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Modeling each GIF with a POJO is an essential step toward storing all our GIF data. In this video, we'll combine all those GIF objects into a single collection and create one method for accessing those GIF objects from the collection.
Code Block for GIF Data
Copy and paste the code below into your GifRepository class:
private static final List<Gif> ALL_GIFS = Arrays.asList(
new Gif("android-explosion", LocalDate.of(2015,2,13), "Chris Ramacciotti", false),
new Gif("ben-and-mike", LocalDate.of(2015,10,30), "Ben Jakuben", true),
new Gif("book-dominos", LocalDate.of(2015,9,15), "Craig Dennis", false),
new Gif("compiler-bot", LocalDate.of(2015,2,13), "Ada Lovelace", true),
new Gif("cowboy-coder", LocalDate.of(2015,2,13), "Grace Hopper", false),
new Gif("infinite-andrew", LocalDate.of(2015,8,23), "Marissa Mayer", true)
);
So now you've had a chance to see the full
flow of data from the storage of GIF
0:01
details in a GIF object to the adding
of a GIF object to a model map and
0:04
finally the access of that object
from a timely template for display.
0:09
There's one problem with our GIF
detail page at this point and
0:13
that is it's only able to display
the details of one hard coded GIF.
0:16
The compiler bot.
0:20
But what if we want
the controller method and
0:22
template to control the display of any GIF
object according to the URL requested?
0:24
For that, we'll need to step up our game.
0:29
In particular, we'll need to store
a collection of GIF objects in memory
0:33
that our application can choose from.
0:36
Next, we'll be adding what's called
a repository of GIF objects.
0:39
A repository is essentially a collection
that we've stored somewhere in memory or
0:44
in a database.
0:48
For this simpler application, we'll store
it in memory using a standard Java list.
0:49
Let's get started.
0:54
Before we make our GIF repository, I'm
going to create a package that would hold
0:56
any data repositories we might want
to include in our application.
1:00
So I'm going to right-click
on the giflib package, and
1:03
choose New, Package, and call it data.
1:07
In this package is where
I'll put the GIF repository,
1:12
which will be a new Java class named,
not surprisingly, GifRepository.
1:15
This class will act as both
our storage device for
1:24
GIF objects as well as methods for
interacting with those GIF objects.
1:26
In a future course we'll show you how to
shift your storage mechanism to a database
1:31
but that's a bit outside
the scope of the current course.
1:35
So for now we'll stick with storing our
GIF objects into a static Java list.
1:37
To begin,
I'll create that list as a field.
1:42
Make sure to import java.util.List and
1:47
com.teamtreehouse.giflib.model.gif.
1:51
And I'll call this ALL_GIFS.
1:56
Notice I'm using the all caps
naming convention because this
1:59
is a class constant.
2:02
In this course,
we're going to predefine our GIFs.
2:04
Though in a production application, again,
this would likely come from a database.
2:07
For this I'm going to use a convenience
method offered by the arrays class called
2:12
asList.
2:16
In to it I can pass any
number of GIF objects.
2:17
So arrays, it comes from
the java.util package, .asList.
2:24
This is, as opposed to
constructing a new array list,
2:32
then using the add method a bunch
of times to add individual objects.
2:35
I'll include six GIF objects here, one for
2:40
each image I've given you
in the GIFS directory.
2:43
In the teacher's notes I've
given you this block of code
2:46
in case you wanna save
yourself some typing.
2:48
I'll go ahead and copy and
paste that now so
2:51
that you don't have to watch
me type all that code.
2:53
Give myself some space there.
2:56
Copy that I will get back in here and
I will paste that right inside there.
2:58
Now, there's one import I need to resolve
and that's of the local date class.
3:03
So I'll hit option enter in Inteli J its
automatically take its first suggestion.
3:07
Might move this back one tab as well.
3:13
Cool, and that's our storage device.
3:16
I simple JAVA list.
3:18
But I also mentioned that
the beyond storing our data,
3:20
this class would offer us methods for
retrieving that data.
3:23
Because this list is private,
we'll need to add some public
3:27
methods in order to access this
list outside of the class.
3:30
Let's add one of those methods now.
3:35
We'll make a method that allows us to
retrieve a GIF object with a given name.
3:37
So it will return a GIF object.
3:42
And I'm gonna call it findByName.
3:45
I'll give it a String parameter, so
that the collar of this method can
3:49
pass at the name to retrieve the GIF
object associated with that name.
3:54
So inside this method,
I'm going to iterate over
3:59
all of my GIF objects in the list,
so I'll use this enhanced for loop.
4:02
Oops, I forgot the name
of my variable here.
4:07
Gif in ALL_GIFS, so it's a for
4:10
each loop or enhanced for
loop for every GIF object.
4:15
In all GIFS I want to do the following.
4:18
If the particular GIF object I'm looking
at has a name that equals the name
4:22
that was passed in, well then what I wanna
do is return exactly that GIF object.
4:29
Now, if I get through the entire
list without ever finding a GIF
4:34
matching this name,
then what I want to do is return null.
4:38
We'll leverage this method for
4:45
our GIF controller class,
which I'll switch to now.
4:46
We'll want to leverage that method we just
wrote from the GIF details method here so
4:52
that we can feed the GIF details
template with any GIF object instead of
4:56
this one that we've hard coded.
5:00
In order to have access to the GIF
repository we'll need a reference to a GIF
5:02
repository object, since we'll likely
access this from any controller method
5:07
I'll add it as an instance field.
5:11
And we'll do that up top.
5:13
Private GifRepository and
5:14
I'll just call it GifRepository.
5:18
Of course, without assigning
anything to GifRepository,
5:23
if we try to call any of its
methods like the find my name
5:26
method in any of our controller methods,
we'll fall on our faces.
5:30
Because the field will be null and
5:33
we'll encounter a null pointer exception
as I'm sure you've seen many times before.
5:35
There are a couple of ways we could go
about initializing this GifRepository
5:41
field.
5:45
One way would be to use
a constructor in this class.
5:46
And when the constructor is called
we'd assign the GifRepository
5:49
field a new instance of
a GifRepository class.
5:53
But there's actually another feature
in spring that we can leverage here to
5:57
reduce our coding.
6:00
It turns out that Spring
can initialize fields for
6:02
us as long as it can find a spring
component of the same class for the field.
6:04
In our case it needs a spring
component for GifRepository.
6:10
To tell spring that we want
it to auto assign our field,
6:13
we use the autowired annotation.
6:17
This tells Spring to construct and
6:20
assign a GifRepository object to this
instance field as soon as it's needed.
6:22
The next question is,
how will Spring know that
6:28
the GifRepository class is a valid
Spring component, as I mentioned?
6:30
Here's a surprise,
we'll use an annotation.
6:36
Remember how we annotated our
AppConfig class with ComponentScan?
6:39
Because of this, Spring will scan that
same package and all of it's sub packages.
6:44
And consider all classes
annotated with component as valid
6:49
options depending on the class name.
6:53
So all we need to do is
switch to the GifRepository
6:57
class and add the component annotation.
7:02
So that's applied at the class level and
it also comes from the Spring framework.
7:05
There we go.
7:11
Now, Spring will pick this up during the
initial component scan as a result of our
7:12
app config being loaded.
7:17
And when the GIF controller
needs a GifRepository class,
7:19
Spring will create one for us or
use one that's already been created.
7:22
The process of this runtime creation
of objects that is the injection
7:27
using the Autowired annotation.
7:32
This process without explicitly
writing code to construct and
7:34
assign objects is called dependency
injection or DI for short.
7:38
That is, we didn't ever write code that
calls the GifRepository constructor and
7:44
assign the resulting object
to our GifRepository field.
7:49
Instead, we let Spring wire our
objects together with Autowire.
7:53
As you continue your study
of Java development, and
7:58
especially with Spring,
you'll be seeing much more DI.
8:01
It's one of Spring's most powerful and
core features.
8:05
Now, back to our gifDetail's
controller method.
8:08
What we can do at this point is replace
the creation of our GIF object with a call
8:11
to the findByName method
of the GifRepository field.
8:15
So instead of creating a new object here,
I will call on a gifRepository object,
8:19
the findByName method.
8:24
And to it we'll pass the name
of the GIF that we'd like
8:28
to grab from our gifRepository.
8:31
Here, I'll use android-explosion.
8:34
Forget my semi colon there.
8:38
While this replacement will produce
the same result, it represents
8:41
a giant step in the direction of
creating a dynamic detail page.
8:44
Let's reboot and redeploy our app to make
sure that we haven't broken everything.
8:49
So I'll start my boot run task, and
8:53
remember it could take a moment, you
start it too soon you might see an error.
8:55
Sometimes it's definitely safe to wait for
9:00
that message in your console saying
that the task has been complete.
9:02
So I'll click bootRun again, And
9:08
after I see all my output come through and
see that Tomcat has started, I will switch
9:13
back to my browser, and I'll refresh
this to make sure nothing is yet broken.
9:18
Excellent.
9:24
All is well.
9:25
It looks like our web app is still
intact from the user's standpoint, so
9:27
we're in great shape!
9:30
Well, that was quite a bit
of information in coding.
9:32
It may seem like a lot
to digest right now, so
9:35
if you're feeling a bit
overwhelmed don't panic.
9:37
You can always go back in the video to
re-watch the parts that are still unclear.
9:40
Or you can come back to them
after you finish the course.
9:45
Also, as you're coding
the application on your own machine,
9:48
if you run into any problems, please use
the forum to post your questions, and
9:52
include your code as necessary.
9:56
Let's take a break now before finishing
the task of making our detail page,
9:59
present the GIF details given
by a specific GIF's URI.
10:03
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