Intro to RESTful Spring

What is REST?

REST stands for REpresentational State Transfer and is an architectural style for designing distributed network applications
More precisely, REST is an architectural style consisting of a coordinated set of architectural constraints applied to components, connectors, and data elements, within a distributed hypermedia system.

Client-Server

Concerns should be separated between clients and servers. This enables client and server components to evolve independently and in turn allows the system to scale.

Stateless

The communication between client and server should be stateless. The server need not remember the state of the client. Instead, clients must include all of the necessary information in the request so that server can understand and process it.

Layered System

Multiple hierarchical layers such as gateways, firewalls, and proxies can exist between client and server. Layers can be added, modified, reordered, or removed transparently to improve scalability.

Cache

Responses from the server must be declared as cacheable or non-cacheable. This would allow the client or its intermediary components to cache responses and reuse them for later requests. This reduces the load on the server and helps improve the performance.

Uniform Interface

All interactions between client, server, and intermediary components are based on the uniformity of their interfaces.
This simplifies the overall architecture as components can evolve independently as long as they implement the agreed-on contract

Code on Demand

Clients can extend their functionality by downloading and executing code on demand. Examples include JavaScript scripts, Java applets, Silverlight, and so on. This is an optional constraint.

URI

Uniform Resource Identifier, or URI, for uniquely identifying resources.
Format: scheme:scheme-specific-part
E.g.: http://zipcoder.io

URI Templates

Resource links can be dynamic
E.g.: “http://blog.zipcoder.io/year/posts”

Representation

RESTful resources are abstract entities, which represent a snap shot of data at a point in time.

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HTTP Methods

HTTP `GET` Method

The GET method is used to retrieve information from the given server using a given URI. Requests using GET should only retrieve data and should have no other effect on the data.

Idempotence

An operation is considered to be idempotent if it produces the same server state whether we apply it once or any number of times. HTTP methods such as GET, HEAD (which are also safe), PUT, and DELETE are considered to be idempotent, guaranteeing that clients can repeat a request and expect the same effect as making the request once.

HTTP `POST` Method

A POST request is used to send data to the server, for example: customer information, file upload, etc. using HTML forms.

HTTP `HEAD` Method

Same as GET, but transfers the status line and header section only.

HTTP `PUT` Method

Replaces all current representations of the target resource with the uploaded content.

HTTP `DELETE` Method

Removes all current representations of the target resource given by a URI.

HTTP `CONNECT` Method

Establishes a tunnel to the server identified by a given URI.

HTTP `OPTIONS` Method

Describes the communication options for the target resource.

HTTP `TRACE` Method

Performs a message loop-back test along the path to the target resource.

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CRUD


Create	Read
Update	Delete

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HTTP Status Codes

1xx Informational
- 100 Continue
2xx Success
- 200 OK
3xx Redirection
- 300 Multiple Choices
4xx Client Error
- 400 Bad Request
5xx Server Error
- 500 Internal Server Error

1xx Informational

100 Continue -
The server has received the request headers; the client should proceed to send the request body (for requests which require a body to be sent; eg: a POST.
101 Switching Protocols –
The requester has asked the server to switch protocols and the server is acknowledging that it will do so
102 Processing -
As a WebDAV request may contain many sub-requests involving file operations, it may take a long time to complete the request. Indicates that the server has received and is processing the request, but no response is available yet

2xx Success

200 OK
- Standard response for successful HTTP requests.
201 CREATED
- Request has been fulfilled and resulted in a new resource being created.
202 Accepted
- Request has been accepted for processing, but the processing has not been completed. The request might or might not eventually be acted upon, as it might be disallowed when processing actually takes place.

3xx Redirection

300 Multiple Choices
- Indicates multiple options for the resource that the client may follow.
301 Moved Permanently
- This and all future requests should be directed to the given URI
308 Permanent Redirect
- The request, and all future requests should be repeated using another URI.

4xx Client Error

400 Bad Request
- The server cannot or will not process the request due to something that is perceived to be a client error
401 Unauthorized
- Similar to 403 Forbidden, but specifically for use when authentication is required and has failed or has not yet been provided.
404 Not Found
- The requested resource could not be found but may be available again in the future. Subsequent requests by the client are permissible

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WEB Socket

A protocol providing full-duplex communication channels over a single TCP connection.

Servlet

A servlet is a small program that runs within a Web server. Servlets receive and respond to requests from Web clients, usually across HTTP, the HyperText Transfer Protocol.

Aspect-Oriented Programming

Aspect-Oriented Programming (AOP) complements Object-Oriented Programming (OOP) by providing another way of thinking about program structure. The key unit of modularity in OOP is the class, whereas in AOP the unit of modularity is the aspect. Aspects enable the modularization of concerns, such as transaction management that cut across multiple types and objects.

ORM

Object-relational mapping (ORM) is a technique (a.k.a. design pattern) of accessing a relational database from an object-oriented language (Java, for example)

Transaction

In computer programming, a transaction usually means a sequence of information exchange and related work (such as database updating) that is treated as a unit for the purposes of satisfying a request and for ensuring database integrity.

Bean

A bean is an object that is instantiated, assembled, and otherwise managed by an IoC container. These beans are created with the configuration metadata that you supply to the container

Inversion Of Control (IOC)

In software engineering, inversion of control (IoC) describes a design in which custom-written portions of a computer program receive the flow of control from a generic, reusable library.

Dependency Injection (DI)

Dependency Injection design pattern allows us to remove the hard-coded dependencies and make our application loosely coupled, extendable and maintainable.