Events

So we have a nicety that we'd like to add to our API. 0:00 We want the creator of the review resource to be set 0:03 as the reviewer when it's created. 0:06 This idea of running certain code at certain times is pretty common request. 0:09 As you can imagine it's usually where the business logic lives and 0:12 since all the controller code is currently tucked away out of sight, 0:16 it might be a little confusing as to where we should add logic like this. 0:19 Well the good news is that this problem has been thought about and 0:23 it has been solved for you. 0:26 Probably, there are eight events that the spring data rest emits. 0:27 These are pretty self-explanatory and 0:31 knowing what you can hook into that will probably make you feel a lot more 0:33 comfortable about not having access to those controllers. 0:37 This is usually where you'd write any custom logic, right? 0:40 So we want to set the reviewer before things are created. 0:44 So we'll use the before create event. 0:47 Let's do this. 0:49 There are a few ways to register events. 0:51 If you wanna capture all entity creation you can write an application listener. 0:53 But in our example we're really only concerned with when reviews are created. 0:56 What we're going to do is write an annotated handler. 1:01 Which we can restrict to a review entity specifically. 1:04 So in our review package, let's make a new class named ReviewEventHandler. 1:07 New Java class ReviewEventHandler. 1:16 Okay and now we'll annotate that with RepositoryEventHandler. 1:24 And with that does is that takes a class and 1:34 it's whatever we're interested in watching which remember that's Review.class. 1:37 So the way that these work is you define what it is that you're 1:41 trying to do in a descriptive method, right. 1:44 So let's go ahead and let's say. 1:46 We're trying to do is we're trying to add the reviewer as it goes, right. 1:49 So let's say public void addReviewerBasedOnLoggedInUser. 1:51 It can be as descriptive as you want. 1:59 So we'll say review review and we want this to happen before, right? 2:01 So we're going to do handle before create. 2:09 So having these as separate methods is pretty nice because each of them are right 2:17 for unit testing right. 2:22 Okay so let's inject our user repository so we can get stuff out of it, so 2:24 we'll say private final UserRepository, 2:28 so users, and I'm gonna go ahead and allow this. 2:33 With this automatically add a constructor parameter and 2:39 then we'll mark our constructor here as auto wired. 2:43 And because we need to have this picked up by a component scan, 2:50 we need to mark it as a component. 2:53 And now let's work our magic. 2:56 So, to get the currently long in user you do this incantation. 2:58 So let's say get user name and that's from security ContextHolder 3:02 has a getContext, I'll go ahead and give us some space. 3:10 Has a getContext, and then it has a getAuthentication, 3:16 and then it has a getName. 3:22 Note that we're going to get a null pointer exception here if they aren't 3:26 authenticated. 3:28 But alas, they should be so we'll go grab our user. 3:29 So we'll say user user = users.findByUserName and 3:33 we'll pass in that username. 3:40 And finally, we'll just set it on the reviewer and 3:50 the review will say setReviewer[user] makes sense right? 3:54 Before things are created, okay? 3:59 I will go and reboot our server here. 4:00 Let's see, let's grab somebody over here to make a review for, 4:06 let's see, let's grab Seth Kroger. 4:12 He is an amazing moderator for us so let's write an appropriate one for him. 4:14 So we're going to make this a post and we're going to erase this one and 4:20 we're gonna go to the authorization we're gonna log in actually as Seth, 4:24 he's got the same password which is password. 4:27 Seth change that, say update request, okay. 4:30 And if we come over here to the body, this is actually a review. 4:33 So what we wanna do is we're gonna have him give us 4:39 a little bit of a harsh rating. 4:42 Let's say the rating. 4:43 Let's do the course first. 4:45 So "course" and now again we've moved this. 4:48 So it's "/api/v1 Courses one so 4:54 basics and we're going to give a rating of two. 4:59 That's pretty harsh stuff, which what, what's he upset about? 5:02 What is Seth upset about? 5:06 Let's see. 5:07 So for the description come here and 5:10 say why why did you use 5:17 system.io.console. 5:22 Well that's a lot isolation points so I have to calm down. 5:27 Do you know how many times I've had to answer 5:30 why this doesn't work in the clip. 5:36 I totally made that up, that's something Seth would never ever say. 5:41 He's one of those amazing moderators that makes everyone feel so 5:45 comfortable in the community and thanks for keeping something so positive and 5:48 being so patient that the students and I really appreciate it. 5:51 Okay let's see if this works. 5:54 So we have not set the reviewer, but Seth is logged in, and 5:56 we're going to click send. 6:00 Here we go. We got a bad request because, 6:02 why did we get bad request? 6:07 No suitable found to read the request body to object. 6:09 Do I have a weird header? 6:15 I did not set this. 6:19 I said it as text that something good to know, right. 6:21 So doesn't know it says and it says right here. 6:23 Can't do with the content type plaintext, right? 6:25 Let's switch this over to my application JSON and they set there. 6:27 Maybe that will be an answer for this one isn't better there in the video. 6:33 So that's maybe one you don't have to answer. 6:36 Boom, there it is and here comes Seth Kroger coming across. 6:39 So as you can imagine, we could do all sorts of other handling in these events, 6:43 including sending notifications, updating caches, some advance validation. 6:46 But whatever business logic you can dream up you can put in there. 6:51 Now one thing to always remember here though is that this action is synchronous 6:54 meaning that it's in the request response loop so users will be waiting for 6:58 this code here to execute. 7:02 So don't do anything too intense In here. 7:04 Awesome, right? 7:07 I know when I was first looking at the spring data rest project 7:08 I was not very trusting. 7:11 I was like, yeah sure I guess we do duplicate 7:13 a lot of code when we write APIs. 7:16 But where's all the business logic code? 7:17 Events are where you can inject that. 7:20 I've also found that these methods make unit testing your business logic 7:22 simple and quick. 7:25 Speaking of testing, it's outside the scope of this workshop. 7:27 But I do beg you to remember that you don't need to test what has 7:30 already been tested by framework creator. 7:33 Remember your boundaries. 7:36 Test only what is your responsibility and what could actually break. 7:37 I suggest you test your validation, your security, and 7:41 that your custom events are working as you intended. 7:43 But please don't go and test status codes and 7:47 error message that you haven't customized. 7:49 Find the right balance, and remember to not test what has been so 7:51 graciously abstracted away for you. 7:54