Robin said:
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 window(desktop window not web). I want to do the same thing on click of a button of jsp page. So I created a servlet(and jsp as well) and call that class(which creates chart) but My servlet is not able to create object of that class. It shows an exception of class not found.
please guide me.
The more evidence you can examine, the better. It sounds like you have a build
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
piece of hard evidence you did provide, "java.lang.ClassNotFoundException",
is indicative.
This hints that you did not build a WAR, and further that you are attempting
to invoke Java code directly from a JSP, which is a big no-no in Java Web
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
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
new to a platform. This means asking the right questions, first of yourself
and then of others.
Here's what you need to learn:
- Using Expression Language (EL) and JSP tags
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 actually
needing to write a custom tag. Good. It would have been more trouble than
it's worth.
Logic, OTOH, I can write in Java. Then you use EL to push and pull values
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 your
"java.lang.ClassNotFoundException" would have been found.
Then you can thoroughly understand the WAR file, which is the Java Web app
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 server.
- The standard build process for Java Web apps.
Your exception stems from not putting the class in the right place, asking
for it from the wrong place, and not having thoroughly read the instructions
yet. That last becomes a lifelong habit. So many times I find the answers to
questions I have in fundamental documentation (i.e., tutorials) that I've
actually read. Many times. And needed to read again.
Besides, a lot of documentation is fun, like "What Every Computer ScientistShould Know About Floating-Point Arithmetic".
