How to define a default handler in Spring Boot 2

Question

How can I define a default handler, or controller action, that will be invoked when no other handler is found for a given URL?

I tried by using a catch-all pattern /** (syntax is Kotlin):

@Controller
class DefaultController {

    @RequestMapping("/**")
    fun default(...) {
        ...
    }
}

But this gets matched with higher precedence that Spring's own handlers, for example the static file path configured in spring.mvc.static-path-pattern is no longer available. I need my default handler to have the lowest precedence.

Andronicus · Accepted Answer · 2019-02-23T14:41:37.637

3

You would have to add your implementation of HandlerMapping and add it to list of handlers. You need to specify the order of handlers taking care of request as well:

@Bean
public SimpleUrlHandlerMapping simpleUrlHandlerMapping() {
    SimpleUrlHandlerMapping simpleUrlHandlerMapping
      = new SimpleUrlHandlerMapping();
    Map<String, Object> urlMap = new HashMap<>();
    urlMap.put("/**", defaultController());
    simpleUrlHandlerMapping.setUrlMap(urlMap);
    simpleUrlHandlerMapping.setOrder(1);
    return simpleUrlHandlerMapping;
}

Here the defaultController() method returns a @Controller, that you have defined for the given mapping, so DefaultController. The setOrder method defines a priority (order) of handlers, starting from 0. Of course some default HandlerMapping must be defined as a @Bean as well. More about such configuration you can find here.

Edit with some thoughts from @Tobia:

You need to remove the @RequestMapping annotation so that the controller is not picked up by RequestMappingHandlerMapping and implement the AbstractController interface to override the definition of controller in handleRequestInternal().

edited Feb 23 '19 at 14:41

answered Feb 23 '19 at 11:06

Andronicus

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Wait, I'm not sure it works. I used `setOrder(Ordered.LOWEST_PRECEDENCE)` instead of 1, but it still overrides the resource handler. I need it to be considered *after* the resource handler. – Tobia Feb 23 '19 at 13:03
I'm using Spring Boot, so there are several default handlers. I just need to add mine. I have inspected the application beans (using `applicationContext.getBeansOfType(HandlerMapping.class)` and I can see that mine is loaded with order=2147483647, which is a higher number (lower precedence) than order=2147483646 resourceHandlerMapping. That one is the default SimpleUrlHandlerMapping for static files, with a clear urlMap of `/static/**`. But whenever I call a static URL, my controller is invoked instead. – Tobia Feb 23 '19 at 13:34
I think I know what's going on. My controller is still being picked up by requestMappingHandlerMapping because it still has the @RequestMapping annotation. But if I remove the annotation, I get `javax.servlet.ServletException: No adapter for handler [...Controller@6da127ce]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler` – Tobia Feb 23 '19 at 13:51
So I had to remove @RequestMapping, implement AbstractController and override `handleRequestInternal()` "the old way" (Spring and Spring Boot have different definitions of what is a "Controller"...) Now it works. Thank you for your support. – Tobia Feb 23 '19 at 14:27
Damn, that is quite a good job. Honestly, I have never implemented it myself, I didn't know there is that much to it. – Andronicus Feb 23 '19 at 14:36
No problem. I've learn a bit myself. I've edited the answer with your information, so that it's complete. – Andronicus Feb 23 '19 at 14:42

How to define a default handler in Spring Boot 2

1 Answers1