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Create a Controller to Handle HTTP Requests7:50 with Chris Ramacciotti
In this video, we'll create a Spring controller that has a method to intercept a URI request, and respond with a simple String message.
Welcome back, and congrats again on the not so 0:04 convincing success of deploying your first Java web app. 0:07 Sure, we got an error when we visited our running application, but 0:11 that was only because our app lacks the code to handle requests to certain URIs. 0:15 Actually, it lacks the code to handle requests to any URI. 0:20 So, let's change that. 0:24 What we're going to do is write a Spring controller. 0:26 In a Spring web application, 0:29 the controller is a Java object whose job is to handle requests to certain URIs. 0:30 We'll apply annotations to methods within this class that indicate 0:36 which URI each method should handle. 0:39 First a quick note on URIs and URLs. 0:43 URI stands for Uniform Resource Identifier, and 0:47 URL stands for Uniform Resource Locator. 0:50 You may have heard the terms used interchangeably, 0:54 but they're actually different. 0:57 In general a URL is an address that includes a method for locating a resource, 0:59 with a protocol like HTTP or FTP. 1:04 In addition a URL will include a host name like teamtreehouse.com, or 1:08 creativecommons.org. 1:13 But a URI doesn't have to. 1:15 Since our application will be coded without regard to the host name, 1:17 and without indicating the protocol, I'll continue to use URI. 1:20 All right, with that said, let's code a controller to handle URI requests. 1:24 Before creating a controller, let's create a package where we can put them. 1:31 To do this, I'll right click on calm.teamtreehouse.giflib, and 1:34 choose new package. 1:39 I'll name this package controller. 1:41 And to create the actual controller, I'll right-click our new package and 1:44 choose New > Java Class. 1:47 Since this will be the controller that handles all of our requests to 1:50 gif related pages, I'll name this one gifcontroller. 1:54 The way that we'll indicate that this class is a spring controller, 1:59 is with the controller annotation on the class itself, @Controller. 2:02 And that comes from the spring framework as well. 2:07 Hit enter so that I get the auto import statement dropped in there. 2:10 In a spring controller you can add as many methods as you like, though in general 2:15 they should be related to the object the controller refers to, in our case a gif. 2:19 I'd like to use this controller to handle requests to 2:24 any page of our application that displays a list of gifs or a single gif. 2:27 Later on, if we'd like to add a controller that shows a list of categories, for 2:32 example, we might add a category controller. 2:36 Let's add a method that will handle all requests to our home page. 2:40 Since our home page would likely be a list of the most recent animated gifs that have 2:44 been uploaded, it makes sense to put that method in our GifController class, 2:48 so I'll add that method now. 2:54 I'm going to call it public String listGifs. 2:56 I chose to name this method listGifs, but 3:02 it really could be named anything you like. 3:05 But, how will the Spring framework know to execute this method 3:08 when a user requests our homepage? 3:11 Now that is accomplished with, you guessed it another annotation. 3:15 This one is called request mapping, which refers to the fact that we want to map 3:19 a certain URI request to a Java method. 3:24 The request mapping annotation has several elements, 3:27 and we'll use just one of them in this course. 3:30 So I'll start by adding the request mapping annotation to the method itself 3:33 request mapping, there it is right there, I'll hit enter on the suggestion. 3:38 So I get that import statement. 3:42 The one element of the annotation that we'll be using is called value. 3:44 And the value we specify here will be the URI pattern that we want to map 3:50 to this method. 3:54 In this case, I'll use a single forward slash indicating that this method will 3:55 handle requests to our application root, or homepage. 3:59 If you like, since the only annotation element we use is called value, 4:03 you can omit that name altogether. 4:08 For now, we'll also need to add the response body annotation to the controller 4:13 method, to indicate that this string we return should 4:17 be used as the response without any further processing. 4:20 So, I'll add the responsebody annotation to the method, as well. 4:23 And, as for the return value, 4:28 I'll choose an arbitrary string to return, list of all the GIFs! 4:30 All right, we're almost there. 4:38 One more step, though. 4:40 If we tried to use the gradle boot run task to build and 4:42 deploy our app, we'd find ourselves left with a bit of disappointment. 4:46 In fact, we'd see the same error message as before in our browser. 4:50 This is because the Spring framework doesn't automatically scan your packages 4:54 for controllers. 4:58 You have to instruct the framework to do so. 4:59 Let's go back to our app config class and 5:03 add the annotation that accomplishes this task. 5:05 Here we'll add a simple annotation to tell the spring framework 5:09 to scan the current package for controllers. 5:12 And this scan we'll include our sub package name, controller. 5:15 The annotation name is component scan. 5:19 Excellent. 5:22 We're ready to test this thing. 5:23 Again, because we're using gradle, this is pretty straight forward. 5:25 If you don't already have your server running, in the gradle tool window you can 5:29 expand tasks, right click boot run and choose run GifLib. 5:33 Since I still have mine running, I'm going to click the stop button first. 5:38 After a few moments, you should see a message in the console here that indicates 5:42 that the process has been stopped. 5:47 There it is, it finished running boot run. 5:49 And in fact, since I just stopped it, I could either go up here and right-click 5:52 boot run and choose run again, or, since it's the task that I just stopped, 5:56 this gives me a convenient rerun button, by clicking this play button right here. 6:00 I'll click that now. 6:06 After a few moments, you should see some output at the bottom of the screen. 6:09 This output is largely the same as we saw before, with one important difference. 6:13 If you look closely, 6:19 you'll see a line that says the root path has been mapped to our list gifs method. 6:20 So if you look here, 6:27 here is the single slash that has been mapped onto java.lang.string. 6:28 That's the return value of our controller method. 6:33 And if we scroll over, we see the fully qualified name of the method, 6:38 meaning package name, class name, there it is. 6:41 Method name. 6:45 The slash URI that is the root of our application, 6:46 has been mapped to our list gifs method. 6:50 Excellent. 6:54 Switching over to a browser, we can again navigate to local host. 6:55 Including the port number 8080 and see our message so plainly, yet 7:01 so wonderfully on display. 7:06 There it is. 7:08 List of all the gifs. 7:09 Try coding another method and gif controller, and add a request mapping 7:11 annotation, and the response body annotation to capture the uri/gif. 7:15 Returning a string message of your choice. 7:22 When you're done writing that method, 7:24 you'll test this in the browser by stopping and restarting the bootrun task. 7:26 Then coming back here to the browser and 7:31 entering /gif at the end of the URI here. 7:34 When you're done, you shouldn't see this error message, but 7:41 rather, the custom message that you've returned in your new controller method. 7:44 Go ahead, give it a shot. 7:49
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