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Capgemini Java Interview | Core Java, Spring Boot and Microservices — Transcript

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0:03Hello. How are you?
0:05>> Hello. I'm fine, thank you. How are you?
0:08>> I'm good, thank you. So, can you tell me
0:11a little about your role and
0:13responsibilities in your project and
0:15your tech stack on which you are working
0:17on?
0:18>> Uh, yes. So I have around uh four years
0:21of experience working in IT industry and
0:23I've worked across various domains uh
0:26starting from banking, insurance uh then
0:28uh telecom, healthcare. So in this four
0:31years uh I've learned a lot about um
0:34Java, Spring Boot, microservices and uh
0:37my current roles and responsibilities uh
0:39is to add new use cases to the
0:42application. Uh try to resolve bugs if
0:45any and try to improve the performance
0:47of the application and uh our
0:50application text tag consists of uh
0:52Java. We are using Java 17 uh then
0:55spring boot. uh we are designing our
0:57applications in uh springboard and we
0:59are using microservices architecture and
1:02finally to deploy the application we are
1:04using um AWS uh specifically EC2 then
1:08for object-oriented storage S3 and the
1:10database that we are using is MySQL so
1:14that is a brief introduction about uh
1:16the project text stack
1:19>> okay so do you have hands-on experience
1:21on Java features or Java 8 features
1:25>> uh yes yes I have hands-on experience on
1:28these features.
1:29>> Okay.
1:30Okay. So, do you know what is
1:33immutability in Java?
1:36>> Uh yes, I know about uh immutability.
1:38So, uh immutability is where once you
1:41create the object, you cannot change
1:43that object. Uh the state of the object
1:45cannot be changed. So, that is uh
1:47immutable object and string is an
1:49example of immutable object. But uh we
1:51can also write our custom uh immutable
1:54classes.
1:58>> Okay. Now can you write some code which
2:01can demonstrate
2:02this use case? Let us consider I have to
2:05create a class uh which will be
2:07immutable. So you can create a class and
2:09tell me how can I make it immutable.
2:12>> Uh great. Okay. So there are a few cases
2:15uh there are few rules for creating
2:17immutable classes. So let's try to
2:19understand that the first thing is I'm
2:22going to uh create a class and the class
2:24name is going to be a uh student. Okay.
2:27So this is my class. I want to make this
2:29object of this class immutable. The
2:32first thing is I'll make this final. So
2:34this will prevent the subclassing. So I
2:37cannot uh I cannot subass this. I cannot
2:39create the child classes. So that is the
2:42first rule. The second rule is um I'm
2:44going to mark all the fields as private
2:47and final. So let's uh try to create
2:50private string uh name. So first thing
2:54is name. So private and final, right? Uh
2:58the second thing is I'm going to do
3:00private final again uh integer role
3:04number. Okay. And uh these are the two
3:07two fields uh private final string. And
3:10the third thing is I'm going to do is uh
3:13I'm going to add one subject list. So
3:16let's try to do private final uh list of
3:21string and I'm going to give the name as
3:25subjects. So private final is done. The
3:28third is uh I want I'm going to uh do
3:31the initialization only through the
3:33constructor. So let's try to create a
3:36constructor out of this. uh right click
3:39uh
3:40right click generate constructor I'm
3:43going to create all the fields right so
3:46this is how I'm going to initialize
3:48these uh fields so initialization is
3:51only possible through uh constructor I'm
3:55going to provide the getters for this
3:57but I'm not going to provide the setters
3:59so once the object is created I'm not
4:02going to change the value through
4:03setters so whatever fields whatever
4:06values you have to provide you have to
4:07provide only through uh the constructor.
4:10So let's provide the getters but not
4:11setters. Okay. So right click uh
4:15generate
4:17generate and I want to provide only
4:19getters. Okay. So I'm going to provide
4:21getters for all of this.
4:23Okay. Uh right. But uh I provided
4:27getters. I did not provide setter. But
4:29uh for uh for fields like list okay we
4:34are not going to directly pro send back
4:36the list itself. What we are going to do
4:38we are going to do the uh defensive copy
4:41of this and then send it back. So let's
4:43try to send it
4:45uh collections. Uh there is something
4:47called as unmodifiable list and to this
4:50unmodifiable list I'm going to pass our
4:53uh subject list. Okay. So
4:58subjects.
5:00Okay. So this is how I am going to
5:02return the unmodifiable list and not the
5:04actual list. So this subject cannot be
5:07changed by the uh client. So just to
5:09summarize uh the what are the rules. So
5:11the first rule is mark the classes final
5:13which we have already marked. Then to
5:16mark the fields as private and final
5:19which we have marked. Uh we are
5:20providing only getters. So no one can
5:23set the value. And we are uh
5:25initializing the values only using the
5:27constructor. Uh so we have done that.
5:29And uh the final thing is whenever there
5:32there is uh a list date so these kind of
5:35object copy of those object should be
5:37made and then returned back to the
5:39client. So this is how I'm going to
5:41create an immutable class in uh Java.
5:46>> Okay. Great. Now uh do one thing. take a
5:49list of numbers and try to find out the
5:52second largest number from that list.
5:54You have to use stream APIs from J.
5:58>> Okay. So I have to take a a list of
6:00number and uh then try to find the
6:03second highest from that uh list. Okay.
6:06>> Correct.
6:06>> So let me create a class uh second
6:11highest number and specifically I have
6:14to use the uh stream API, right?
6:18Yes, correct.
6:19>> Yeah. So, uh let's try to create a list
6:22of uh integer. Okay. I'm going to call
6:25this as numbers. Uh let me import the
6:29list. Importing is very important.
6:31Numbers equal to new sorry I'm going to
6:34uh initialize in one line only. So
6:36arrays dot um as list and uh I'm going
6:40to provide uh the values 10 20 uh 35
6:46then 35 then 50 then 40 some values.
6:50Okay, this is my list and the goal is to
6:53find the uh second highest uh number
6:55from this using stream API. So let's try
6:57to find this. So the first thing is uh
7:00numbers dot stream. Okay, once I get the
7:04stream, uh the first thing I'm going to
7:06do is uh there are repeated numbers 35
7:08and 35. So let's try to remove the uh
7:12repeated numbers
7:15dot distinct. The distinct will remove
7:17the uh duplicate numbers. Then as I have
7:20to find the second highest then I'm
7:23going to sort this in the descending
7:25order. So let's try to use sorted. uh
7:28and how do we want to sort this from uh
7:32from the largest number to the smallest
7:35number. So we are going to use
7:37comparator
7:39uh dot reverse order. Okay. So this will
7:43sort uh my list into descending order.
7:46And once I sort the list into the
7:48descending order, I'm going to skip the
7:50first element because I want to find the
7:52second highest number. So let's uh skip
7:55the first element. Okay, skip one and
8:00after skipping the uh first element,
8:03whatever is remaining from that list, I
8:06want to find the first element. So, how
8:07to how to find the first element? Find
8:11first. Okay. And if there is uh nothing
8:14in the list, then we are going to uh
8:17return null. Okay. So, let me try to
8:20explain the logic. First, we extracted
8:22the stream. Then, we uh did the distinct
8:25on it. So we remove the duplicate once.
8:28Then we sorted the list in the reverse
8:31order. That means our list will be
8:32sorted from highest element to the
8:35lowest element. Okay. And after sorting,
8:38we are skipping the first element
8:41because we want to find the second
8:42highest number. Okay. And then whatever
8:45is remaining from that list, we are
8:47trying to find the first element. Okay.
8:50Using find first. So let's try to take
8:53this into integer.
8:55uh second highest
8:59number
9:00equal to this right and I'm going to do
9:04uh system dot out dot print uh ln okay
9:13and the number itself the second highest
9:15uh number uh let me try to run this if
9:18I'm able to run this
9:24okay it's building
9:32H. So the second hash number is 40. If
9:35you see 10, 20, 30, 35, uh, 50 and 40.
9:39So 40 is the second highest. So this is
9:41how I'm going to find the second hash
9:43number.
9:45>> No. Okay, great. Uh, can you tell me
9:48what is functional interace in Java?
9:52>> Uh, yeah. So functional interface uh is
9:54an interface where we have only one
9:57method defined one abstract method
9:59defined and we annotate uh this uh
10:02interface with addit functional
10:03interface annotation. So if we have more
10:06than one abstract method then that is
10:09not a functional interface. So
10:11functional interface has only one and
10:12one abstract method uh which class can
10:14implement.
10:17>> Okay. Can you create one function
10:18interface and show me how to create a
10:21function interface? Yeah. So let me try
10:24to create a functional interface. I'm
10:26going to uh name this as um I print
10:32tableable. Okay. And uh
10:36uh public void print. Uh it's not
10:40necessary to add public but uh still I'm
10:43going to do public void print and I can
10:46annotate this with functional interface.
10:49Okay. So this is a functional interface.
10:50Now let's try to do one more thing.
10:52Let's try to I'll try to add one more
10:55method
10:57I printable and uh is printable.
11:03Okay, you see uh it's giving me an error
11:05because I can have only one abstract
11:07method. So if I remove this that error
11:10will be gone. So this is how I'm going
11:11to create a functional interface.
11:15>> Okay. So can I write static and default
11:18methods inside this interface? Uh yeah
11:21so writing default method and static
11:23method is possible in uh functional
11:25interfaces. The default methods are when
11:28um there are multiple classes
11:29implementing this interface and you want
11:31to introduce a method but you don't want
11:33to break the existing implementation of
11:36the classes. So that is where you write
11:38default methods and you can have a
11:41method bodies for default method and
11:43static method in the interface.
11:49Okay, great. Uh, how about Spring Boot?
11:53How much you are comfortable? If I ask
11:54you to rate ourself out of five, what
11:56would be your rating?
11:57>> Uh, yeah. So, I can give uh around four
12:00for spring boot.
12:02>> Okay. So, let us consider I have to
12:06create application employee management
12:08system where I have to perform four
12:11operations basically create, read,
12:13update and delete CL operations. Okay.
12:15So you have to tell me all the steps
12:17which will be required to perform these
12:19operations. You have to explain all the
12:21packages, all the layers, how you are
12:23going to connect with the database, what
12:25are the dependencies which will be
12:26required, how you are going to create
12:28the project, all the things which will
12:29be required to perform these four
12:31operations. Instead of four operations,
12:32you can take one operation but I need uh
12:34end to end flow. Can you explain me?
12:37>> Uh yeah. So uh I'm going to explain you.
12:40Uh the first thing is I'm going to
12:43create I'm going to go to spring.io. IO
12:45and uh try to create a spring boot
12:47project. Okay. And um uh I I'm going to
12:51download that and import it to my uh
12:53Eclipse or any ID IntelliJ Eclipse or
12:56any ID you want. So after that uh import
13:00I'm going to write the first layer that
13:02we have is a controller layer. So
13:04controller layer is essential for REST
13:07API and I'm going to annotate that uh
13:10controller layer with at the rest
13:12controller annotation. So this is where
13:14I can write methods which client can
13:16call from outside as a rest API. So I'm
13:19going to write four methods. One for um
13:22get, one for post, one for uh update and
13:25one for delete. So for get I'm going to
13:28use get mapping. For uh adding a new
13:31thing or for creating an entity I'm
13:32going to use post mapping. For updating
13:35an entity I'm going to use put mapping.
13:37And for deleting I'm going to use delete
13:39mapping. So this is my controller layer.
13:42And from this controller layer we
13:44generally call a service layer. So this
13:46service layer has all the business logic
13:49which we want to execute on that
13:51request. So service layer will uh
13:53include all the business logic or the
13:56business rules that we want to
13:57implement. And this service layer is uh
13:59annotated with additate uh service
14:02annotation. Okay. And from once you
14:05write all the business logic and uh you
14:07want to save something into the database
14:09then from service layer you call the
14:12repository layer. Okay. And this
14:13repository layer we specifically use JPA
14:16repository. Okay. So this JPA repository
14:19we call it from the service layer and it
14:21has all the operation for saving for
14:24updating and fetching the entity. Okay.
14:27And this JPA represent uh repository
14:29works on underlying entity. So what is
14:32the entity? For every table in your uh
14:35uh database in your database there is
14:38corresponding entity and we create a
14:41class with the fields for example
14:43student entity. So we have role number
14:45we have name we have uh class and we
14:49annotate this uh student entity with
14:52adderate entity annotation. Once we do
14:56all this, we also create a table in the
14:58database or we set a flag uh hbm to DDL
15:04or update. So what what that will do
15:07when you run the application uh that
15:09will create the table automatically if
15:11it does not exist in your uh database.
15:13So that is about the flow. But there is
15:15one more important thing uh in the if
15:18you want to connect to the database then
15:19you want to include u the JPA uh starter
15:25uh uh the J the JPA starter um
15:29what do we say starter uh package in
15:33your pom.xml. So that will bring all the
15:36uh required entities or all the required
15:38jars in your application and then we
15:40have to include the driver. So whatever
15:42database we are connecting to, we are
15:44connecting to MySQL database. So we need
15:46MySQL driver in your um application and
15:50after that we have to create
15:51application.properties
15:52and we have to give the location or the
15:54URL of the database, the username by
15:57which we are going to connect and the
15:59password. Okay. So this is how uh the
16:02flow is designed for CR application.
16:06>> Okay. Can you tell me the annotations
16:09which will be required for
16:11implementation of this uh student
16:14management system or employee management
16:16system?
16:17>> Okay. So annotations you want
16:19annotations.
16:21>> Uh yes annotations basic annotations
16:24which will be required for implementing
16:25this flow.
16:26>> Okay. So the first annotation is uh add
16:28the rate uh rest controller for writing
16:31my controllers. Okay. Then I need add
16:34the rate uh service add the rate
16:36repository for writing my repositories.
16:38Add the rate spring boot application for
16:41my main uh main class. Add the rate
16:43entity for my uh entities. Add the
16:46generated value for my uh primary keys.
16:50Okay. And if I'm creating some custom
16:52beans then add the red bean uh for that
16:55or at the method level. And uh if I'm
16:57creating a generic component then add
16:59the red uh component. Okay. So this and
17:02then a few more annotations um enable
17:05discovery client if I'm creating uh
17:08discovery server and so on and so forth.
17:10So these are a few annotations that I've
17:12used.
17:13>> Okay. Do you know add direct auto direct
17:17request body annotation?
17:18>> Yeah. So I know about add autoire. So at
17:22the rate autowire tries to find a bean
17:25uh in your application context and then
17:27it finds the object of that bean and
17:29assigns that object uh to the field
17:32which is autodired. Uh I don't have much
17:35idea about uh the response body request
17:38body.
17:41Okay. Okay. Fine. Not an issue.
17:45Uh let's move to the next question. So
17:47uh now we are done with the floor right
17:51now where do you deploy this
17:52application?
17:54>> Yeah. So to deploy this application uh
17:56we are using EC2 machines on AWS. So AWS
18:00is Amazon web services. We have set of
18:02dedicated machines for this uh and we
18:05deploy our application to that EC2
18:07instance.
18:11>> Okay. Can you tell me the steps which
18:13will be uh required for the deployment
18:15process? Yeah. So there are few steps
18:18which we want. Uh so the first step is
18:21we want to uh dockerize the application.
18:24Okay. So let's let's try to understand
18:25how to dockerize the application. So the
18:27first thing we want is we want Maven. So
18:30uh MBN clean install or MBN package
18:34whatever command you want to use. Uh
18:35this will create a jar out of it. Okay.
18:38But uh we want to dockerize the
18:40application first. So there is a concept
18:42of docker file. We create a docker file
18:44in the application. uh which which can
18:46be used to create the image out of your
18:49application. So how do we create the
18:50image? We use uh docker build and then
18:54uh docker build dot. So this is how we
18:56create the image out of our application.
18:59Once the image is created then we take
19:01this image and uh push the image to the
19:04docker repository using docker push.
19:07Okay. So that this image becomes
19:09available to everyone uh once it is in
19:12the into the docker repository. And
19:14whenever you want to uh use that image
19:16uh we docker pull and uh then we uh do
19:20docker run. So whenever we do docker run
19:22on an image a docker docker container is
19:25spin spin up. So you can say uh the
19:27container is started from the image.
19:29Okay. Uh so this is how we uh do it. But
19:32how how we do uh into the EC2
19:35environment, we upload the jar into the
19:38EC2 environment which is uh where we
19:40have docker installed and uh we run the
19:43uh docker run command there and it it
19:46spins up the docker container on that
19:48EC2 machine and then our application is
19:50uh deployed to the uh EC2 and we use
19:54CI/CD for building the application and
19:56transferring the jar to the EC2 machine.
19:59So this is how we uh do the deployment.
20:03No. Okay. So you must be having a
20:06different environments like t stage prod
20:10right?
20:11>> Uh yeah we have different environments
20:12in the applications. Yes.
20:16>> So do you know the profiles in spring
20:18boot?
20:19>> Yeah. So profile is uh uh an important
20:23concept in spring boot. And uh if you
20:25want to create uh uh different set of
20:28beans for different sets of environment
20:30then we can use uh profiles. Okay. So uh
20:34how it works? Okay. In the development
20:35environment sometimes we use H2 database
20:38and in the testing environment we want
20:40mocking and in the production
20:41environment we want the actual actual
20:44run and connecting to the database. So
20:45how we handle this? We handle this with
20:48the uh use of profiles. Okay. So we
20:51create different classes and we annotate
20:54them with different profiles. For
20:55example, dev
20:57uh QA
20:59and production. Okay. And how do we say
21:02which profile is active? There are
21:04various ways to say which profile is
21:06active. We can say through um uh
21:09application.properties uh spring
21:12profile.active equal to dev. So a dev
21:15profile will be activated and all the
21:17beans which are corresponding to dev
21:19profile will be uh initialized during
21:22startup. If uh we want to give uh uh
21:25this active profile through a different
21:29um way uh so we can also give through
21:31the environment variable or uh we can uh
21:35give through command line parameters. So
21:36we can activate the profile using these
21:39three methods. So this is how we use
21:41profiles in the spring boot application.
21:48Now okay great uh now you mentioned you
21:53are using microservices based
21:54architecture so what are the components
21:56you have used from microservices
21:58architecture
22:00>> yeah so we have used uh various
22:02components uh one of them is API gateway
22:05uh then we have used uh service
22:07discovery uh then uh after service or
22:10database per service uh we have used uh
22:14then uh we have also used uh CQRS in our
22:18application. Okay. So these are a few
22:20things which we have used in the
22:22application.
22:25>> Okay. What is the purpose of uh API
22:28gateway or how do you configure or which
22:30API gateway you are using in your
22:32application?
22:33>> Yeah. So our application so generally
22:36what happens in microservices
22:37environment there are various components
22:39uh various microservices we can say
22:41there are consider we have three
22:42microservices microservices A and C okay
22:47so uh if if we give address of these
22:50microservices to the client then there
22:52there is a problem because tomorrow if
22:54we want to uh increase the number of uh
22:57instances of these microservices or add
22:59new microservices then we have to give
23:01those addresses to the client
23:03But um with the introduction of API
23:06gateway this problem is resolved. What
23:07we do? All the microservices will be
23:10behind this API gateway. So any
23:12communication from outside to the
23:14microservices will go through the API
23:16gateway. So API gateway is an entry
23:19point uh to the application. Okay. So if
23:21client wants to make any request, it
23:24will make a request to the API gateway
23:26and API gateway will in turn call the
23:29microservices depending upon uh the uh
23:32URL. Okay. So this is a single entry
23:34point and uh there are few common things
23:36which we can do in API gateway. For
23:39example, we can uh do rate limiting, we
23:42can do authentication and uh
23:44authorization and we can do logging. uh
23:47we can try to do some kind of uh
23:49analysis how many requests are coming.
23:52So all this common logic uh we put in
23:54API gateway and we use Netflix zuul.
23:58This is old but we use Netflix. There
24:00are uh new versions or new things which
24:03we can use. We can use Kong, we can use
24:06uh APG or uh we can use some other
24:10frameworks. So but we are using Netflix
24:12tool for the application.
24:15No. Okay.
24:18And what about service discovery?
24:21Do you know what is meant by service
24:23discovery?
24:24>> Yeah. So service discovery um as we have
24:27many microservices and each microser can
24:30have several instances. Okay. And
24:32consider one microser wants to call or
24:35communicate with other microser. In that
24:37case what will happen? We need address
24:39of that microser. Okay. And finding the
24:41address is very difficult uh if we keep
24:43on hard coding it. So that is the reason
24:46service discovery comes into picture.
24:48How it works?
24:50We have microservices and whenever uh we
24:53uh start a microser. So during startup
24:56that microser registers itself to the
25:00service discovery and service discovery
25:03knows where that microser is running on
25:06which host it is running and on which
25:08port it is running. Okay. So service
25:10discovery is like a index where it has
25:13all the details about all the running
25:15microservices and about their instances.
25:17Okay. So uh consider this scenario. Now
25:21microser A wants to call microser B.
25:24Then what will microser A do? Microser A
25:27will go to service discovery and ask uh
25:31give me the instance or give me the
25:32address of microser B. Then service
25:35discovery will return back the address
25:37of microser B. And then this address
25:40will be used to communicate uh to
25:42establish the communication between
25:44microser A and microser B. Okay. So uh
25:47there are few um there are few libraries
25:51which we can use. Uh we can use either
25:54ureka or we can use console. These are
25:58two things which we can use. Uh so we
26:01are using ureka. Okay. And then uh there
26:04are a few annotations uh at the rate um
26:06enable discovery client if you want to
26:09enable discovery server if you want to
26:11disco enable the server side of the uh
26:14we want to say that this is the server
26:15and this is the uh client. So this is
26:18how uh service discovery works.
26:26No. Okay. Okay. Fine. and how services
26:29communicates with each other.
26:32>> Uh so services communicate with each
26:34other. Uh there are two types of
26:36communication. One is synchronous
26:38communication and one is a asynchronous
26:39communication. So synchronous
26:41communication is either through rest
26:43template or through fine client and
26:46asynchronous communication is either
26:48through Kafka or message MQ rabbit MQ.
26:52So through one of the message broker or
26:54event broker. So uh let's try to
26:56understand about synchronous
26:58communication. So uh we can do
27:00synchronous communication through rest
27:02template rest template exchange method
27:05and we can uh specify the uh type of
27:08method we want to call either post, get,
27:11put or delete. Okay. But there is one
27:13better way of doing it through fine
27:15client. So find client is where we
27:17create an interface uh and uh we
27:20annotate that interface and we say about
27:23the service name that we are referring
27:24to and we give one method and this
27:27method will contain all the parameters
27:29that we want to pass to the uh rest API
27:32and the return type. Okay. So once we
27:36write the interface now if you want to
27:38call the interface we directly call uh
27:39the method of that interface and that
27:41underlying service call is automatically
27:44made. So that is how we do uh call uh
27:48the service through fine client. And if
27:50you want to do a a synchronous
27:52communication then we use either Kafka
27:54or uh rabbit MQ and uh uh then the uh
27:58service we are calling to subscribe to
28:01the uh Kafka topic and fetch the
28:05messages or fetch the events uh from the
28:09Kafka. So that is how the communication
28:11happens.
28:13>> No. Okay. Good. So, I'm done from my
28:16side. Do you have any questions for me?
28:18>> Uh, no. Thank you. Thanks for your time.
28:22>> Yeah. Thank you. Thanks. Bye-bye.
28:23>> Thanks. Bye-bye.

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