Web Services-Web API Beginner Tutorial

Topics included/covered

Introduction to Web Service
- 1.1. What is Web Service?
- 1.2. Advantages of Web Service
- 1.3. Web service Architecture
- 1.4. Web Service Features
- 1.5. How Web Service works?
- 1.6. Types of Web Services
- 1.7. Components of Web Services
Introduction to SOAP Web Services
- 2.1. What are SOAP Web Services?
- 2.2. SOAP Web Services Specifications/standards
- 2.3. Disadvantages of SOAP Web Services
Introduction to REST Web Services
- 3.1. What is REST API?
- 3.2. What are RESTful Web Services?
- 3.3. Principles of REST API
- 3.4. Features of REST API
- 3.5. Method s of REST API
- 3.6. Advantages of REST API
SOAP Vs REST
- 4.1. SOAP vs REST Web Services

1 Introduction to Web Service

1.1. What is Web Service?

Web Service is a standardized way or medium for communication between client and server applications to exchange data on the World Wide Web

Web Services provides a standard protocol/format and helps to communicate between two different application and make sure all things happening smooth-proper and successful

Web Services provide a common platform that allows multiple applications built on various programming languages to communicate and have the ability to communicate with each other

Scenario: Java programming language can interact with PHP/ASP and .Net, JavaScript by using Web Services

Example:

Hotel/Restaurant

The waiter is a mediator (Act as a Web Service/Bridge) between two application ie. customer and kitchen

Flight Booking websites

All airlines companies (Air India, Indigo, Jet Airways) have exposed their Web Service through an API,
All agents and different flight booking websites like makemytrip.com, cleartrip.com, etc. access an API and populate data/status accordingly

1.2. Advantages of Web Service

1.2. Why Web Service

1.2. Benefits of Web Service

Here are some of the benefits and advantages of using Web Services:

Platform independent communication: Web Service provides platform/Operating System independent communication
Applications can Exchange Data: Through Web Services, different applications/implementations can talk to each other and exchange data/information
Exposing Business Functionality/existing functions on the network so other applications can use the functionality of your program
Interoperability amongst applications (Web services allow various applications to talk/share data and services among themselves)
Web Services use standardized industry protocol for the communication which everybody understands
Reduction in cost of communication/Low-Cost Communication

1.3. Web Service Architecture

The Web Services architecture consists of three distinct roles as given below:

Service Provider: The provider creates/implements the Web Service and makes it available on the internet to other client application who want to use it
Service Requestor: Requestor is a consumer/client application that utilizes an existing web service by sending an XML request. The client application can be a .Net, Java, JavaScript or other language application which looks some sort of functionality via a web service
Service Registry/Broker: The registry is a logically centralized directory of services where developers can publish new services or find existing ones ( like centralized clearinghouse or brokerage house for companies and their services). The broker is an application provides access to the UDDI (Universal Description, Discovery, and Integration) which enables the client application to locate the web service

1.4. Web Service Features

1.4. Web Service Characteristics

Web Services must have the following special behavioral features/characteristics:

XML-Based: Web Services uses XML to represent the data
Loosely Coupled: Client/Consumer and the web service are not fixed/bound/tied to each other directly
Ability to Synchronous or Asynchronous functionality: Synchronicity specifies the binding of the client to the execution of the function, Asynchronous clients fetch their result at a later point in time, while synchronous clients receive their effect when the service has completed
Supports Remote Procedure Calls(RPCs): Web services allow consumers to invoke procedures, functions, and methods on remote objects using an XML-based protocol. Remote systems expose input and output framework that a web service must support
Supports Document Exchange: One of the essential benefits of XML is its generic way of representing not only data but also complex documents, it can be as simple as representing a current address, or they can be as complex as representing an entire book or Request for Quotation (RFQ)
Coarse-Grained: Object-oriented technologies such as Java expose their functions through individual methods or coarse-grained services that approach the right amount of business logic

1.5. How Web Service works?

                  Client                          Server
                  sends REQUEST ->                <- gives RESPONSE
                  (Consume Services)              (Provide various services to use) 
                                [ ueses Medium - HTTP/INTERNET                 
                                Format - XML/JSON ]

The client program bundle information into a SOAP message which is sent to web service as the body of an HTTP POST request
The web service unpacks the SOAP request and converts to a command that application can understand and gives a response with required data/information
The web service packages response into another SOAP message and sends back to the client program
The client program unpacks the SOAP message and starts with the necessary process

1.6. Types of Web Services

1.6. Popular Web Services

There are mainly/major two ways of implementing Web Services, popular Web Services Protocols are:

SOAP Web Services: (Simple Object Access Protocol): [ Medium: HTTP (post), Format: XML ]
REST Web Services: (REpresentational State Transfer): [ Medium: HTTP (get, post, put, delete), Format: XML/JSON/Text ]

1.7. Components of Web Services

1.7. Components of Web Services: SOAP, WSDL, and UDDI

While using/consuming web services, Service Consumer (client) needs to know:

What the Web Service is?
What are the different services available?
What are the various components of Web Service?
What's the structure and description of Web Service?
What are the different/various functionalities/return types/parameters with Web Service?
What are the request and response parameters?
How to call, use and consume the Web Service?

All the standard Web Services work using the following components:

SOAP (Simple Object Access Protocol):
- SOAP is a W3C recommendation for communication between applications and format for sending messages
- SOAP is an XML-based protocol for accessing web services and for exchanging information between computers/applications
- SOAP is simple and extensible also a platform, language-independent
WSDL (Web Services Description Language):
- WSDL is an XML-based language for describing web services and how to access them
- It's an XML based interface for the Web Services which describe all the attributes and functionalities, method name/parameter of the Web Service published by all Service Providers
- WSDL is the standard format for describing a web service which UDDI uses
UDDI (Universal Description, Discovery, and Integration):
- UDDI is an XML-based standard for describing, publishing, finding/discovering and integrating web services
- A Web Service Provider publishes his Web Service through WSDL on an online directory/registry from where consumers can query and search the Web Services
- UDDI is a platform-independent and open framework can communicate via SOAP, CORBA, and Java RMI Protocol

2 Introduction to SOAP Web Services

2.1. What are SOAP Web Services?

SOAP (Simple Object Access Protocol), a W3C recommendation for communication between two applications
SOAP is an XML-based protocol for accessing web services over HTTP
Any Web Service that complies and follows some guidelines which are led down by SOAP Web Services specifications is a SOAP Web Service

2.2. SOAP Web Services Specifications/standards

2.2. SOAP Building blocks

There are two categories of SOAP Web Services specifications: as Basic specification and Extended specification:

Basic
- SOAP
  - Protocol / Rules / Definitions related to how two different applications will talk to each other over the web
  - All SOAP message/information exchange happens with the common format: XML
    - XML messages have a pre-defined structure as SOAP MESSAGE which consists of Envelope, Header, and Body
      - Envelope - root element of a message
      - Header - components, complex types, authentication parameters
      - Body - actual request to be sent to the server
- WSDL (Web Services Description Language)
- UDDI (Universal Description, Discovery, and Integration)
Extended
- Web Services Security (WS-Security)
- Web Services Policy (WS-Policy)

Who defines Web Services Specifications/standards

W3C (World Wide Web Consortium) - [An International community that develops open standards for worldwide web] defines and dictates all standards for Web Services

2.3. Disadvantages of Soap Web Services

Slow: SOAP uses XML format, whose parsing is slow and consumes more bandwidth and resource
WSDL dependent: SOAP uses WSDL and doesn't have other mechanisms to discover the service

3 Introduction to REST Web Services

3 Introduction to REST API

3.1. What is REST API?

REST (REpresentational State Transfer)
REST is an architectural style
- REST is not a protocol,
- there are no strict specifications,
- no central body like W3C to control specifications
REST is a design principle, one can use design principles/methods to create a service, which creates RESTful Web Services

REST is an architectural style as well as an approach for communications purpose that is often used in various web services development

Introduced by Roy Fielding in the year 2000
It is often regarded as the "language of the internet"
It is a stateless client and server model
REST is used to build Web Services that are lightweight, maintainable, and scalable

3.2. What are RESTful Web Services?

Any Web Service that complies and follows some guidelines which are led down by REST architecture/principles is a called a RESTful Web Service [A service which is built on the REST architecture is called a RESTful service]

3.3. Principles of REST API

3.3. RESTFul Principles and Constraints

There are many principles/constraints of REST architecture a Web Service needs to follow to become/deemed as REST API / RESTful API-Web Service:

Uniform Interface:
- Resource - Everything is a resource
  - any platform, any Database, any language - we can create a module or resource for Students, Employees or anything
- URI - Any resource/data can be accessed by a URI
  - URI = Uniform Resource Identifier
  - http://domain.name/resource
  - http://website.com/students
  - https://website.com/employee/id=100
- HTTP - Make explicit use of HTTP methods
  - HTTP = HyperText Transfer Protocol
  - HTTP methods are: GET, POST, PUT, DELETE
  - Using HTTP methods along with URI, we can REQUEST and can access/modify any resource or resource information
Client-Server:
- Client & Server are separate identities, Clients send REQUEST and Server RESPONDS with headers, status or response body
Stateless:
- All client-server communications are stateless
- In case of REST, the server does not maintain any state of the system and client has to send the request which is complete/proper in itself (every request will be independent and will not be dependent on any previous requests)
- Each request from the client to the server - must contain all the data that is necessary to handle the request, no need to store any data on the server
- A server should not require to store the state of a session
- As the server does not store any old/past/unwanted data, it improves Web Service performance
Cacheable:
- Caching happens at the client-side
- The client uses the Cache-Control header to determine whether to cache the resource (make a local copy) or not
- The server generates responses that indicate whether they are cacheable or not to improve the performance by reducing number of requests for duplicate resources [server does it with the help of Cache-Control and Last-Modified (date value)]
Layered System:
- Multiple Layers can exist between client and server
- Layers can include Proxies, Gateways, Caching they are HTTP intermediaries
- Layers can be used for message translations / improving performance with caching etc.
- Enables security, load-balancing and share caching to improve application performance
- Proxies - Proxy server evaluates, control its complexity and simplify the request
- Gateways - Used to manage traffic on the network, protocol translations, etc.
- Caching - Improves performance and scalability
Code On Demand:
- Ability to download and execute code on the client-side

3.4. Features of REST API

Simpler than SOAP API
Proper Documentation available
Throws/Log proper Error messages

3.5. Methods of REST API

- Creat        =   POST method
- Read         =   GET method  
- Update       =   PUT method
- Delete       =   DELETE method

POST – Create a new data/info/record using the RESTful web service
GET - Get a list of all data/info/record
PUT - Update all data/info/record
DELETE - Delete all data/info/record

3.6. Advantages of REST API

Fast: Due to no strict specification like SOAP, REST consumes less bandwidth and resource
Language and Platform independent: Can be written in any programming language and executed in any platform
Permits different data format: Plain Text, HTML, XML and JSON
Can use SOAP: RESTful web services can use SOAP API/web services as the implementation

4 SOAP Vs REST

4 SOAP Vs. REST: Difference between Web API Services

4.1. SOAP vs REST Web Services

There are many differences between SOAP and REST web services, some important differences are given below:

SOAP Web Services/API	REST Web Services/API
SOAP stands for `Simple Object Access Protocol`	REST stands for `REpresentational State Transfer`
SOAP is a `protocol`	REST is an `architectural style`
SOAP can't use REST because it is a protocol but REST is an architectural pattern	REST can use SOAP web services as it is an architectural pattern/concept and can use any protocol like HTTP, SOAP
SOAP uses `service interfaces` to expose the business logic	REST uses `URI (URL path)` to expose business logic
SOAP requires `more bandwidth and resource` than REST	REST requires `less bandwidth and resource` than SOAP
SOAP is `slow` as compared to REST	REST is `fast` as compared to SOAP
SOAP permits `XML` data format only	REST permits different data format such as `Plain text, HTML, JSON, XML` etc.
SOAP is `less preferred` than REST	REST IS `more preferred` than SOAP

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