In this article, I am going to describe how to throw an exception in JSP. To throw an exception, the
throw keyword is used, followed by the exception object to be thrown. The
code to throw an exception looks as follows:
throw new IOException("Some
required files are missing");
Some commonly thrown Exceptions
IllegalArgumentException : If your method only accepts arguments within a
particular range, e.g. only positive numbers, then you should check for invalid
parameters and throw an IllegalArgumentException.
NullPointerException : If you know that a parameter to your method cannot
be null, then it is best to explicitly check for null and throw a
NullPointerException.
IllegalStateException :
This one is a little less common, but is useful a method relies on a previous
method having been called.
UnsupportedOperationException : This exception is designed for cases
where you override an abstract class or implement an interface, but don't want
or can't to implement certain methods.
Runtime Exception :These essentially mean "that should never happen and I
don't know what to do if it does", with different degrees of seriousness. You
basically want the application to "bomb out" of whatever it's doing at that
moment. If essentially the application can go on working after the unexpected
condition, throw a RuntimeException.
Now we are going to develop an JSP application to throw
Exception. For this application we follow the following steps
Steps 1: Create New Project
In this step we select a new project option from File menu.
![new project.jpg]()
Step 2: Choose Project
In this step we select a Web Application project from the Java Web Categories and click the
next button.
![new web application.jpg]()
Step 3: Name and Location
In this step we give a specific name to the project and save it in a specific
location then click on the Next button.
![name and location.jpg]()
Step 4: Server and Setting
In this step we choose a specific server and Java EE version then click on the
next button.
![server and setting.jpg]()
Step 5: Select Framework
There is no need to select any framework in this application, just click
on the Next button, after this step the project is open and you are ready
for coding.
![frameworks.jpg]()
Step 6: Create JSP file
In this application we create two JSP files; first one is index.jsp and
ExceptionthrowMethod.jsp.
![create new file.jpg]()
Index.jsp
In this JSP file we throw the exception; only throw the throw keyword.
<html>
<head>
<title>Throwing an Exception</title>
</head>
<body
bgcolor="skyblue">
<title>Throwing
an Exception in a JSP page</title>
<%
try
{
throw new ArithmeticException("Mathmatics
Exception!");
}
catch(ArithmeticException e)
{
out.println("Exception
Message: " + e);
}
%>
</body>
</html>
ActionThrowMethod.jsp
In this JSP file we throw the exception throw the methods.
<HTML>
<HEAD>
<TITLE>Throwing Exceptions From Methods</TITLE>
</HEAD>
<BODY
bgcolor="brown">
<H1>Throwing
Exceptions From Methods in a JSP page</H1>
<%!
void doWork() throws
ArrayIndexOutOfBoundsException
{
int array[] = new
int[10];
array[200] = 200;
}
%>
<%
try
{
doWork();
}
catch (ArrayIndexOutOfBoundsException e) {
out.println("Array out of
bounds exception");
}
%>
</BODY>
</HTML>
Compiling and Running the application
Now we first compile and then run this application in server and found the
given output
Output
index.jsp
![index.jsp.jpg]()
ActionThrowMethod.jsp
![method.jsp.jpg]()
Resources
Here are some useful related resources: