@ExceptionHandler is able to process Error thrown from handler method

Issue: SPR-11106

Author: jhoeller

spring-web/src/main/java/org/springframework/web/method/annotation/ExceptionHandlerMethodResolver.java

@@ -31,6 +31,7 @@
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ReflectionUtils.MethodFilter;
 import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.util.NestedServletException;
 
 /**
  * Discovers {@linkplain ExceptionHandler @ExceptionHandler} methods in a given class,
@@ -98,8 +99,8 @@ private List<Class<? extends Throwable>> detectExceptionMappings(Method method)
 	}
 
 	protected void detectAnnotationExceptionMappings(Method method, List<Class<? extends Throwable>> result) {
-		ExceptionHandler annot = AnnotationUtils.findAnnotation(method, ExceptionHandler.class);
-		result.addAll(Arrays.asList(annot.value()));
+		ExceptionHandler ann = AnnotationUtils.findAnnotation(method, ExceptionHandler.class);
+		result.addAll(Arrays.asList(ann.value()));
 	}
 
 	private void addExceptionMapping(Class<? extends Throwable> exceptionType, Method method) {
@@ -124,7 +125,11 @@ public boolean hasExceptionMappings() {
 	 * @return a Method to handle the exception, or {@code null} if none found
 	 */
 	public Method resolveMethod(Exception exception) {
-		return resolveMethodByExceptionType(exception.getClass());
+		Method method = resolveMethodByExceptionType(exception.getClass());
+		if (method == null && exception instanceof NestedServletException && exception.getCause() != null) {
+			method = resolveMethodByExceptionType(exception.getCause().getClass());
+		}
+		return method;
 	}
 
 	/**
@@ -133,7 +138,7 @@ public Method resolveMethod(Exception exception) {
 	 * @param exceptionType the exception type
 	 * @return a Method to handle the exception, or {@code null} if none found
 	 */
-	public Method resolveMethodByExceptionType(Class<? extends Exception> exceptionType) {
+	public Method resolveMethodByExceptionType(Class<? extends Throwable> exceptionType) {
 		Method method = this.exceptionLookupCache.get(exceptionType);
 		if (method == null) {
 			method = getMappedMethod(exceptionType);
@@ -145,7 +150,7 @@ public Method resolveMethodByExceptionType(Class<? extends Exception> exceptionT
 	/**
 	 * Return the {@link Method} mapped to the given exception type, or {@code null} if none.
 	 */
-	private Method getMappedMethod(Class<? extends Exception> exceptionType) {
+	private Method getMappedMethod(Class<? extends Throwable> exceptionType) {
 		List<Class<? extends Throwable>> matches = new ArrayList<Class<? extends Throwable>>();
 		for (Class<? extends Throwable> mappedException : this.mappedMethods.keySet()) {
 			if (mappedException.isAssignableFrom(exceptionType)) {

spring-webmvc/src/main/java/org/springframework/web/servlet/DispatcherServlet.java

@@ -972,13 +972,19 @@ protected void doDispatch(HttpServletRequest request, HttpServletResponse respon
 			catch (Exception ex) {
 				dispatchException = ex;
 			}
+			catch (Error err) {
+				// As of 4.3, we're processing Errors thrown from handler methods as well,
+				// making them available for @ExceptionHandler methods and other scenarios.
+				dispatchException = new NestedServletException("Handler dispatch failed", err);
+			}
 			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
 		}
 		catch (Exception ex) {
 			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
 		}
 		catch (Error err) {
-			triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
+			triggerAfterCompletion(processedRequest, response, mappedHandler,
+					new NestedServletException("Handler processing failed", err));
 		}
 		finally {
 			if (asyncManager.isConcurrentHandlingStarted()) {
@@ -1304,16 +1310,6 @@ private void triggerAfterCompletion(HttpServletRequest request, HttpServletRespo
 		throw ex;
 	}
 
-	private void triggerAfterCompletionWithError(HttpServletRequest request, HttpServletResponse response,
-			HandlerExecutionChain mappedHandler, Error error) throws Exception {
-
-		ServletException ex = new NestedServletException("Handler processing failed", error);
-		if (mappedHandler != null) {
-			mappedHandler.triggerAfterCompletion(request, response, ex);
-		}
-		throw ex;
-	}
-
 	/**
 	 * Restore the request attributes after an include.
 	 * @param request current HTTP request

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/ExceptionHandlerExceptionResolver.java

@@ -95,7 +95,7 @@ public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExce
 
 	public ExceptionHandlerExceptionResolver() {
 		StringHttpMessageConverter stringHttpMessageConverter = new StringHttpMessageConverter();
-		stringHttpMessageConverter.setWriteAcceptCharset(false); // See SPR-7316
+		stringHttpMessageConverter.setWriteAcceptCharset(false);  // see SPR-7316
 
 		this.messageConverters = new ArrayList<HttpMessageConverter<?>>();
 		this.messageConverters.add(new ByteArrayHttpMessageConverter());
@@ -364,7 +364,15 @@ protected ModelAndView doResolveHandlerMethodException(HttpServletRequest reques
 			if (logger.isDebugEnabled()) {
 				logger.debug("Invoking @ExceptionHandler method: " + exceptionHandlerMethod);
 			}
-			exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, handlerMethod);
+			if (exception.getCause() != null) {
+				// Expose root cause as provided argument as well
+				exceptionHandlerMethod.invokeAndHandle(
+						webRequest, mavContainer, exception, exception.getCause(), handlerMethod);
+			}
+			else {
+				// Otherwise, just the given exception as-is
+				exceptionHandlerMethod.invokeAndHandle(webRequest, mavContainer, exception, handlerMethod);
+			}
 		}
 		catch (Exception invocationEx) {
 			if (logger.isDebugEnabled()) {

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ExceptionHandlerExceptionResolverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,12 +42,9 @@
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
 import org.springframework.web.servlet.ModelAndView;
+import org.springframework.web.util.NestedServletException;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 /**
  * Test fixture with {@link ExceptionHandlerExceptionResolver}.
@@ -240,6 +237,22 @@ public void resolveExceptionWithHandlerMethodArg() throws Exception {
 		assertEquals("HandlerMethod: handle", this.response.getContentAsString());
 	}
 
+	@Test
+	public void resolveExceptionWithAssertionError() throws Exception {
+		AnnotationConfigApplicationContext cxt = new AnnotationConfigApplicationContext(MyConfig.class);
+		this.resolver.setApplicationContext(cxt);
+		this.resolver.afterPropertiesSet();
+
+		AssertionError err = new AssertionError("argh");
+		HandlerMethod handlerMethod = new HandlerMethod(new ResponseBodyController(), "handle");
+		ModelAndView mav = this.resolver.resolveException(this.request, this.response, handlerMethod,
+				new NestedServletException("Handler dispatch failed", err));
+
+		assertNotNull("Exception was not handled", mav);
+		assertTrue(mav.isEmpty());
+		assertEquals(err.toString(), this.response.getContentAsString());
+	}
+
 	@Test
 	public void resolveExceptionControllerAdviceHandler() throws Exception {
 		AnnotationConfigApplicationContext cxt = new AnnotationConfigApplicationContext(MyControllerAdviceConfig.class);
@@ -349,6 +362,11 @@ public String handleException(IllegalStateException ex) {
 		public String handleWithHandlerMethod(HandlerMethod handlerMethod) {
 			return "HandlerMethod: " + handlerMethod.getMethod().getName();
 		}
+
+		@ExceptionHandler(AssertionError.class)
+		public String handleAssertionError(Error err) {
+			return err.toString();
+		}
 	}
 
 

spring-webmvc/src/test/java/org/springframework/web/servlet/mvc/method/annotation/ServletAnnotationControllerHandlerMethodTests.java

@@ -139,30 +139,23 @@
 import org.springframework.web.servlet.support.RequestContextUtils;
 import org.springframework.web.servlet.view.InternalResourceViewResolver;
 
-import static org.junit.Assert.assertArrayEquals;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertNotNull;
-import static org.junit.Assert.assertNull;
-import static org.junit.Assert.assertSame;
-import static org.junit.Assert.assertTrue;
-import static org.junit.Assert.fail;
+import static org.junit.Assert.*;
 
 /**
  * The origin of this test class is {@link ServletAnnotationControllerHandlerMethodTests}.
  *
  * Tests in this class run against the {@link HandlerMethod} infrastructure:
  * <ul>
- * 	<li>RequestMappingHandlerMapping
- * 	<li>RequestMappingHandlerAdapter
- * 	<li>ExceptionHandlerExceptionResolver
+ * <li>RequestMappingHandlerMapping
+ * <li>RequestMappingHandlerAdapter
+ * <li>ExceptionHandlerExceptionResolver
  * </ul>
  *
  * <p>Rather than against the existing infrastructure:
  * <ul>
- * 	<li>DefaultAnnotationHandlerMapping
- * 	<li>AnnotationMethodHandlerAdapter
- * 	<li>AnnotationMethodHandlerExceptionResolver
+ * <li>DefaultAnnotationHandlerMapping
+ * <li>AnnotationMethodHandlerAdapter
+ * <li>AnnotationMethodHandlerExceptionResolver
  * </ul>
  *
  * @author Rossen Stoyanchev
@@ -181,6 +174,18 @@ public void emptyValueMapping() throws Exception {
 		assertEquals("test", response.getContentAsString());
 	}
 
+	@Test
+	public void errorThrownFromHandlerMethod() throws Exception {
+		initServletWithControllers(ControllerWithErrorThrown.class);
+
+		MockHttpServletRequest request = new MockHttpServletRequest("GET", "/foo");
+		request.setContextPath("/foo");
+		request.setServletPath("");
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		getServlet().service(request, response);
+		assertEquals("test", response.getContentAsString());
+	}
+
 	@Test
 	public void customAnnotationController() throws Exception {
 		initServletWithControllers(CustomAnnotationController.class);
@@ -1808,6 +1813,25 @@ public void myPath2(Exception ex, HttpServletResponse response) throws IOExcepti
 		}
 	}
 
+	@Controller
+	private static class ControllerWithErrorThrown {
+
+		@RequestMapping("")
+		public void myPath2(HttpServletResponse response) throws IOException {
+			throw new AssertionError("test");
+		}
+
+		@RequestMapping("/bar")
+		public void myPath3(HttpServletResponse response) throws IOException {
+			response.getWriter().write("testX");
+		}
+
+		@ExceptionHandler
+		public void myPath2(Error err, HttpServletResponse response) throws IOException {
+			response.getWriter().write(err.getMessage());
+		}
+	}
+
 	@Controller
 	static class MyAdaptedController {