1 00:00:01,060 --> 00:00:07,560 Not let's look at another interesting topic called civilization NDC realization at the end of the lesson 2 00:00:07,920 --> 00:00:11,700 we would also do a short demo of what we learned. 3 00:00:12,210 --> 00:00:20,370 So what we have seen how we can read and write data such as images as well as text but sometimes we 4 00:00:20,400 --> 00:00:26,940 also come across situations where we need to write wriggler Djala objects to disk and then at a later 5 00:00:26,940 --> 00:00:31,880 time read them back from the disk with the same state. 6 00:00:31,890 --> 00:00:35,810 So we're talking about saving objects to disk. 7 00:00:35,910 --> 00:00:38,710 Typically you would say objects declare a database. 8 00:00:38,760 --> 00:00:45,660 But sometimes as we will soon see you would want to save the entire Java object along with it to the 9 00:00:45,720 --> 00:00:50,290 disk know the source and the destination need not be a disk. 10 00:00:50,310 --> 00:00:57,060 It can also be something like Malmedy serialization is nothing but the process of writing Djala objects 11 00:00:57,180 --> 00:01:03,190 to some destination that is Java objects get saved us byte streams. 12 00:01:03,750 --> 00:01:09,180 He had a job object A named eight Izard and to some destination let's say it is their desk. 13 00:01:09,240 --> 00:01:16,200 So in this case we said that object has been serialized now at some point in the future we may want 14 00:01:16,200 --> 00:01:20,230 to reconstruct object it from its serialized version. 15 00:01:21,030 --> 00:01:24,380 And this is done through the process of DCD allegation. 16 00:01:24,600 --> 00:01:31,000 So DC deliberation we reconstruct Dala objects back from there byte strings. 17 00:01:31,020 --> 00:01:37,130 So the reconstructed Djala object will have the same state that it had when it was serialized that is 18 00:01:37,130 --> 00:01:37,190 . 19 00:01:37,190 --> 00:01:41,370 Instance variables but have the values as before. 20 00:01:41,920 --> 00:01:47,350 Not this DC realization can happen on the same JVM or even on a remote JVM. 21 00:01:47,430 --> 00:01:54,990 So as objects can also be transmitted across JVM is not the same deal as an object. 22 00:01:55,000 --> 00:02:02,070 We need to first make sure that X class implements this interface class Serializable which is a marker 23 00:02:02,070 --> 00:02:09,670 interface from the Java dog IO package and do the actual serialization NDC delegation. 24 00:02:09,750 --> 00:02:16,320 We make use of these classes object output stream an object input stream object output stream is 4C 25 00:02:16,340 --> 00:02:24,090 realization while object input stream is for D.S. realization and these classes implement the interfaces 26 00:02:24,240 --> 00:02:29,310 object output an object input respectably. 27 00:02:29,340 --> 00:02:31,880 And here is an example of serialization. 28 00:02:31,890 --> 00:02:38,830 We must create an instance of Object or put stream bitches and Chambery a buffer stream that is Intan 29 00:02:38,830 --> 00:02:45,780 chain Guia file or putzed in which does the actual writing off bytes on here the objects are written 30 00:02:45,870 --> 00:02:51,410 with this file called s object but s e r so the filename can be anything. 31 00:02:51,420 --> 00:02:58,560 It need not be object not as here but the extension ACR is normally used as a convention but you can 32 00:02:58,560 --> 00:02:59,790 use a different extension. 33 00:02:59,790 --> 00:03:07,230 All you can even altogether omit the extension to not buffer output stream is also not required. 34 00:03:07,440 --> 00:03:10,180 You would use it only for performance reasons. 35 00:03:10,470 --> 00:03:16,620 So you can directly chain object or put stream through the file output stream not to write an object 36 00:03:16,890 --> 00:03:23,940 when the method or write object on the object output stream instance here one string object and one 37 00:03:23,940 --> 00:03:26,890 date object are being returned to the file object. 38 00:03:26,910 --> 00:03:28,230 S E R. 39 00:03:28,690 --> 00:03:33,990 Now what string as well as did Garces doing and does Serializable interface. 40 00:03:33,990 --> 00:03:37,660 Otherwise these objects cannot be serialized. 41 00:03:38,160 --> 00:03:40,190 And here are the steps for ABC television. 42 00:03:40,200 --> 00:03:41,370 It's just the opposite. 43 00:03:41,400 --> 00:03:47,560 We just use input strings here an object input stream or buffered input stream because and don't change 44 00:03:47,560 --> 00:03:51,600 to the file and pushed him which is reading from the file object. 45 00:03:51,630 --> 00:03:58,130 As you do read an object from the object stream read object that is used. 46 00:03:58,150 --> 00:04:04,440 No the important thing here is that Vinita ensured that we are reading objects in the same order in 47 00:04:04,440 --> 00:04:06,800 which they have been returned to the desk. 48 00:04:07,050 --> 00:04:13,560 So the first object right will be the string object and the second one would be need also read object 49 00:04:13,560 --> 00:04:16,410 motard written an object instance. 50 00:04:16,530 --> 00:04:23,870 So we need a dongas appropriately so as you can see here in the first line we are casting a string whereas 51 00:04:23,870 --> 00:04:28,700 in the second line we are downcasting it to identify the list. 52 00:04:28,710 --> 00:04:35,550 We will also do a short demo of both serialization NBC realization here in this example we are serializing 53 00:04:35,550 --> 00:04:41,880 string under it but in the demo we will actually serialize our own custom object that has some state 54 00:04:43,560 --> 00:04:50,830 known it took a few use cases of serialization one to alleviate it is useful isn't websites that how 55 00:04:50,830 --> 00:04:57,970 high traffic rapid is on these web pages are dynamic web pages that is defined this what pages come 56 00:04:57,970 --> 00:05:05,140 from sources like a database model and the content in this for pages is pretty much constant that is 57 00:05:05,140 --> 00:05:09,000 you will see the same content for a long period of time. 58 00:05:09,100 --> 00:05:16,060 So it's such VEP biggest most of the time did is it from the database but not create into the database 59 00:05:16,060 --> 00:05:17,110 . 60 00:05:17,110 --> 00:05:22,270 And this date I might have to be right from Mike Dipali tables and that would be an expensive operation 61 00:05:22,270 --> 00:05:23,180 . 62 00:05:23,180 --> 00:05:29,020 Now if you're familiar with D-W Asus you may understand that it may require joining of multiple tables 63 00:05:29,630 --> 00:05:32,750 and the join operation would be very expensive. 64 00:05:33,520 --> 00:05:39,220 Mundelein once the data is right you would use it to construct you are Java objects and then pass them 65 00:05:39,220 --> 00:05:45,860 to the front end on you are performing these actions for every single piece axis. 66 00:05:45,940 --> 00:05:51,360 But if you are performing the expense you do opposite operation along that constructing of the Java 67 00:05:51,430 --> 00:05:52,930 object. 68 00:05:52,930 --> 00:05:58,270 And as mentioned earlier if the Lapidus have heavy traffic then it would affect the response time of 69 00:05:58,270 --> 00:05:59,510 the radius. 70 00:05:59,650 --> 00:06:03,700 That is it could drastically skewed on the response times. 71 00:06:03,700 --> 00:06:10,180 So in such cases since the content does not change frequently we can construct that Djala object once 72 00:06:10,510 --> 00:06:12,880 when the pitches access for the very first time. 73 00:06:13,120 --> 00:06:17,710 And then we can serialize a Java object subsequently with every bit axes. 74 00:06:17,830 --> 00:06:21,690 The page can be built using the serialized object. 75 00:06:21,690 --> 00:06:28,020 This way you are whining the costly database operation and also the object construction operation. 76 00:06:28,180 --> 00:06:33,850 You can store the serialized object on the desk or even better cash it in the memory using a tool like 77 00:06:33,850 --> 00:06:41,500 memcached memcached is an open source distributed object caching system and it also requires your objects 78 00:06:41,650 --> 00:06:44,620 to implement the Serializable interface. 79 00:06:45,040 --> 00:06:49,320 If you're interested you can google for that and check it out under his breath. 80 00:06:49,330 --> 00:06:57,370 Easy to use and one project that I worked on to do this kind of an issue VCL is Java objects to disk 81 00:06:58,110 --> 00:07:01,100 undergirded a huge difference in response time. 82 00:07:01,300 --> 00:07:09,640 So the web pages in this case where mostly constant sickener area is when you want to pass Java objects 83 00:07:09,740 --> 00:07:17,170 at cross-overs for instance your web service implementation might require Djala objects to be paused 84 00:07:17,170 --> 00:07:18,150 as input. 85 00:07:18,670 --> 00:07:23,750 In that case you can see that as the Del object on Pasic to the web service which is hosted on that 86 00:07:23,750 --> 00:07:31,480 remote server on the web service will end don't BCPL as the serialist Joe object. 87 00:07:31,480 --> 00:07:37,180 Another interesting use case seems to be post-mortem analysis which just perform when you run into any 88 00:07:37,180 --> 00:07:44,200 serious errors for instance if an object is causing some error then you would serialize that object 89 00:07:44,210 --> 00:07:44,450 . 90 00:07:44,680 --> 00:07:48,970 Let's say you were booted from the catch block later you can. 91 00:07:48,970 --> 00:07:57,030 DC realized it using a debugger and can investigate why the object caused that particular error. 92 00:07:57,040 --> 00:08:02,440 I've never done this but I'm including a go for a pointer in the resources section. 93 00:08:02,440 --> 00:08:06,510 There one particular user is discussing this use case on Harvard. 94 00:08:06,510 --> 00:08:07,720 How would this be. 95 00:08:08,140 --> 00:08:14,410 As you have time you can take a look at it not just look at some more things that we need to know about 96 00:08:14,410 --> 00:08:15,890 serialization. 97 00:08:16,110 --> 00:08:22,580 First is that both primitives as well as are is are both Serializable by default. 98 00:08:22,780 --> 00:08:24,640 No this would mean two things. 99 00:08:24,640 --> 00:08:31,750 First is that if an object to see more then any Prema do variables as well as any it was that it has 100 00:08:31,900 --> 00:08:32,920 will also be saved. 101 00:08:32,920 --> 00:08:34,580 Good risk. 102 00:08:34,600 --> 00:08:42,670 Second is that you can spasmed directly to the White object Mathare off object or put stream next to 103 00:08:42,670 --> 00:08:46,290 serialization saved and object Goffe. 104 00:08:46,660 --> 00:08:53,890 That is if an object is serialized than any objects it references or any object doughs objects reference 105 00:08:54,310 --> 00:08:56,620 will all be serialized. 106 00:08:57,560 --> 00:09:03,220 Now if at least one object and object graph does not implement the Serializable interface then seeing 107 00:09:03,220 --> 00:09:11,220 an addition of the original object is also within the object graph of the same object is referenced 108 00:09:11,250 --> 00:09:11,300 . 109 00:09:11,320 --> 00:09:18,340 Mike Dipali times that is there are multiple references to the same object density tradition is smart 110 00:09:18,340 --> 00:09:23,820 enough to save the object only once so it's not going to say multiple times. 111 00:09:25,610 --> 00:09:31,720 Know dystopic videos I'm not serializable and that's because serialization is about objects. 112 00:09:31,720 --> 00:09:39,510 It will start to really be not class variables on hence on not to any particular object. 113 00:09:39,590 --> 00:09:46,520 So during B.C.E. realization is Dodik variable will be assigned the value the class has a particular 114 00:09:46,520 --> 00:09:48,240 instance of. 115 00:09:49,190 --> 00:09:56,240 Next one as if a superclass is serializable then it's subclasses are automatically Serializable that 116 00:09:56,240 --> 00:10:04,610 a subclass us do not have to explicitly implement the Serializable interface superclasses Nazirite risible 117 00:10:05,050 --> 00:10:08,000 then some classes can still be mere serializable. 118 00:10:08,570 --> 00:10:14,360 So if a third party grows that you want to use is not serializable then you can always suppress it and 119 00:10:14,360 --> 00:10:17,370 make the subclass serializable. 120 00:10:18,280 --> 00:10:21,220 No you do not want an instance variable to be serialized. 121 00:10:21,410 --> 00:10:24,080 Then you can model that with the last transmission. 122 00:10:24,560 --> 00:10:30,470 So content is a keyword that you would include in the variables declaration. 123 00:10:30,500 --> 00:10:39,070 And with that the variables valuable squibbed during serialization and doing DC idealisation that TRONSON 124 00:10:39,130 --> 00:10:43,040 variable gets their default value based on its type. 125 00:10:43,070 --> 00:10:51,220 So I an object reference variable it will be null unforgettable like and it would be zero non-literary 126 00:10:51,240 --> 00:10:52,290 total eclipse. 127 00:10:52,370 --> 00:10:53,810 Googoosh shut them all off. 128 00:10:53,810 --> 00:10:56,870 Serialization NDC transition. 129 00:10:58,220 --> 00:11:03,320 OK here we are in the demo class and some antiquated package. 130 00:11:03,620 --> 00:11:06,920 And here we're going to see the as a Java object. 131 00:11:06,920 --> 00:11:08,150 NBC realized that. 132 00:11:08,290 --> 00:11:12,030 OK so let's just go ahead and look at the class itself. 133 00:11:12,740 --> 00:11:17,300 The class of the object and here it is at the top. 134 00:11:17,780 --> 00:11:25,610 It's called the Serializable demo and it is a nested class stocktake nested class which means that it 135 00:11:25,610 --> 00:11:29,380 is a class that is nested within the class I or. 136 00:11:29,840 --> 00:11:30,480 OK. 137 00:11:30,800 --> 00:11:34,200 And we still did not discuss nested classes so that we discuss later. 138 00:11:34,220 --> 00:11:35,530 So let's not worry about it. 139 00:11:35,760 --> 00:11:37,590 But this Serializable demo class. 140 00:11:37,610 --> 00:11:41,900 It could also have been an external It need not. 141 00:11:41,900 --> 00:11:43,130 It need not be a strict class. 142 00:11:43,130 --> 00:11:45,390 It can also be a separate class by itself. 143 00:11:45,680 --> 00:11:50,130 But I just made it an abstract class ok under a static master class. 144 00:11:50,330 --> 00:11:56,660 And if you recall from our coding conventions we said that's all stocktake masterclasses should be placed 145 00:11:56,660 --> 00:11:58,750 before static methods. 146 00:11:58,850 --> 00:12:01,090 So I would a more class has all static methods. 147 00:12:01,100 --> 00:12:01,930 We know that. 148 00:12:02,180 --> 00:12:06,480 So this particular stocktake master class is placed before the starting mothers. 149 00:12:06,560 --> 00:12:09,190 OK so we are following the standard convention. 150 00:12:09,200 --> 00:12:15,310 And in order for its objects to be serializable we know that it needs to implement Serializable interface 151 00:12:15,320 --> 00:12:15,590 . 152 00:12:15,650 --> 00:12:16,810 So that's what we are doing. 153 00:12:16,850 --> 00:12:22,780 So it's a marker interface interface on this particular class has a variable name and there is a getter 154 00:12:22,810 --> 00:12:23,760 on set name for that. 155 00:12:23,810 --> 00:12:25,970 So we are going to set the stage for that. 156 00:12:26,270 --> 00:12:31,640 And there is also another variable ID so name is an instance variable ID is also an instance variable 157 00:12:31,970 --> 00:12:36,340 but ID is marked as transients which means that it should not be serialized. 158 00:12:36,930 --> 00:12:39,560 And it is initialized with the value for. 159 00:12:40,100 --> 00:12:42,200 And here there is another variable gender. 160 00:12:42,320 --> 00:12:46,670 But let's not worry about it for now so I just call him undernote on which also not worry about this 161 00:12:46,670 --> 00:12:48,930 moment with a look at it later. 162 00:12:48,950 --> 00:12:54,980 So let's just go back to the main method and here it is. 163 00:12:55,010 --> 00:12:56,850 So we are for sequential serializer. 164 00:12:57,170 --> 00:13:03,700 And in order to do the serialization we are passing a parameter to the an argument to the I order more 165 00:13:03,730 --> 00:13:05,930 glass if the argument Bosnia's true. 166 00:13:05,990 --> 00:13:10,610 Only then we pull home the Syrian opposition and otherwise we do not. 167 00:13:10,960 --> 00:13:15,280 And there is also in order to perform the serialization we have this method called Boosey realization 168 00:13:15,420 --> 00:13:16,030 . 169 00:13:16,220 --> 00:13:21,470 And in order to perform B.C.E. tradition we have written this matter Boosey that position do B.C.E. 170 00:13:21,470 --> 00:13:22,600 demonization. 171 00:13:22,700 --> 00:13:25,350 So let's look at this matter Boosey television. 172 00:13:25,700 --> 00:13:26,620 Here it is. 173 00:13:26,630 --> 00:13:31,790 So you are first creating an instance off Serializable demat because we want to see Golez that particular 174 00:13:31,790 --> 00:13:36,210 object and we are said in the state of mean Kujawa. 175 00:13:36,740 --> 00:13:43,090 And we are simply printing the name value and the ID value which is a transient variable. 176 00:13:43,310 --> 00:13:49,430 So this is before serialization and we will also print after Signa mission to do the actual serialization 177 00:13:49,430 --> 00:13:49,940 . 178 00:13:49,940 --> 00:13:55,430 Here we are we are creating an object output stream which is chained to a buffer output stream which 179 00:13:55,430 --> 00:14:01,740 is intention to fight or put stream on we are writing the object of this file called City or Daut SDR 180 00:14:03,110 --> 00:14:09,710 and we are using that right object method and we are simply passing the Serializable to a more object 181 00:14:09,830 --> 00:14:10,910 object reference. 182 00:14:10,910 --> 00:14:13,540 OK so we are writing the object here. 183 00:14:13,550 --> 00:14:16,580 Now let's look at the DC validation method. 184 00:14:16,580 --> 00:14:17,510 Here it is. 185 00:14:17,510 --> 00:14:19,330 So here we are using input streams. 186 00:14:19,340 --> 00:14:24,290 So object input stream buffered input stream on file input stream on the file and this city Aldora as 187 00:14:24,330 --> 00:14:27,790 E.R and we are using the read object method here. 188 00:14:27,920 --> 00:14:30,470 So once again we are using a try catch block here. 189 00:14:30,530 --> 00:14:36,650 I tried with resources read object but read object against an object an instance of Object. 190 00:14:36,650 --> 00:14:42,980 So we need to gaster it here to see it rise above them all and we are ending the values after serialization 191 00:14:43,010 --> 00:14:45,440 the state one is the mean on the other is I-T. 192 00:14:45,680 --> 00:14:52,470 OK so let's just go ahead and fundus but it's busto value due to the configuration. 193 00:14:52,460 --> 00:14:54,550 So it's going to the configuration or an ass 194 00:14:58,450 --> 00:14:59,200 here. 195 00:14:59,410 --> 00:15:01,980 So Program arguments should be true. 196 00:15:02,480 --> 00:15:09,220 It's like an electronic case or printed some output here in Demel. 197 00:15:09,290 --> 00:15:16,280 If I refresh it you can see that it created this city or not as E.R So that's byte streams that God 198 00:15:16,280 --> 00:15:17,450 created. 199 00:15:17,510 --> 00:15:18,910 OK so the duckster file. 200 00:15:19,130 --> 00:15:19,940 And here it is. 201 00:15:19,940 --> 00:15:27,550 So before in the Boosey deposition method the name is Java ideas for but after the D.C. delegation process 202 00:15:27,910 --> 00:15:34,230 the name is once again we are reconstructing the object and we have the value of name as Java. 203 00:15:34,460 --> 00:15:39,890 But what ID since it's a transient variable it is initialized with the default value. 204 00:15:40,010 --> 00:15:42,820 So if it is a constant variable it's not going to be serialized. 205 00:15:42,820 --> 00:15:43,680 We know that. 206 00:15:43,860 --> 00:15:50,780 And so during these utilization it will assign the value of its type the default value of its type since 207 00:15:50,780 --> 00:15:53,240 it's on and it got assigned zero. 208 00:15:53,350 --> 00:15:56,500 OK now let's make a small change. 209 00:15:56,540 --> 00:16:02,430 Let's go back to this matter here and let me let's see. 210 00:16:02,660 --> 00:16:04,050 So the object has been set. 211 00:16:04,050 --> 00:16:05,440 Now let's see. 212 00:16:05,920 --> 00:16:10,670 You know using a time machine we went into the future and B how changed. 213 00:16:10,940 --> 00:16:14,050 We have ordered this new instance variable called gender. 214 00:16:14,060 --> 00:16:14,660 OK. 215 00:16:15,020 --> 00:16:17,280 So let's assume that it's a new release. 216 00:16:17,300 --> 00:16:19,250 And so we have a better class. 217 00:16:19,580 --> 00:16:24,750 But the object is from an older of these. 218 00:16:24,770 --> 00:16:27,410 So let's see if it will give us any problems. 219 00:16:27,410 --> 00:16:32,110 So let's go into a run configuration let's not beat Eleazer this let's not see the lizard this time 220 00:16:32,100 --> 00:16:32,200 . 221 00:16:32,210 --> 00:16:39,670 So in our city modus and let's say a polite unmix Ron on and you can see that. 222 00:16:39,740 --> 00:16:45,170 So naughty delegation has been done on the DC idolization off the object that we'll see realized earlier 223 00:16:45,650 --> 00:16:49,320 is being performed on Nix's invalid class exception. 224 00:16:49,340 --> 00:16:54,130 So there is an exception here it says local class incompatible. 225 00:16:54,170 --> 00:16:57,050 So what is happening is the class has evolved. 226 00:16:57,260 --> 00:17:00,650 But the object that we see realized was an old object. 227 00:17:00,650 --> 00:17:05,420 So it's like a legacy object and it should not be that way. 228 00:17:05,420 --> 00:17:08,920 So the object should be compatible with that class. 229 00:17:09,250 --> 00:17:09,820 OK. 230 00:17:09,950 --> 00:17:11,600 So there is a version mismatch. 231 00:17:11,720 --> 00:17:17,720 So there is something that we need to still learn about utilization and we will see how we can fix this 232 00:17:18,170 --> 00:17:26,090 by making some changes and that we are going to learn in the next lesson or at least some of the problems 233 00:17:26,300 --> 00:17:28,010 can be addressed by doing that. 234 00:17:28,370 --> 00:17:31,490 But that will be something that we look at the next lesson. 235 00:17:31,620 --> 00:17:32,040 Okay. 236 00:17:32,240 --> 00:17:32,720 Thank you. 237 00:17:32,720 --> 00:17:34,080 And happy coding.