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Okay, we need to communicate
a little bit better

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with our users about the state
of their experience.

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And of course, because the only
state the exist is what we've made

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appeared to be stateful, we're gonna need
to jump through some hoops to get there.

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A common approach to solve the problem
of keeping the user informed about their

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actions is to use what is
known as a flash message.

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You've seen them, they're usually
displayed in a box on a page.

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It says something like this,
see the message here that says,

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all right your details were updated.

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Now most fully featured frameworks
provide this nice to have feature, but

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some micro-frameworks, ours in
particular,don't quite have those yet.

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But that doesn't mean
we can't craft our own.

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The really nice thing that our
micro-framework provides is the handling

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of exceptions.

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Let's improve the user experience.

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Okay, so first, let's take a quick look
at the built-in exception handling.

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So we kicked off a few of our
own custom NotFoundExceptions.

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Let's go to the definition here.

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So we're gonna go to
the NotFoundException, and I'm gonna

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click in here and I'm gonna do a Cmd+B,
which is gonna go to the declaration.

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And then it's going to zip over to where
we did it before which is in this find by

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slug method.

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Okay, so
anytime we findByslug is called and

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it can't find that slug it's
gonna throw a NotFoundException.

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But, that's what we want to have happen.

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So, let's go ahead and
we'll handle this NotFoundException

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when it happens because right now
it just kinda a gross page right.

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So lets flip over to our main method.

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And let's scroll down here to the bottom.

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Now the name of the,
Its a static method and,

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as you might expect its called exception.

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And then it takes the class
that were gonna try to catch.

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So again that is our not found exception.

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And we'll do .class because we'll
get the handle on the class.

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And then it takes a handler here, and the
handler will return an exception and then

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of course our request and our response, so
it's very similar to the other handlers.

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Okay, when something's not found,

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the proper way to tell the client
is that they got a 404.

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Now, we can make this page
look however we want, but

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we wanna make sure that we send
the header, the status of 404.

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It's an http status code.

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Okay, now unfortunately
this exception handler

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isn't set up using this template style
like we were doing before right?

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Where there's the three parameters and we
pass this new handlebars template engine,

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but that doesn't mean we can't
use the template engine still.

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So this will help actually demystify
what was happening using that so

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what we can do,
is we can create our own engine.

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So let's do that we'll
a handlebars templating engine.

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We'll say engine = new
HandlebarsTemplateEngine.

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And really the only thing this
is doing is calling render.

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There's a thing on
the engine called render.

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And it returns html, so we'll =
engine say it's String html- .render.

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This is what was passed in here, right?

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So it takes whatever was here,
creates a new one of these and

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then pushes this into the render method.

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So we'll just push that in here.

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So we'll say new ModelAndView.

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And we don't have a model right now so
we'll just say null.

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But we're going to pass in a new template
that we're going to build here in

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a second, so not found.hbs.

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Remember, if stuff starts
getting a little out of control,

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you can always add it to a new line,
everything will still be happy.

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There we go.

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Okay, so now we have html and string and

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we need to just set
the body of the response.

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Now, you don't return from this
exception handler, you set the body.

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Here we go.

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Okay, so, let's go make our new template.

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Make a new file

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Called not found.hps.

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Okay, and we will again,
everything will start working like normal,

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cuz we're using that engine.

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So we'll say content, partial content, and

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let's set the h1 to be what the You
can do something clever in here.

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So we couldn't find what

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you were looking for.

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Of course we could also override
that title if we wanted to.

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Say partial title and not found.

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And of course we need to get our
base in here to be implemented.

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So we can definitely
make this prettier and

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push more information into the model
that displays on this page.

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There's some more in the teacher's notes.

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Okay, so let's make sure that we caught
our exception, so I'm gonna go over and

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I'm gonna start my server,
and say Run Main.

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Okay, so he's running.

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Okay, so let's go over to the page and
I'm gonna go ahead and log in.

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Let's go ahead and let's make a new

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Idea here, again we Spark Testing

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now that Spark Testing exists I'm
going to click on Spark Testing.

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And if I come and
I change this just to be a little bit off,

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we're going to change the slug to
be spelled wrong and press enter.

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Now I'll get our what the page.

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And you'll see that there is a status
code, a 404 not found, awesome.

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Now, if we wanted more specific pages,
we'd just make more specific exceptions.

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It's pretty straightforward, right?

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So now that we've explored the built in
messaging, let's take a quick break right

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here, and then we'll drive right back
into making our own flash messages.