How can i check whether a package like javax.servlet.* exists or not in my installation of java?
Java can only tell you if it can load a class. It can't tell you if a package exists or not because packages aren't loaded, only classes.
The only way would be by trying to load a class from that package. e.g., For javax.servlet.* you could do:
try {
Class.forName("javax.servlet.Filter");
return true;
} catch(Exception e) {
return false;
}