Interceptor is very useful in SpringMVC based Java Web application development. It is especially helpful when comes to authentication and authorization. We can centralize permision management by using interceptor.

Many documents online introduce the detail of execution order and conception of interceptor. After reading javadoc, I found something new beyond them.

Handler

Handlers are the actual method that deal with requests. Methods that are annotated with @RequestMapping are handlers.
Handlers will be invoked only if all preHandler methods return true.

Execution chain

Execution chain are a chain that contains all the interceptors that need to execute. The order of execution depends on MVC configuration, so you can always reorder them if you want.

preHandler

execution sequence

The execution order complies to the execution chain.

execution position

Executed after HandlerMapping determines an appropriate handler, but just before invoking handler method.

result

If this method returns true, the next interceptor in execution chain, or the handler if no more interceptors after, it will be invoked.
If this method returns false or throws an exception, DispatcherServlet assumes this interceptor has already taken care of the response itself.

When throwing an exception, the servlet container or a controller advisor will handle the exception for you.
When returning false, Spring will reply with the HttpResponse in the method parameter. You can either fill something necessary into the response object or redirect to somewhere else.

postHandler

execution sequence

Execution order is inverse to that of the execution chain.

execution position

This method will be executed after invocation of the handler, but right before DispatcherServlet renders the view.

significance

This method is to do some modification or surviliance to the response object.

afterCompletion

execution sequence

Execution order is inverse to that of the execution chain; thus first registered interceptor will be the last one to execute.

execution position:

This method will only be invoked if the preHandler method returns true. This means that throwing an exception or returning false will not enter this method.
This method will be invoked after the view was rendered by DispatcherServlet

significance:

This method is designed to do some cleanup work.