CrazyTechThoughts

My latest project involves JQuery for UI development. Frankly speaking, I did not have much idea of JQuery before. But I found it very easy to understand. All APIs are well documented with lots of examples available on Internet. The best feature of JQuery is its plugins. There are thousands of plugins available to play with. For every need of my web app I could find a plugin. In my web app I am using JQuery Form plugin to submit the forms through AJAX. The return from my servlet is JSON object. The form plugin works great for all my forms. Well almost all, there is a HTML form which has a file upload box along with other input fields. This form was not able to get the response in JSON format. Though it worked in Google Chrome, but Firefox was presenting me with a file save dialog box. I did a lot of googling to find out whats going on. Finally I observed that the problem is with HTTP headers that the form submit request has. Here are the headers captured by Chrome Request heade...

I could not post anything last month though all the time I was dying to post something. The reason behind this was I change in my profession profile. Actually, I changed my employer. All of the last month I was busy in official work and to settle down in my new office. The last week of the year is normally a holiday in the new company. So, I could rest a while in my home and able to write the blog post. Though I had a couple of other topics in mind but writing them will take more time which I don't want to spend during the festivities. So, I'll discuss about a simple but useful thing. How many of us in Java sphere use log4j for logging? You know the answer. log4j is a very popular logging framework. Configuring log4j is quite simple. Still when you get the task of doing it, you try to find an example (I do the same). That is why I'll show a simple log4j configuration to print to a file. There are 2 ways to configure log4j, log4j.properties and log4j.xml. I prefer the...

JDK 7 is the next release of Java language. There are lot of expectations from this release. For the first time Java is being modeled outside Sun Microsystems. Now JDK 7 has got a net host, openJdk community. There are quite a few features planned in JDK 7. Some of them may prove to be a milestone for Java language. But my personal liking is a very small feature rather project called Project Coin . Coin serves to add small language features to Java which will make programmer's life easy. The JavaOne 2010 presentation for Project Coin lists the following features as accepted ones in JDK 7 time frame. Binary literals and underscores in literals Strings in switch Varargs warnings Diamond Multi-catch and more precise rethrow try-with-resources (formerly known as Automatic Resource Management, ARM) Out of these features, the most attractive to me was "Strings in switch". This is something I've longed for from my college days. I mean, though it was not Java (it...

Few days back I was disturbed with some maven build issues in office. I got back home pretty late. Already, as you can understand, mood was off. I thought of relaxing by watching a good movie but next day I had an interview scheduled. So, I had to brush up my skills a bit (I don't use them often in office :-) ). The first topic I started with was Singleton pattern. This one is so famous among interviewers that you better be able to explain it. I had read the pattern many a times already. Nothing to prove the book wrong, never occurred to me. But that day, may be due the horrible mood, I challenged the pattern. I thought I'll find ways to break the pattern down. I wanted to create 2 Singleton instances in same JVM. Thats how the attack began. Below is the code for creating a Singleton class Here is the code to test the pattern I have used VisualVM (comes as part of JDK 6) tool to check the no. of instances for Singleton class. You just need to pass a VM argu...

Maven is a popular software project management tool. It is used heavily for building you project deliverables. More information about maven can be found here . Maven works on the dependency concept. It essentially means that every project should identify its required artifacts. These artifacts can be found in repositories. Repository is a central place where you keep all your required jars (or other resources). There is a specific structure required to put your artifacts into the repository. We can not just copy every thing at same place. To identify a resource through dependency mentioned in pom.xml, maven looks for the specific structure. Also ther should be a .POM file at the same location of the artifact. Normally the artifacts generated by maven build comes with the POM for it. So that, any other project wanting to use this artifact can do that. But if the artifact is created from a build other than maven (e.g. ant, Makefile etc), it will not have the POM generated. So this ar...

Drools is a very popular rule engine. It is based on Rete algorithm. To understand what is a rule engine and how to use it check here . But here I will assume that you have some working knowledge on Drools. What I am going to discuss in this post is 'how to use multi-threading with Drools'. Below is a snippet which creates a KnowledgeBase from a DRL file. If this method is called from multiple threads I get below exception - Exception in thread "Thread-60" [Error: incomplete statement: (possible use of reserved keyword as identifier: )] [Near : {... globals != empt ....}] ^ [Line: 0, Column: 0] at org.mvel2.MVELInterpretedRuntime.parseAndExecuteInterpreted(* MVELInterpretedRuntime.java:153*) at org.mvel2.MVELInterpretedRuntime.parse(* MVELInterpretedRuntime.java:44*) at org.mvel2.MVEL.eval(*MVEL.java:514*) at org.mvel2.templates.res.IfNode.eval(*IfNode.java:61*) at org.mvel2.templates.res.TextNode.eval(*TextNode.java:46*) at org.mvel2.templates.res...

D o you have a web resource in your application which is dynamically generated/modified? And do you use JavaScript/Ajax (i.e. you do not have the resource mapped to a servlet in your application web.xml) to read that resource? If both answers are yes, then you may have seen that the request for the resource does not return the updated file always. The reason is DefaultServlet class of Tomcat which implements a caching technique for resources. If there is a HTTP request to access the resource before 5 sec of the last modification time, DefaultServlet will send the file from its cache (older content). DefaultServlet is a servet provided by Tomcat distribution (and JBoss too). As the name suggests, it is the default choice. If your web application does not map a web resource to some servlet, DefaultServlet serves that resource. Only exception is JSP pages. Check out DefaultServlet Javadoc  and source code . The servlet mapping is defined in Tomcat web.xml which is normally present ...