Use the type of the actual return value in @MVC

The new @MVC support classes select a HandlerMethodArgumentResolver
and a HandlerMethodReturnValueHandler statically, i.e. based on
the signature of the method, which means that a controller method
can't declare a more general return type like Object but actually
return a more specific one, e.g.  String vs RedirectView, and
expect the right handler to be used.

The fix ensures that a HandlerMethodReturnValueHandler is selected
based on the actual return value type, which is something that was
supported with the old @MVC support classes. One consequence
of the change is the selected HandlerMethodReturnValueHandler can
no longer be cached but that matches the behavior of the old
@MVC support classes.

Issues: SPR-9218

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2011 the original author or authors.
+ * Copyright 2002-2012 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.
@@ -15,9 +15,10 @@
  */
 
 package org.springframework.web.servlet.mvc.method.annotation;
-import static org.junit.Assert.*;
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 
 import java.lang.reflect.Method;
 
@@ -30,17 +31,20 @@ import org.springframework.http.HttpStatus;
 import org.springframework.http.converter.HttpMessageNotWritableException;
 import org.springframework.mock.web.MockHttpServletRequest;
 import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.web.bind.annotation.ResponseStatus;
 import org.springframework.web.context.request.NativeWebRequest;
 import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.method.annotation.RequestParamMethodArgumentResolver;
 import org.springframework.web.method.support.HandlerMethodArgumentResolverComposite;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
 import org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite;
 import org.springframework.web.method.support.ModelAndViewContainer;
+import org.springframework.web.servlet.view.RedirectView;
 
 /**
  * Test fixture with {@link ServletInvocableHandlerMethod}.
- * 
+ *
  * @author Rossen Stoyanchev
  */
 public class ServletInvocableHandlerMethodTests {
@@ -53,6 +57,8 @@ public class ServletInvocableHandlerMethodTests {
 
 	private ServletWebRequest webRequest;
 
+	private MockHttpServletRequest request;
+
 	private MockHttpServletResponse response;
 
 	@Before
@@ -60,8 +66,9 @@ public class ServletInvocableHandlerMethodTests {
 		returnValueHandlers = new HandlerMethodReturnValueHandlerComposite();
 		argumentResolvers = new HandlerMethodArgumentResolverComposite();
 		mavContainer = new ModelAndViewContainer();
+		request = new MockHttpServletRequest();
 		response = new MockHttpServletResponse();
-		webRequest = new ServletWebRequest(new MockHttpServletRequest(), response);
+		webRequest = new ServletWebRequest(request, response);
 	}
 
 	@Test
@@ -92,29 +99,45 @@ public class ServletInvocableHandlerMethodTests {
 		webRequest.getNativeRequest(MockHttpServletRequest.class).addHeader("If-Modified-Since", 10 * 1000 * 1000);
 		int lastModifiedTimestamp = 1000 * 1000;
 		webRequest.checkNotModified(lastModifiedTimestamp);
-		
+
 		ServletInvocableHandlerMethod handlerMethod = getHandlerMethod("notModified");
 		handlerMethod.invokeAndHandle(webRequest, mavContainer);
 
 		assertTrue("Null return value + 'not modified' request should result in 'request handled'",
 				mavContainer.isRequestHandled());
 	}
-	
-	@Test
+
+	@Test(expected=HttpMessageNotWritableException.class)
 	public void exceptionWhileHandlingReturnValue() throws Exception {
 		returnValueHandlers.addHandler(new ExceptionRaisingReturnValueHandler());
 
 		ServletInvocableHandlerMethod handlerMethod = getHandlerMethod("handle");
-		try {
-			handlerMethod.invokeAndHandle(webRequest, mavContainer);
-			fail("Expected exception");
-		} catch (HttpMessageNotWritableException ex) {
-			// Expected..
-			// Allow HandlerMethodArgumentResolver exceptions to propagate..
-		}
+		handlerMethod.invokeAndHandle(webRequest, mavContainer);
+		fail("Expected exception");
 	}
 
-	private ServletInvocableHandlerMethod getHandlerMethod(String methodName, Class<?>... argTypes) 
+	@Test
+	public void dynamicReturnValue() throws Exception {
+		argumentResolvers.addResolver(new RequestParamMethodArgumentResolver(null, false));
+		returnValueHandlers.addHandler(new ViewMethodReturnValueHandler());
+		returnValueHandlers.addHandler(new ViewNameMethodReturnValueHandler());
+
+		// Invoke without a request parameter (String return value)
+		ServletInvocableHandlerMethod handlerMethod = getHandlerMethod("dynamicReturnValue", String.class);
+		handlerMethod.invokeAndHandle(webRequest, mavContainer);
+
+		assertNotNull(mavContainer.getView());
+		assertEquals(RedirectView.class, mavContainer.getView().getClass());
+
+		// Invoke with a request parameter (RedirectView return value)
+		request.setParameter("param", "value");
+		handlerMethod.invokeAndHandle(webRequest, mavContainer);
+
+		assertEquals("view", mavContainer.getViewName());
+	}
+
+
+	private ServletInvocableHandlerMethod getHandlerMethod(String methodName, Class<?>... argTypes)
 			throws NoSuchMethodException {
 		Method method = Handler.class.getDeclaredMethod(methodName, argTypes);
 		ServletInvocableHandlerMethod handlerMethod = new ServletInvocableHandlerMethod(new Handler(), method);
@@ -133,13 +156,16 @@ public class ServletInvocableHandlerMethodTests {
 		@ResponseStatus(value = HttpStatus.BAD_REQUEST, reason = "400 Bad Request")
 		public void responseStatus() {
 		}
-		
+
 		public void httpServletResponse(HttpServletResponse response) {
 		}
-		
+
 		public void notModified() {
 		}
-		
+
+		public Object dynamicReturnValue(@RequestParam(required=false) String param) {
+			return (param != null) ? "view" : new RedirectView("redirectView");
+		}
 	}
 
 	private static class ExceptionRaisingReturnValueHandler implements HandlerMethodReturnValueHandler {