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Newsgroups: comp.lang.java.programmer
Date: Mon, 1 Jul 2013 04:06:06 -0700 (PDT)
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Subject: Re: Desktop application and web application Linking...
From: Lew <lewbloch@gmail.com>
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Xref: csiph.com comp.lang.java.programmer:24550

Robin Saini wrote:
> I have a method that creates a bar chart of some hard-code data(in array)=
. I can call this method in Main method and it shows me the chart in new wi=
ndow(desktop window not web). I want to do the same thing on click of a but=
ton of jsp page. So I created a servlet(and jsp as well) and call that clas=
s(which creates chart) but My servlet is not able to create object of that =
class. It shows an exception of class not found.
>=20
> please guide me.

The more evidence you can examine, the better. It sounds like you have a bu=
ild=20
problem, that is to say, you need to examine how you build your web app.

You haven't given us much evidence, just a vague description, but the one=
=20
piece of hard evidence you did provide, "java.lang.ClassNotFoundException",=
=20
is indicative.

This hints that you did not build a WAR, and further that you are attemptin=
g=20
to invoke Java code directly from a JSP, which is a big no-no in Java Web=
=20
apps. That's even if you are using correct syntax, let alone modern syntax.

So the bad news is, absent contrary evidence, you have a lot of mistakes=20
in your application, some fatal and some more slowly so.

Which is normal, especially as one is learning. And then forever after that=
.

The tricky part is figuring out what you did wrong, especially when you are=
=20
new to a platform. This means asking the right questions, first of yourself=
=20
and then of others.=20

Here's what you need to learn:
- Using Expression Language (EL) and JSP tags=20
  to eliminate the appearance of Java code in your JSP pages.
  Most of the tags you need should exist already. I can't recall ever actua=
lly=20
  needing to write a custom tag. Good. It would have been more trouble than=
=20
  it's worth.

  Logic, OTOH, I can write in Java. Then you use EL to push and pull values=
=20
  to the display.

  Logic, of the model kind, does not belong in the presentation layer, the =
JSP.
  Look up "Model-View-Controller (MVC)".

- How to build a Java package, properly.
  This begins with thoroughly understanding the JAR file, which is where yo=
ur=20
  "java.lang.ClassNotFoundException" would have been found.=20

  Then you can thoroughly understand the WAR file, which is the Java Web ap=
p=20
  supersized JAR file, which in turn is Java's megawatt ZIP file.

  Then you can read how to deploy a WAR to Tomcat or other favorite app ser=
ver.

- The standard build process for Java Web apps.

Your exception stems from not putting the class in the right place, asking=
=20
for it from the wrong place, and not having thoroughly read the instruction=
s=20
yet. That last becomes a lifelong habit. So many times I find the answers t=
o=20
questions I have in fundamental documentation (i.e., tutorials) that I've=
=20
actually read. Many times. And needed to read again.

Besides, a lot of documentation is fun, like "What Every Computer Scientist=
 Should Know About Floating-Point Arithmetic".

--=20
Lew