Restful API for Beginners

Introduction:

Everyone is saying Rest API. Sometimes people say  only API to rest apis.RESTful API is for accessing blah blah service or to do blah blah functionality. In corporate world, fresher get confused when seniors give them task to create new api to call blah blah service or to do blah blah functionality.

So what is this REST API?

• REST (REpresentational State Transfer) is an architectural style, and an approach to communications.Using this REST whatever functionality we create known as REST API.
• We can implement  rest-api using various providers but usually people use Jersey and Spring .
• As per my choice personally I would like to use jersey which keep code neat and clean.

Rest follows client-server architecture with Front Controller Design Pattern.

It completely depends on http protocol .REST implementation is very easy and run in  less memory compared to SOAP.

Rest Support following parameter techniques to pass input for our web service.

• Query/Request parameter(e.g. "http://localhost:8080/app?id=10&name=shashank")
• Path Parameter(e.g.  "http://localhost:8080/app/id/100/name/shashank")
• Matrix Parameter(e.g. "http://localhost:8080/app;id=100;name=shashank")
• Form Parameter
• Header Parameter

REST supports sending data using XML , JSON, Plain Text etc.

Now the thing is that what are the XML, JSON and Plain Text?

So we are going to use JSON so I will not waste your time by explaining XML and Plain Text.

JSON- JSON is JavaScript Object Notation which is very lightweight as compared to XML
and self-descriptive.While transferring it to Network it improves lot of performance.

e.g. =>

{

        "Id": 100,

       "Name": "shashank"

}

Now we need convertor to  convert Object to JSON and JSON to Object.So for that purpose we will use JACKSON.

1. Front Controller is a servlet, which follows URL Pattern directory Pattern. It can even follow extensions Pttern but not recommended (does not support parameter passing.)
2. All services or you can say api are classes ,every class must contain  a unique path(no duplicate path)
3. Every method inside the class must follow one type( GET or POST or PUT or DELETE)
4. Webservice/api may return some data which is known as Entity and this entity can wrapped into Response object and sent to the client over network.
5. When using Jersey common annotations are @Path, @GET, @POST, @PUT, @DELETE.

REST Architecture Workflow:

REST- Service Provider Implementation

1. Create a New Dynamic Web Project(J2EE) : File-> New->Dynamic Web Project-> Enter -> Name -> Finish.
2. Download and extract jersey-bundle.
3. Add these jars into lib folder in an application: WebContent->WEB-INF->lib->paste here
4. Configure Front Controller in web.xml,
5. Don’t fear Front Controller is nothing but predefined class from jersey.You just need to give name with package name in web.xml

       Front Controller class = com.sun.jersey.spi.container.servlet.ServletContainer

       Even if you do Ctrl+Shift+T in eclipse, It will search ServletContainer class for you.

web.xml

<web-app>

<servlet>

<servlet-name>sample</servlet-name>

<servlet-class> com.sun.jersey.spi.container.servlet.ServletContainer</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>sample</servlet-name>

<url-pattern>/rest/*</url-pattern>

</servlet-mapping>

</web-app>

Now We will create the web service or API for that we took this much above boring theoretical knowledge –

Right click on src ->  New -> class -> Enter class name  and package

package com.app;

import javax.ws.rs.GET

import javax.ws.rs.Path

@Path(“hello”)

public class WebService{

     @Path(“world”)

     @GET

     public String sayHello(){

          return “Hello World”;

      }

}

Run as Server and access request using as web browser.

URL will be "http://localhost:8080/app-name/rest/hello/world"

Thank you…..!!!