How to create a custom EL function to invoke a sta

Im new to JSF 2. My question is related to BalusC's answer to this question jsf2 ajax update parts based on request parameters I tried the kickstart code BalusC posted and I encountered an EL parsing error:

 /nameofpage.xhtml @12,64 rendered="#{bean.panels.contains('u1')}"
 Error Parsing: #{bean.panels.contains('u1')}

I guess that this is caused because I'm not running a Servlet 3.0 / EL 2.2 capable container with a /WEB-INF/web.xml declared as per Servlet 3.0 spec. I'm using Tomcat 6.

BalusC suggested in his answer to create a custom EL function. But how do I accomplish this using a custom EL function? Or can this be fixed by just configuring certain parts of my project?

Below is my web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5">
  <servlet>
    <servlet-name>Faces Servlet</servlet-name>
    <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Faces Servlet</servlet-name>
    <url-pattern>*.jsf</url-pattern>
  </servlet-mapping>
  <context-param>
    <param-name>javax.faces.PROJECT_STAGE</param-name>
    <param-value>Development</param-value>    
  </context-param>      
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>index.html</welcome-file>
  </welcome-file-list>
</web-app>

标签： function jsf jsf-2 el static-methods

1条回答

何处买醉

2楼-- · 2018-12-31 06:08

First create a final class with a public static method which does exactly the job you want:

package com.example;

import java.util.Collection;

public final class Functions {

    private Functions() {
        // Hide constructor.
    }

    public static boolean contains(Collection<Object> collection, Object item) {
        return collection.contains(item);
    }

}

Then define it as a facelet-taglib in /WEB-INF/functions.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/functions</namespace>

    <function>
        <function-name>contains</function-name>
        <function-class>com.example.Functions</function-class>
        <function-signature>boolean contains(java.util.Collection, java.lang.Object)</function-signature>
    </function>
</facelet-taglib>

Then familarize Facelets with the new taglib in the existing /WEB-INF/web.xml:

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

(note: if you already have the javax.faces.FACELETS_LIBRARIES definied, then you can just add the new path semicolon separated)

Then define it in the Facelets XHTML file as new XML namespace:

<html 
    xmlns="http://www.w3.org/1999/xhtml"
    xmlns:f="http://java.sun.com/jsf/core"
    xmlns:h="http://java.sun.com/jsf/html"
    xmlns:func="http://example.com/functions"
    ...
>

Finally you can use it as intended:

rendered="#{func:contains(bean.panels, 'u1')}"

As a completely different alternative, you can also include JBoss EL in your project. It works on Tomcat 6.0 and you'll be able to invoke non-getter methods in EL. Drop jboss-el.jar file in /WEB-INF/lib and add the following to your web.xml:

<context-param>     
    <param-name>com.sun.faces.expressionFactory</param-name>
    <param-value>org.jboss.el.ExpressionFactoryImpl</param-value>   
</context-param>

Since EL 2.2 there's another approach: create an @ApplicationScoped bean with methods in turn referring to those static functions. See also a.o. Utility methods in application scoped bean.

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