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These are the user uploaded subtitles that are being translated: 1 1 00:00:01,176 --> 00:00:02,036 In this video, 2 2 00:00:02,036 --> 00:00:05,869 we're gonna cover spring dependency injection. 3 3 00:00:06,937 --> 00:00:09,947 So, what exactly is dependency injection? 4 4 00:00:09,947 --> 00:00:11,625 Here's a textbook definition, 5 5 00:00:11,625 --> 00:00:12,884 allows a program design 6 6 00:00:12,884 --> 00:00:15,499 to follow the dependency inversion principle. 7 7 00:00:15,499 --> 00:00:19,277 The client will delegate the XOR code, the injector, 8 8 00:00:19,277 --> 00:00:22,512 the responsibility of providing it's dependencies. 9 9 00:00:22,512 --> 00:00:27,122 Whoa (laughs) if that didn't confuse you, 10 10 00:00:27,122 --> 00:00:28,716 I don't know what will. 11 11 00:00:28,716 --> 00:00:32,126 So let's kind of break it down into normal layman's terms 12 12 00:00:32,126 --> 00:00:34,959 that a mere mortal can understand. 13 13 00:00:37,141 --> 00:00:38,985 In things that I can understand. 14 14 00:00:38,985 --> 00:00:41,441 So, say for example, I'm going to buy a car 15 15 00:00:41,441 --> 00:00:45,038 and this car is built at the factory on demand. 16 16 00:00:45,038 --> 00:00:46,951 So, there's nothing in the car lot. 17 17 00:00:46,951 --> 00:00:49,093 You have to actually talk to the factory 18 18 00:00:49,093 --> 00:00:52,037 and put in a request and they'll build a car for you; 19 19 00:00:52,037 --> 00:00:53,333 So, at the factory, you have 20 20 00:00:53,333 --> 00:00:55,819 all the different parts for the car. 21 21 00:00:55,819 --> 00:00:58,802 You have the car chassis, you have the engine, 22 22 00:00:58,802 --> 00:01:00,276 the tires, the seats, 23 23 00:01:00,276 --> 00:01:02,643 the electronics, the exhaust, and so on. 24 24 00:01:02,643 --> 00:01:04,743 And the mechanics or the assemblers there 25 25 00:01:04,743 --> 00:01:07,379 or the technicians, they'll actually aseemble the car 26 26 00:01:07,379 --> 00:01:10,798 for you and then deliver to you the final car. 27 27 00:01:10,798 --> 00:01:13,160 So, you don't have to actually build the car. 28 28 00:01:13,160 --> 00:01:15,993 The car's already built for you at the factory. 29 29 00:01:15,993 --> 00:01:18,520 So, they actually inject all 30 30 00:01:18,520 --> 00:01:20,432 of the dependencies for the car. 31 31 00:01:20,432 --> 00:01:24,094 So they inject the engine, they inject the tires, 32 32 00:01:24,094 --> 00:01:25,406 the seats and so on. 33 33 00:01:25,406 --> 00:01:27,592 So that's basically what you have here 34 34 00:01:27,592 --> 00:01:29,603 with dependency injection. 35 35 00:01:29,603 --> 00:01:32,588 So you simply outsource the construction 36 36 00:01:32,588 --> 00:01:35,922 and injection of your object to an external entity. 37 37 00:01:35,922 --> 00:01:39,005 In this case, that's the car factory. 38 38 00:01:42,071 --> 00:01:44,389 Alright, so that was a basic car example. 39 39 00:01:44,389 --> 00:01:46,304 How do this work in the Spring world? 40 40 00:01:46,304 --> 00:01:49,707 Well remember that Spring has am object factory, right? 41 41 00:01:49,707 --> 00:01:53,439 So then, when you retrieve an object like a coach object, 42 42 00:01:53,439 --> 00:01:57,085 this coach object may have some addition dependencies. 43 43 00:01:57,085 --> 00:01:59,790 So these dependencies are really just helper objects, 44 44 00:01:59,790 --> 00:02:03,055 other objects that it needs to perform it's operation. 45 45 00:02:03,055 --> 00:02:06,120 So instead of you have to manually build the coach object 46 46 00:02:06,120 --> 00:02:07,951 and all of it's dependencies, 47 47 00:02:07,951 --> 00:02:09,156 the Spring framework 48 48 00:02:09,156 --> 00:02:12,860 of the Spring factory will actually do this work for you. 49 49 00:02:12,860 --> 00:02:15,164 So just like you get a car that's ready to drive, 50 50 00:02:15,164 --> 00:02:18,997 here you'll get an object that's ready to use. 51 51 00:02:20,387 --> 00:02:21,770 Alright, so that's Spring container. 52 52 00:02:21,770 --> 00:02:22,613 So we've kind of covered 53 53 00:02:22,613 --> 00:02:25,030 the two major functions of the container. 54 54 00:02:25,030 --> 00:02:27,975 IN previous videos, we learned the idea 55 55 00:02:27,975 --> 00:02:31,065 of creating and managing objects with inversion of control 56 56 00:02:31,065 --> 00:02:33,243 and now here we'll focus on injecting 57 57 00:02:33,243 --> 00:02:36,631 object's dependencies with that dependency injection. 58 58 00:02:36,631 --> 00:02:37,607 And these are the two core features 59 59 00:02:37,607 --> 00:02:39,867 and we'll kind of have this all covered once we finish 60 60 00:02:39,867 --> 00:02:41,784 this section of videos. 61 61 00:02:44,241 --> 00:02:46,723 Alright so, we'll walk through this with an example again. 62 62 00:02:46,723 --> 00:02:49,851 So our coach already provides daily workouts. 63 63 00:02:49,851 --> 00:02:53,920 Now our coach will also provide daily fortunes, 64 64 00:02:53,920 --> 00:02:55,622 like your good luck fortune. 65 65 00:02:55,622 --> 00:02:57,052 This coach will actually make use 66 66 00:02:57,052 --> 00:02:59,541 of a helper called FortuneService 67 67 00:02:59,541 --> 00:03:01,779 and this is what they call a dependency 68 68 00:03:01,779 --> 00:03:04,125 because a coach depends on a fortune service 69 69 00:03:04,125 --> 00:03:07,458 in order to serve up the daily fortunes. 70 70 00:03:10,249 --> 00:03:11,405 Now, there's different types 71 71 00:03:11,405 --> 00:03:13,611 of injections you can use in Spring. 72 72 00:03:13,611 --> 00:03:14,654 Actually, there's a lot 73 73 00:03:14,654 --> 00:03:17,611 but we'll the two most common injection types 74 74 00:03:17,611 --> 00:03:18,724 that you'll use. 75 75 00:03:18,724 --> 00:03:20,914 It's called constructor injection 76 76 00:03:20,914 --> 00:03:23,449 and there's also setter injection. 77 77 00:03:23,449 --> 00:03:24,282 And we'll cover these in a set 78 78 00:03:24,282 --> 00:03:26,829 of videos here in this section. 79 79 00:03:26,829 --> 00:03:30,440 We'll also talk about auto-wiring beings 80 80 00:03:30,440 --> 00:03:34,607 in the annotations section that we'll cover a little later. 81 81 00:03:37,675 --> 00:03:40,461 Alright so, we'll start off with the constructor injection 82 82 00:03:40,461 --> 00:03:41,869 and here's the development process 83 83 00:03:41,869 --> 00:03:45,138 and you know me, I like to do things step by step. 84 84 00:03:45,138 --> 00:03:46,305 So the first thing we're gonna do 85 85 00:03:46,305 --> 00:03:49,939 is define the dependency interface in it's class. 86 86 00:03:49,939 --> 00:03:52,506 Then we'll go through and create a constructor 87 87 00:03:52,506 --> 00:03:54,017 in our class for injections 88 88 00:03:54,017 --> 00:03:56,280 and then the final step is configuring 89 89 00:03:56,280 --> 00:04:00,244 the dependency injection in the Spring configuration file. 90 90 00:04:00,244 --> 00:04:01,461 And again, we'll do all 91 91 00:04:01,461 --> 00:04:04,628 of this step by step and from scratch. 92 92 00:04:06,589 --> 00:04:07,920 Okay, so let's start with step one. 93 93 00:04:07,920 --> 00:04:10,623 Defining the dependency interface and class. 94 94 00:04:10,623 --> 00:04:13,528 So, in the top left, we're gonna have this fortune service. 95 95 00:04:13,528 --> 00:04:15,033 It's simply an interface 96 96 00:04:15,033 --> 00:04:17,521 that's gonna have a method called get fortune. 97 97 00:04:17,521 --> 00:04:19,385 And that returns a string and that's it. 98 98 00:04:19,385 --> 00:04:22,496 So it's simply the specification or the interface. 99 99 00:04:22,496 --> 00:04:23,941 In the bottom of the slide, 100 100 00:04:23,941 --> 00:04:25,886 line:15% we hace this happy fortune service. 101 101 00:04:25,886 --> 00:04:29,602 line:15% This person actually implements the fortune service 102 102 00:04:29,602 --> 00:04:31,522 line:15% and when I say implement, meaning, 103 103 00:04:31,522 --> 00:04:35,728 line:15% they provide an implementation of that method get fortune. 104 104 00:04:35,728 --> 00:04:39,271 line:15% So here, for the fortune, they'll simple hard code something 105 105 00:04:39,271 --> 00:04:41,592 line:15% to say, today is your lucky day 106 106 00:04:41,592 --> 00:04:43,366 line:15% and they return it as a string. 107 107 00:04:43,366 --> 00:04:44,822 So that's a very simple example 108 108 00:04:44,822 --> 00:04:47,177 of an implementation of the fortune service. 109 109 00:04:47,177 --> 00:04:50,784 You can think of more advanced implementations. 110 110 00:04:50,784 --> 00:04:52,343 Maybe an implementation 111 111 00:04:52,343 --> 00:04:54,661 that could read something from the file system 112 112 00:04:54,661 --> 00:04:59,201 or maybe from a data base or possibly a web service 113 113 00:04:59,201 --> 00:05:00,659 but we'll keep it simple for now 114 114 00:05:00,659 --> 00:05:01,943 and we'll talk about some 115 115 00:05:01,943 --> 00:05:05,860 of those other advance features a little later. 116 116 00:05:08,484 --> 00:05:09,574 Alrighty, so that's step one. 117 117 00:05:09,574 --> 00:05:12,008 So now, step two, create a constructor 118 118 00:05:12,008 --> 00:05:13,864 in your class for injections. 119 119 00:05:13,864 --> 00:05:15,651 So again, we're gonna make use 120 120 00:05:15,651 --> 00:05:17,504 of this constructor injection. 121 121 00:05:17,504 --> 00:05:20,731 So they're going to inject dependencies here 122 122 00:05:20,731 --> 00:05:23,048 by calling a constructor, 123 123 00:05:23,048 --> 00:05:25,508 so I have my class baseball coach. 124 124 00:05:25,508 --> 00:05:28,587 I need to create a constructor baseball coach 125 125 00:05:28,587 --> 00:05:30,817 that will accpet this dependency. 126 126 00:05:30,817 --> 00:05:33,500 So it has to accept a fortune service. 127 127 00:05:33,500 --> 00:05:36,709 So I have private field called fortune service 128 128 00:05:36,709 --> 00:05:37,950 and then I simply assign 129 129 00:05:37,950 --> 00:05:40,675 that field inside of a constructor here. 130 130 00:05:40,675 --> 00:05:44,258 Fortune service equals the fortune service. 131 131 00:05:46,415 --> 00:05:48,932 Okay great, now we configure the dependency injection 132 132 00:05:48,932 --> 00:05:51,032 in the Spring config file. 133 133 00:05:51,032 --> 00:05:52,601 So what I'll do at the top here 134 134 00:05:52,601 --> 00:05:56,227 in my Spring config application conteot.XML. 135 135 00:05:56,227 --> 00:05:57,283 What I'll do is I'll define 136 136 00:05:57,283 --> 00:06:00,792 this bean called my fortune service that's the ID, 137 137 00:06:00,792 --> 00:06:04,158 and tehn the class, the actual implementation class 138 138 00:06:04,158 --> 00:06:07,188 of that service and that's our happy fortune service 139 139 00:06:07,188 --> 00:06:09,870 that we just saw on the previous slide. 140 140 00:06:09,870 --> 00:06:11,632 So that's our dependency. 141 141 00:06:11,632 --> 00:06:15,053 Now, what we need to do Is actually inject 142 142 00:06:15,053 --> 00:06:19,553 that dependency into our class and how do we do it? 143 143 00:06:19,553 --> 00:06:23,681 So now I have my coach here, bean ID equals my coach, 144 144 00:06:23,681 --> 00:06:26,102 class, baseball coach. 145 145 00:06:26,102 --> 00:06:28,670 Now what I do is I tell Spring, hey, 146 146 00:06:28,670 --> 00:06:33,107 inject a dependency into this baseball coach. 147 147 00:06:33,107 --> 00:06:35,198 So I have constructor arg 148 148 00:06:35,198 --> 00:06:37,983 and I have ref equals my fortune service. 149 149 00:06:37,983 --> 00:06:42,150 That's the same ID name of the bean up top. 150 150 00:06:43,294 --> 00:06:45,567 So, ref equals my fortune service, 151 151 00:06:45,567 --> 00:06:47,781 that's the ID of the fortune service 152 152 00:06:47,781 --> 00:06:50,620 that we have up top, so they're gonna inject this. 153 153 00:06:50,620 --> 00:06:52,403 Now, what'll happen behind the scenes is 154 154 00:06:52,403 --> 00:06:54,587 that when Spring makes it to this line 155 155 00:06:54,587 --> 00:06:57,555 of code in your config file, 156 156 00:06:57,555 --> 00:07:00,662 they'll actually look at your baseball coach, 157 157 00:07:00,662 --> 00:07:03,441 they'll ball your baseball coach's constructor 158 158 00:07:03,441 --> 00:07:07,779 and they'll pass in a reference to the my fortune service. 159 159 00:07:07,779 --> 00:07:10,263 So Spring willa ctually construct your object 160 160 00:07:10,263 --> 00:07:13,461 and pass in the appropriate data into the constructor 161 161 00:07:13,461 --> 00:07:15,412 and that happens behind the scenes. 162 162 00:07:15,412 --> 00:07:18,423 Because remember, Spring has an object factory. 163 163 00:07:18,423 --> 00:07:21,711 Spring is responsible for creating objects 164 164 00:07:21,711 --> 00:07:23,062 and, also, it's responsible 165 165 00:07:23,062 --> 00:07:25,843 for injecting their dependencies. 166 166 00:07:25,843 --> 00:07:28,032 So we're kind of covering everything, 167 167 00:07:28,032 --> 00:07:31,412 right here in this configuration. 168 168 00:07:31,412 --> 00:07:33,265 Alright, so I know that was a lot of heavy stuff. 169 169 00:07:33,265 --> 00:07:36,513 What we're gonna is actually move into eclipse 170 170 00:07:36,513 --> 00:07:39,087 and then we'll actually write this code from scratch 171 171 00:07:39,087 --> 00:07:42,319 and we'll also run it so you can kind of see it real time 172 172 00:07:42,319 --> 00:07:44,278 as far as how all this works out. 173 173 00:07:44,278 --> 00:07:48,361 So hold tight and I'll see you in the next video. 15249