1 00:00:01,570 --> 00:00:09,750 In the previous step, we were able to create a REST service very easily. In the step, we will understand what 2 00:00:09,780 --> 00:00:11,770 is auto configuration. 3 00:00:11,810 --> 00:00:14,680 How did all the things that are needed for the REST 4 00:00:14,720 --> 00:00:18,700 service to be up and running get configured automatically. 5 00:00:18,710 --> 00:00:20,490 Let's look at it in this step. 6 00:00:20,660 --> 00:00:26,450 We have the Spring Boot in 10 steps application where we have the at SpringBootApplication 7 00:00:26,450 --> 00:00:33,220 annotation. The annotation at SpringBootApplication indicates that this is a Spring context file. 8 00:00:33,230 --> 00:00:34,430 That's number one. 9 00:00:34,430 --> 00:00:39,180 Number two, it enables something called auto configuration. 10 00:00:39,200 --> 00:00:43,350 Number three, it enables something called component scan. 11 00:00:43,820 --> 00:00:49,820 Component scan is one of the important features of Spring where it would start automatically scanning 12 00:00:49,850 --> 00:00:52,470 these classes in this package. 13 00:00:52,550 --> 00:00:56,660 And this sub package for any beans. 14 00:00:56,720 --> 00:01:00,840 So we have added in an annotation at restController. 15 00:01:00,980 --> 00:01:05,540 This is one of the annotations which is scanned for it. 16 00:01:05,540 --> 00:01:12,160 So this would be registered as a component. So the bookController would be registered as a bean and it would be managed 17 00:01:12,290 --> 00:01:14,420 by the Spring framework. 18 00:01:14,750 --> 00:01:19,750 There are three things that are essentially done by at Spring Boot application. 19 00:01:19,760 --> 00:01:22,130 It indicates that this is a Spring context. 20 00:01:22,130 --> 00:01:27,060 The second thing is the fact that this enables auto configuration. 21 00:01:27,080 --> 00:01:32,920 The third thing is that it enables automatic scan of this specific package. 22 00:01:32,920 --> 00:01:39,650 Now if we want to look at auto configuration in dept. Spring application dot run method is used to run 23 00:01:39,740 --> 00:01:41,690 a Spring context. 24 00:01:41,690 --> 00:01:47,990 So I'm giving a Spring context as an input to it and it would be able to run that. The run method also 25 00:01:47,990 --> 00:01:52,740 returns something. So it returns a application context. 26 00:01:52,760 --> 00:01:59,750 So Ill actually get the application context back. So I'm getting the application context back. 27 00:01:59,880 --> 00:02:04,630 This returns the application context. Im taking it and I would say application context.. 28 00:02:04,790 --> 00:02:06,200 I would want to loop around it. 29 00:02:06,200 --> 00:02:15,480 So, for each, control one. Control space actually. I would want to loop around the application context. 30 00:02:15,690 --> 00:02:17,410 dot get beans. 31 00:02:17,450 --> 00:02:24,380 I want to get the names of all the beans which are configured and I would call this name and I would 32 00:02:24,380 --> 00:02:29,620 want to log them. Ill for now do a sysout. Taking a shortcut here. 33 00:02:29,620 --> 00:02:32,550 Ideally I should have been using a logger. But Im a lazy guy. 34 00:02:32,700 --> 00:02:36,910 I would go ahead and print all the beans which are present in here. 35 00:02:36,920 --> 00:02:38,270 Let's see what would happen. 36 00:02:38,270 --> 00:02:40,300 Run us Java application. 37 00:02:40,640 --> 00:02:45,160 OK! I'm getting an error saying, its failed to start because 8080 is already used. 38 00:02:45,170 --> 00:02:45,830 Let's see. 39 00:02:45,980 --> 00:02:46,880 It's already being used. 40 00:02:46,880 --> 00:02:48,020 I'll kill that. 41 00:02:48,350 --> 00:02:49,640 And let's start again. 42 00:02:49,670 --> 00:02:50,970 Ok, cool! 43 00:02:51,080 --> 00:02:53,590 There are a lot of things that are printed right now. 44 00:02:53,600 --> 00:02:59,990 So there are a host of things that are getting configured for us automatically. 45 00:03:00,020 --> 00:03:02,340 How are these being configured? 46 00:03:02,720 --> 00:03:10,120 That's basically the feature called auto configuration. What Spring Boot does is as part of the Spring Boot 47 00:03:10,130 --> 00:03:14,260 framework, there is something called Spring Boot autoconfigure. 48 00:03:14,270 --> 00:03:22,040 So if I look at, one of the dependencies is Spring Boot auto configure. And this Spring Boot auto configure 49 00:03:22,310 --> 00:03:28,820 has a lot of logic built into it. So you can see that there is a lot of classes that are written. 50 00:03:28,850 --> 00:03:34,850 So if you look at the auto configuration Jar, it's a very very very big jar. 51 00:03:34,910 --> 00:03:36,680 And if we go to the Web, 52 00:03:36,720 --> 00:03:41,900 We will find our configurations for all the things that we are looking at right now. 53 00:03:42,110 --> 00:03:47,960 I'm going in to the auto configure web servlet and you would see something called dispatcher servlet 54 00:03:48,020 --> 00:03:49,730 auto configuration. 55 00:03:50,030 --> 00:03:56,020 These auto configuration classes are what are creating these beans. 56 00:03:56,360 --> 00:04:03,060 What would happen at startup is the Spring Boot framework would trigger the auto configuration jar. 57 00:04:03,350 --> 00:04:07,480 And it would loop through classes which are on the classpath. 58 00:04:07,660 --> 00:04:09,590 So it would see that, OK, 59 00:04:09,820 --> 00:04:16,220 do I have a specific class on the classpath? It would see that I have a Spring web MVC framework on 60 00:04:16,220 --> 00:04:16,720 the classpath. 61 00:04:16,730 --> 00:04:20,330 What does this Spring Boot auto configure do? 62 00:04:20,330 --> 00:04:26,310 It says, Oh! There is Spring web MVC on the classpath, then I would need to configure a dispatcher 63 00:04:26,320 --> 00:04:30,130 servlet. It would say, Oh! there is Spring MVC on the classpath, 64 00:04:30,130 --> 00:04:33,560 so I would need to configure a view resolver. 65 00:04:33,680 --> 00:04:43,220 So all those kind of things happen and you'd be able to see all the beans which were created in here. 66 00:04:43,370 --> 00:04:45,280 How does the configuration work? 67 00:04:45,330 --> 00:04:47,270 Spring Boot basically looks at two things. 68 00:04:47,270 --> 00:04:53,690 One is frameworks available on the classpath. There's a website called springboottutorial dot com, where we have 69 00:04:53,690 --> 00:04:54,970 a lot of articles on Spring Boot. 70 00:04:54,980 --> 00:04:57,220 I'm referring to one of the articles there. 71 00:04:57,320 --> 00:05:03,200 So Spring Boot looks at A) the frameworks which are available on the classpath and also, B) It looks 72 00:05:03,200 --> 00:05:10,280 at the existing beans which are configured for the application. And based on that, it provides the 73 00:05:10,310 --> 00:05:11,900 configuration needed. 74 00:05:11,900 --> 00:05:16,650 So for example, if you are using a web starter, the basic things that you would need would be a dispatcher 75 00:05:16,650 --> 00:05:23,150 servlet, you would need a, probably, some internationalization, you need some messaging. All that kind of 76 00:05:23,150 --> 00:05:25,850 stuff would get autoconfigured for you. 77 00:05:25,880 --> 00:05:31,660 Now, we are looking at one of the auto configuration beans which is data source auto configuration. 78 00:05:31,940 --> 00:05:37,800 If you see the code of data source auto configuration which is inside the Spring boot auto configure jar. 79 00:05:38,060 --> 00:05:43,970 You would see that it's conditional on class data source dot class and an embedded database type dot class to 80 00:05:43,970 --> 00:05:45,110 be present on the classpath. 81 00:05:45,120 --> 00:05:49,220 But so what happens is only these classes are on the classpath, 82 00:05:49,220 --> 00:05:55,670 then this specific bean would be created. The data source bean would be only created when these are on 83 00:05:55,670 --> 00:05:56,330 the classpath. 84 00:05:56,340 --> 00:06:02,660 But you can see the code in here. So data base auto configuration is conditional on a specific class being 85 00:06:02,720 --> 00:06:03,810 available on the classpath. 86 00:06:03,830 --> 00:06:09,730 But you can also see another example in here, So embedded data source database configuration. 87 00:06:09,810 --> 00:06:16,930 This is only created when there is no datasource, when there is no bean created with a data source or 88 00:06:16,940 --> 00:06:17,700 a XA datasource. 89 00:06:17,720 --> 00:06:24,410 Spring Boot would then create an embedded database configuration for us. If you want to find out more about 90 00:06:24,440 --> 00:06:26,770 what auto configuration is happening, 91 00:06:26,870 --> 00:06:34,500 what we can do is we can turn on debug logging. What I can do is go to application dot properties. 92 00:06:34,550 --> 00:06:37,280 That's one of the files which is present in here. 93 00:06:37,280 --> 00:06:40,100 We'll talk about application properties a little later. 94 00:06:40,400 --> 00:06:50,300 I'm turning on the logging level. All that you need to do is say logging dot level dot org dot Spring 95 00:06:50,850 --> 00:06:54,460 Framework is equal to debug. 96 00:06:54,560 --> 00:06:56,840 This would start the application in a debug mode. 97 00:06:56,840 --> 00:07:00,280 Let me kill this up. Start the application again. 98 00:07:00,320 --> 00:07:03,640 You can see a lot more logging being printed right now. 99 00:07:03,650 --> 00:07:07,530 So a lot of things are being printed along with which 100 00:07:07,700 --> 00:07:12,970 youd actually have a lot of logging about auto configuration which is printed in here. 101 00:07:13,130 --> 00:07:19,570 So this will actually say all the stuff which was auto configured and which was not auto configured. 102 00:07:19,580 --> 00:07:19,870 So its saying 103 00:07:19,870 --> 00:07:27,510 dispatcher servlet auto configuration has matched because I found something of this kind in the classpath. So its saying, 104 00:07:27,860 --> 00:07:33,470 I found a servlet called dispatcher servlet on the classpath. So I've configured dispatcher servlet automatically. 105 00:07:34,220 --> 00:07:42,260 Its saying I've configured an error MVC auto configuration. I've already configured default error controller. 106 00:07:42,350 --> 00:07:49,910 I've configured a cache, generic cache configuration. I've configured Jackson for doing binding and Ive auto 107 00:07:49,910 --> 00:07:52,130 configured validation as well. 108 00:07:52,130 --> 00:07:57,540 You can also see that there are things like view resolver and everything that were auto configured. 109 00:07:57,770 --> 00:08:03,000 Not only that, the auto configuration report also shows what are the things that were not auto configured 110 00:08:03,060 --> 00:08:10,640 So it would show why the rest of the auto configuration things did not match and why they were not 111 00:08:11,120 --> 00:08:12,770 executed. 112 00:08:12,770 --> 00:08:15,270 Why beans for them were not created. 113 00:08:15,320 --> 00:08:20,930 Auto configuration is a very very important concept regarding Spring Boot. One of the most important 114 00:08:20,930 --> 00:08:27,380 things to understand is you were still a beginner with Spring Boot and auto configuration is something 115 00:08:27,380 --> 00:08:32,380 which will grow on you as you keep building more and more Spring Boot application. 116 00:08:32,560 --> 00:08:36,760 If complete concept of auto configuration did not fit in your mind right 117 00:08:36,770 --> 00:08:38,800 right now, that's not a problem at all. 118 00:08:38,810 --> 00:08:45,260 You would definitely learn it by the time you end this course. Auto configuration is one of the fundamental 119 00:08:45,260 --> 00:08:45,930 things 120 00:08:46,070 --> 00:08:52,130 why Spring Boot is so famous and so easy to use. In this step, 121 00:08:52,160 --> 00:08:55,610 We looked at the basics of auto configuration. 122 00:08:55,610 --> 00:09:01,120 We looked at some of the beans which were automatically created and also we looked at where the code for 123 00:09:01,130 --> 00:09:04,160 Spring Boot auto configuration is. 124 00:09:04,580 --> 00:09:05,780 Until the next step, bye-bye.