Rework mechanism for registering external components

[GlebDurygin]

Consider using annotation instead of xsd for defining component model

Port:

• ExternalUIComponentsSource interface
• WebExternalUIComponentsSource class

Without this mechanism, the user cannot register custom or composite component

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Changes

The mechanism of registering/overriding UI components is simplified to defining spring bean (ComponentRegistration) with component information.

For instance:

@Configuration
public class MyComponentsConfiguration {

    @Bean
    protected ComponentRegistration newButton() {
        return ComponentRegistrationBuilder.create(NewButton.NAME)
                .withComponentClass(NewWebButton.class)
                .withComponentLoaderClass(NewButtonLoader.class)
                .build();
    }
}

The code above will register new Button component with:

• name: NewButton.NAME;
• class: NewWebButton.class;
• XML tag name: NewButton.NAME;
• loader class: NewButtonLoader.class;

ComponentRegistration is an interface for registering components.
ComponentRegistrationBuilder is a builder class for creating registration bean.

Order of registering components

It is possible to use spring @Order annotation to handle the order of registering components. For instance, we have two configurations:

• configuration from some add-on:

@Bean
@Order(200)
protected ComponentRegistration newButton() {
    return ComponentRegistrationBuilder.create(Chart.NAME)
            .withComponentClass(WebChart.class)
            .withComponentLoaderClass(ChartLoader.class)
            .build();
}

• project configuration with component overriding WebChart component:

@Bean
@Order(100)
protected ComponentRegistration newButton() {
    return ComponentRegistrationBuilder.create(Chart.NAME)
            .withComponentClass(MyWebChart.class)
            .withComponentLoaderClass(ChartLoader.class)
            .build();
}

So with the above configurations will be registered component with the smallest @Order value (MyWebChart).

Important note
You must specify loader class for MyWebChart component as it "replace" registration of WebChart component and all information about WebChart is lost.