Spartan Java

Afraid of malicious injections in your web app requests, heres a simple way to improve your application security. Push every request parameter through a filtering function before it’s feeded to your application code.

Such a function can be as simple as:

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private String cleanParameter(String value) {
   if (value != null) {
      value = value.replaceAll("<", "&lt;").replaceAll(">", "&gt;");
      value = value.replaceAll("\\(", "&#40;").replaceAll("\\)", "&#41;");
      value = value.replaceAll("'", "&#39;");
      value = value.replaceAll("eval\\((.*)\\)", "");
      value = value.replaceAll("[\\\"\\\'][\\s]*javascript:(.*)[\\\"\\\']", "\"\"");
   }
   return value;
}

This will escape/remove potentially dangerous Javascript code and HTML/XML tags.

You can implement this on a web filter or a struts interceptor or a DWR filter depending on the technology you use for you app.

Back in April I wrote about Java to/from JSON serialization using XStream. After developing several AJAX applications using PHP and JQuery, I found that for a lot of scenarios a very simple approach is not only easy but very effective. In the case of PHP, you can effectively enable AJAX in your apps using jQuerys $.getJSON() and PHP json_encode().

I think we can use a very similar approach for Java web applications, enabling the use of AJAX through a very simple, elegant and extensible architecture, without the use of complex frameworks and extra configurations.
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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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I decided to try out the new Java based version of Google Appengine. So i wrote a very simple web app that allows the user to generate one time passwords (OTP) using the HMAC-SHA1 algortihm (see OATH).

You can check it out at http://obovweb.appspot.com. As the name suggests its based on my obov library.
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The best tool I’ve found so far to serialize POJOs to JSON (and back again) is XStream, it’s automatic, simple and elegant, check it out.

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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Most web servers are missing the new MIME types needed for Office 2007 files (docx, xslx, etc.) and when you server one of this files from your web application the users browser typically tries to open them as ZIP files.
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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.