John Topley's Weblog
June 2004 Article ArchiveJakarta Struts De-Mystified Part 1Wednesday, 23 June 2004Just over a year ago I started to learn how to use the Jakarta Struts J2EE web application framework. During this journey it became apparent to me that there were some aspects of Struts that I found confusing at first, and that many other developers were going through the same difficulties. This series of articles is an attempt to address this problem. There are now many good books on the framework and the online documentation is quite mature for an open-source project; but in spite of this, I have found myself having to refer to lots of resources to build a good understanding of Struts. Moreover, there are still some areas where the documentation is sparse. However, this occasional series isn't an attempt to provide a definitive source of documentation; I don't claim that my knowledge of Struts is at the level needed to be able to produce that. Rather, it's intended to allow newcomers to Struts to hit the ground running and to get a feel for what the framework is like and what it can and can't do. The Struts example applications I have seen, I have found to be too trivial or too complex, with the complex ones having lots of external dependencies that have to be resolved before the example can even be compiled and run. With my example I'm attempting to hit a sweet spot between the two extremes, and I've deliberately created an application that has the minimum of external dependencies, so you should be able to actually run the code without too much difficulty! Everything you'll need is open-source and can be downloaded for free—one of the advantages of J2EE. The example application that we're going to be building is an online discussion forum—which I've given the rather generic name of “Web Forum”. I've chosen an application of this type because it should be familiar and because you can create quite a lot of functionality without the complexity getting out of hand. It's fully functional, reasonably well-debugged and hopefully it should be fun learning how it all fits together. It's important to state at the start that this code shouldn't be used as an example of a production-quality J2EE system. In particular, the exception handling is extremely and deliberately simplistic. This isn't a tutorial on persistence strategies, OO design or web application GUI design, it's simply a vehicle for learning Struts. There are doubtless aspects of what I've created that could be improved upon, but that's not important right now. So without further ado, let's crack on! IngredientsI'm going to start by talking about the ingredients you'll need to create the application. I developed it using Oracle JDeveloper 9.0.3 because that's the IDE I'm familiar with from my day job. You can use your tool of choice for writing the code. Note that throughout this series I'll be providing the source code as a download in both JDeveloper and non-JDeveloper form. The JDeveloper version will simply include JDeveloper's workspace and project files, so the project can be opened quickly and easily within that IDE. This is a list of what else you will need:
*I use the embedded OC4J server that comes with JDeveloper. I also use the MySQL Control Centre for creating the database and controlling the database server, although the MySQL command line can be used if preferred. The ApplicationI'm now going to give a brief tour of the Web Forum's functionality. Some of this I'd thought about before I wrote a line of code, other aspects become apparent as I was building it. It helped that there are plently of existing forums to serve as inspiration! Upon starting the application, the user is presented with a list of topics and information about each topic, such as the date and time it was posted, the number of replies and the topic's author. The most recent sixteen topics are displayed, ordered from the newest to the oldest:
At this point the user can click on a topic to view it and any follow-up replies:
The date and time of the post are displayed, as well as the author's name, the date they registered with the system and the number of posts they've made. The user can register if they are a new user, or log in if they are an existing user. A user must be logged in before they can create a new topic or a new reply. They can elect to automatically log in during registration or at the Login screen:
The auto-log in feature uses a cookie that expires after thirty days. During registration they must provide a unique user name, their real name (or screen alias) and a password. All of these fields are mandatory apart from surname and they must confirm their chosen password by entering it twice:
After they have successfully registered they are taken back to the topics screen where they can create a new topic:
Both the subject and message fields are mandatory. They are allowed to use the HTML <b>, <i> or <u> tags for basic text variations (bold, italic or underline) in the message field. Once they have created a new topic they are taken back to the Topics screen. The hyperlink to a topic contains an encoding of the number of replies to that topic, which ensures that the user can see which topics they have read, because the hyperlinks to those topics are displayed using the browser's visited link colour. Therefore, new replies to a topic cause that topic's hyperlink to be displayed using the browser's unvisited colour. Thanks to Joel Spolsky for this brilliantly simple idea. When viewing a topic they can compose a new reply and again, the message field is mandatory and accepts basic formatting tags as before:
Next TimeThis article defined the boundaries within which this tutorial will operate and introduced the example application that we'll end up creating. Next time I'll introduce the data model and the class model that do the work behind the scenes, and we'll get practical and write the code to display the list of topics. The RDD AdvantageWednesday, 16 June 2004Starting a new J2EE project is a daunting undertaking. The technology choices alone are myriad and bewildering. Can you afford to fail by not using RDD? Chances are you've not heard of this new approach to software development. Not many have right now, but it's growing fast. It's no exaggeration to say that those who follow RDD wonder how they ever managed without it. RDD uses an industry standard toolset to simplify J2EE technology strategies and implementation choices. Furthermore, RDD supports all common J2EE solutions in the marketplace, with support for new ones is being added all the time. So RDD can accommodate your future needs. The unique and powerful algorithm underlying RDD takes into account the current skillset and any gaps, with the result that your project is guaranteed to use the most appropriate technology. No RDD project has ever ended up in a technological cul-de-sac. Research has conclusively shown that RDD practitioners have increased marketability and earning potential. There is a direct correlation between the use of RDD and personal empowerment.
RDD is Resume-Driven Development. Find those buzzword gaps on your CV and plug them. JDeveloper, Apache And MIME TypesMonday, 07 June 2004I've just got to the bottom of a fairly obscure problem that occurs when using Mozilla Firefox to access a web application developed using Oracle JDeveloper. The JSPs in my application link to an external stylesheet, but the pages weren't styled when viewed using a Gecko-based browser, such as Firefox. However, they were fine when using Internet Explorer or Opera. Changing to an inline stylesheet declaration fixed the problem, which suggested that there might have been something about my external stylesheet declaration that Firefox didn't like: <link rel="stylesheet" type="text/css" href="/webforum/assets/css/webforum.css" /> —There's nothing out of the ordinary there. Using the JavaScript Console in Firefox showed that the error was occurring because the CSS file was being served with a MIME type of application/octet-stream instead of text/css:
—This opened up another avenue of investigation. JDeveloper includes a cut-down, embedded version of Oracle's OC4J J2EE application server. This enables J2EE components and web applications to be run from within the IDE. I know that OC4J uses Apache as its web server, which led me to suspect that I was dealing with an Apache configuration problem and not a JDeveloper or OC4J problem. I sniffed around in the configuration directory for the embedded container and found a file named mime.types, which seemed a likely candidate for modification. I added the line: text/css css …restarted the application and all was now well. I could admire the results of my beautiful stylesheet in Firefox and marvel at how different it looked from IE. According to a message on the Oracle Technology Network JDeveloper forum, this quirk is still present in the latest JDeveloper release. For the benefit of other developers with this problem who want to work around it, simply download this mime.types file from my standalone Apache 1.3 installation and overwrite the existing file in: <JDEVHOME>/jdev/systemX.X.X.X.XXXX/oc4j-config —for the embedded OC4J server, or: <JDEVHOME>/j2ee/home/config —for the standalone server. Job done! |
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