How are Spring HandlerInterceptors instantiated?

Question

Is there a new instance of Spring HandlerInterceptors for each request?

I have an interceptor in Spring, which has a class field.

public class MyInterceptor extends HandlerInterceptorAdapter {
    Private boolean state = false;

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
        state = true;
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) {
        if (state == true) {
        System.out.println("Success");
        }
}

If this interceptor is used will it always print "Success"? (No matter how many threads are doing this at the same time?)

Answer 1

How the interceptor is instantiated depends how you configiure it as a bean. If you don't explicitly specify a scope for the bean, then it'll be a singleton like any other bean, and so the state field will be shared by all requests.

In this sense, interceptors are no different to controllers - be very careful about putting conversation state in them, since the objects will be shared across requests.

if you really need a stateful interceptor and you don't want to share the state between requests, then use a request-scoped bean.