Authority to spring to create objects
@Component -- for DAO layer works fine but readability/visibility wise its bad
@Service -- Service layer
@Controller -- Business Logic
@Repository -- we use this annotation to DAO layer -- Benifits this helps to handle persistance level exceptions that spring provides
DataAccessException is the root class which spring provides for handling exceptions
@PostConstruct
Called first during initialisation(Creating data base connections)
@Predestroy
called B4 the container is destroyed and bean is out of container(Close all the DB connections/clean up work)
Rest client
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Rest template --- Client to consume the data (make a call to get , put,post)
getForEntity and getForObject -- methods belong to resttemplate
getForObject -- returns object
getForEntity -- returns header,body , what ever we want
Exchange method - same purpose belongs to rest template
While wrting an API , what are the advantages of returning entity??
We can send http status and body and headers
For delete API, what kinld of status code you will return
204 /200
Time out when ever we are going for rest template?
Basically when connecting to server connections are made with threads.
Thread is blocked if the connection is not establised and then another user tries and another thread is blocked .
So just to avoid that time out is needed so that thread is released
Can we have many threads inside the server?
yes
Server time out -- connection not established
Read time out -- connection established but not able to read some data
Versioning in rest
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Adding a new functionality to the API and user should use the new one
Can be defined using request parameters and can be mentioned in headers
URi also it can be defined
How authentication in rest web services and how we make rest web servives secure?
Security configuration class which will be extending securityconfigurationAdapter class
Hitting a request goes to authentication filter which will give us authentication object and this object is paased to authentication builder which will provide proper authentication provider which will validate this object.
Some of the authentication providers are DAO Authentication Provider, we can define even our own
Authentication provider internally passes back to builder which will pass to security holder So next time when user logs in object will be checked by the security holder and user will be allowed to sign in
Header we pass the tokens , like jwt tokens which will be used for authentication and server will validate it.These are stateless i.e server wont store any inf and client will alwyas send relavant information via header.
Bearer is written in jwt token??Means syou are the owner .JWT used for authorisation .Once we give uname and pwd we get authorisation token which weill again be sending to the server which will in turn verify the token
In basic authentication where we give username and pwd where we can use base64 encoded
Content Negotiation?
What kinld of content API should accept/produce.It can be achieved using MediaType
Cross Cutting Concerns in spring?And do you implement that?
Belongs to spring AOP used for logging purpose .We want to log after the particular method or so..
Monitoring , secutity.after one method we have to perform security then it can be done
In micro services suppose we want to implement logging,tracing??Where will be implementing these?
At gateway level we ill be doing
Custom validators in spring can be created by implementing validator class
There is a method over ride and write the logic
Core Java
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We have define ArrayList as Size 2 and then add 3 elements ..Will third elemt be added?
Yes it will be added as the arraylist dynamicallu grows in size
1 million string objects to array list added with out specifying size and in a for loop you are adding then it takes total og 613 ms to complete else if you specify size then it will run in 193 ms.
Internally it regrows and calls Arrays.Copyof which will create a new Array and then copy all the elements, so suppose if we have lot of elements and if its size is specified then it allocates so much and then no copy of array or new array creation is needed
Fail fast and fail safe collections
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Iterators
fail fast used by arraylist/ linked list --During itration if we try to add /modify it gives concurrent modification exception
Fail safe : Thread safe ..CopyOnWriteArrayList , Concurrent hash map ...Modification during iteration it works perfectly fine
Fail safe is going to consume more memory , modification operations will be perfomred on a copy of collections not on the orinal collections
Arrays.asList will give us an unmodifyable list , which we cannoot alter
SingleTon Design pattern
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Object for the class can be created only one(For the entire run time)
Scope Single ton in spring means one bean per container(one per application context)
