All posts by denish

Poll: A yes/no question in a web form, which control(s) would you use?

We’re creating a web application that asks a number of questions about pumps (as it happens). Some of these questions are typical yes/no questions. But we need to make sure the user makes a positive choice. We don’t want to impose a choice on them. Which controls would you use?

Here’s the question with the three options we’ve currently got:

Do you need a sealless pump?
Do you need a sealless pump?
Do you need a sealless pump?

Jakob Nielsen at in his article Checkboxes vs Radio Buttons tells us that radio buttons are used “when there is a list of two or more options that are mutually exclusive and the user must select exactly one choice” and a single checkbox is used “for a single option that the user can turn on or off”. But this case is a little special since we don’t want the user to forget to select something. The nice thing about using the radio buttons or the drop-down is that you have a way of detecting if the user has actually chosen anything yet. On the whole though, the drop-down list is probably the least user-friendly though perhaps the easiest to generate programmatically.


(This poll is a great WordPress plugin developed by Lester Chan)

Following symbolic links in Tomcat

We have several web applications derived from the same code base and as well as sharing the jars in WEB-INF/lib, we provide set of administration pages to allow users to configure and administer the applications. Until now, we’ve always had to make copies of the admin pages and this has caused us configuration headaches as we try and make sure that all the applications have the latest versions of all the pages.

But now I’ve finally managed to work out how to make Tomcat follow symbolic links—and it’s very easy! Continue reading Following symbolic links in Tomcat

Groovy, DSLs and Rules engines

This article describes how we used Groovy to create a DSL for the clauses in a rules engine. We have been collaborating in the development of an “expert system” application for KnowledgeBench Ltd. This application uses a forward chaining rules engine to provide a “smart” system capable of creating formulations in domains such as pharmaceutical tablet formulation, inhalers, paints, food & drink and cosmetics. Continue reading Groovy, DSLs and Rules engines

Internet Explorer caches Ajax pages, and how to stop it

Caching pages leads to a speedier browsing experience and so is a good idea. Replacing information within a web page using Ajax similarly improves the user’s experience. The problem comes when the browser caches the information from the Ajax request. It’s a logical thing to do, but it’s not normally what the developer wants.

There are a number of ways round this. Continue reading Internet Explorer caches Ajax pages, and how to stop it

Firefox has overtaken IE on our site

I’m afraid that I don’t know exactly when it happened, but looking at our web-stats (produced by AWStats), the top ten browsers used to access our site are as shown below. It’s not representative of course, but it’s interesting that Firefox is so far above Internet Explorer. Continue reading Firefox has overtaken IE on our site

Plesk, Apache, Tomcat and multiple hosts

In addition to having problems with JNDI not working properly, I’ve also been bashing my head against Plesk–that is supposedly “designed to simplify the management and administration of web sites”.

It’s the interaction between Plesk and Tomcat that’s the particular problem and how both of them negotiate dealing with multiple domains (or rather don’t deal with it). Continue reading Plesk, Apache, Tomcat and multiple hosts

JNDI problems with Tomcat 5.5.15

I’ve recently been having difficulty getting JNDI lookup for MySQL connection pools working on our public server.

This proved very difficult to track down as all the stuff that I could find on the web said that I had to have:

  • commons-dbcp-1.2.1.jar
  • commons-pool-1.2.jar
  • mysql-connector-java-3.1.6-bin.jar

(or the latest appropriate versions)

Unfortunately this didn’t work and my little test JSP (using the JSTL sql tags) just gave me the error: DataSource invalid:
“java.sql.SQLException: No suitable driver.

However, next I tried connecting to MySQL directly using Class.forName(""com.mysql.jdbc.Driver") and that worked. So the problem wasn’t in loading the driver. Continue reading JNDI problems with Tomcat 5.5.15

Outputting stack traces in a JSP using JSTL

If you’re writing a JSP using the JSTL tag <c:catch var=”myError”> … </c:catch> then I’m sure that you know that the next thing to do is to check after the closing catch tag to see if myError is empty. If not you can output some useful error message having successfully caught any exception. However, sometimes it’s useful to actually output the stack trace (when debugging a site for example). It turns out not to be difficult to do this. Simply copy in the following:

<c:if test="${not empty myError}">
<p class="error">An error occured: <c:out value="${myError}"/></p>
<c:forEach var="stackTraceElem" items="${myError.stackTrace}">
<c:out value="${stackTraceElem}"/><br/>

HTML Testing, Ruby and Selenium

One of the problems with using HTML as the user interface is testing it (in fact testing user interfaces has always been a bit of a problem) so I’m always on the look out for good UI testing tools.

For a while I’ve known about and used Watir which scripts Internet Explorer (and now Firefox with FireWatir though it’s a bit more tricky to set up). Watir allows you to write simple but powerful scripts in Ruby that will instruct IE to load up a page, fill in a form, click a button or whatever and then you can make assertions about what should have happened. It’s not difficult to use and even if you don’t know Ruby, if you know other languages, you can soon pick it up.

Today however I came across Selenium (also on the same OpenQA site). This is neat for two reasons: (1) it’s all written in JavaScript so the same script runs in both IE and Firefox, on the PC or Mac; and (2) it has an IDE (a Firefox extension in fact) which lets you record the tests rather than having to write them yourself (you can then save them away and create test suites; you can also load up tests and single step them, etc.). (There is a Watir recorder on the OpenQA site but it’s only version 0.1 so far. There’s also WET which I haven’t tested, but is a Windows application written in Ruby which wraps around Watir.)

The thing I’m currently looking for though is a test environment where I don’t have to install a large infrastructure and which works easily on both PCs and Macs, supporting both IE and Firefox. Selenium seems to give me exactly that. In fact the project’s customer could probably install it on their PC and be able to run the tests (or even record new tests) which would be great.

Please let me know if you know of other tools that would fit the bill or what your experience is with these tools.

Dragging and dropping table rows in Javascript

Summary: This article tells you how to implement drag and drop for HTML tables in Javascript. You can download the source here and play with the demo here.

Updated: now copes with multiple tables on the same page, non-drag and non-drop rows (such as headers) and embedding form elements. Also see my jQuery plug-in which does much more. Continue reading Dragging and dropping table rows in Javascript