Spartan Java

Someone asked me about the implementation details of the Google Appengine sample I published a few weeks ago (http://obovweb.appspot.com/). Well, you can get a hold of the source code here.

There’s not much to tell, apart from the specific HMAC-SHA1 implementation (which you can check out in Obovs source code) it’s a very simple JSP/DWR application.

I’ve faced this problem a few times before, but this time I decided to find a generic solution to it. I needed to prevent users from clicking action links in a web application multiple times and therefore triggering some server side action a lot of times when only one time was enough/needed.

After looking around for a few hours for an elegant solution I just couldn’t find one, all the articles/answers I found required controls on each link and/or special handling on the server side code that reacted to them.
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In our first installment we reviewed the front-end part of developing a paginated list using AJAX and Java. Now we will dive into the back-end of our pagination mechanism.
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Download a file using Java from a URL should be a simple task, well it is :P. If you just don’t want to think too much about it here is a sample method to do it.
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Check it out at http://www.styledisplay.com/mootoolsdatepicker/, it’s quite simple to use and looks great.

obov stands for OATH Based OTP validator. It’s a 100% pure Java library that provides simple to use methods to validate (and related utilities) one time passwords generated by OATH compliant devices.
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You have to display a list of items in a web application, for each item allowing several operations (ie modification, deletion, etc.). The list can potentially be quite long, so pagination is required.
This scenario is common in backoffice web applications and public web sites, be it for administering information or as search results display, etc.

I’ll describe a simple way to implement a lightweight pagination engine that minimizes load on the server and gives the user the better experience possible. In this first installment I’ll focus on the front-end side, describing how to lay out the HTML, load it using AJAX and implementing the basic operations the user needs to navigate in your paginated list.
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There are plenty of times when you need a cache for Java objects in your code. A very easy to use and simple implementation of a cache is provided with Apache ORO, wisely called CacheFIFO (http://jakarta.apache.org/oro/api/org/apache/oro/util/CacheFIFO.html).
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It’s usually very nice, and sometimes a requirement, to validate usernames and passwords using existing credentials. And in most situations big frameworks or single sign-on systems are just damn overkill and complex.

If you need to check your users credentials via an existing Unix system (that supports PAM) or a Windows domain controller check out (continue reading…)

Do you really need to have a database table with all existing countries? What’s the benefit? Apart from adding one more database query to each page hit and an array to each users context while loading that form…

Think it over, every software component’s goal must be, first of all, to satisfy the users needs as fast and as reliably as possible. Considering the “fast” part, you must always evaluate if it’s really necessary to store this kind of info in a database table, and penalize the applications overall performance by adding another database query, recordset run through and a whole bunch of new objects in an array in request or session context.

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