RESTFul Services

 REST stands for 'Representational State Transfer'.

-> RESTFul services are used to develop Distributed Applications with Intereoperability.

-> If one application is communicating with another application then those are called as 'Distributed Apps'.

-> Intereoperability means irrespective of the platform and language applications can communicate.

java app <-----------> .Net app

.Net app <----------> Python app

Python app <---------> Java App

-> Distributed applications are used for B 2 B communications.

-> B2B means Business to Business Communication.

-> Distributed Application will re-use services of one application in another application.

-> RESTful Services are providing 'Intereoperability'.

-> Two Actors will be involved in Distributed Applications development.

1) Provider 

2) Consumer

-> The application which is providing business services is called as Provider Application.

-> The application which is accessing business services is called as Consumer Application.

Note: One provider application can have multiple consumer applications.

-> Provider and Consumer will communicate using HTTP as a mediator

-> Provider and Consumer will exchange the data in Text / XML / JSON format

Note: In Industry we will use JSON format to exchange data from one application to another application

-> To start our journey with RESTFul services development we should be good in below areas

1) HTTP Protocol (Methods, Status Codes, Req structure & Res Structure)

2) XML and JAX-B Api

3) JSON and Jackson Api

What is HTTP ?

###########

-> HTTP stands for Hyper Text Transfer Protocol.

-> It acts as a mediator between client & server  ( Consumer & Provider ).

-> Consumer application will send HTTP Req to Provider application.

-> Provider application will process the request and it will send HTTP response to Consumer.

HTTP Methods

##########

-> HTTP methods are used to send request from Consumer application to Provider application.

-> HTTP method will represent what type of operation  client / consumer wants to perform with Provider.

a) GET

b) POST

c) PUT

d) DELETE

-> GET request is used to retrieve data from Server / Provider application.

-> GET request will not have body to send data in the request.

-> To send any data using GET request then we will use Path Params & Query Params.

Note: Path Params & Query Params data will be displayed in the URL.

Note: It is not recommended to send sensitive / secret data using Path Params & Query Params.

-> GET request is Idempotent (means if you send same GET request for multiple times also nothing will change at server).

-> POST request is used to create a new record at server .

-> When consumer wants to send huge data/ sensitive data then Consumer will use POST request

-> POST request contains request body

-> POST request is Non-Idempotent

Note: In POST request we can send data in URL and in Request Body.

Note: Request Body is the recommended approach to send sensitive data to server

-> PUT request is used to update a record at server.

-> When consumer wants to update a record at then consumer will send PUT request to Provider.

-> PUT request contains request body.

-> PUT request is Idempotent.

Note: In PUT request we can send data in URL and in Request Body.

Note: Request Body is the recommended approach to send sensitive data to server.

-> DELETE request is used to delete a record at server.

-> DELETE request contains request body.

-> DELETE request is Idempotent.

Note: In DELETE request we can send data in URL and in Request Body.

HTTP Request Structure

#################

1) Intial Request Line  ( HTTP method + URL )

2) Request Headers ( key-value )

3) Blank Line to seperate Header & Body

4) Request Body (Request Payload)

HTTP Response Structure

##################

1) Initial Response line (Protocl Version + Status Code + Status msg)

2) Response Headers (Key-value)

3) Blank Line to seperate Header & Body

4) Response Body (Response Payload)

HTTP Status Codes

#############

-> HTTP Status codes will represent how the request process by server / provider.

1xx (100 - 199)  ---> INFO

2xx  (200 - 299)  ---> OK (success)

3xx  (300 - 399)  ---> Redirect

4xx (400 - 499) ---> Client Error

5xx (500 - 599) ---> Server Error