Velocity Reviews - questions on J2EE

> Cool Guy wrote:

Please do not top post.

"gandhi.pat...@gmail.com" wrote:
>> 1). If i create 10 different request from 10 browser windows for the
>> same servlet, then how we can ensure that same servlet instance is
>> willing to serve all the requests?

"willing to" - by writing the servlet in a thread-safe manner.

"actually does" - I don't believe you can. Or would want to.

You can write a servlet to implement the SingleThreadModel
<http://java.sun.com/javaee/5/docs/tutorial/doc/Servlets5.html#wp75172>
to force that one instance sequentially serves each request it receives, but
not that there be only one such instance.

From the link:
"A web container can implement this guarantee by synchronizing access to a
single instance of the servlet, or by maintaining a pool of web component
instances and dispatching each new request to a free instance. This interface
does not prevent synchronization problems that result from web components
accessing shared resources such as static class variables or external objects.
In addition, the Servlet 2.4 specification deprecates the SingleThreadModel
interface."

>> 2).What is the difference between valueobject and plain javabean
>> class?

"Value object' is a generic term for any object whose job is to represent a
set of attributes - a "noun" in your object model. A "JavaBean" object is
often a value object, and it follows a set of nomenclature and structural
conventions put forward by the Java API. When a JavaBean is used as a value
object, it is a particular way to implement a value object.

>> why valueobject is preferred over javabean class?

There is no such preference. You can use either, or both at once in the sense
that a JavaBean in this scenario would also be a value object. I write all my
value objects as JavaBeans.

For many projects it is a good practice to separate the value objects
(implemented as JavaBeans or not) from the "process objects" or "behavioral
objects" that use the value objects. Consider EJBs, which can be entity beans
or session beans. (An entity object is a specialization of a value object,
also implementable as a JavaBean.)

>> 3).If i write code like
>> request.getRequestDispatcher("www.yahoo.com/login.jsp")?
>> would it work or not?

That would depend on whether there were a directory "www.yahoo.com/" relative
to the current location within the context root, and a "login.jsp" within it
(assuming that by "work" you mean "return a non-null RequestDispatcher object").

>> what will be the output?

A RequestDispatcher object or null.
<http://java.sun.com/j2ee/1.4/docs/api/javax/servlet/ServletRequest.html#getRequestDispatcher(java.lang .String)>
<http://java.sun.com/j2ee/1.4/docs/api/javax/servlet/RequestDispatcher.html>

- Lew