...
    }
}

@Test
public void formWithJQuery() {
    Form form = new Form(new JQueryMock());
    // ...
}

take away

errai basics

```
Dependency Injection
```

@Inject

@Templated

@DataField

```
Templating
```

@Model

@Bound

```
Data-Binding
```

@Bindable

errai JSInterop Support

```
Use native DOM wrappers with UI logic
```

Easily define custom element and web component wrappers

Inject wrappers for elements, web components, and JS library APIs for unit-testable code

Thank you

Some Links

Tutorial:
github.com/errai/errai-tutorial

Errai Framework Website:
erraiframework.org

GWT Con 2016

By Max Barkley

GWT Con 2016

Presentation slides for GWT Con 2016

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Max Barkley

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