HandlerMethodArgumentResolver is now asynchronous

spring-web-reactive/src/main/java/org/springframework/reactive/web/dispatch/method/HandlerMethodArgumentResolver.java

@@ -16,6 +16,8 @@
 
 package org.springframework.reactive.web.dispatch.method;
 
+import org.reactivestreams.Publisher;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.http.server.ReactiveServerHttpRequest;
 
@@ -27,6 +29,12 @@ public interface HandlerMethodArgumentResolver {
 
 	boolean supportsParameter(MethodParameter parameter);
 
-	Object resolveArgument(MethodParameter parameter, ReactiveServerHttpRequest request);
+	/**
+	 * The returned Publisher must produce a single value. As Reactive Streams
+	 * does not allow publishing null values, if the value may be {@code null}
+	 * use {@link java.util.Optional#ofNullable(Object)} to wrap it.
+	 */
+	Publisher<Object> resolveArgument(MethodParameter parameter, ReactiveServerHttpRequest request);
+
 
 }

spring-web-reactive/src/main/java/org/springframework/reactive/web/dispatch/method/InvocableHandlerMethod.java

@@ -19,8 +19,14 @@ package org.springframework.reactive.web.dispatch.method;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.ArrayList;
-import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
+import java.util.Optional;
+
+import org.reactivestreams.Publisher;
+import reactor.Publishers;
+import reactor.fn.tuple.Tuple;
+import reactor.rx.Streams;
 
 import org.springframework.core.DefaultParameterNameDiscoverer;
 import org.springframework.core.GenericTypeResolver;
@@ -32,9 +38,6 @@ import org.springframework.web.method.HandlerMethod;
 
 
 /**
- * 90% overlap with the existing one in spring-web except for the different
- * HandlerMethodArgumentResolver contract.
- *
  * @author Rossen Stoyanchev
  */
 public class InvocableHandlerMethod extends HandlerMethod {
@@ -55,53 +58,74 @@ public class InvocableHandlerMethod extends HandlerMethod {
 	}
 
 
-	public Object invokeForRequest(ReactiveServerHttpRequest request, Object... providedArgs) throws Exception {
-		Object[] args = getMethodArgumentValues(request, providedArgs);
-		if (logger.isTraceEnabled()) {
-			logger.trace("Invoking [" + getBeanType().getSimpleName() + "." +
-					getMethod().getName() + "] method with arguments " + Arrays.asList(args));
-		}
-		Object returnValue = doInvoke(args);
-		if (logger.isTraceEnabled()) {
-			logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]");
-		}
-		return returnValue;
+	public Publisher<Object> invokeForRequest(ReactiveServerHttpRequest request,
+			Object... providedArgs) {
+
+		List<Publisher<Object>> argPublishers = getMethodArguments(request, providedArgs);
+
+		Publisher<Object[]> argValues = (!argPublishers.isEmpty() ?
+				Streams.zip(argPublishers, this::unwrapOptionalArgValues) : Publishers.just(new Object[0]));
+
+		return Publishers.map(argValues, args -> {
+			if (logger.isTraceEnabled()) {
+				logger.trace("Invoking [" + getBeanType().getSimpleName() + "." +
+						getMethod().getName() + "] method with arguments " +
+						Collections.singletonList(argPublishers));
+			}
+			Object returnValue = null;
+			try {
+				returnValue = doInvoke(args);
+				if (logger.isTraceEnabled()) {
+					logger.trace("Method [" + getMethod().getName() + "] returned [" + returnValue + "]");
+				}
+			}
+			catch (Exception ex) {
+				// TODO: how to best handle error inside map? (also wrapping hides original ex)
+				throw new IllegalStateException(ex);
+			}
+			return returnValue;
+		});
 	}
 
-	private Object[] getMethodArgumentValues(ReactiveServerHttpRequest request, Object... providedArgs) throws Exception {
+	private List<Publisher<Object>> getMethodArguments(ReactiveServerHttpRequest request,
+			Object... providedArgs) {
+
 		MethodParameter[] parameters = getMethodParameters();
-		Object[] args = new Object[parameters.length];
+		List<Publisher<Object>> valuePublishers = new ArrayList<>(parameters.length);
 		for (int i = 0; i < parameters.length; i++) {
 			MethodParameter parameter = parameters[i];
 			parameter.initParameterNameDiscovery(this.parameterNameDiscoverer);
 			GenericTypeResolver.resolveParameterType(parameter, getBean().getClass());
-			args[i] = resolveProvidedArgument(parameter, providedArgs);
-			if (args[i] != null) {
+			Object value = resolveProvidedArgument(parameter, providedArgs);
+			if (value != null) {
+				valuePublishers.add(Publishers.just(value));
 				continue;
 			}
+			boolean resolved = false;
 			for (HandlerMethodArgumentResolver resolver : this.argumentResolvers) {
 				if (resolver.supportsParameter(parameter)) {
 					try {
-						args[i] = resolver.resolveArgument(parameter, request);
+						valuePublishers.add(resolver.resolveArgument(parameter, request));
+						resolved = true;
 						break;
 					}
 					catch (Exception ex) {
-						if (logger.isDebugEnabled()) {
-							logger.debug(getArgumentResolutionErrorMessage("Error resolving argument", i), ex);
-						}
-						throw ex;
+						String msg = buildArgErrorMessage("Error resolving argument", i);
+						valuePublishers.add(Publishers.error(new IllegalStateException(msg, ex)));
+						break;
 					}
 				}
 			}
-			if (args[i] == null) {
-				String msg = getArgumentResolutionErrorMessage("No suitable resolver for argument", i);
-				throw new IllegalStateException(msg);
+			if (!resolved) {
+				String msg = buildArgErrorMessage("No suitable resolver for argument", i);
+				valuePublishers.add(Publishers.error(new IllegalStateException(msg)));
+				break;
 			}
 		}
-		return args;
+		return valuePublishers;
 	}
 
-	private String getArgumentResolutionErrorMessage(String message, int index) {
+	private String buildArgErrorMessage(String message, int index) {
 		MethodParameter param = getMethodParameters()[index];
 		message += " [" + index + "] [type=" + param.getParameterType().getName() + "]";
 		return getDetailedErrorMessage(message);
@@ -125,6 +149,27 @@ public class InvocableHandlerMethod extends HandlerMethod {
 		return null;
 	}
 
+	private void unwrapOptionalArgValues(Object[] args) {
+		for (int i = 0; i < args.length; i++) {
+			if (args[i] instanceof Optional) {
+				Optional optional = (Optional) args[i];
+				args[i] = optional.isPresent() ? optional.get() : null;
+			}
+		}
+	}
+
+	private Object[] unwrapOptionalArgValues(Tuple tuple) {
+		Object[] args = new Object[tuple.size()];
+		for (int i = 0; i < tuple.size(); i++) {
+			args[i] = tuple.get(i);
+			if (args[i] instanceof Optional) {
+				Optional optional = (Optional) args[i];
+				args[i] = optional.isPresent() ? optional.get() : null;
+			}
+		}
+		return args;
+	}
+
 	protected Object doInvoke(Object... args) throws Exception {
 		ReflectionUtils.makeAccessible(getBridgedMethod());
 		try {

spring-web-reactive/src/main/java/org/springframework/reactive/web/dispatch/method/annotation/RequestBodyArgumentResolver.java

@@ -23,6 +23,7 @@ import java.util.Collections;
 import java.util.List;
 
 import org.reactivestreams.Publisher;
+import reactor.Publishers;
 
 import org.springframework.core.MethodParameter;
 import org.springframework.core.ResolvableType;
@@ -66,9 +67,7 @@ public class RequestBodyArgumentResolver implements HandlerMethodArgumentResolve
 	}
 
 	@Override
-	@SuppressWarnings("unchecked")
-	public Object resolveArgument(MethodParameter parameter, ReactiveServerHttpRequest request) {
-
+	public Publisher<Object> resolveArgument(MethodParameter parameter, ReactiveServerHttpRequest request) {
 		MediaType mediaType = resolveMediaType(request);
 		ResolvableType type = ResolvableType.forMethodParameter(parameter);
 		List<Object> hints = new ArrayList<>();
@@ -85,12 +84,10 @@ public class RequestBodyArgumentResolver implements HandlerMethodArgumentResolve
 			}
 			elementStream = deserializer.decode(inputStream, elementType, mediaType, hints.toArray());
 		}
-		if (conversionService.canConvert(Publisher.class, type.getRawClass())) {
-			return conversionService.convert(elementStream, type.getRawClass());
-		}
-		else {
-			return elementStream;
+		if (this.conversionService.canConvert(Publisher.class, type.getRawClass())) {
+			return Publishers.just(this.conversionService.convert(elementStream, type.getRawClass()));
 		}
+		return Publishers.map(elementStream, element -> element);
 	}
 
 	private MediaType resolveMediaType(ReactiveServerHttpRequest request) {

spring-web-reactive/src/main/java/org/springframework/reactive/web/dispatch/method/annotation/RequestMappingHandlerAdapter.java

@@ -79,14 +79,8 @@ public class RequestMappingHandlerAdapter implements HandlerAdapter, Initializin
 		InvocableHandlerMethod handlerMethod = new InvocableHandlerMethod((HandlerMethod) handler);
 		handlerMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
 
-		try {
-			Object result = handlerMethod.invokeForRequest(request);
-			return Publishers.just(new HandlerResult(handlerMethod, result));
-		}
-		catch (Exception e) {
-			// TODO: remove throws declaration from InvocableHandlerMethod
-			return Publishers.error(e);
-		}
+		Publisher<Object> resultPublisher = handlerMethod.invokeForRequest(request);
+		return Publishers.map(resultPublisher, result -> new HandlerResult(handlerMethod, result));
 	}
 
 }

spring-web-reactive/src/main/java/org/springframework/reactive/web/dispatch/method/annotation/RequestParamArgumentResolver.java

@@ -17,6 +17,11 @@
 package org.springframework.reactive.web.dispatch.method.annotation;
 
 
+import java.util.Optional;
+
+import org.reactivestreams.Publisher;
+import reactor.Publishers;
+
 import org.springframework.core.MethodParameter;
 import org.springframework.http.server.ReactiveServerHttpRequest;
 import org.springframework.reactive.web.dispatch.method.HandlerMethodArgumentResolver;
@@ -40,11 +45,12 @@ public class RequestParamArgumentResolver implements HandlerMethodArgumentResolv
 
 
 	@Override
-	public Object resolveArgument(MethodParameter param, ReactiveServerHttpRequest request) {
+	public Publisher<Object> resolveArgument(MethodParameter param, ReactiveServerHttpRequest request) {
 		RequestParam annotation = param.getParameterAnnotation(RequestParam.class);
 		String name = (annotation.value().length() != 0 ? annotation.value() : param.getParameterName());
 		UriComponents uriComponents = UriComponentsBuilder.fromUri(request.getURI()).build();
-		return uriComponents.getQueryParams().getFirst(name);
+		String value = uriComponents.getQueryParams().getFirst(name);
+		return Publishers.just(Optional.ofNullable(value));
 	}
 
 }

spring-web-reactive/src/test/java/org/springframework/reactive/web/dispatch/method/annotation/RequestMappingIntegrationTests.java

@@ -180,6 +180,11 @@ public class RequestMappingIntegrationTests extends AbstractHttpHandlerIntegrati
 		capitalizeCollection("http://localhost:" + port + "/stream-capitalize");
 	}
 
+	@Test
+	public void personCapitalize() throws Exception {
+		capitalizePojo("http://localhost:" + port + "/person-capitalize");
+	}
+	
 	@Test
 	public void completableFutureCapitalize() throws Exception {
 		capitalizePojo("http://localhost:" + port + "/completable-future-capitalize");
@@ -376,6 +381,13 @@ public class RequestMappingIntegrationTests extends AbstractHttpHandlerIntegrati
 			});
 		}
 
+		@RequestMapping("/person-capitalize")
+		@ResponseBody
+		public Person personCapitalize(@RequestBody Person person) {
+			person.setName(person.getName().toUpperCase());
+			return person;
+		}
+		
 		@RequestMapping("/completable-future-capitalize")
 		@ResponseBody
 		public CompletableFuture<Person> completableFutureCapitalize(@RequestBody CompletableFuture<Person> personFuture) {