Friday, April 18, 2014

JSF 2.2 Tip of the Day: Naughty Expression Language (EL)

Unexpected Effects

Many of you may know this already, but I was reminded the other day how this can catch even some of the most brilliant JSF developers. When you comment out a component in your xhtml page that has EL bindings, you may not be REALLY disabling it.
Expression Language (EL) is parsed and evaluated as the page is being rendered. As a result, any exposed EL syntax will be processed including functions which could have deleterious effects. For example, take a look at the following code, and guess what it will do.

So what happens?

Scary things happen....
  1. It executes
  2. Parser exception. The parser will try to find a property called doSomething
  3. It will execute, please note that there is no <h:form/>. It is not required since we are evaluating the EL.
  4. Parser exception. The parser will try to find a property called doSomethingElse

Sensei what do I do?

You have a couple of options. The first option is the easiest, and it is likely what you want anyway with your JSF pages. You can disable the comments. No need to transmit your development comments to the end users anyway. The second option is to add a - between the # and the { like this #-{indexBean.doSomethingElse()}.
The first option is handled by adding a configuration parameter to the web.xmlfile as shown below. Here is a more complete example: The result of the code is as follows:

The complete code example was developed using NetBeans 8.0 and GlassFish 4.0 on JDK 8. The code can be found here: auto-execute-el

Wednesday, February 12, 2014

JSF 2.2 Tip of the Day: Using JSF AJAX Events

Please wait...


The JSF framework provides an easy to use AJAX event handling mechanism. The jsf.js library is included in Mojarra and MyFaces. There are two particular methods of interest: jsf.ajax.addOnError(callback) and jsf.ajax.addOnEvent(callback). I will be covering the latter handler.

The JsDoc does not really explain the jsf.ajax.addOnEvent(callback) code very well. Since it is Javascript, you can read it, but I think a simple example of its flexibility with some comments might work better.

Using the addOnEvent is very simple. You register the callback, and it gets called during the lifecycle. The important thing here to remember is that the callback must be a function. Otherwise, it will throw an error. You can control what event processing occurs during the lifecycle.


The callback is invoked during the AJAX request and response lifecycle. The status passed to the callback are listed below.

Event Description
begin This is the start of the AJAX request.
complete This is invoked right after AJAX response is returned.
success This is invoked right after successful processing of AJAX response and update of HTML DOM.

Based on the status, we can take appropriate action on the AJAX event. A great example to demonstrate AJAX event handling is to provide feedback to the user to indicate the status of their request. I will demonstrate how to create an AJAX based progress loader to demonstrate the events.


The code for our AJAX loader is very simple, and could be moved into a composite component if necessary. The NetBeans developed Maven project can be downloaded from the references section below.


This code controls our progress bar by making changes to the CSS in DOM. The CSS idea is not mine, but it is clever. Here is the CSS.


A simple CSS layout, and our Javascript callback to jsf.ajax.addOnEvent(callback) is all it takes to make a cool progress loader.


Monday, January 20, 2014

RichFaces 4.3.x Tip of the Day: Complex RichFaces Data Tables


I have been working on JSF tables for the various projects I have been involved with over the years. Starting in 2012, I began looking at RichFaces <rich:dataTable /> for some projects at my day job. The research into how to handle a number of complex situations has been enlightening to say the least.

The table is the most complex component in HTML. It is seemingly boundless in its extensibility. You can have multi-column headers that span multiple rows, you can multi-row cells, or multi-column cells. Tables can be displayed left-to-right, or right-to-left, top-to-bottom and vice-versa. As a result, when developing components for JSF, or any component framework, decisions must be made on how to generate them.

A couple of the component frameworks like PrimeFaces, and RichFaces allow developers to create more complex tables with more ease. However there are limitations with each of these frameworks. We trade flexibility for consistency, and this is fine in most cases.

The demonstration code in this post is about getting some of the flexibility back, or taking advantage of the flexibility that comes with a framework like RichFaces. We will gain the flexibility back, but it is a function of complexity. The examples will show you techniques for doing the "same thing" in multiple ways. For example, sorting can be done on the server, client, or a combination of both.

The question is where we put the complex bits. The answer to that question depends on you as a developer. You need to examine the problem domain, and understand the limits to the techniques presented.


Please let me confess something. I like building HTML objects programmatically. There I said it. In this case I am trading the ease of development for flexibility. The solutions below will demonstrate the different techniques for accomplishing the same functionality. Please examine the code carefully before discounting it. I spent a lot of time playing with it to make it look simple.

The code for this project was developed using NetBeans and Apache Maven. The code was tested on GlassFish and 4.0. It should work on other application servers, but I have not tested it on other servers. This project assumes you are using NetBeans which includes a sample database that these examples require. If you are not using NetBeans, you will need to create your own database with sample data to display some of the tables.

The code can be downloaded from Bitbucket at the link below, or in the references section at the end of the post.


Dynamic Data Table with Sorting

Dynamic Table with Sorting
This example uses the binding attribute of the <rich:dataTable /> to bind our table to a CDI @ManagedBean. The bean is responsible for generating the table programmatically, and returning it back to the page. The data is sortable by column.
As you can see the page is very simple. In fact, most of the page is plumbing and navigation. The <rich:dataTable /> is the smallest part of the page. The code to generate the table is much more complex.
As you can see we have traded simplicity in the page for complexity in the @ManagedBean. If you are satisfied with this technique, lets take a look at another one.

Dynamic Data Table with Sorting Revisited

Dynamic Table
This table uses the same dynamic binding as the example above on the JSF page, but uses helper utilities to create JSF components dynamically from a library that I have written. It is a separate project that you can download (Please see references). This reduces the chances for errors creating common components, but it is still a lot of code. To check our sorting, I have made a "random" data generator for the table data for the code to sort.
The more simplified code in the @ManagedBean is shown below.
The code above was written before I added more functionality to my jsf-utils project. The new methods would shorten this considerably, but it would still be fairly complex.

Dynamic Table using JSP/JSTL Tags with JSF

JSF/JSTL Dynamic Table
Let me start this example with a warning. If you are using JSP/JSTL tags in your JSF pages, you may encounter very bad behavior. This technique should only be used as a last resort. I will not labor a point. If you don't understand why this is a bad idea, take a look at this post for links: JSF 2.x Tip of the Day: Great Blog Posts Explaining JSTL vs. JSF.
In this example, I will generate the rows and columns using <c:forEach />. This transfers a lot of the complexity to the page and away from the @ManagedBean. Since we are using <c:forEach />, our mechanism for sorting has to change. I used Query jquery.tablesorter.js to allow sorting of the headers.
As you can see we have much simpler code in the page bean. It looks like what you would expect for a normal JSF data table.

Complex Data Table Design

Complex Table Design
This table has a lot of really cool features, but the code is complex in the page, and the page bean is relatively simple.


RichFaces supports complex table designs, and produces nice results. The amount of work required to create dynamic data tables depends on the technique chosen, and limitations on the data being presented. There is no "one good way" to create data tables. Suffice to say that the easiest path should be chosen.


SourceServlet: Displaying the Source Code and Pages from a Project on your Blog

I had been working on a way to create nice examples that include a way to display the page and source code for it. I created a servlet that will display the code as plain text that I would like to share with all of you.

Sunday, January 19, 2014

JSF 2.x: Nested Templates, Decorators, Fragments, and Includes

Ugly for Illustrative Purpose
I was looking at some JSF pages that I had been playing with to see about using decorators, fragments, etc. I thought someone might find it instructional, so I thought I would publish it before deleting the project. It demonstrates using a combination of methods to composite a JSF page into a cohesive unit.





JSF 2.x Tip of the Day: Custom JSF AJAX Error Handling on Client


One of the holes in JSF, in my professional judgement, is the lack of really good exception handling on the client for AJAX exceptions. A number of client frameworks like PrimeFaces, OmniFaces, and RichFaces attempt to cleanup for this shortcoming, it is still a deficiency.

The capabilities are present to make AJAX exception handling more robust. The "chemistry" is present in the framework, but it is not really standardized.

In this short example, I am demonstrating how to use the jsf.ajax.addOnError functionality to make client exception handling better. We will display at a minimum, an alert to let them know something bad has happened to their request.

Additionally, I will demonstrate how to use XPath to get additional information from the response.


The solution is to add the following code to the <head />: of the JSF page, or to an external JavaScript file that is included in the head. In my case, I am using an external JS file called jsf.ajax.handler.js that is loaded using JSF <h:outputScript />.

Here are the contents of the file.


JSF 2.2.x Tip of the Day: Custom JSF Exception Page including the default Facelets Exception Page

If you want to create a custom exception page in JSF and include the default exception page, you simply need to include one line of code.

This is an example of a custom exception page using the code above.

The resulting page will look like the image below. Please note that we are including the default JSF exception page.

Saturday, January 18, 2014

Java EE Tip of the Day: @WebFilter (Servlet Filter) Redirection

There is a common case to check a condition in a filter, and if the condition is not satisfied to redirect back to the context root of the application. This may be the case in a login filter, or a filter that performs some session management.

Here is a simple code example of how to perform the redirection:

HOWTO: Adding SyntaxHighlighter to Blogger

If you want to use SyntaxHighlighter in your blog, you can simply add the code below to the <head /> element in the template for your Blogger blog.

JSF 2.x Tip of the Day: Redirecting to the context path with parameters

This is just a quick code example that demonstrates how to do a redirect to the Servlet context path with parameters.

The code above will correctly format parameters to be passed as part of the redirection.

Here is an example using bogus parameters.

Here is the JSF Form I used to generate the output below.