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Let’s explore how to handle exceptions with grace and ease. You will write your own Flash messaging tool which you will use to inform your users one time over redirects.
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- One way you to get around the duplication is by taking advantage of the request.attributes and creating a model object in a global before filter. That would allow you to do whatever injecting of the model that was common to all requests. In the controller you just then pull out request.attributes[“model”] and add specific information, but it would have the flash message.
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Okay, we need to communicate
a little bit better
0:00
with our users about the state
of their experience.
0:03
And of course, because the only
state that exists is what we've made
0:05
appear to be stateful, we're gonna need
to jump through some hoops to get there.
0:09
A common approach to solve the problem
of keeping the user informed about their
0:13
actions is to use what is
known as a flash message.
0:17
You've seen them, they're usually
displayed in a box on a page.
0:21
It says something like this,
see the message here that says,
0:23
all right your details were updated.
0:26
Now most fully featured frameworks
provide this nice to have feature, but
0:28
some micro-frameworks, ours in
particular, don't quite have those yet.
0:32
But that doesn't mean
we can't craft our own.
0:36
The really nice thing that our
micro-framework provides is the handling
0:38
of exceptions.
0:42
Let's improve the user experience.
0:43
Okay, so first, let's take a quick look
at the built-in exception handling.
0:46
So we kicked off a few of our
own custom NotFoundExceptions.
0:50
Let's go to the definition here.
0:54
So we're gonna go to
the NotFoundException, and I'm gonna
0:55
click in here and I'm gonna do a Cmd+B,
which is gonna go to the declaration.
0:58
And then it's going to zip over to where
we did it before which is in this
1:03
findBySlug method.
1:05
Okay, so
anytime we findBySlug is called and
1:07
it can't find that slug it's
gonna throw a NotFoundException.
1:10
But, that's what we want to have happen.
1:13
So, let's go ahead and
we'll handle this NotFoundException
1:15
when it happens because right now
it just kinda a gross page right.
1:19
So let's flip over to our main method.
1:22
And let's scroll down here to the bottom.
1:26
Now the name of the,
its a static method and,
1:31
as you might expect it's called exception.
1:36
And then it takes the class
that we're gonna try to catch.
1:40
So again, that is our NotFoundException.
1:42
And we'll do .class because we'll
get the handle on the class.
1:47
And then it takes a handler here, and the
handler will return an exception and then
1:51
of course our request and our response, so
it's very similar to the other handlers.
1:56
Okay, when something's not found,
2:01
the proper way to tell the client
is that they got a 404.
2:03
Now, we can make this page
look however we want, but
2:07
we wanna make sure that we send
the header, the status of 404.
2:09
It's an http status code.
2:15
Okay, now unfortunately
this exception handler
2:19
isn't set up using this template style
like we were doing before right?
2:23
Where there's the three parameters and we
pass this new handlebars template engine,
2:26
but that doesn't mean we can't
use the template engine still.
2:30
So this will help actually demystify
what was happening using that so
2:34
what we can do,
is we can create our own engine.
2:39
So let's do that we'll
a handlebars templating engine.
2:42
We'll say engine = new
HandlebarsTemplateEngine.
2:45
And really the only thing this
is doing is calling render.
2:51
There's a thing on
the engine called render.
2:55
And it returns html, so we'll =
engine say it's String html- .render.
2:57
This is what was passed in here, right?
3:05
So it takes whatever was here,
creates a new one of these and
3:07
then pushes this into the render method.
3:11
So we'll just push that in here.
3:14
So we'll say new ModelAndView.
3:15
And we don't have a model right now so
we'll just say null.
3:20
But we're going to pass in a new template
that we're going to build here in
3:23
a second, so not-found.hbs.
3:26
Remember, if stuff starts
getting a little out of control,
3:29
you can always add it to a new line,
everything will still be happy.
3:32
There we go.
3:37
Okay, so now we have html and string and
3:39
we need to just set
the body of the response.
3:40
Now, you don't return from this
exception handler, you set the body.
3:43
Here we go.
3:47
Okay, so, let's go make our new template.
3:51
Make a new file
3:53
Called not-found.hps.
4:01
Okay, and we will again,
everything will start working like normal,
4:07
cuz we're using that engine.
4:12
So we'll say content, partial content, and
4:14
let's set the h1 to be what the You
can do something clever in here.
4:19
So we couldn't find what
4:27
you were looking for.
4:32
Of course we could also override
that title if we wanted to.
4:40
Say partial title and not found.
4:44
And of course we need to get our
base in here to be implemented.
4:52
So we can definitely
make this prettier and
5:00
push more information into the model
that displays on this page.
5:02
There's some more in the teacher's notes.
5:05
Okay, so let's make sure that we caught
our exception, so I'm gonna go over and
5:07
I'm gonna start my server,
and say Run Main.
5:11
Okay, so he's running.
5:19
Okay, so let's go over to the page and
I'm gonna go ahead and log in.
5:21
Let's go ahead and let's make a new
5:25
Idea here, again we Spark Testing
5:32
now that Spark Testing exists I'm
going to click on Spark Testing.
5:36
And if I come and
I change this just to be a little bit off,
5:40
we're going to change the slug to
be spelled wrong and press enter.
5:45
Now I'll get our what the page.
5:48
And you'll see that there is a status
code, a 404 not found, awesome.
5:49
Now, if we wanted more specific pages,
we'd just make more specific exceptions.
5:57
It's pretty straightforward, right?
6:01
So now that we've explored the built in
messaging, let's take a quick break right
6:03
here, and then we'll drive right back
into making our own flash messages.
6:06
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