Spring MVC Tutorials 28 - Exception Handling 01 Video Lecture | MVC Tutorials: Web Programming Course - Web Development

guys my name is Akash Gaurav and I
welcome you to gone to series in this
tutorial we can learn how to handle
exceptions in a spring MVC web
application so in general what happens
when your spring MVC application throws
some XYZ exception without having any
code to handle that let's check it out
when the user requests for this webpage
this method in this controller class
gets executed and this web page is sent
to the user as a response so if
everything goes fine on the server while
processing this request user is going to
get this web page as a response
now during some developers mistake or
some other reason if while processing
the request this method shows some
exceptions a null pointer resource not
form or any other what's gonna happen
what user is going to get in that case
as it spawns as an example let's
consider a case when it's going to
through nullpointerexception for this
users request so here now after adding
this code snippet in this method when I
would request for this flat page this
method is going to throw null pointer
exception an important point to note is
nowhere in this controller class I am
handling null pointer exception so now
when I would request for admission form
the page what's going to happen what I
would get as a response let's check it
out
oops it has sent this error web page on
this page it's talking about three
important things on top it has mentioned
hgtv status code has five hundred then
the brief description of the error which
occurred on the server and related
stacktrace
information here because normally when
any exception occurs for which there is
no exception handling code written in
the controller class the application by
default sends an ad of a page like this
now many times developers would like to
send a customized of a page instead of
this default error web page which
doesn't seem so much user friendly so
question is what does I will need to
perform in this application so that I
would be able to send a customized error
page when this method would through
nullpointerexception while processing
the request guys to tackle this
requirement I just need to perform these
two simple steps and I will be done
first I need to include an error web
page in the application null point
exception dot JSP page which I would
like to show to the user when get
admission form method would throw a null
pointer and second I would need to
include a method in the student
admission controller dot Java class
which has exception handler annotation
on top of it like this
so let me very clear all these changes
in the application and show you the
concept working on the browser and later
I will explain these two steps in detail
all right so here I have included
nullpointerexception dot JSP page with
this content and here in the controller
class that is in the student admission
controller dot java where this method is
present I am here adding a method handle
null pointer exception with exception
handler annotation on top of it and
value as null pointer exception block
class pass to it as a parameter and here
it's returning the view name that is
null pointer exception this JSP web page
so here I am done with making these two
changes which are required now let us
see this concept working on the browser
and later we would understand in detail
these two changes mean to us cool
so this time the application then send
us the default error of a page and
instead send this customized another
page means the content of null point
exception dot JSP web page now let us
understand what exactly happened here
this time when I requested for this web
page get admission form method through
nullpointerexception here and
immediately after that spring MVC
framework started looking for a method
in the same controller class which has
exception handler annotation on top of
it and value as null point exception but
class because we provided such a method
in this controller class so spring MVC
simply transferred the control of
execution to this method and here this
method returned null point exception
view name means this JSP page as a
result I got the content of null point
exception dot JSP web page like this
because here an important point to note
is in this controller class we are
handling only null pointer exception so
if this method throws any other
exception at runtime while processing
the request you know like IO exception
automatic exception means the exception
for which we have not put any exception
handler method the application is going
to send the default errors are paid to
the user as a response as we saw in case
of null point exception before putting
exception and the method for it in this
control class so very quickly let's see
it with our exception so if this method
throws are your exception for which we
have not written exception handler
method let's see what happens
cool as expected it through this HTTP
status 500 error page means the default
error page
now to tackle this problem again we need
to follow the same steps as we followed
in case of nullpointerexception so here
I have added IO exception dot JSP web
page with this content which I would
want to send to the user in case of 5
exception and here in the controller
class the way we added exception handler
method for null point exception I would
add a method for IO exception which
returns higher exception means this web
page so now if I request for this same
web page let's see what happens cool as
expected
I got the customized and web page for IO
exception so the idea is very clear
whatever exceptions you think the
controller class can through at one time
while processing the users requests you
simply go on adding exception handler
methods for all those exceptions now an
important point to note here is your
controller class might through a lot of
exceptions at runtime and it may not be
so convenient for you to write exception
handler method for each exception so to
drag on such a problem what we can do we
can add a generic exception handler
method in this controller class such
that when this controller class throws
some exception for which spring MVC
framework it doesn't find related
exception handler method then it would
go on searching for generic exception
handler method and if it find it there
it would simply go on executing that so
question is how we can add such method
in this controller class the way to add
such method is just this an exception
handler method which has value equal to
exception or class is known as generic
exception handler method so here it's
returning exception view so here I would
add exception dot JSP page means this
one
let's check it out
so now if this controller class throws
some exception for which there is no
related exception handler method present
then spring MVC framework would go on
executing this generic exception handler
method so here if this method throws
automatic exception at one time and
there is no exception handler method for
automatic exception here then spring MVC
FEMA should execute this method let's
check it out cool the application has
sent this customized error webpage when
a through automatic exception here by
executing this generic exception handler
method all right guys
in the next tutorial we'll learn how to
handle exceptions globally at one place
for all controller classes without
writing exception handler methods
individually in all controller classes
alright guys a big thank you for
learning spring MVC with me if you have
any feedback or comments please provide
them below the video or simply write to
me on this email id for all of your
queries please hit the like button if
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series and I'm going to catch you in the
next part of this tutorial