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