WebFlux constructs model attribute via DataBinder

See gh-26721

spring-web/src/main/java/org/springframework/web/bind/support/WebExchangeDataBinder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 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.
@@ -71,14 +71,30 @@ public class WebExchangeDataBinder extends WebDataBinder {
 	}
 
 
+	/**
+	 * Use a default or single data constructor to create the target by
+	 * binding request parameters, multipart files, or parts to constructor args.
+	 * <p>After the call, use {@link #getBindingResult()} to check for bind errors.
+	 * If there are none, the target is set, and {@link #bind} can be called for
+	 * further initialization via setters.
+	 * @param exchange the request to bind
+	 * @return a {@code Mono<Void>} that completes when the target is created
+	 * @since 6.1
+	 */
+	public Mono<Void> construct(ServerWebExchange exchange) {
+		return getValuesToBind(exchange)
+				.doOnNext(map -> construct(new MapValueResolver(map)))
+				.then();
+	}
+
 	/**
 	 * Bind query parameters, form data, or multipart form data to the binder target.
 	 * @param exchange the current exchange
-	 * @return a {@code Mono<Void>} when binding is complete
+	 * @return a {@code Mono<Void>} that completes when binding is complete
 	 */
 	public Mono<Void> bind(ServerWebExchange exchange) {
 		return getValuesToBind(exchange)
-				.doOnNext(values -> doBind(new MutablePropertyValues(values)))
+				.doOnNext(map -> doBind(new MutablePropertyValues(map)))
 				.then();
 	}
 
@@ -128,4 +144,22 @@ public class WebExchangeDataBinder extends WebDataBinder {
 		}
 	}
 
-}
+
+	/**
+	 * Resolve values from a map.
+	 */
+	private static class MapValueResolver implements ValueResolver {
+
+		private final Map<String, Object> map;
+
+		private MapValueResolver(Map<String, Object> map) {
+			this.map = map;
+		}
+
+		@Override
+		public Object resolveValue(String name, Class<?> type) {
+			return this.map.get(name);
+		}
+	}
+
+}

spring-webflux/src/main/java/org/springframework/web/reactive/BindingContext.java

@@ -24,6 +24,7 @@ import reactor.core.publisher.Mono;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ReactiveAdapterRegistry;
+import org.springframework.core.ResolvableType;
 import org.springframework.lang.Nullable;
 import org.springframework.ui.Model;
 import org.springframework.validation.DataBinder;
@@ -92,8 +93,7 @@ public class BindingContext {
 
 
 	/**
-	 * Create a {@link WebExchangeDataBinder} to apply data binding and
-	 * validation with on the target, command object.
+	 * Create a binder with a target object.
 	 * @param exchange the current exchange
 	 * @param target the object to create a data binder for
 	 * @param name the name of the target object
@@ -101,51 +101,54 @@ public class BindingContext {
 	 * @throws ServerErrorException if {@code @InitBinder} method invocation fails
 	 */
 	public WebExchangeDataBinder createDataBinder(ServerWebExchange exchange, @Nullable Object target, String name) {
-		WebExchangeDataBinder dataBinder = new ExtendedWebExchangeDataBinder(target, name);
-		if (this.initializer != null) {
-			this.initializer.initBinder(dataBinder);
-		}
-		return initDataBinder(dataBinder, exchange);
-	}
-
-	/**
-	 * Initialize the data binder instance for the given exchange.
-	 * @throws ServerErrorException if {@code @InitBinder} method invocation fails
-	 */
-	protected WebExchangeDataBinder initDataBinder(WebExchangeDataBinder binder, ServerWebExchange exchange) {
-		return binder;
+		return createDataBinder(exchange, target, name, null);
 	}
 
 	/**
-	 * Create a {@link WebExchangeDataBinder} without a target object for type
-	 * conversion of request values to simple types.
+	 * Shortcut method to create a binder without a target object.
 	 * @param exchange the current exchange
 	 * @param name the name of the target object
 	 * @return the created data binder
 	 * @throws ServerErrorException if {@code @InitBinder} method invocation fails
 	 */
 	public WebExchangeDataBinder createDataBinder(ServerWebExchange exchange, String name) {
-		return createDataBinder(exchange, null, name);
+		return createDataBinder(exchange, null, name, null);
 	}
 
 	/**
-	 * Variant of {@link #createDataBinder(ServerWebExchange, Object, String)}
-	 * with a {@link MethodParameter} for which the {@code DataBinder} is created.
-	 * That may provide more insight to initialize the {@link WebExchangeDataBinder}.
-	 * <p>By default, if the parameter has {@code @Valid}, Bean Validation is
-	 * excluded, deferring to method validation.
+	 * Create a binder with a target object and a {@code MethodParameter}.
+	 * If the target is {@code null}, then
+	 * {@link WebExchangeDataBinder#setTargetType targetType} is set.
 	 * @since 6.1
 	 */
 	public WebExchangeDataBinder createDataBinder(
-			ServerWebExchange exchange, @Nullable Object target, String name, MethodParameter parameter) {
+			ServerWebExchange exchange, @Nullable Object target, String name, @Nullable MethodParameter parameter) {
+
+		WebExchangeDataBinder dataBinder = new ExtendedWebExchangeDataBinder(target, name);
+		if (target == null && parameter != null) {
+			dataBinder.setTargetType(ResolvableType.forMethodParameter(parameter));
+		}
 
-		WebExchangeDataBinder dataBinder = createDataBinder(exchange, target, name);
-		if (this.methodValidationApplicable) {
-			MethodValidationInitializer.updateBinder(dataBinder, parameter);
+		if (this.initializer != null) {
+			this.initializer.initBinder(dataBinder);
 		}
+		dataBinder = initDataBinder(dataBinder, exchange);
+
+		if (this.methodValidationApplicable && parameter != null) {
+			MethodValidationInitializer.initBinder(dataBinder, parameter);
+		}
+
 		return dataBinder;
 	}
 
+	/**
+	 * Initialize the data binder instance for the given exchange.
+	 * @throws ServerErrorException if {@code @InitBinder} method invocation fails
+	 */
+	protected WebExchangeDataBinder initDataBinder(WebExchangeDataBinder binder, ServerWebExchange exchange) {
+		return binder;
+	}
+
 
 	/**
 	 * Extended variant of {@link WebExchangeDataBinder}, adding path variables.
@@ -170,7 +173,7 @@ public class BindingContext {
 	 */
 	private static class MethodValidationInitializer {
 
-		public static void updateBinder(DataBinder binder, MethodParameter parameter) {
+		public static void initBinder(DataBinder binder, MethodParameter parameter) {
 			if (ReactiveAdapterRegistry.getSharedInstance().getAdapter(parameter.getParameterType()) == null) {
 				for (Annotation annotation : parameter.getParameterAnnotations()) {
 					if (annotation.annotationType().getName().equals("jakarta.validation.Valid")) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/ModelAttributeMethodArgumentResolver.java

@@ -17,10 +17,7 @@
 package org.springframework.web.reactive.result.method.annotation;
 
 import java.lang.annotation.Annotation;
-import java.lang.reflect.Constructor;
-import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 
 import reactor.core.publisher.Mono;
 import reactor.core.publisher.Sinks;
@@ -31,7 +28,6 @@ import org.springframework.context.i18n.LocaleContextHolder;
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ReactiveAdapter;
 import org.springframework.core.ReactiveAdapterRegistry;
-import org.springframework.core.ResolvableType;
 import org.springframework.lang.Nullable;
 import org.springframework.ui.Model;
 import org.springframework.util.Assert;
@@ -100,72 +96,74 @@ public class ModelAttributeMethodArgumentResolver extends HandlerMethodArgumentR
 	public Mono<Object> resolveArgument(
 			MethodParameter parameter, BindingContext context, ServerWebExchange exchange) {
 
-		ResolvableType type = ResolvableType.forMethodParameter(parameter);
-		Class<?> resolvedType = type.resolve();
-		ReactiveAdapter adapter = (resolvedType != null ? getAdapterRegistry().getAdapter(resolvedType) : null);
-		ResolvableType valueType = (adapter != null ? type.getGeneric() : type);
-
-		Assert.state(adapter == null || !adapter.isMultiValue(),
-				() -> getClass().getSimpleName() + " does not support multi-value reactive type wrapper: " +
-						parameter.getGenericParameterType());
+		Class<?> resolvedType = parameter.getParameterType();
+		ReactiveAdapter adapter = getAdapterRegistry().getAdapter(resolvedType);
+		Assert.state(adapter == null || !adapter.isMultiValue(), "Multi-value publisher is not supported");
 
 		String name = ModelInitializer.getNameForParameter(parameter);
-		Mono<?> attributeMono = prepareAttributeMono(name, valueType, context, exchange);
 
-		// unsafe(): we're intercepting, already serialized Publisher signals
+		Mono<WebExchangeDataBinder> dataBinderMono = initDataBinder(
+				name, (adapter != null ? parameter.nested() : parameter), context, exchange);
+
+		// unsafe() is OK: source is Reactive Streams Publisher
 		Sinks.One<BindingResult> bindingResultSink = Sinks.unsafe().one();
 
 		Map<String, Object> model = context.getModel().asMap();
 		model.put(BindingResult.MODEL_KEY_PREFIX + name, bindingResultSink.asMono());
 
-		return attributeMono.flatMap(attribute -> {
-			WebExchangeDataBinder binder = context.createDataBinder(exchange, attribute, name, parameter);
-			return (!bindingDisabled(parameter) ? bindRequestParameters(binder, exchange) : Mono.empty())
-					.doOnError(bindingResultSink::tryEmitError)
-					.doOnSuccess(aVoid -> {
-						validateIfApplicable(binder, parameter, exchange);
-						BindingResult bindingResult = binder.getBindingResult();
-						model.put(BindingResult.MODEL_KEY_PREFIX + name, bindingResult);
-						model.put(name, attribute);
-						// Ignore result: serialized and buffered (should never fail)
-						bindingResultSink.tryEmitValue(bindingResult);
-					})
-					.then(Mono.fromCallable(() -> {
-						BindingResult errors = binder.getBindingResult();
-						if (adapter != null) {
-							return adapter.fromPublisher(errors.hasErrors() ?
-									Mono.error(new WebExchangeBindException(parameter, errors)) : attributeMono);
-						}
-						else {
-							if (errors.hasErrors() && !hasErrorsArgument(parameter)) {
-								throw new WebExchangeBindException(parameter, errors);
-							}
-							return attribute;
-						}
-					}));
-		});
+		return dataBinderMono
+				.flatMap(binder -> {
+					Object attribute = binder.getTarget();
+					Assert.state(attribute != null, "Expected model attribute instance");
+					return (!bindingDisabled(parameter) ? bindRequestParameters(binder, exchange) : Mono.empty())
+							.doOnError(bindingResultSink::tryEmitError)
+							.doOnSuccess(aVoid -> {
+								validateIfApplicable(binder, parameter, exchange);
+								BindingResult bindingResult = binder.getBindingResult();
+								model.put(BindingResult.MODEL_KEY_PREFIX + name, bindingResult);
+								model.put(name, attribute);
+								// Ignore result: serialized and buffered (should never fail)
+								bindingResultSink.tryEmitValue(bindingResult);
+							})
+							.then(Mono.fromCallable(() -> {
+								BindingResult errors = binder.getBindingResult();
+								if (adapter != null) {
+									Mono<Object> mono = (errors.hasErrors() ?
+											Mono.error(new WebExchangeBindException(parameter, errors)) :
+											Mono.just(attribute));
+									return adapter.fromPublisher(mono);
+								}
+								else {
+									if (errors.hasErrors() && !hasErrorsArgument(parameter)) {
+										throw new WebExchangeBindException(parameter, errors);
+									}
+									return attribute;
+								}
+							}));
+				});
 	}
 
-	private Mono<?> prepareAttributeMono(
-			String name, ResolvableType type, BindingContext context, ServerWebExchange exchange) {
-
-		Object attribute = context.getModel().asMap().get(name);
+	private Mono<WebExchangeDataBinder> initDataBinder(
+			String name, MethodParameter parameter, BindingContext context, ServerWebExchange exchange) {
 
-		if (attribute == null) {
-			attribute = removeReactiveAttribute(context.getModel(), name);
+		Object value = context.getModel().asMap().get(name);
+		if (value == null) {
+			value = removeReactiveAttribute(name, context.getModel());
 		}
-
-		if (attribute == null) {
-			return createAttribute(name, type.toClass(), context, exchange);
+		if (value != null) {
+			ReactiveAdapter adapter = getAdapterRegistry().getAdapter(null, value);
+			Assert.isTrue(adapter == null || !adapter.isMultiValue(), "Multi-value publisher is not supported");
+			return (adapter != null ? Mono.from(adapter.toPublisher(value)) : Mono.just(value))
+					.map(attr -> context.createDataBinder(exchange, attr, name, parameter));
+		}
+		else {
+			WebExchangeDataBinder binder = context.createDataBinder(exchange, null, name, parameter);
+			return constructAttribute(binder, exchange).thenReturn(binder);
 		}
-
-		ReactiveAdapter adapter = getAdapterRegistry().getAdapter(null, attribute);
-		Assert.isTrue(adapter == null || !adapter.isMultiValue(), "Model attribute must be single-value publisher");
-		return (adapter != null ? Mono.from(adapter.toPublisher(attribute)) : Mono.justOrEmpty(attribute));
 	}
 
 	@Nullable
-	private Object removeReactiveAttribute(Model model, String name) {
+	private Object removeReactiveAttribute(String name, Model model) {
 		for (Map.Entry<String, Object> entry : model.asMap().entrySet()) {
 			if (entry.getKey().startsWith(name)) {
 				ReactiveAdapter adapter = getAdapterRegistry().getAdapter(null, entry.getValue());
@@ -181,66 +179,24 @@ public class ModelAttributeMethodArgumentResolver extends HandlerMethodArgumentR
 		return null;
 	}
 
-	private Mono<?> createAttribute(
-			String attributeName, Class<?> clazz, BindingContext context, ServerWebExchange exchange) {
-
-		Constructor<?> ctor = BeanUtils.getResolvableConstructor(clazz);
-		return constructAttribute(ctor, attributeName, context, exchange);
-	}
-
-	private Mono<?> constructAttribute(Constructor<?> ctor, String attributeName,
-			BindingContext context, ServerWebExchange exchange) {
-
-		if (ctor.getParameterCount() == 0) {
-			// A single default constructor -> clearly a standard JavaBeans arrangement.
-			return Mono.just(BeanUtils.instantiateClass(ctor));
-		}
-
-		// A single data class constructor -> resolve constructor arguments from request parameters.
-		WebExchangeDataBinder binder = context.createDataBinder(exchange, null, attributeName);
-		return getValuesToBind(binder, exchange).map(bindValues -> {
-			String[] paramNames = BeanUtils.getParameterNames(ctor);
-			Class<?>[] paramTypes = ctor.getParameterTypes();
-			Object[] args = new Object[paramTypes.length];
-			String fieldDefaultPrefix = binder.getFieldDefaultPrefix();
-			String fieldMarkerPrefix = binder.getFieldMarkerPrefix();
-			for (int i = 0; i < paramNames.length; i++) {
-				String paramName = paramNames[i];
-				Class<?> paramType = paramTypes[i];
-				Object value = bindValues.get(paramName);
-				if (value == null) {
-					if (fieldDefaultPrefix != null) {
-						value = bindValues.get(fieldDefaultPrefix + paramName);
-					}
-					if (value == null && fieldMarkerPrefix != null) {
-						if (bindValues.get(fieldMarkerPrefix + paramName) != null) {
-							value = binder.getEmptyValue(paramType);
-						}
-					}
-				}
-				value = (value instanceof List<?> list ? list.toArray() : value);
-				MethodParameter methodParam = MethodParameter.forFieldAwareConstructor(ctor, i, paramName);
-				if (value == null && methodParam.isOptional()) {
-					args[i] = (methodParam.getParameterType() == Optional.class ? Optional.empty() : null);
-				}
-				else {
-					args[i] = binder.convertIfNecessary(value, paramTypes[i], methodParam);
-				}
-			}
-			return BeanUtils.instantiateClass(ctor, args);
-		});
+	/**
+	 * Protected method to obtain the values for data binding.
+	 * @deprecated and not called; replaced by built-in support for
+	 * constructor initialization in {@link org.springframework.validation.DataBinder}
+	 */
+	@Deprecated(since = "6.1", forRemoval = true)
+	public Mono<Map<String, Object>> getValuesToBind(WebExchangeDataBinder binder, ServerWebExchange exchange) {
+		throw new UnsupportedOperationException();
 	}
 
 	/**
-	 * Protected method to obtain the values for data binding. By default this
-	 * method delegates to {@link WebExchangeDataBinder#getValuesToBind}.
-	 * @param binder the data binder in use
+	 * Extension point to create the attribute, binding the request to constructor args.
+	 * @param binder the data binder instance to use for the binding
 	 * @param exchange the current exchange
-	 * @return a map of bind values
-	 * @since 5.3
+	 * @since 6.1
 	 */
-	public Mono<Map<String, Object>> getValuesToBind(WebExchangeDataBinder binder, ServerWebExchange exchange) {
-		return binder.getValuesToBind(exchange);
+	protected Mono<Void> constructAttribute(WebExchangeDataBinder binder, ServerWebExchange exchange) {
+		return binder.construct(exchange);
 	}
 
 	/**

spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/InitBinderBindingContextTests.java

@@ -56,7 +56,7 @@ public class InitBinderBindingContextTests {
 	public void createBinder() throws Exception {
 		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		BindingContext context = createBindingContext("initBinder", WebDataBinder.class);
-		WebDataBinder dataBinder = context.createDataBinder(exchange, null, null);
+		WebDataBinder dataBinder = context.createDataBinder(exchange, null);
 
 		assertThat(dataBinder.getDisallowedFields()).isNotNull();
 		assertThat(dataBinder.getDisallowedFields()[0]).isEqualTo("id");
@@ -69,7 +69,7 @@ public class InitBinderBindingContextTests {
 
 		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		BindingContext context = createBindingContext("initBinder", WebDataBinder.class);
-		WebDataBinder dataBinder = context.createDataBinder(exchange, null, null);
+		WebDataBinder dataBinder = context.createDataBinder(exchange, null);
 
 		assertThat(dataBinder.getConversionService()).isSameAs(conversionService);
 	}
@@ -78,7 +78,7 @@ public class InitBinderBindingContextTests {
 	public void createBinderWithAttrName() throws Exception {
 		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		BindingContext context = createBindingContext("initBinderWithAttributeName", WebDataBinder.class);
-		WebDataBinder dataBinder = context.createDataBinder(exchange, null, "foo");
+		WebDataBinder dataBinder = context.createDataBinder(exchange, "foo");
 
 		assertThat(dataBinder.getDisallowedFields()).isNotNull();
 		assertThat(dataBinder.getDisallowedFields()[0]).isEqualTo("id");
@@ -88,7 +88,7 @@ public class InitBinderBindingContextTests {
 	public void createBinderWithAttrNameNoMatch() throws Exception {
 		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		BindingContext context = createBindingContext("initBinderWithAttributeName", WebDataBinder.class);
-		WebDataBinder dataBinder = context.createDataBinder(exchange, null, "invalidName");
+		WebDataBinder dataBinder = context.createDataBinder(exchange, "invalidName");
 
 		assertThat(dataBinder.getDisallowedFields()).isNull();
 	}
@@ -97,7 +97,7 @@ public class InitBinderBindingContextTests {
 	public void createBinderNullAttrName() throws Exception {
 		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		BindingContext context = createBindingContext("initBinderWithAttributeName", WebDataBinder.class);
-		WebDataBinder dataBinder = context.createDataBinder(exchange, null, null);
+		WebDataBinder dataBinder = context.createDataBinder(exchange, null);
 
 		assertThat(dataBinder.getDisallowedFields()).isNull();
 	}
@@ -106,8 +106,7 @@ public class InitBinderBindingContextTests {
 	public void returnValueNotExpected() throws Exception {
 		MockServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"));
 		BindingContext context = createBindingContext("initBinderReturnValue", WebDataBinder.class);
-		assertThatIllegalStateException().isThrownBy(() ->
-				context.createDataBinder(exchange, null, "invalidName"));
+		assertThatIllegalStateException().isThrownBy(() -> context.createDataBinder(exchange, "invalidName"));
 	}
 
 	@Test
@@ -118,7 +117,7 @@ public class InitBinderBindingContextTests {
 		this.argumentResolvers.add(new RequestParamMethodArgumentResolver(null, adapterRegistry, false));
 
 		BindingContext context = createBindingContext("initBinderTypeConversion", WebDataBinder.class, int.class);
-		WebDataBinder dataBinder = context.createDataBinder(exchange, null, "foo");
+		WebDataBinder dataBinder = context.createDataBinder(exchange, "foo");
 
 		assertThat(dataBinder.getDisallowedFields()).isNotNull();
 		assertThat(dataBinder.getDisallowedFields()[0]).isEqualToIgnoringCase("requestParam-22");