Implementing REST Web Service Using Spring MVC

Using spring MVC it is very easy to enable a rest back-end for our web application.  Rest is a representation based architecture style. Everything we access in rest is a representation and every representation has a unique resource identifier (URI). These are two important concepts we must remember in rest.

Spring MVC provide a very easy implementation on rest framework. Assuming you has a working spring MVC project.  Please see below a spring rest controller.

There is couple of things that we need to keep in mind while writing this code. 

	<!-- To switch on  default message converters -->
	<mvc:annotation-driven/>

@XmlRootElement
public class Order implements Serializable
{

@Id
private String orderId;

//Define all other fields 

}

 In the above code, we used couple of important annotations. 

• @RequestMapping  - This annotation maps web requests onto specific handler classes and/or handler methods. 
  
• @PathVariable – Used to access the URI value and pass that value to corresponding method argument. 
  

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
		 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
         version="2.5">
        
    <servlet>
       <servlet-name>Dispatcher</servlet-name>
       <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
       <load-on-startup>1</load-on-startup>       
    </servlet>
  
    <servlet-mapping>
       <servlet-name>Dispatcher</servlet-name>
       <url-pattern>/</url-pattern>       
    </servlet-mapping>

   <listener>
     <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
   </listener>
 
   <context-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>/WEB-INF/application.xml</param-value>
   </context-param>

</web-app>

Also attaching a copy of the dispatcher servlet.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns:context="http://www.springframework.org/schema/context"
	xmlns:mvc="http://www.springframework.org/schema/mvc"
	
	xsi:schemaLocation="http://www.springframework.org/schema/beans 
	                    http://www.springframework.org/schema/beans/spring-beans.xsd
	                    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
	                    http://www.springframework.org/schema/mvc 
	                    http://www.springframework.org/schema/mvc/spring-mvc.xsd">

	<!--  We need to autowire the controllers -->
	<context:component-scan base-package="com.tutorial.rest.controllers"/>

	<!-- To switch on  default message converters -->
	<mvc:annotation-driven/>

</beans>

Once the controller is setup as explained here and application is deployed and started, we can issue http request on the browser and get xml or json representation of the order object.