[[mvc-exceptionhandlers]]
= Exceptions

[.small]#xref:web/webflux/dispatcher-handler.adoc#webflux-dispatcher-exceptions[See equivalent in the Reactive stack]#

If an exception occurs during request mapping or is thrown from a request handler (such as
a `@Controller`), the `DispatcherServlet` delegates to a chain of `HandlerExceptionResolver`
beans to resolve the exception and provide alternative handling, which is typically an
error response.

The following table lists the available `HandlerExceptionResolver` implementations:

[cols="1,2", options="header"]
.HandlerExceptionResolver implementations
|===
| `HandlerExceptionResolver` | Description

| `SimpleMappingExceptionResolver`
| A mapping between exception class names and error view names. Useful for rendering
  error pages in a browser application.

| {spring-framework-api}/web/servlet/mvc/support/DefaultHandlerExceptionResolver.html[`DefaultHandlerExceptionResolver`]
| Resolves exceptions raised by Spring MVC and maps them to HTTP status codes.
  See also alternative `ResponseEntityExceptionHandler` and xref:web/webmvc/mvc-ann-rest-exceptions.adoc[Error Responses].

| `ResponseStatusExceptionResolver`
| Resolves exceptions with the `@ResponseStatus` annotation and maps them to HTTP status
  codes based on the value in the annotation.

| `ExceptionHandlerExceptionResolver`
| Resolves exceptions by invoking an `@ExceptionHandler` method in a `@Controller` or a
  `@ControllerAdvice` class. See xref:web/webmvc/mvc-controller/ann-exceptionhandler.adoc[@ExceptionHandler methods].
|===


[[mvc-exceptionhandlers-handling]]
== Chain of Resolvers

You can form an exception resolver chain by declaring multiple `HandlerExceptionResolver`
beans in your Spring configuration and setting their `order` properties as needed.
The higher the order property, the later the exception resolver is positioned.

The contract of `HandlerExceptionResolver` specifies that it can return:

* a `ModelAndView` that points to an error view.
* An empty `ModelAndView` if the exception was handled within the resolver.
* `null` if the exception remains unresolved, for subsequent resolvers to try, and, if the
exception remains at the end, it is allowed to bubble up to the Servlet container.

The xref:web/webmvc/mvc-config.adoc[MVC Config] automatically declares built-in resolvers for default Spring MVC
exceptions, for `@ResponseStatus` annotated exceptions, and for support of
`@ExceptionHandler` methods. You can customize that list or replace it.


[[mvc-ann-customer-servlet-container-error-page]]
== Container Error Page

If an exception remains unresolved by any `HandlerExceptionResolver` and is, therefore,
left to propagate or if the response status is set to an error status (that is, 4xx, 5xx),
Servlet containers can render a default error page in HTML. To customize the default
error page of the container, you can declare an error page mapping in `web.xml`.
The following example shows how to do so:

[source,xml,indent=0,subs="verbatim,quotes"]
----
	<error-page>
		<location>/error</location>
	</error-page>
----

Given the preceding example, when an exception bubbles up or the response has an error status, the
Servlet container makes an ERROR dispatch within the container to the configured URL
(for example, `/error`). This is then processed by the `DispatcherServlet`, possibly mapping it
to a `@Controller`, which could be implemented to return an error view name with a model
or to render a JSON response, as the following example shows:

[tabs]
======
Java::
+
[source,java,indent=0,subs="verbatim,quotes"]
----
	@RestController
	public class ErrorController {

		@RequestMapping(path = "/error")
		public Map<String, Object> handle(HttpServletRequest request) {
			Map<String, Object> map = new HashMap<>();
			map.put("status", request.getAttribute("jakarta.servlet.error.status_code"));
			map.put("reason", request.getAttribute("jakarta.servlet.error.message"));
			return map;
		}
	}
----

Kotlin::
+
[source,kotlin,indent=0,subs="verbatim,quotes"]
----
	@RestController
	class ErrorController {

		@RequestMapping(path = ["/error"])
		fun handle(request: HttpServletRequest): Map<String, Any> {
			val map = HashMap<String, Any>()
			map["status"] = request.getAttribute("jakarta.servlet.error.status_code")
			map["reason"] = request.getAttribute("jakarta.servlet.error.message")
			return map
		}
	}
----
======

TIP: The Servlet API does not provide a way to create error page mappings in Java. You can,
however, use both a `WebApplicationInitializer` and a minimal `web.xml`.



