1 00:00:00,000 --> 00:00:02,004 - [Instructor] Before we implement our POC, 2 00:00:02,004 --> 00:00:05,009 we need to take a look at our use case diagram, 3 00:00:05,009 --> 00:00:08,008 as there is one change we need to make. 4 00:00:08,008 --> 00:00:10,001 We were initially thinking 5 00:00:10,001 --> 00:00:12,004 of connecting directly to USDA DB, 6 00:00:12,004 --> 00:00:15,008 but later we decided to have the data loaded 7 00:00:15,008 --> 00:00:19,002 upfront into our own Red30 DB. 8 00:00:19,002 --> 00:00:22,001 So we will not show it in this diagram any more, 9 00:00:22,001 --> 00:00:24,002 because any database that is fully 10 00:00:24,002 --> 00:00:26,002 controlled by our application 11 00:00:26,002 --> 00:00:28,007 is part of the system that we are creating, 12 00:00:28,007 --> 00:00:31,005 and not an external actor. 13 00:00:31,005 --> 00:00:34,005 Now, about the functionality for POC. 14 00:00:34,005 --> 00:00:37,003 A good idea is to take something that is simple, 15 00:00:37,003 --> 00:00:40,000 is part of one of the core use cases, 16 00:00:40,000 --> 00:00:42,007 and cuts across the entire technology stack. 17 00:00:42,007 --> 00:00:45,008 So how about just printing the number of products 18 00:00:45,008 --> 00:00:47,006 that are there in the database? 19 00:00:47,006 --> 00:00:50,006 I think it checks all the boxes. 20 00:00:50,006 --> 00:00:52,007 So starting from the front end, 21 00:00:52,007 --> 00:00:55,008 there was this UI mock-up, which we saw earlier. 22 00:00:55,008 --> 00:00:59,005 So we do have some idea of the look and feel. 23 00:00:59,005 --> 00:01:01,007 Instead of implementing the functionalities, 24 00:01:01,007 --> 00:01:04,002 such as search, compare, et cetera, 25 00:01:04,002 --> 00:01:08,001 all we need here is a POC link, which when I click, 26 00:01:08,001 --> 00:01:11,004 it should display the product map sites. 27 00:01:11,004 --> 00:01:15,000 To get that going, I have used the classic approach 28 00:01:15,000 --> 00:01:17,007 of iteratively moving between sequence diagram, 29 00:01:17,007 --> 00:01:19,008 class diagram, and code. 30 00:01:19,008 --> 00:01:22,004 It helped me model the behavioral 31 00:01:22,004 --> 00:01:24,009 and structural aspects of the system, 32 00:01:24,009 --> 00:01:28,008 so whatever I'm going to show you did not come in one shot. 33 00:01:28,008 --> 00:01:31,003 It took some back and forth between modeling 34 00:01:31,003 --> 00:01:34,000 and coding to get this straight. 35 00:01:34,000 --> 00:01:35,009 So let us see what we got. 36 00:01:35,009 --> 00:01:39,003 Very early in the cycle, I realized that if I sent 37 00:01:39,003 --> 00:01:41,001 an SQL query to the database 38 00:01:41,001 --> 00:01:44,002 for every search or comparison request, 39 00:01:44,002 --> 00:01:46,008 the response time gets really poor. 40 00:01:46,008 --> 00:01:49,004 And since all food product-related data 41 00:01:49,004 --> 00:01:52,002 coming from USDA is read-only, 42 00:01:52,002 --> 00:01:56,003 there is no need to read it afresh for every query, 43 00:01:56,003 --> 00:01:59,007 so I decided to load all food products-related data 44 00:01:59,007 --> 00:02:02,007 into memory when the application starts. 45 00:02:02,007 --> 00:02:06,000 And I did that by creating a DataLoader servlet 46 00:02:06,000 --> 00:02:10,000 whose init is involved when application starts up. 47 00:02:10,000 --> 00:02:13,004 This init does the job of initial data loading. 48 00:02:13,004 --> 00:02:16,001 Another class I created here is Dao. 49 00:02:16,001 --> 00:02:19,002 That is data access object, which will connect with 50 00:02:19,002 --> 00:02:22,008 the data source that we defined in context XML. 51 00:02:22,008 --> 00:02:25,006 Let us model this init sequence diagram. 52 00:02:25,006 --> 00:02:27,003 Starting from top left, 53 00:02:27,003 --> 00:02:30,006 when server calls init on DataLoader, 54 00:02:30,006 --> 00:02:33,002 the DataLoader reaches out to Dao, 55 00:02:33,002 --> 00:02:37,002 whose instance establishes connection with red30db, 56 00:02:37,002 --> 00:02:40,005 and then passes itself to DataLoader. 57 00:02:40,005 --> 00:02:43,006 The DataLoader then loads all the data. 58 00:02:43,006 --> 00:02:46,001 So my final class diagram 59 00:02:46,001 --> 00:02:48,009 for initial data load looks like this. 60 00:02:48,009 --> 00:02:52,008 Here we have DataLoader extending HttpServlet, 61 00:02:52,008 --> 00:02:56,009 that has in it destroy and three methods for loading data. 62 00:02:56,009 --> 00:03:00,007 It contains an instance of Dao that has two maps, 63 00:03:00,007 --> 00:03:02,008 Product map and Nutrient map, 64 00:03:02,008 --> 00:03:06,000 which is where DataLoader loads all the data. 65 00:03:06,000 --> 00:03:08,006 Product and Nutrient are two beans 66 00:03:08,006 --> 00:03:11,009 that have their properties, sectors, and getters. 67 00:03:11,009 --> 00:03:15,000 I have also created non-default constructors 68 00:03:15,000 --> 00:03:18,002 which initialize some of their properties. 69 00:03:18,002 --> 00:03:21,008 Okay, now let us take a look at Eclipse. 70 00:03:21,008 --> 00:03:24,005 First, the overall structure. 71 00:03:24,005 --> 00:03:28,002 In JavaResources inside sourceMainJava, 72 00:03:28,002 --> 00:03:31,000 I have a package, commHPlus4_red30, 73 00:03:31,000 --> 00:03:35,002 that has Dao, DataLoader, and PocController, 74 00:03:35,002 --> 00:03:38,002 which will implement the functionality for POC. 75 00:03:38,002 --> 00:03:42,000 Then in beans I have Nutrient and Product beans. 76 00:03:42,000 --> 00:03:45,001 The JSPs are inside webapp. 77 00:03:45,001 --> 00:03:49,005 Inside src main I have css folder here. 78 00:03:49,005 --> 00:03:51,000 That has stylecss. 79 00:03:51,000 --> 00:03:53,008 Images, that has the logo image. 80 00:03:53,008 --> 00:03:57,003 Jsp folder, that has another folder, POC, 81 00:03:57,003 --> 00:04:00,006 with pocResults.jsp. 82 00:04:00,006 --> 00:04:03,002 Jsp also has header.jsp, 83 00:04:03,002 --> 00:04:06,006 which is the common header across all pages. 84 00:04:06,006 --> 00:04:09,002 WEB-INR, which has web.xml. 85 00:04:09,002 --> 00:04:14,001 And index.jsp, that is where everything gets started. 86 00:04:14,001 --> 00:04:19,009 Now let us take a look at code inside all these files. 87 00:04:19,009 --> 00:04:23,003 Starting with Dao, 88 00:04:23,003 --> 00:04:27,008 in Dao class there is a private constructor at line 30 89 00:04:27,008 --> 00:04:30,003 in which it creates an initial context, 90 00:04:30,003 --> 00:04:33,000 and then looks up the DataSource resource, 91 00:04:33,000 --> 00:04:36,002 which we have defined in our context XML file. 92 00:04:36,002 --> 00:04:38,003 It uses this resource to initialize 93 00:04:38,003 --> 00:04:41,008 the connection variable in line 36. 94 00:04:41,008 --> 00:04:46,000 In line 43 the getInstance method checks 95 00:04:46,000 --> 00:04:49,002 if the private member variable Dao is null. 96 00:04:49,002 --> 00:04:53,009 If yes, it invokes the constructor and returns its instance. 97 00:04:53,009 --> 00:04:56,009 This is singleton pattern, which ensures that we have 98 00:04:56,009 --> 00:05:00,000 only one instance of Dao running in our system, 99 00:05:00,000 --> 00:05:01,009 which then ensures that we have 100 00:05:01,009 --> 00:05:05,001 just one connection to database at a time. 101 00:05:05,001 --> 00:05:08,007 Now let us look at DataLoader. 102 00:05:08,007 --> 00:05:13,007 In its init method, we get Dao's instance in line 30, 103 00:05:13,007 --> 00:05:17,008 and then invoke the three methods for loading data. 104 00:05:17,008 --> 00:05:20,003 The destroy method just cleans up the memory 105 00:05:20,003 --> 00:05:22,008 and closes the connection. 106 00:05:22,008 --> 00:05:26,002 And then there are three data loading methods: 107 00:05:26,002 --> 00:05:32,006 loadProducts, loadNutrients, and loadProductNutrients. 108 00:05:32,006 --> 00:05:36,000 These methods use SQL queries to pull the data 109 00:05:36,000 --> 00:05:39,009 and load the Product and Nutrient maps. 110 00:05:39,009 --> 00:05:43,002 Product and Nutrient are two beans. 111 00:05:43,002 --> 00:05:49,005 Nutrient has id, name, and unit_name as three properties. 112 00:05:49,005 --> 00:05:52,004 I have used these same names as the field names 113 00:05:52,004 --> 00:05:56,000 in database table for better understandability. 114 00:05:56,000 --> 00:05:59,006 Product similarly has many properties, 115 00:05:59,006 --> 00:06:03,007 all named as per field names in the database tables. 116 00:06:03,007 --> 00:06:07,005 There is this productNutrientMap in line 15 117 00:06:07,005 --> 00:06:09,004 which will store all nutrients 118 00:06:09,004 --> 00:06:12,002 and their amounts in the product. 119 00:06:12,002 --> 00:06:14,004 Now let us take a look at JSPs, 120 00:06:14,004 --> 00:06:17,003 which will help us understand the flow. 121 00:06:17,003 --> 00:06:20,009 They're all in the src main, as I showed you earlier. 122 00:06:20,009 --> 00:06:23,007 Starting with index.jsp, 123 00:06:23,007 --> 00:06:27,007 here we have header.jsp included in line 11, 124 00:06:27,007 --> 00:06:30,007 followed by some simple text. 125 00:06:30,007 --> 00:06:34,004 Then in header.jsp we have image logo 126 00:06:34,004 --> 00:06:36,006 and a set of links that you see 127 00:06:36,006 --> 00:06:40,007 for index, POC, search, compare, and login. 128 00:06:40,007 --> 00:06:42,004 We will implement the search, 129 00:06:42,004 --> 00:06:44,009 compare, login functionalities later. 130 00:06:44,009 --> 00:06:47,008 For now, we will have POC, 131 00:06:47,008 --> 00:06:51,000 which is pointing to our PocController, 132 00:06:51,000 --> 00:06:53,000 so let's take a look at that. 133 00:06:53,000 --> 00:06:54,009 In PocController we have 134 00:06:54,009 --> 00:06:58,005 just simple doGet and doPost methods. 135 00:06:58,005 --> 00:07:01,006 The doGet method is forwarding 136 00:07:01,006 --> 00:07:05,006 the request to pocResults.jsp, 137 00:07:05,006 --> 00:07:09,001 and pocResults.jsp is simply printing 138 00:07:09,001 --> 00:07:12,005 the productMap.size in line 14. 139 00:07:12,005 --> 00:07:16,008 Okay, now let us run the application. 140 00:07:16,008 --> 00:07:23,000 I go into project, run as, run on server. 141 00:07:23,000 --> 00:07:25,008 This will take a little bit of a time, 142 00:07:25,008 --> 00:07:28,008 because it has to load all the data, as you can see, 143 00:07:28,008 --> 00:07:31,006 and the loading is completed, 144 00:07:31,006 --> 00:07:35,005 and our application is up and running. 145 00:07:35,005 --> 00:07:38,003 If I click on POC I can see 146 00:07:38,003 --> 00:07:41,002 the number of products in database. 147 00:07:41,002 --> 00:07:43,007 So the entire flow that you just looked at, 148 00:07:43,007 --> 00:07:47,004 I have traced it out in a sequence diagram here. 149 00:07:47,004 --> 00:07:49,008 I see several benefits of doing so. 150 00:07:49,008 --> 00:07:52,005 First, by laying out the entire flow, 151 00:07:52,005 --> 00:07:55,003 it helps me think clearly about my design, 152 00:07:55,003 --> 00:07:57,002 and identify any incorrect 153 00:07:57,002 --> 00:08:00,008 or unnecessary objects, loops, or flows. 154 00:08:00,008 --> 00:08:03,007 Second, it helps anyone else reading 155 00:08:03,007 --> 00:08:06,003 and trying to understand my code and design. 156 00:08:06,003 --> 00:08:08,009 And third, it is a great pedagogical tool, 157 00:08:08,009 --> 00:08:11,008 because it helps one teach and learn. 158 00:08:11,008 --> 00:08:15,001 Using the objects identified in this sequence diagram, 159 00:08:15,001 --> 00:08:17,007 here is the final class diagram. 160 00:08:17,007 --> 00:08:20,003 You can find this and many other diagrams 161 00:08:20,003 --> 00:08:23,003 in the artifacts provided along with this course. 162 00:08:23,003 --> 00:08:26,000 Now that we have looked at implementation, 163 00:08:26,000 --> 00:08:29,000 it's time to move all this to production server.