SPR-7608 Add fallback mechanism for instantiating a model attribute from a path variable

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/support/PathVariableMethodArgumentResolver.java

@@ -64,9 +64,9 @@ public class PathVariableMethodArgumentResolver extends AbstractNamedValueMethod
 	@Override
 	@SuppressWarnings("unchecked")
 	protected Object resolveName(String name, MethodParameter parameter, NativeWebRequest request) throws Exception {
-		String key = HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE;
+		Map<String, String> uriTemplateVars = 
-		int scope = RequestAttributes.SCOPE_REQUEST;
+			(Map<String, String>) request.getAttribute(
-		Map<String, String> uriTemplateVars = (Map<String, String>) request.getAttribute(key, scope);
+					HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);
 		return (uriTemplateVars != null) ? uriTemplateVars.get(name) : null;
 	}
 

org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/mvc/method/annotation/support/ServletModelAttributeMethodProcessor.java

@@ -16,17 +16,31 @@
 
 package org.springframework.web.servlet.mvc.method.annotation.support;
 
+import java.beans.PropertyEditor;
+import java.util.Map;
+
 import javax.servlet.ServletRequest;
 
 import org.springframework.beans.BeanUtils;
+import org.springframework.core.MethodParameter;
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.validation.DataBinder;
 import org.springframework.web.bind.ServletRequestDataBinder;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.support.WebDataBinderFactory;
 import org.springframework.web.context.request.NativeWebRequest;
+import org.springframework.web.context.request.RequestAttributes;
 import org.springframework.web.method.annotation.support.ModelAttributeMethodProcessor;
+import org.springframework.web.servlet.HandlerMapping;
 
 /**
- * A Servlet-specific {@link ModelAttributeMethodProcessor} variant that casts the {@link WebDataBinder}
+ * A Servlet-specific {@link ModelAttributeMethodProcessor} variant with the following further benefits:
+ * <ul>
+ * 	<li>Casts the data binder down to {@link ServletRequestDataBinder} prior to invoking bind on it
+ * 	<li>Attempts to instantiate the model attribute using a path variable and type conversion
+ * </ul>
+ *  that casts
  * instance to {@link ServletRequestDataBinder} prior to invoking data binding.
  *
  * @author Rossen Stoyanchev
@@ -44,12 +58,43 @@ public class ServletModelAttributeMethodProcessor extends ModelAttributeMethodPr
 	}
 
 	/**
-	 * {@inheritDoc}
+	 * Instantiates the model attribute by trying to match the model attribute name to a path variable.
-	 * <p>This method downcasts the binder instance to {@link ServletRequestDataBinder} and invokes
+	 * If a match is found an attempt is made to convert the String path variable to the expected 
-	 * its bind method passing a {@link ServletRequest} to it.
+	 * method parameter type through a registered {@link Converter} or {@link PropertyEditor}.
+	 * If this fails the call is delegated back to the parent for default constructor instantiation.   
 	 */
 	@Override
-	protected void doBind(WebDataBinder binder, NativeWebRequest request) {
+	@SuppressWarnings("unchecked")
+	protected Object createAttribute(String attributeName, 
+									 MethodParameter parameter, 
+									 WebDataBinderFactory binderFactory, 
+									 NativeWebRequest request) throws Exception {
+		Map<String, String> uriTemplateVars = 
+			(Map<String, String>) request.getAttribute(
+					HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, RequestAttributes.SCOPE_REQUEST);
+
+		if (uriTemplateVars != null && uriTemplateVars.containsKey(attributeName)) {
+			try {
+				String var = uriTemplateVars.get(attributeName);
+				DataBinder binder = binderFactory.createBinder(request, null, attributeName);
+				return binder.convertIfNecessary(var, parameter.getParameterType());
+
+			} catch (Exception exception) {
+				logger.info("Model attribute '" + attributeName + "' matches to a URI template variable name. "
+						+ "The URI template variable however couldn't converted to a model attribute instance: "
+						+ exception.getMessage());
+			}
+		}
+		
+		return super.createAttribute(attributeName, parameter, binderFactory, request);
+	}
+
+	/**
+	 * {@inheritDoc}
+	 * <p>This implementation downcasts to {@link ServletRequestDataBinder} before invoking the bind operation.
+	 */
+	@Override
+	protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
 		ServletRequest servletRequest = request.getNativeRequest(ServletRequest.class);
 		ServletRequestDataBinder servletBinder = (ServletRequestDataBinder) binder;
 		servletBinder.bind(servletRequest);

org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/mvc/method/annotation/SerlvetModelAttributeMethodProcessorTests.java

@@ -0,0 +1,123 @@
+/*
+ * Copyright 2002-2011 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.servlet.mvc.method.annotation;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+
+import java.lang.reflect.Method;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.springframework.beans.TestBean;
+import org.springframework.core.MethodParameter;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.support.WebDataBinderFactory;
+import org.springframework.web.context.request.NativeWebRequest;
+import org.springframework.web.context.request.ServletWebRequest;
+import org.springframework.web.method.support.ModelAndViewContainer;
+import org.springframework.web.servlet.HandlerMapping;
+import org.springframework.web.servlet.mvc.method.annotation.support.ServletModelAttributeMethodProcessor;
+
+/**
+ * Test fixture for {@link ServletModelAttributeMethodProcessor} specific tests.
+ * Also see org.springframework.web.method.annotation.support.ModelAttributeMethodProcessorTests
+ * 
+ * @author Rossen Stoyanchev
+ */
+public class SerlvetModelAttributeMethodProcessorTests {
+
+	private ServletModelAttributeMethodProcessor processor;
+
+	private MethodParameter testBeanModelAttr;
+	
+	private MethodParameter testBeanWithoutStringConstructorModelAttr;
+
+	private ModelAndViewContainer mavContainer;
+
+	private NativeWebRequest webRequest;
+
+	private MockHttpServletRequest request;
+
+	private WebDataBinderFactory binderFactory;
+
+	@Before
+	public void setUp() throws Exception {
+		processor = new ServletModelAttributeMethodProcessor(false);
+
+		Method method = getClass().getDeclaredMethod("modelAttribute", 
+				TestBean.class, TestBeanWithoutStringConstructor.class);
+		
+		testBeanModelAttr = new MethodParameter(method, 0);
+		testBeanWithoutStringConstructorModelAttr = new MethodParameter(method, 1);
+		
+		binderFactory = new ServletRequestDataBinderFactory(null, null);
+		mavContainer = new ModelAndViewContainer();
+		
+		request = new MockHttpServletRequest();
+		webRequest = new ServletWebRequest(request);
+	}
+
+	@Test
+	public void createAttributeViaPathVariable() throws Exception {
+		Map<String, String> uriTemplateVars = new HashMap<String, String>();
+		uriTemplateVars.put("testBean1", "pathy");
+		request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, uriTemplateVars);
+
+		// Type conversion from "pathy" to TestBean via TestBean(String) constructor
+
+		TestBean testBean = 
+			(TestBean) processor.resolveArgument(testBeanModelAttr, mavContainer, webRequest, binderFactory);
+		
+		assertEquals("pathy", testBean.getName());
+	}
+
+	@Test
+	public void createAttributeAfterPathVariableConversionError() throws Exception {
+		Map<String, String> uriTemplateVars = new HashMap<String, String>();
+		uriTemplateVars.put("testBean1", "pathy");
+		request.setAttribute(HandlerMapping.URI_TEMPLATE_VARIABLES_ATTRIBUTE, uriTemplateVars);
+
+		TestBeanWithoutStringConstructor testBean = 
+			(TestBeanWithoutStringConstructor) processor.resolveArgument(
+				testBeanWithoutStringConstructorModelAttr, mavContainer, webRequest, binderFactory);
+		
+		assertNotNull(testBean);
+	}
+
+	
+	@SuppressWarnings("unused")
+	private void modelAttribute(@ModelAttribute("testBean1") TestBean testBean1, 
+								@ModelAttribute("testBean2") TestBeanWithoutStringConstructor testBean2) { 
+	}
+
+
+	@SuppressWarnings("unused")
+	private static class TestBeanWithoutStringConstructor {
+
+		public TestBeanWithoutStringConstructor() {
+		}
+		
+		public TestBeanWithoutStringConstructor(int i) {
+		}
+		
+	}
+
+}

org.springframework.web/src/main/java/org/springframework/web/method/annotation/support/ModelAttributeMethodProcessor.java

@@ -18,11 +18,12 @@ package org.springframework.web.method.annotation.support;
 
 import java.lang.annotation.Annotation;
 
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
 import org.springframework.beans.BeanUtils;
 import org.springframework.core.MethodParameter;
 import org.springframework.validation.BindException;
 import org.springframework.validation.BindingResult;
-import org.springframework.validation.DataBinder;
 import org.springframework.validation.Errors;
 import org.springframework.web.bind.WebDataBinder;
 import org.springframework.web.bind.annotation.ModelAttribute;
@@ -50,6 +51,8 @@ import org.springframework.web.method.support.ModelAndViewContainer;
  */
 public class ModelAttributeMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {
 
+	protected Log logger = LogFactory.getLog(this.getClass());
+	
 	private final boolean useDefaultResolution;
 	
 	/**
@@ -82,26 +85,33 @@ public class ModelAttributeMethodProcessor implements HandlerMethodArgumentResol
 	 * default constructor. Data binding and optionally validation is then applied through a {@link WebDataBinder}
 	 * instance. Validation is invoked optionally when the method parameter is annotated with an {@code @Valid}.
 	 *
-	 * @throws Exception if a {@link WebDataBinder} could not be created or if data binding and validation result in
+	 * @throws BindException if data binding and validation result in an error and the next method parameter 
-	 * an error and the next method parameter is not of type {@link Errors} or {@link BindingResult}.
+	 * is neither of type {@link Errors} nor {@link BindingResult}.
+	 * @throws Exception if a {@link WebDataBinder} could not be created.
 	 */
 	public final Object resolveArgument(MethodParameter parameter,
 										ModelAndViewContainer mavContainer,
-										NativeWebRequest webRequest,
+										NativeWebRequest request,
 										WebDataBinderFactory binderFactory) throws Exception {
-		WebDataBinder binder = createDataBinder(parameter, mavContainer, webRequest, binderFactory);
+		String name = ModelFactory.getNameForParameter(parameter);
+		Object target = (mavContainer.containsAttribute(name)) ?
+				mavContainer.getAttribute(name) : createAttribute(name, parameter, binderFactory, request);
+				
+		WebDataBinder binder = binderFactory.createBinder(request, target, name);
 
 		if (binder.getTarget() != null) {
-			doBind(binder, webRequest);
+			bindRequestParameters(binder, request);
 			
-			if (shouldValidate(binder, parameter)) {
+			if (isValidationApplicable(binder, parameter)) {
 				binder.validate();
 			}
 			
-			if (failOnError(binder, parameter) && binder.getBindingResult().hasErrors()) {
+			if (binder.getBindingResult().hasErrors()) {
+				if (isBindExceptionRequired(binder, parameter)) {
 					throw new BindException(binder.getBindingResult());
 				}
 			}
+		}
 
 		mavContainer.addAllAttributes(binder.getBindingResult().getModel());
 
@@ -109,23 +119,22 @@ public class ModelAttributeMethodProcessor implements HandlerMethodArgumentResol
 	}
 
 	/**
-	 * Creates a {@link WebDataBinder} for a target object.
+	 * Creates an instance of the specified model attribute. This method is invoked only if the attribute is
+	 * not available in the model. This default implementation uses the no-argument constructor. 
+	 * Subclasses can override to provide additional means of creating the model attribute.
+	 * 
+	 * @param attributeName the name of the model attribute
+	 * @param parameter the method argument declaring the model attribute
+	 * @param binderFactory a factory for creating {@link WebDataBinder} instances
+	 * @param request the current request
+	 * @return the created model attribute; never {@code null}
+	 * @throws Exception raised in the process of creating the instance
 	 */
-	private WebDataBinder createDataBinder(MethodParameter parameter,
+	protected Object createAttribute(String attributeName, 
-										   ModelAndViewContainer mavContainer,
+									 MethodParameter parameter, 
-										   NativeWebRequest webRequest,
+									 WebDataBinderFactory binderFactory, 
-										   WebDataBinderFactory binderFactory) throws Exception {
+									 NativeWebRequest request) throws Exception {
-		String attrName = ModelFactory.getNameForParameter(parameter);
+		return BeanUtils.instantiateClass(parameter.getParameterType());
-		
-		Object target;
-		if (mavContainer.containsAttribute(attrName)) {
-			target = mavContainer.getAttribute(attrName);
-		}
-		else {
-			target = BeanUtils.instantiateClass(parameter.getParameterType());
-		}
-		
-		return binderFactory.createBinder(webRequest, target, attrName);
 	}
 	
 	/**
@@ -134,17 +143,17 @@ public class ModelAttributeMethodProcessor implements HandlerMethodArgumentResol
 	 * @param binder the binder with the target object to apply request values to
 	 * @param request the current request
 	 */
-	protected void doBind(WebDataBinder binder, NativeWebRequest request) {
+	protected void bindRequestParameters(WebDataBinder binder, NativeWebRequest request) {
 		((WebRequestDataBinder) binder).bind(request);
 	}
 
 	/**
-	 * Whether to validate the target object of the given {@link WebDataBinder} instance.
+	 * Whether to validate the model attribute inside the given data binder instance.
 	 * @param binder the data binder containing the validation candidate
-	 * @param parameter the method argument for which data binding is performed
+	 * @param parameter the method argument declaring the validation candidate
-	 * @return true if {@link DataBinder#validate()} should be invoked, false otherwise.
+	 * @return {@code true} if validation should be applied, {@code false} otherwise.
 	 */
-	protected boolean shouldValidate(WebDataBinder binder, MethodParameter parameter) {
+	protected boolean isValidationApplicable(WebDataBinder binder, MethodParameter parameter) {
 		Annotation[] annotations = parameter.getParameterAnnotations();
 		for (Annotation annot : annotations) {
 			if ("Valid".equals(annot.annotationType().getSimpleName())) {
@@ -160,7 +169,7 @@ public class ModelAttributeMethodProcessor implements HandlerMethodArgumentResol
 	 * @param parameter the method argument for which data binding is performed
 	 * @return true if the binding or validation errors should result in a {@link BindException}, false otherwise.
 	 */
-	protected boolean failOnError(WebDataBinder binder, MethodParameter parameter) {
+	protected boolean isBindExceptionRequired(WebDataBinder binder, MethodParameter parameter) {
 		int i = parameter.getParameterIndex();
 		Class<?>[] paramTypes = parameter.getMethod().getParameterTypes();
 		boolean hasBindingResult = (paramTypes.length > (i + 1) && Errors.class.isAssignableFrom(paramTypes[i + 1]));

org.springframework.web/src/test/java/org/springframework/web/method/annotation/support/ModelAttributeMethodProcessorTests.java

@@ -83,7 +83,7 @@ public class ModelAttributeMethodProcessorTests {
 	
 	@Before
 	public void setUp() throws Exception {
-		processor = new ModelAttributeMethodProcessor(true);
+		processor = new ModelAttributeMethodProcessor(false);
 
 		Method method = ModelAttributeHandler.class.getDeclaredMethod("modelAttribute", 
 				TestBean.class, Errors.class, int.class, TestBean.class, TestBean.class);
@@ -103,68 +103,86 @@ public class ModelAttributeMethodProcessorTests {
 	}
 
 	@Test
-	public void supportParameter() throws Exception {
+	public void supportedParameters() throws Exception {
-		processor = new ModelAttributeMethodProcessor(true);
+		// Only @ModelAttribute arguments
 		assertTrue(processor.supportsParameter(paramNamedValidModelAttr));
-		assertTrue(processor.supportsParameter(paramErrors));
-		assertFalse(processor.supportsParameter(paramInt));
 		assertTrue(processor.supportsParameter(paramModelAttr));
-		assertTrue(processor.supportsParameter(paramNonSimpleType));
 		
-		processor = new ModelAttributeMethodProcessor(false);
-		assertTrue(processor.supportsParameter(paramNamedValidModelAttr));
 		assertFalse(processor.supportsParameter(paramErrors));
 		assertFalse(processor.supportsParameter(paramInt));
-		assertTrue(processor.supportsParameter(paramModelAttr));
 		assertFalse(processor.supportsParameter(paramNonSimpleType));
 	}
 	
 	@Test
-	public void supportsReturnType() throws Exception {
+	public void supportedParametersInDefaultResolutionMode() throws Exception {
 		processor = new ModelAttributeMethodProcessor(true);
-		assertTrue(processor.supportsReturnType(returnParamNamedModelAttr));
-		assertFalse(processor.supportsReturnType(returnParamNonSimpleType));
 		
+		// Only non-simple types, even if not annotated
+		assertTrue(processor.supportsParameter(paramNamedValidModelAttr));
+		assertTrue(processor.supportsParameter(paramErrors));
+		assertTrue(processor.supportsParameter(paramModelAttr));
+		assertTrue(processor.supportsParameter(paramNonSimpleType));
+
+		assertFalse(processor.supportsParameter(paramInt));
+	}
+	
+	@Test
+	public void supportedReturnTypes() throws Exception {
 		processor = new ModelAttributeMethodProcessor(false);
 		assertTrue(processor.supportsReturnType(returnParamNamedModelAttr));
 		assertFalse(processor.supportsReturnType(returnParamNonSimpleType));
 	}
 	
 	@Test
-	public void shouldValidate() throws Exception {
+	public void supportedReturnTypesInDefaultResolutionMode() throws Exception {
-		assertTrue(processor.shouldValidate(null, paramNamedValidModelAttr));
+		processor = new ModelAttributeMethodProcessor(true);
-		assertFalse(processor.shouldValidate(null, paramNonSimpleType));
+		assertTrue(processor.supportsReturnType(returnParamNamedModelAttr));
+		assertFalse(processor.supportsReturnType(returnParamNonSimpleType));
 	}
 	
 	@Test
-	public void failOnError() throws Exception {
+	public void validationApplicable() throws Exception {
-		assertFalse("Shouldn't failOnError with BindingResult", processor.failOnError(null, paramNamedValidModelAttr));
+		assertTrue(processor.isValidationApplicable(null, paramNamedValidModelAttr));
-		assertTrue("Should failOnError without BindingResult", processor.failOnError(null, paramNonSimpleType));
 	}
 	
 	@Test
-	public void createBinderFromModelAttribute() throws Exception {
+	public void validationNotApplicable() throws Exception {
-		createBinderFromModelAttr("attrName", paramNamedValidModelAttr);
+		assertFalse(processor.isValidationApplicable(null, paramNonSimpleType));
-		createBinderFromModelAttr("testBean", paramModelAttr);
-		createBinderFromModelAttr("testBean", paramNonSimpleType);
 	}
 
-	private void createBinderFromModelAttr(String expectedAttrName, MethodParameter param) throws Exception {
+	@Test
+	public void bindExceptionRequired() throws Exception {
+		assertTrue(processor.isBindExceptionRequired(null, paramNonSimpleType));
+	}
+
+	@Test
+	public void bindExceptionNotRequired() throws Exception {
+		assertFalse(processor.isBindExceptionRequired(null, paramNamedValidModelAttr));
+	}
+
+	@Test
+	public void getAttributeFromModel() throws Exception {
+		testGetAttributeFromModel("attrName", paramNamedValidModelAttr);
+		testGetAttributeFromModel("testBean", paramModelAttr);
+		testGetAttributeFromModel("testBean", paramNonSimpleType);
+	}
+
+	private void testGetAttributeFromModel(String expectedAttributeName, MethodParameter param) throws Exception {
 		Object target = new TestBean();
-		mavContainer.addAttribute(expectedAttrName, target);
+		mavContainer.addAttribute(expectedAttributeName, target);
 
 		WebDataBinder dataBinder = new WebRequestDataBinder(target);
-		WebDataBinderFactory binderFactory = createMock(WebDataBinderFactory.class);
+		WebDataBinderFactory factory = createMock(WebDataBinderFactory.class);
-		expect(binderFactory.createBinder(webRequest, target, expectedAttrName)).andReturn(dataBinder);
+		expect(factory.createBinder(webRequest, target, expectedAttributeName)).andReturn(dataBinder);
-		replay(binderFactory);
+		replay(factory);
 		
-		processor.resolveArgument(param, mavContainer, webRequest, binderFactory);
+		processor.resolveArgument(param, mavContainer, webRequest, factory);
 		
-		verify(binderFactory);
+		verify(factory);
 	}
 
 	@Test
-	public void createBinderWithAttributeConstructor() throws Exception {
+	public void createAttribute() throws Exception {
 		WebDataBinder dataBinder = new WebRequestDataBinder(null);
 
 		WebDataBinderFactory factory = createMock(WebDataBinderFactory.class);
@@ -177,7 +195,7 @@ public class ModelAttributeMethodProcessorTests {
 	}
 
 	@Test
-	public void bindAndValidate() throws Exception {
+	public void automaticValidation() throws Exception {
 		Object target = new TestBean();
 		mavContainer.addAttribute("attrName", target);
 		
@@ -193,7 +211,7 @@ public class ModelAttributeMethodProcessorTests {
 	}
 	
 	@Test(expected=BindException.class)
-	public void bindAndFail() throws Exception {
+	public void bindException() throws Exception {
 		Object target = new TestBean();
 		mavContainer.getModel().addAttribute(target);