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React Rendering in DXP

This article describes DXP infrastructure to render React components from the server side perspective. This includes taglibs as well as low-level services.

React Renderer Service

This is the low-level service to render React components.

⚠ Note that it only renders React components, not any React code, so you must provide a source which exports a React component to render. ⚠

It has one method:

public void renderReact(
		ComponentDescriptor componentDescriptor, Map<String, Object> data,
		HttpServletRequest httpServletRequest, Writer writer)
	throws IOException;

which receives:

  1. A ComponentDescriptor describing the source of the React component to render. More on this in the next section.
  2. A Map containing arbitrary data that will be injected to the React component as initial properties. Note that the data inside the map must be compatible with JavaScript, so you cannot inject any Java object you like, only primitive types, Maps, Arrays, ... that can be serialized to JSON.
  3. The current HttpServletRequest for which the component is being rendered.
  4. A Writer where the rendered HTML and JavaScript are written to.

Note that parameter 4 is not intended to be used to write the rendered HTML and JavaScript to any place you like but to pass the PrintWriter from the HttpServletResponse or the JspWriter from the PageContext you have available when invoking the method.

Also, take into account that, if you don't render the JavaScript inline (see option positionInline of ComponentDescriptor), the JavaScript will be written to the bottom of the current HttpServletResponse, while the HTML will be inlined into the passed Writer.

What the ComponentDescriptor contains

ComponentDescriptor instances are value objects that describe what needs to be rendered. A ComponentDescriptor may have up to five fields (of which only the first one is mandatory):

  1. module: the name of the AMD module that exports the React component to be rendered. Note that you need to provide the canonical name of the module (including its version number, like foo@1.3.2/js/Foo). To avoid hardcoding any version number you may use the instance of the NPMResolver service tied to the OSGi bundle containing the AMD module to be rendered, or alternatively, call any of the NPMResolverUtil methods (f.e.: NPMResolverUtil.resolveModuleName(this.class, 'js/Foo.')).
  2. componentId: the componentId that will be given to the component's JavaScript as an initial property. Note that this field is only used if the data map passed to renderReact does NOT contain a componentId property.
  3. dependencies: this is a reserved parameter which can be used in the future to declare additional dependencies. For now, it has no effect.
  4. positionInline: a flag to render the JavaScript directly in the current position of the HTML response or defer it to the bottom of the page. By default false.
  5. propsTransformer: optional name of an AMD module exporting a function to transform the properties before they are passed to the component. It has to follow the same rules as the module attribute (you must include the resolved version number).

How the React component is rendered

Say you run the following code:

ComponentDescriptor componentDescriptor =
	new ComponentDescriptor(
		"my-bundle@1.0.0/component/button", "myButton", null, false,
		"my-bundle@1.0.0/propsTransformer");

Map<String, Object> data = new HashMap<>();

data.put("color", "red");

reactRenderer.renderReact(
	componentDescriptor, data, httpServletRequest,
	httpServletResponse.getWriter());

This will cause HTML like this to be rendered in the current position of the HttpServletResponse:

<div id="XJAZ"></div>

(where XJAZ is a random placeholder id).

Note that the React component will be mounted in the parent element of this <div> as per the render method in the helper render.es module.

And JavaScript like this to be appended at the end of the page:

Liferay.Loader.require(
	'portal-template-react-renderer-impl@1.2.3/render.es',
	'my-bundle@1.0.0/component/button',
	'my-bundle@1.0.0/propsTransformer'
	function (render, renderFunction, propsTransformer) {
		render(renderFunction, propsTranformer({'color': 'red'}));
	}
);

If you are curious about what portal-template-react-renderer-impl@1.2.3/render.es contains, you can see its content in liferay-portal's source code. It is simply a helper to connect the generated JavaScript and the React component but, in general, it's a level of indirection to be able to add any extra infrastructure code we may need in the future.

react:component Tag

This tag is a wrapper for the low-level React renderer service. It leverages OSGi service com.liferay.portal.template.react.renderer.ReactRenderer to render the HTML and JavaScript.

The tag has five attributes (all optional but the module one):

  1. componentId: the component identifier. It can be used to reference the React component with Liferay.component(componentId).
  2. data: deprecated, use props (described below) instead.
  3. module: the name of the AMD module which exports the React component. Note that you don't need to provide the package name, just the module name and it will be resolved according to the provided servletContext's package.json file using the com.liferay.frontend.js.loader.modules.extender.npm.NPMResolver service.
  4. props: a Map with properties to be passed to the React component. See the data parameter in the renderReact method of the React renderer service.
  5. servletContext: the ServletContext that will be used to obtain the com.liferay.frontend.js.loader.modules.extender.npm.NPMResolver to resolve the module name. If not given, the servletContext of the JSP invoking <react:component> will be used.

Sample usage

<react:component
	componentId="myButton"
	module="component/button"
	props="<%=
		HashMapBuilder.<String, Object>put(
			"color", "red"
		).build()
	%>"
	servletContext="<%= application %>"
/>

liferay-clay Tag Library

The liferay-clay taglib provides several tags to render Clay components (for example: <liferay-clay:alert>, <liferay-clay:button>, ...). This is indirectly related to React because Clay components are implemented as React components.

Each tag has its own attributes, which are modeled according to the visual component the tag is rendering. See the documentation of each tag to learn about its attributes. A good place to do start is the taglib's TLD file.

All Clay tags are supposed to extend from com.liferay.frontend.taglib.clay.internal.servlet.taglib.BaseContainerTag which, in turn, leverages com.liferay.portal.template.react.renderer.ReactRenderer.

Then, at this low-level, all Clay components are created with a ComponentDescriptor containing:

  1. A moduleName which is defined by each tag, and corresponds to the JavaScript module that exports the React component.
  2. A data map which is filled with the attributes of the tag, like cssClass, defaultEventHandler, id, etc...

Sample usages

<clay:label
	displayType="warning"
	label="pending"
/>
<clay:alert
	message="you-do-not-belong-to-an-organization"
/>