REST-APIs

Objectives : You will learn how to ...

• Create REST APIs/ Web Services with Spring
• Discuss REST concepts, JSON and HTTP messaging
• Install REST client tool: Postman
• Develop REST APIs/ Web Services with @RestController
• Build a CRUD interface to the database with Spring REST

REST HTTP Basics

Most common use of REST is over HTTP. Below is the list of HTTP methods for CRUD operations.

• POST - Create a new entity
• GET - Read a list of entities or single entity
• PUT - Update an existing entity
• DELETE - Deleting an existing entity

HTTP Request Message

It consists of three areas

• Request Line - the HTTP command
• Header Variables - request metadata
• Message body - contents of message

HTTP Response Message

It also consists of three areas

• Response Line - server protocol and status code
• Header variables - response metadata
• Message body - contents of message

HTTP Response

Code Range	Description
100-199	Informational
200-299	Successful
300-399	Redirection
400-499	Client Error
500-599	Server Error

MIME Content Types

• The message format is described by MIME content type
• Multipurpose Internet Mail-Extention
• Basic Syntax: type/sub-type
• Examples
  1. text/html, text/plain
  2. application/json, application/xml, ....

NOTE : When we add @RestController Annotation it adds the REST support.

Java JSON Data Binding

• Data binding is the process of converting JSON data to a java POJO
• Also known as Mapping, Serialization/ Deserialization, Marshalling/ Unmarshalling.
• Spring uses the Jackson Project behind the scenes, jackson handles data binding between JSON and Java POJO

Path Variables

• Retrieve a single student by id /api/students/{studentId}
• This studentId is known as path variable

Exception Handling

• Create a custom error response class
• Create a custom exception class
• Update REST service to throw exception if student not found
• Add an exception handler method using @ExceptionHandler