Custom Facelet component in JSF

It are in essence taghandlers. I.e. classes extending from TagHandler.

Here's a Hello World taghandler.

com.example.HelloTagHandler

public class HelloTagHandler extends TagHandler {

    public HelloTagHandler(TagConfig config) {
        super(config);
    }

    @Override
    public void apply(FaceletContext context, UIComponent parent) throws IOException {
        // Do your job here. This example dynamically adds another component to the parent.
        if (ComponentHandler.isNew(parent)) {
            UIOutput child = new HtmlOutputText();
            child.setValue("Hello World");
            parent.getChildren().add(child);
        }

        nextHandler.apply(context, parent); // Delegate job further to first next tag in tree hierarchy.
    }

}

/WEB-INF/my.taglib.xml

<?xml version="1.0" encoding="UTF-8"?>
<facelet-taglib
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-facelettaglibrary_2_0.xsd"
    version="2.0"
>
    <namespace>http://example.com/my</namespace>
    <tag>
        <tag-name>hello</tag-name>
        <handler-class>com.example.HelloTagHandler</handler-class>
    </tag>
</facelet-taglib>

/WEB-INF/web.xml (note: this part is not mandatory when my.taglib.xml is in /META-INF folder of a JAR file inside /WEB-INF/lib like as with JSF component libraries):

<context-param>
    <param-name>javax.faces.FACELETS_LIBRARIES</param-name>
    <param-value>/WEB-INF/my.taglib.xml</param-value>
</context-param>

Usage in /some.xhtml

<html ... xmlns:my="http://example.com/my">
...
<my:hello />

To see the source code of Mojarra implementation of <ui:composition> and <ui:include>, click the links.

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