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3-7 Years Interview Experience | Java | Spring Boot | Microservices | SQL | Nagarro — Transcript

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0:01okay so in your spring boot
0:05application how do you manage the code
0:08coverage so what steps do you follow and
0:12what is code
0:14coverage yeah so whenever we write the
0:17test cases right so we see that how much
0:22the portion of the code is covered under
0:25that so uh code coverage is nothing but
0:30it shows the percentage of the code
0:33which is covered using the test case we
0:36have written so basically it reduces the
0:40chances of having bugs in the
0:43application by covering the maximum code
0:47so in my current organization we follow
0:51minimum 90% of the uh code coverage MH
0:55so in all the uh code check-ins we do so
1:00before that we make sure that the 90% of
1:04the code is uh covered M so uh for that
1:08we use uh
1:10eemma so that is the STS tool which we
1:14can integrate with the STS and it
1:17basically whatever the code is covered
1:19so that will come into green and the
1:22portion is not covered will be in the uh
1:25red and it will be yellow if it is
1:28partially covered so so under the hood
1:30it uses Joko this is how we follow the
1:34code coverage in our uh spring boot
1:38application okay okay okay so how do you
1:43perform testing in your spring boot
1:46application yeah so so the testing can
1:50be of many types it can be either you
1:53need testing it can be integration
1:56testing into in testing or it can be
1:59perform testing so whenever we do the
2:03unit testing in that case uh like we
2:06test the methods and classes like uh
2:11individually we have three layers in our
2:14spring boot application our controller
2:17uh service and repository layer so we
2:21write the separate uh test cases for
2:24these three and suppose uh we are
2:27testing the controller and uh that is
2:30calling the service from there right so
2:35we can uh mock that service so since we
2:38also do the unit testing for that
2:40service class as well so uh wherever it
2:43is calling uh another service or
2:48any um uh API call or any other calls
2:53are happening so those calls we can mock
2:56it and we can write the standard return
2:58of it and that return return we can
3:01assume that okay that actual uh actual
3:04call is being made and that is the
3:05response based on that response we can
3:08further proceed so that is how we do the
3:11unit testing so in integration testing
3:13we test like uh how different units or
3:18components they work together when we
3:20combine them so when they interact with
3:22each other then how they perform so that
3:25is what we say integration testing then
3:27in case of into end testing we test the
3:30whole application as a component and we
3:33see if that does not have any issue then
3:37we also do performance testing so we
3:40check whenever the huge load is there on
3:43the application then how it
3:45performs so that is also there so yeah
3:49this is how we do the testing okay so
3:53how you do performance testing so
3:55performance testing usually we don't do
3:59and test
4:00perform that testing so they uh normally
4:04use uh J meter and all so they do like
4:08load testing and stress testing all that
4:10they do but uh I have not worked much on
4:14it okay so how do you perform logging in
4:17your
4:18application yeah logging we perform
4:22using uh slf
4:254J so that we use for logging and uh
4:30uh we use
4:32lombok so using that uh we don't have
4:36to uh write so that can remove the bar
4:40plate code and we can simply use
4:43annotation uh like at the rate of uh
4:46self 4J and then simply we can give uh
4:50log. debug or whatever we want so we can
4:54simply give the logging related
4:56properties in uh application Properties
5:00or EML file so whatever the loging level
5:04is there that we can Define there and
5:06also whatever the log output format will
5:09be there so like with date month timings
5:13whatever so all those things we can
5:15mention in the properties orl file so
5:19yeah so that is how we do logging okay
5:22so how do you perform centralized
5:25logging in
5:27microservices yeah we use uh
5:30uh elk stack for
5:33that and for visualization we also use
5:38kibana okay so what are the different
5:40loging levels are
5:42there yeah so we have debug
5:46info uh warn error Trace fatle so yeah
5:54okay okay okay how do you maintain code
5:58quality in your project so what are the
6:00steps you follow yeah for code
6:03quality uh so we have a test cases right
6:08so we see the uh the coverage of that so
6:12that is one way then we have uh uh sonar
6:17lint sonar Cube so sonar lint basically
6:20we can integrate with our ID and we can
6:24get the real time feedback on if any
6:27code is uh like not written properly so
6:32any proper syntax we have not given and
6:34all right so those things we can find
6:38out so sonar CU we can use for that so
6:43it it
6:45basically uh connects with the central
6:48uh sonar Cube server and based on the
6:51rules it validates the whatever the code
6:53is written and uh it uh applies all the
6:58rules to to the across the projects and
7:02across the all the team members also we
7:05review uh each other's code yeah so
7:08these are the various uh okay what are
7:11the design patterns you follow in
7:14microservices yeah there are various
7:17design patterns API Gateway pattern is
7:19there uh circuit break breaker pattern
7:22is there so whenever uh we have uh uh
7:27any services not reach table or
7:30something like that so we write the
7:31fallback method for that then we have a
7:35service Discovery pattern is there so
7:38this helps microsof dynamically discover
7:40each other so they using the
7:45registry and then we have Saga design
7:48pattern so this manages distributed
7:51transactions across the micro services
7:53using the uh series of local
7:56transactions with uh uh compan set
7:59actions so yeah these are the design
8:02patterns are there okay how do you
8:04resolve version conflict in m in a
8:07spring boot yeah we resolve version
8:11conflict
8:12using uh we have a command I think MH uh
8:16M dependency then tree so that we used
8:21to visualize the entire dependency tree
8:24and
8:25identify uh where the conflict is so
8:29basically this command shows us uh which
8:31dependencies are pulling in Conflict
8:33version that is one way also if the
8:37dependency is brought in
8:39transitively so maybe uh by any other
8:44dependency then we can explicitly Define
8:47the version of that dependency to
8:51resolve uh if we have to downgrade or
8:54upgrade that so we can do that so it
8:58will override the uh by default uh
9:01version apart from that we can also use
9:03exclusions if we don't want any uh like
9:08interdependency uh like if any
9:11dependency is downloading other
9:13dependency and we don't want that then
9:15we can use exclusions for that as well
9:19so yeah so these are the ways okay what
9:22is the difference between war and
9:25embedded
9:26containers yeah War basically contains
9:30the one application it does not have the
9:36external server like Tom cat or Jos
9:40whatever we use but embedded container
9:44will have the embedded server so default
9:48will be Tomcat so we don't have to
9:51explicitly download server and deploy
9:54the application over there so this is
9:57the main difference between uh dig to
9:59what is a spring boot
10:01profiles yeah spring boot profiles are a
10:05way to segregate parts of our
10:09application uh and make it available
10:11only in certain environments like we can
10:15have multiple environments like uh we
10:18can have Dev environment we can have QA
10:20we can have production right so uh
10:24sometimes we want certain settings to or
10:28certain configurations to work only with
10:31the uh specific environment so profiles
10:35comes into picture and we use profiles
10:38for this purpose so we can have uh
10:41separate Properties or EML files for
10:45different uh profiles like maybe
10:49application uh dev. properties
10:52application test. properties like that
10:55and uh whatever the profiles will will
10:59be set if it is profile is dev then
11:02application dev. properties will be
11:04picked up there are some common
11:07properties are also there so that can be
11:10picked from the application properties
11:12only but those which are a specific to
11:16the dev or test environment so apart
11:18from those application properties those
11:21application Dev properties also will be
11:23picked if the profile is Dev to access
11:27the active profiles I think think uh we
11:31have one environment object so that we
11:34can uh inject to the class wherever we
11:38want that so with that environment. get
11:43active profiles will give us the uh
11:46active
11:47profile so yeah okay what are the
11:51advantages and this advantages of spring
11:55boot yeah there are various advantages
11:58of a spring boot
12:00so uh it it it has removed lots of
12:04configuration Parts which we used to do
12:07in Spring
12:10so um so spring boot provides many Auto
12:14configurations so that allows basically
12:17the developers to focus only on to
12:20writing the
12:22Logics uh so and not focusing on the
12:25configuration part and also it provides
12:29the embedded server so we don't have to
12:33explicitly uh add go and add the servers
12:36right so we have Tom cut by default and
12:40then in Spring we had lots of XML
12:43configurations and all that is not
12:45required uh anymore in Spring boot right
12:48so so all the bu plate codes has been
12:52REM spring also we can achieve without
12:55writing the XML right we don't have to
12:58write the XML yeah yeah uh you are right
13:02so basically from the spring 3.0 onwards
13:06the that framework introduced the uh
13:10capability to use a Java based
13:12configurations with uh add
13:14configurations and add dat to Bean
13:16annotations so user no need to uh use
13:22XML based configuration
13:24anymore but in Spring boot uh from the
13:28very beginning itself if there is
13:29nothing uh we have to do with the xmls
13:33so the configuration part is uh has been
13:37automated so spring boot starter
13:41dependencies uh that package the
13:43commonly used libraries together so we
13:46don't have to worry about the versions
13:49and
13:50compatibility of the different libraries
13:52with each other because this comes in a
13:55bundle
13:56so yeah so these are the uh advantages
14:00are
14:01there okay and
14:05disadvantages yeah disadvantages are
14:08like um whenever we have a very a small
14:12application so we should not go for the
14:17uh spring Boot and all we can go with
14:20the uh simple monolithic
14:23application so I mean for simple
14:27applications or microservices
14:29so spring boot is kind of maybe
14:34unnecessary so we can go for other
14:38lightweight Frameworks in that
14:40case and uh
14:43also sometimes uh the auto configuration
14:46behavior in a spring
14:48boot uh we Face uh we may face the
14:53conflicts so we have to uh debug it and
14:57see like which version of which jar has
15:00been downloaded and all so we have to
15:03resolve it right and also we have uh
15:07various microservices right so suppose
15:11uh um whatever
15:15the uh
15:18data we have in one of the micros
15:22service so we have to make sure that all
15:25the microservices are in sync with each
15:27other so sometimes any of the
15:30microservice is not working or it is
15:33down or its database is not getting
15:35updated we have to make sure when it is
15:38up it should be in sync so these are the
15:41challenges are also there so yeah these
15:43are the uh disadvantages are there okay
15:47okay what is the difference between rest
15:50controller and
15:52controller yeah rest controller is
15:54nothing but controller with response
15:57body so that is what we say rest
16:00controller we use uh
16:03controller uh when we have the uh MBC
16:07architecture we are working with and the
16:10response we want to uh return to uh JSP
16:16page or similar so in that case we work
16:20we go for
16:22controller but uh if we have restful web
16:26service so in that case we use rest
16:29controller so we don't have to
16:31explicitly write uh at rate of response
16:35body in this case so whenever we have to
16:38return model and view object so in that
16:40case we use uh add controller but
16:43whenever it is uh uh restful uh web
16:47service in that case we go go for the
16:50add dat of rest controller okay what is
16:52the difference between get mapping and
16:55request mapping yeah request mapping is
16:59like kind of more generic way of uh
17:03getting the mapping so we can have get
17:07post put delete all that with along with
17:10the request
17:11mapping so we can use as per our but get
17:16mapping is like more specialized to
17:19getting the data so request mapping and
17:22Method equal to get is similar to get
17:24mapping so get mapping is more
17:27convenient to use whenever we have the
17:30get request also request mapping we can
17:33use for broader use cases like uh uh we
17:37can specify the request parameters
17:40headers media types and all that also
17:44this consumes and produces also we can
17:46give so request mapping can be used for
17:49all but uh we have been provided with
17:53get mapping post mapping put mapping
17:56delete mapping so we have any speci
17:58specific kind of mapping we want to do
18:01so we can go with these okay what are
18:04the common security
18:06vulnerabilities found in web
18:10applications uh there are many of them
18:13so one is the injection attack then we
18:17have cross site scripting uh not using
18:20of https using HTTP instead and trying
18:23to use uh directly uh accessing the
18:27sensitive resources maybe some files or
18:30database without any proper
18:32authentication or
18:34authorization so to have these uh we
18:38should do proper authentication and
18:40authorization so whatever the inputs are
18:42coming from the users we should have the
18:46proper validation of those inputs so
18:49that they can not run the any kind of
18:53scripting and all to our application and
18:57also uh we should not allow from the
19:00cross site so we have the uh uh
19:07configuration uh using which we can
19:10disable this uh cross site uh access of
19:15the application also we should try
19:17avoiding and secure apis apis that do
19:21not Implement proper authentication
19:24validation or encryption so that can
19:27also exploit
19:29that can also be exploited by attackers
19:31to access or uh manipulate any sensitive
19:34data so yeah so these are the
19:37vulnerabilities we have how do you
19:40handle complex queries using spring data
19:44jpa so spring data jpa basically gives
19:48uh the it has whole lots of
19:50documentation in which we have uh let's
19:53say very complex query so such as uh
19:57let's say some employee which has salary
20:00or some greater than some amount so we
20:04have inbuilt method so find uh employees
20:08with salary greater than we can use for
20:11that so uh we don't have to write the
20:14whole query uh Native query in this case
20:17but wherever the uh jpql so this is
20:21basically called the jpql so which is
20:25provided by uh spring data jpa so uh
20:29wherever this JP jpql is not allowed or
20:34uh sorry jpql is uh we cannot write
20:38suppose we cannot write that then in
20:40that case we can also go with the native
20:44queries so so that we can write using uh
20:48at the rate of query and there we can
20:50give value and there we can write the
20:53whole query right so that way we can
20:56write the uh native queries we can also
21:00write the procedures if required and
21:04that procedure we can directly call from
21:06our repository class apart from that we
21:10can also use a
21:11specifications so for dynamic and
21:14complex queries we can use a
21:16specification API uh provided by Spring
21:20data jpa so that allows us to build
21:23queries programmatically using criteria
21:26API so we can use criteria builder for
21:29that and then we can use that okay so
21:32suppose you have a huge data in your
21:35database and you have to se all this
21:39data to
21:40UI so what approach you
21:43follow can you explain yeah so whenever
21:47we have a huge data in that case uh if
21:52uh we have to S it to some UI so we
21:55don't s all of them all together
21:59so we can use pagin basically MH so um
22:03at a time let's say if the UI has the
22:06capability to S like 10 items so we will
22:11uh share only 10 items to the uh UI
22:15whatever the request is passed from the
22:18UI so that will have the information of
22:22the offset and limit like limit means
22:27like how many items it wants and offset
22:29me from which like suppose already we
22:31are on the third page so maybe 31st to
22:3640th item we would like to process and
22:39show to UI MH so uh limit will be 10 and
22:43offset will be uh like
22:4631st okay so we can show uh like 10 or
22:51nine items uh whatever it
22:54is so for that uh we have a payable
22:58object
22:59so we prepare the pageable object from
23:02the uh whatever the request has come and
23:06that response will basically can be used
23:08by UI to show the data okay okay okay so
23:14what is multi- threading
23:16multithreading is a
23:19concept that allows multiple threads to
23:22run concurrently uh within a single
23:24process so whenever we have multicore
23:28process processors so we can leverage
23:31the processor uh capability so basically
23:34it utilizes a CPU uh
23:38resources efficiently by performing uh
23:41multiple operations
23:43simultaneously so each thread can
23:45execute a part of the program
23:48independently so that enables the
23:51parallel execution and improves the
23:54performance of application especially on
23:57the multicore for
23:59processors okay so what are the
24:01different states of threat in Java yeah
24:05we have a new runable blocked
24:09waiting and
24:13terminated yeah so these are the states
24:15we have okay okay so what are the
24:19various ways you can create multi
24:22threading in
24:23Java yeah there are various ways one is
24:27uh we can use extends
24:29keyword and um uh we can say with any
24:33class we can extend thread so we can
24:36create new thread by extending the
24:37thread class and we can override its run
24:41method so that is one way then we can
24:46also uh create a thread by implementing
24:49the renable interface and we can pass an
24:53instance of the class to a uh thread
24:57object
24:58so this is another way then we have the
25:02uh executor framework so the executor
25:06framework provides
25:08a uh high level replacement for managing
25:11threats so that allows us to create a
25:15thread pool and manage task execution uh
25:18more
25:19efficiently so we have executor service
25:22for that so yeah so these are the ways
25:25uh we can create the thread okay what is
25:27Java memory model yeah the Java memory
25:30model defines how threads interact
25:34through memory and uh how changes made
25:38by one thread become visible to another
25:41so it specifies rules for reading and
25:44writing variables handling threads
25:47synchronization and providing uh
25:50guarantees on visibility ordering and
25:53atomicity okay what are the different
25:56types of exception in Java
25:59yeah we can categorize the exceptions in
26:02mostly uh three parts actually one is
26:05checked then unchecked and then
26:08errors so uh checked exceptions are
26:12those which must be caught or declared
26:15in the method
26:17signature like uh we have IU exception
26:20SQL exception or file not found
26:23exception right so whenever we write the
26:26code so there itself uh the compiler
26:30suggest
26:32to uh I mean that enforce that will
26:35enforce us to handle it if we are not
26:38writing it so we write in the exception
26:42block like IU exception X exception and
26:44then we further we can continue our code
26:47then coming to unchecked exception so
26:50unchecked exception include uh runtime
26:54exception that do not need to be
26:56explicitly handled so so some exceptions
27:00like null pointer array out out of bond
27:03exception then current concurrent
27:06modification exception so all these
27:08comes under uh unchecked exception so
27:12this is basically going to happen at
27:13runtime so we cannot predict that in
27:17advance and then uh uh we have errors so
27:22the errors are the kind of we can say uh
27:27which we cannot handle at all so this is
27:31a this is an irrecoverable situation so
27:35which cannot be handled so and this we
27:38can say very serious problems and
27:40application uh cannot catch it so like
27:43out of memory error is there stack
27:45Overflow is there is there yeah so these
27:48are the various types of uh exceptions
27:51are there okay can you explain the
27:54difference between string string Builder
27:57and string buffer yeah string is uh
28:02immutable and string Builder and string
28:05buffer is
28:06mutable
28:07so uh basically um string once created
28:13its value cannot be changed in case of a
28:16string but in a string
28:18Builder uh its values can be changed so
28:21that is why it is
28:23mutable and uh string Builder is
28:26designed for single threaded
28:28uh uh use and is faster than a string
28:32buffer and string buffer is thread safe
28:36it is
28:37synchronized and it makes it suitable
28:40for multi- trading environments so it is
28:43uh slower than a string
28:45Builder so yeah okay what is the purpose
28:48of transient keyword in Java yeah the
28:51transient keyword is used to include the
28:55that a field should not be serialized
28:58when an object is serialized transient
29:01fields are ignored so whatever the
29:04suppose we have a bean class and in that
29:07bean class we have multiple
29:10properties right so out of those
29:14properties in if any of the properties
29:16have transient keyword so that won't be
29:20cized so that field will be ignored and
29:24their values are not included in the
29:27cized presentation okay what is the
29:30difference between hashmap and
29:32concurrent hashmap so hashmap is not
29:36thread safe and it can lead to uh
29:40inconsistent data in a multi-threaded
29:43environment uh while concurrent has map
29:46is designed for uh concurrent access and
29:49allows multiple threats to read and
29:51write
29:52simultaneously without locking the
29:54entire map so the uh locking is uh done
29:58only on on the particular bucket not on
30:02the entire U map then concurrent has
30:06map uh performs better uh in a
30:10concurrent environment uh because it's
30:13uh uh because uh it uses segment locking
30:17so that allows concurrent rights so
30:21concurrently writing is possible in this
30:24case and then uh uh in hashmap allows
30:28one null key and multiple null values
30:31while concurrent hashmap does not allow
30:33null keys or values okay what are memory
30:37leaks and how you can prevent them yeah
30:42memory leak in Java occurs when objects
30:44are no longer used but are still being
30:47referenced so this prevents the garbage
30:53collector from reclaiming the memory so
30:57the common causes includes static uh
31:00references or any long lived objects or
31:04improperly managed collections or we
31:07have not closed the connections so those
31:09things so we can prevent uh using uh
31:14weak uh
31:15references so uh we can use weak hmap
31:18for objects that can be uh garbage
31:21collected uh when not in use and uh we
31:26can avoid a static references uh unless
31:29it is
31:30necessary and also we can monitor memory
31:33uh uses uh with uh profiling tools like
31:38visual VM or J
31:40profiler so yeah okay what is the
31:44optional class in Java
31:478 yeah the optional class in Java 8 has
31:51been introduced to handle uh null
31:53pointer exception so earlier uh before
31:56Java 8 we used to write the manually we
32:00used to write the uh logic to handle
32:04null so maybe in case of string we used
32:07to use sing utils
32:10Dot and all and uh if or in case of
32:13other objects equal to equal to null so
32:16all that we used to write but now from
32:18java 8 onwards we don't have to write
32:20that so it helps us to prevent null
32:24pointer exception and represents a value
32:27that
32:28could be absent so we can use it when a
32:32method might not return a value so let's
32:36say we have find by ID and it is not
32:38returning a value may not return the
32:40value so we can use optional in that
32:42case as a uh return type of that and
32:46then to express the intention of uh
32:51possibly absent values also we can use
32:53it and to chain method calls safely
32:58without null checks we can use this so
33:02yeah okay what is Method referencing in
33:05Java 8 yeah method reference in Java 8
33:09are we can say it is s hand of Lambda
33:13expression to call a method so they
33:17provide a way to reference a method
33:19without invoking it making the code
33:21cleaner and more readable so we can use
33:25a double colon for that so any class has
33:30any suppose a static method so uh uh we
33:35can use double colon uh in front of that
33:38class and we can give the method name
33:41and like this way we can fetch that so
33:44yeah okay what is the difference between
33:46join and a subquery in which scenario
33:50you will prefer to use join and in which
33:53scenario you will prefer to use subquery
33:56so they used to combine data from
33:57multiple tables so join is used to
34:00combine uh Row from two or more tables
34:03so we can have inner join uh then we
34:06have left join right join then full join
34:09so these are the types of join we have
34:13so we will have the uh uh the relatable
34:18column between the tables and based on
34:21those columns we can perform the join
34:24operation then uh coming to subquery so
34:27subquery is a query nested within
34:32another query so we for example we have
34:37uh some star from something and then in
34:41we can write and then we can have
34:42another query so that query we say as a
34:46subquery so it can return a single value
34:49a list of values or a complete table
34:52itself so subquery can be used in select
34:56or from or where or having Clauses so
34:59normally we try not to use subqueries if
35:03it possible because uh they are normally
35:08less efficient than the joints so mostly
35:11we try to use joints only wherever
35:13possible okay what is the difference
35:15between having and wear clause in esql
35:19yeah the having and wear Clause both
35:22used to filter records in SQL but they
35:26are little bit different
35:28uh based on the scenarios like uh where
35:32Clause is used to filter records before
35:34any groupings are
35:36made uh but having Clause is used to
35:40filter records after the agregation so
35:44it basically works on the aggregated
35:47data like uh it is used with uh uh Group
35:52by uh to filter groups based on the
35:55aggregated function like some count or
35:58average so we Clause uh basically used
36:01to filter records based on the specific
36:04conditions on columns so we can write
36:07like select a start from employee where
36:09salary uh greater than uh some amount
36:13and whenever we have to uh use the
36:16having Clause so that we use we can use
36:20with the group by like let's say select
36:24some ID and then count of a star
36:27and that from uh employee Group by
36:32employee ID having count of a star
36:34greater than 10 so in this case we can
36:37use the having
36:39Clause so yeah okay okay

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