转载：http://www.seamframework.org/Documentation/CreatingCustomELFunctions

 

In the WebContent/META-INF/ (JBDS) or view/META-INF/ (seam-gen) create a file called elfunctions.taglib.xml. If the META-INF/ dir does not exist, create it also. The content of elfunctions.taglib.xml should be:

 

<?xml version="1.0"?> <!DOCTYPE facelet-taglib PUBLIC "-//Sun Microsystems, Inc.//DTD Facelet Taglib 1.0//EN" "facelet-taglib_1_0.dtd"> <facelet-taglib> <library-class>org.el.func.FnLibrary</library-class> </facelet-taglib> Create another src package src/facelets with the packagename: org.el.func and add

 

package org.el.func; import com.sun.facelets.tag.AbstractTagLibrary; import java.lang.reflect.Method; import java.lang.reflect.Modifier; public class FnLibrary extends AbstractTagLibrary { public final static String Namespace = "http://org.el.func/SeamFunc"; public static final FnLibrary INSTANCE = new FnLibrary(); public FnLibrary() { super(Namespace); try { Method[] methods = SeamFunc.class.getMethods(); for (int i = 0; i < methods.length; i++) { if (Modifier.isStatic(methods[i].getModifiers())) { this.addFunction(methods[i].getName(), methods[i]); } } } catch (Exception e) { throw new RuntimeException(e); } } }

The above will dynamically add any of the static methods in a class called SeamFunc.java to be available in the EL. Now create org.el.func.SeamFunc.java:

package org.el.func; import org.jboss.seam.core.Expressions; public class SeamFunc { public static String concat(String... strings) { StringBuilder buff = new StringBuilder(); if (strings != null) { for (String str : strings) { buff.append(str); } } return buff.toString(); } public static Object evalEl(String expression) { String framedExpr = "#{" + expression + "}"; Object value = Expressions.instance().createValueExpression(framedExpr).getValue(); return value; } }

Now the last piece is to define the location of the elfunctions.taglib.xml in web.xml:

<context-param> <param-name>facelets.LIBRARIES</param-name> <param-value> /META-INF/elfunctions.taglib.xml </param-value> </context-param>

Create a test.xhtml page and add:

xmlns:e="http://org.el.func/SeamFunc"

and to the body:

#{e:concat('Hello ', 'World!')} / #{e:evalEl('conversation')}

These are just two examples of functions, you can create as many as you'd like. The evalEL seems useless, until you realize you can do something like:

#{e:evalEL(e:concat('person', 'Home'))}

which correctly resolves the value of the Seam component named personHome.

 

备注

facelets本身提供了jstl函数，所以jstl中的函数可以使用