Spring MVC interceptors (learn more about interceptor design pattern here) can be used to plug in functionality that needs to be executed as part of handling a request. These interceptors can be an ideal place to reuse functionality that is applicable for non-web application related scenarios. Interceptors can be used to execute horizontal, cross cutting concerns – e.g. security, metrics, logging, etc. If you have an existing component that was developed for a command-line application or a JMS event handler and need to reuse it in a web app, an interceptor would be an ideal choice.
Here is an example implementation for a a Spring Interceptor extending the HandlerInterceptorAdapter:
package com.yourapp.learn;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.handler.HandlerInterceptorAdapter;
public class LoginInterceptor extends HandlerInterceptorAdapter {
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
Object handler) throws Exception {
Boolean userAuthenticated = (Boolean)request.getSession().getAttribute("userAuthenticated");
if (userAuthenticated) {
return true;
} else {
return false;
}
}
}
This interceptor simply checks to see if the user is authenticated by looking for a session attribute. If the result is true, the request is processed further.
Here is an example bean definition fragment for utilizing the above:
<bean id="testInterceptor" /> <bean id="testSimpleUrlHandlerMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="testInterceptor"/> </list> </property> <property name="mappings"> <props> <prop key="/test">someController</prop> </props> </property> </bean>
The actual logic can be in another component that is leveraged in the interceptor. The component itself could be reused across several apps. If such a component isn’t available, you can refactor existing logic to carve out the common functionality.
Posted by vijaynarayanan 
