interceptors in spring MVC

Question

I am trying learn Interceptors in spring but not able to understand it. I tried a sample example but get no success. I have created a simple interceptor like

@Component("testInterceptor")
public class testInterceptor extends HandlerInterceptorAdapter {      
  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response,   Object handler){
//I suppose this method will be called when I open my login page so just write something here       
        System.out.println("Inside Interceptor...");
        ModelAndView mv = new ModelAndView();
        mv.addObject("name", "test name");
        return true;
}

}

In my spring-servlet.xml I have

<context:component-scan base-package="com.test.interceptor" />
 <mvc:interceptors>
            <bean class="com.test.interceptors.testInterceptor " />         
</mvc:interceptors>

On my login page I write somewhere ${name}

So I can't even see even ${name} value or sysout anywhere.

I am not even able to understand when postHandler or afterCompletion method will be called and how I can test them before implementing. This may be because I am new to spring also and I am not able to understand it fully. It would be great help if you suggest some good link to read which shows some examples.

Thanks in advance

Edited: Now I can see my sysout commnet when I call my login page but it displaying it 16 times why is this so?

Answer 1

First have a look at the Interface HandlerInterceptor it is very well documented! (HandlerInterceptorAdapter is only a subclass that helps you if you do not want to implement all 3 methods) .

Then you will notice that there are 3 methods, each belong to one step in the "processing" chain.

Then you will notice that you used the wrong method: use postHandle instead of preHandle.

Then you will notice that the model map that you have created in your filter ModelAndView mv = new ModelAndView(); is not connected to something, and therefore it can not work! But fortunately postHandle has a ModelAndView modelAndView parameter. And you must use this instead of creating your unconnected model map.

Maybe later you will notice that you created the filter twice. Once by component scan and once by xml declaration. (In this case I would recommend to remove the @Compnent Annotation)

So at the end your class would look like:

public class testInterceptor extends HandlerInterceptorAdapter {      
   @Override
   public boolean postHandle(HttpServletRequest request,
            HttpServletResponse response,
             Object handler,
            ModelAndView modelAndView){
       modelAndView.addObject("name", "test name");
   }
 }

At the end you will notice (I am not 100% sure) that this interceptor is not invoked for the spring security login request (j_spring_security_check) or logout. Because this is handled in a spring security filter that is applied before any HandlerInterceptor is called.

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(comment) Now I can see my sysout comment when I call my login page but it is displaying it 16 times why is this so?

Maybe because you are loading some resources (images, css, js) though a controller.

Answer 2

Why not try putting the name attribute to the request.