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JSP custom tags example with body

Created by Fang on January 28, 2012 13:24:09 Last update: January 28, 2012 13:31:22

This is a simple JSP custom tags library with tag body. Just like the JSF counterpart , it splits a string and repeats the body for each word, i.e., with this markup: <%@ taglib uri="http://custom.tag.com/demo" prefix... output:

<html>
 
 <body>
 
 	<p>Hello Tigger!</p>
 
 	<p>H...

With Maven, this is the directory structure:

./src
 
 ./src/main
 
 ./src/main/resources
 
 ./s...

There are three files to write: pom.xml : <project xmlns="http://maven.apache.org/POM/4.0.0"... src/main/java/tagdemo/IterateTag.java :

package tagdemo;
 
 
 
 import java.io.IOException...

src/main/resources/META-INF/demotag.tld :

<?xml version="1.0" encoding="UTF-8"?>
 
 
 
 <!DO...

Build with: mvn clean install To use it as a dependency in other Maven projects:

<dependency>
 
 	    <groupId>tag-demo</groupId>
 ...

Introduce JSF EL implicit variables by custom EL resolver

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......

A simple JSF facelets taglib example

Created by Fang on November 03, 2011 19:47:38 Last update: November 08, 2011 20:24:47

This is a step-by-step example to create a really simple facelet taglib (in JSF 2 with Maven). Create a simple Maven project with: mvn archetype:create -DgroupId=com.example -Dartif... Three files are created as a result: pom.xml src/main/java/com/example/App.java src/test/java/com/example/AppTest.java This project should be able to build with: mvn package Add facelet API dependencies to pom.xml : <project xmlns="http://maven.apache.org/POM/4.... The compiler plugin section is optional. Remove src/main/java/com/example/App.java , create a new Java class as the facelet Tag Handler ( HelloTagHandler.java ): package com.example; import java.io.IOExcep... This tag handler simply prints a "Hello" message. Create facelet tag declaration file src/main/resources/META-INF/hello.taglib.xml : <?xml version="1.0" encoding="UTF-8"?> <facelet... Build the JAR with mvn clean package Optionally, install it to the local repository: mvn install To use the taglib, simply drop the...

A simple JSF facelet template example

Created by Fang on October 28, 2011 13:49:40 Last update: October 30, 2011 19:23:25

This is a simple example to demonstrate the templating power of JSF facelets. If you've used struts tiles before, you'll recognize the simplicity of templating with facelets. I've stripped out everything else except the pages themselves, just to put our focus on facelets. This is a Maven based project, and you need Tomcat (or any servlet container) to run the resulting webapp. To begin with this is the list of files: ./pom.xml ./src/main/webapp/home.xhtml ./src... I left faces-config.xml in there for completeness sake, it may not be needed. The Maven POM ( pom.xml ): <?xml version="1.0" encoding="UTF-8"?> <project... Web app configuration ( WEB-INF/web.xml ): <?xml version="1.0" encoding="UTF-8"?> <web-app... Empty WEB-INF/faces-config.xml : <?xml version="1.0" encoding="UTF-8"?> <!-- Thi... index.jsp is simply a redirect to home.jsf : <% response.sendRedirect("home.jsf"); %>...

Including authenticated user info in log analyzer with a servlet filter

Created by Dr. Xi on March 24, 2011 12:11:14 Last update: March 24, 2011 12:22:03

This is the task: your client wants to know how the web application is used. That is pretty easy. A plethora of commercial tools or any of the free log analysis tools such as analog and AWStats would fit the bill. But here's the catch: they want to know not only what pages are visited by how many people and when, but also who logged in and did what. Your application is using form based authentication and therefore, everyone is anonymous in the web access log. What to do? This is a servlet filter that generates a web access log with authenticated user info that can be fed to log analysis tools such as analog and AWStats . Filter code (the output format is Apache...

Java Servlet GZIP commpression filter

Created by Dr. Xi on November 23, 2010 20:20:01 Last update: March 01, 2011 13:38:51

I tried to find a GZIP compression servlet filter to compress a large log file that we send down to the browser. Most of the implementations I found were overly complicated and many buggy. This is a simple implementation that worked for me. The filter: package filter.demo; import java.io.*; i... Config web.xml : <filter> <filter-name>gzipFilter</filte... The ugly anonymous inner class could have been avoided if the servlet API did not insist on ServletResponse.getOutputStream returning the bogus ServletOutputStream class (instead of the plain OutputStream ). Additional Note: In an earlier version of this filter, the gzip headers were added in doFilter , like this: // This is NOT good! if (supportsGzip) { ... It turned out that the ServletResponse methods sendError bypasses the gzip...

Java ServletOutputStream and PrintWriter examples

Created by Dr. Xi on November 23, 2010 22:11:54 Last update: November 23, 2010 22:12:49

JavaDoc says that you can call getOutputStream or getWriter on ServletResponse , but you cannot call both. The second call will get IllegalStateException . So this works:

import java.io.*;
 
 import javax.servlet.*;
 
 im...

So does this:

import java.io.*;
 
 import javax.servlet.*;
 
 im...

But not this:

import java.io.*;
 
 import javax.servlet.*;
 
 im...

You can make the last servlet work if you insert a filter like this:

import java.io.*;
 
 import javax.servlet.*;
 
 im...

But depending on the underlying implementation, the order of the output strings may be undetermined.

Java gzip decompress example

Created by Dr. Xi on August 27, 2010 22:35:53 Last update: August 27, 2010 22:35:53

This example decompresses a gzip compressed file with java.util.zip.GZIPInputStream . The input is assumed to be Base64 encoded after being gzipped (such would be the case when binary data is transmitted within an XML file). You don't need the Base64InputStream if the data is not Base64 encoded.

import java.io.*;
 
 import java.util.zip.GZIPInpu...

Decode a Base64 encoded file in Java

Created by Dr. Xi on August 24, 2010 21:59:22 Last update: August 24, 2010 21:59:22

This class decodes a Base64 encoded file with the Apache commons codec package:

import java.io.*;
 
 import org.apache.commons.cod...

Encode a binary file with Base64 encoder in Java

Created by Dr. Xi on June 03, 2010 22:43:43 Last update: June 20, 2010 14:13:05

Using the Sun BASE64Encoder :

import java.io.*;
 
 import sun.misc.BASE64Encoder...

However, the Sun encoder is awfully slow. The Apache encoder is a lot faster. Here's the code with Apache encoder:

import java.io.*;
 
 import org.apache.commons.cod...

Performance comparisons between Apache and Sun:

C:\>bash
 
 bash-3.2$ time java EncodeFileWithBase...

Ant task to merge properties files

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...

Start a webapp (web application) project with Maven

Created by Fang on September 07, 2009 16:39:37 Last update: September 07, 2009 18:43:04

It's easiest to use the archetype plugin to start a new Maven project. I'll use struts 1 as example since it's not in the built-in archetypes for archetype:generate . Generate a simple webapp with archetype:generate : C:\work\maven>mvn archetype:generate -DarchetypeAr... It generates a directory structure like this: struts1app struts1app/pom.xml struts1app/src... with a simple POM: <project xmlns="http://maven.apache.org/POM/4.0.0"... Create settings.xml in $HOME/.m2 , add Java.net repository for Java EE dependencies: <?xml version="1.0" encoding="UTF-8"?> <setting... Add Java EE and Struts dependencies in pom.xml . Note that the Java EE dependency has scope provided , meaning that the web app container provides the jars, therefore we don't need to bundle them with our war fie. <project xmlns="http://maven.apache.org/POM/4.0.0"... Create a directory named java under main , create the Struts form and...

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