Using java.ext.dirs to ease setting classpath

If U are in a hurry to compile code and there is a big list of Jar files to include in the classpath, there U don't have to struggle to include the names of all the jar's in the classpath.

There is a neat trick - use the "java.ext.dirs" JVM param to point to the directory containing the jar files.

java -Djava.ext.dirs=c:\java\axis-1_1\lib -classpath classes MyJavaClass

Prevent web images from being saved.

Many novice web-developers struggle with the idea of preventing users from stealing the images present on a HTML page.
The truth is that it is impossible to prevent the user from saving the images on a HTML page.
We can watermark them and prove that they belong to us and enter comments that say this in clear text, but it still doesn't keep people from issuing an HTTP request and saving the image.

Funny thing about URL's

Recently after years of web-programming I noticed a subtle thing.
Whenever we make a request for a website, say http://narencoolgeek.blogspot.com, the URL in the browser changes to http://narencoolgeek.blogspot.com/ . (Notice the forward slash at the end of the URL)

I put in a sniffer to see what is exactly happening. The server on receiving the first URL sends a 301/302 (temporary moved) response redirecting the client to the new URL. Why is this necessary? Maybe some legacy reason, or maybe this is necessary to pick up the default page of the website directory.

Sorting objects in a Java collection

We all have felt the need to sort our custom objects based on the value of ainstance varaible of that object..For e.g. sorting of a Vector of AddressCard objects according to theDisplayName.i.e Consider the following class:
class AddressCard{ public String sDisplayName; // Other instance variables.}

Now say we want to sort a Vector of AddressCard objects according to the valueof sDisplayName.Though we can write a custom sorting mechanism for this, we have another neatsolution which requires miminal coding.We make use of the TreeMap object as follows, which is sorted internally..Given below is the code snippet.

//Instantiate a TreeMap object....If Case sensitive is desired, use a emptyconstructor.
TreeMap tMap = new TreeMap(String.CASE_INSENSITIVE_ORDER);

//keep on adding the object's field (to be sorted) as the key and the object reference as the value.
for loop:
tMap.put(sDisplayName, AddressCardObject);
//-------------------end of for loop

Once all the objects have been entered into the TreeMap, they are sorted automatically..So if U want the sorted Vector ofobjects then just do the following:
Collection c = tMap.values();
Vector v = new Vector(c); //Pass the collection in the constructor.

And Voila !!!....we have a sorted Vector of objects sorted according to therequired field...and that too in just 4-5 lines of code.

Why execute() replaced perform() in Struts

Recently a friend of mine asked me why the "perform()" method in Struts was replaced with the "execute()" method?
A closed look at the signatures of the two methods revealed that the "execute()" method throws java.lang.Exception whereas the old "perform()" method throws IOException and ServletException.

This new execute method was necessary because of this reason. Due to the declarative exception handling that has been added,the framework needs to catch all instances of java.lang.Exception from theAction class.
Instead of changing the method signature for the perform() method and breakingbackwards compatibility, the execute() method was added.

Currently, the execute() method just turns around and invokes the perform() method anyway.