Recent Notes

Displaying keyword search results 1 - 8
Created by Fang on April 16, 2012 12:58:35    Last update: April 16, 2012 12:58:35
To implement a JSP custom tag with dynamic attributes (for example, to pass-thru arbitrary attributes not handled by the JSP tag): Set the dynamic-attributes element to true in the TLD: <tag> <name>mark</name> <tag-class>c... The tag handler must implement javax.servlet.jsp.tagext.DynamicAttributes : package com.example.jsp; import java.io.*; ...
Created by Fang on December 06, 2011 19:03:25    Last update: December 07, 2011 08:54:11
Our custom tag, as implemented in the previous note , is broken when a template is used. Create a template file ( home-template.xhtml ): <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Stric... and a test page that uses it ( home.xhtml ): <?xml version="1.0" encoding="UTF-8"?> <ui:comp... Then request the page with URL: http://localhost:8080/facelet-demo/home.jsf?name=Jack . You'll find that our hello tag works inside ui:repeat but fails to get the value defined by ui:param ! What's the problem? Our hello tag implementation evaluated the EL with the wrong EL context! This is the corrected implementation: package com.example; import java.io.IOExcep...
Created by Fang on November 10, 2011 13:19:13    Last update: December 01, 2011 19:10:43
You can add custom implicit variables to JSF pages by using a custom EL resolver, in two simple steps: Write an ELResolver class to resolve the variable Add the ELResolver to faces-config.xml Starting from the Maven Hello World example: Add faces API and EL dependencies to pom.xml : <dependencies> <dependency> <groupId>o... Add a simple greeter class ( src/main/java/com/example/Greeter.java ): package com.example; public class Greeter {... Add our custom EL resolver ( src/main/java/com/example/ELResolver.java ): package com.example; import java.util.Itera... Add the custom EL resolver to src/main/resources/META-INF/faces-config.xml <?xml version="1.0" encoding="UTF-8"?> <faces-c... Build JAR with mvn package Drop the JAR into WEB-INF/lib of a webapp and test the new EL with: <h:outputText value="#{Greeter.sayHi('Mike')}"/> Fixed: the setValue method used to throw an exception, which is wrong. @Override public void setValue(ELContext ctx, O......
Created by Fang on November 21, 2011 15:57:49    Last update: November 22, 2011 09:51:26
The improved custom taglib works with existing facelet ui taglibs. For example: <ui:param name="theName" value="John"/> <my:hel... produces the expected output. However, a problem exists with the ui:repeat tag: <h3>With ui:repeat</h3> <ui:repeat var="theName... When tested with a URL like: http://localhost:8080/facelet-demo/?name=Zack&name... the raw EL prints out the correct names, but my custom tag substitutes empty string for theName2 ! In theory, the response is rendered in the Render Response phase, way after the Apply Request Values phase, actual values should be available to EL. The answer to this anomaly turned out to be very deep ! Yes, right there in the code! I would consider this a bug in facelets implementation, but the JSF spec did not tell what the expected behavior should be. In my custom...
Created by Fang on August 23, 2010 22:55:58    Last update: August 24, 2010 15:45:04
The tags XML flow control tags are exactly the same as their Core flow control equivalents, except that the test condition with a boolean EL expression is replaced by the select condition with an XPath expression. In the case of the forEach tag, the items attribute is replaced with the select attribute. In a test condition, the XPath expression is evaluated to a boolean value by the rules of the XPath boolean() function, which converts its argument to a boolean as follows: a number is true if and only if it is neither positive or negative zero nor NaN. a node-set is true if and only if it is non-empty. a string is true if and only if its length is non-zero. an object of...
Created by Fang on July 26, 2010 19:18:28    Last update: August 18, 2010 19:13:02
The tags <c:import> The <c:import> tag imports the contents of a URL and expose that in one of three ways: Import contents from a URL and write it out to the page (url may be relative or absolute): <c:import url="theUrl" /> Import contents from a URL and save it to a scoped variable string named by the var attribute. Use the scope attribute to define the scope of the exported variable. <c:import url="theUrl" var="importTest" scope="ses... Import a URL and expose to a Reader object named by the varReader attribute. The scope attribute does not apply. The varReader scoped variable can only be accessed within the body of <c:import> . <c:import url="theUrl" varReader="theReader"/> <c:url> The <c:url> tag constructs a URL and writes it out to the...
Created by Dr. Xi on January 08, 2010 03:53:37    Last update: January 08, 2010 03:54:56
This is an Ant custom task to merge Properties files I lifted from http://marc.info/?l=ant-user&m=106442688632164&w=2 , with some minor bug fixes. Example usage: <taskdef name="mergeProperty" classname="ant.task.... Implementation: package ant.task.addon; import java.io.Buff...
Created by Dr. Xi on February 09, 2009 23:14:15    Last update: February 09, 2009 23:14:15
This example demonstrates the general steps in creating a custom Java class loader. Normally a class loader would consult its parent class loader when asked to load a class. If it's not loaded by the parent class loader, then the class loader would try to load the class on its own. This class loader tries to load the requested class on its own first, and delegates to the parent only when a java.lang.SecurityException is thrown (which happens when it tries to load core Java classes such as java.lang.String ). The classes are loaded from CLASSPATH through the getResourceAsStream call. It's important to note that when a class is loaded with a certain class loader, all classes referenced from that class are also loaded through the...