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JSF facelet taglib backed by a UI component 

Fang
Joined:
08/13/2009
Posts:
164

November 08, 2011 20:55:00    Last update: November 21, 2011 18:19:44
In the simple taglib example, I used a tag handler class to implement a taglib. This is an example to implement a taglib with a UI component. The purpose is to use a custom tag to split a string and print each part in a separate paragraph, i.e., print 
<p>john</p>
<p>steve</p>
<p>mike</p>

with custom tag <my:foreach>: 
<my:foreach var="who" value="john steve mike">
	    <p>#{who}</p>
</my:foreach>


These are the files:
  1. pom.xml 
    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>component-tag</artifactId>
    <version>1.0</version>
    <packaging>jar</packaging>

    <name>component-tag</name>
    <url>http://www.example.com</url>

    <properties>
	<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
	<dependency>
	    <groupId>org.apache.myfaces.core</groupId>
	    <artifactId>myfaces-api</artifactId>
	    <version>2.1.3</version>
	    <scope>provided</scope>
	</dependency>

	<dependency>
	    <groupId>javax.el</groupId>
	    <artifactId>javax.el-api</artifactId>
	    <version>2.2.3</version>
	    <scope>provided</scope>
	</dependency>

	<dependency>
	    <groupId>junit</groupId>
	    <artifactId>junit</artifactId>
	    <version>3.8.1</version>
	    <scope>test</scope>
	</dependency>
    </dependencies>

    <build>
	<plugins>
	    <plugin>
		<groupId>org.apache.maven.plugins</groupId>
		<artifactId>maven-compiler-plugin</artifactId>
		<version>2.3.2</version>
		<configuration>
		    <source>1.6</source>
		    <target>1.6</target>
		</configuration>
	    </plugin>
	</plugins>
  </build>
</project>

  2. src/main/java/com/example/UIForeash.java: 
    package com.example;

import java.io.IOException;
import java.util.Iterator;
import java.util.Map;

import javax.el.ValueExpression;
import javax.faces.component.UIComponent;
import javax.faces.component.UIComponentBase;
import javax.faces.context.FacesContext;

public class UIForeach extends UIComponentBase {
    public static final String COMPONENT_TYPE = "com.example.Foreach";
    public static final String COMPONENT_FAMILY = "com.example";

    // data object
    private Object value;

    // variable name
    private String var;

    public UIForeach() {
    }

    public String getFamily() {
	return COMPONENT_FAMILY;
    }

    public String getVar() {
	return this.var;
    }

    public void setVar(String var) {
	this.var = var;
    }

    // value is set only when the value attribute does not contain EL.
    // otherwise, setValueExpression is called with the EL value.
    public Object getValue() {
	if (this.value == null) {
	    ValueExpression vex = this.getValueExpression("value");
	    if (vex != null) {
		return vex.getValue(getFacesContext().getELContext());
	    }
	}
	return this.value;
    }

    public void setValue(Object value) {
	this.value = value;
    }

    public void encodeChildren(FacesContext ctx) throws IOException {
	if (!isRendered()) {
	    return;
	}

	String[] values = ((String) this.getValue()).split("\\s+");
	for (int i = 0; i < values.length; i++) {
	    Map<String, Object> attrs = ctx.getExternalContext().getRequestMap();
	    attrs.put(this.var, values[i]);

	    Iterator<UIComponent> it = this.getChildren().iterator();
	    while (it.hasNext()) {
		UIComponent c = it.next();
		c.encodeAll(ctx);
	    }
	}
    }

    public boolean getRendersChildren() {
	return true;
    }
}

  3. src/main/resources/META-INF/faces-config.xml: 
    <?xml version="1.0" encoding="UTF-8"?>
<faces-config 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-facesconfig_2_1.xsd"
    version="2.1">
    <component>
	<component-type>com.example.Foreach</component-type>
	<component-class>com.example.UIForeach</component-class>
    </component>
</faces-config>

  4. src/main/resources/META-INF/foreach.taglib.xml: 
    <?xml version="1.0" encoding="UTF-8"?>
<facelet-taglib
    xmlns="http://java.sun.com/xml/ns/javaee"
    version="2.0">
    <namespace>http://www.example.com/ns/mytags</namespace>
    <tag>
	<tag-name>foreach</tag-name>
	<component>
	    <component-type>com.example.Foreach</component-type>
	</component>
    </tag>
</facelet-taglib>



How to use:
  1. Put the JAR file generated by the above project in the WEB-INF/lib folder of the web app. If the web app is a Maven project, just add the taglib project as a dependency: 
    <dependency>
	<groupId>com.example</groupId>
	<artifactId>component-tag</artifactId>
	<version>1.0</version>
</dependency>

  2. In the facelet page: 
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 
<html  xmlns="http://www.w3.org/1999/xhtml"
   xmlns:h="http://java.sun.com/jsf/html"
   xmlns:ui="http://java.sun.com/jsf/facelets"
   xmlns:my="http://www.example.com/ns/mytags">
    <h:head>
    <title>Facelets Taglib Demo</title>
    </h:head>

    <h:body>
    <div id="header"><h2>Facelets Taglib Demo</h2></div>
    <div id="content">
        <my:foreach var="who" value="john steve mike">
	    <p>#{who}</p>
        </my:foreach>
    </div>
   </h:body>
</html>

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