GH-1675: Validation on @KafkaHandler Methods

Resolves #1675

Add support for payload validation with `@KafkaHandler` methods.

* Fix javadoc.
# Conflicts:
#	src/reference/asciidoc/whats-new.adoc

Author: garyrussell

spring-kafka/src/main/java/org/springframework/kafka/config/KafkaListenerEndpointRegistrar.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2020 the original author or authors.
+ * Copyright 2014-2021 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.
@@ -187,6 +187,10 @@ public void afterPropertiesSet() {
 	protected void registerAllEndpoints() {
 		synchronized (this.endpointDescriptors) {
 			for (KafkaListenerEndpointDescriptor descriptor : this.endpointDescriptors) {
+				if (descriptor.endpoint instanceof MultiMethodKafkaListenerEndpoint
+						&& this.validator != null) {
+					((MultiMethodKafkaListenerEndpoint) descriptor.endpoint).setValidator(this.validator);
+				}
 				this.endpointRegistry.registerListenerContainer(
 						descriptor.endpoint, resolveContainerFactory(descriptor));
 			}

spring-kafka/src/main/java/org/springframework/kafka/config/MultiMethodKafkaListenerEndpoint.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2019 the original author or authors.
+ * Copyright 2016-2021 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.
@@ -25,6 +25,7 @@
 import org.springframework.kafka.listener.adapter.MessagingMessageListenerAdapter;
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.handler.invocation.InvocableHandlerMethod;
+import org.springframework.validation.Validator;
 
 /**
  * The {@link MethodKafkaListenerEndpoint} extension for several POJO methods
@@ -44,11 +45,16 @@ public class MultiMethodKafkaListenerEndpoint<K, V> extends MethodKafkaListenerE
 
 	private final Method defaultMethod;
 
+	private Validator validator;
+
 	/**
 	 * Construct an instance for the provided methods and bean with no default method.
 	 * @param methods the methods.
 	 * @param bean the bean.
+	 * @deprecated in favor of
+	 * {@link #MultiMethodKafkaListenerEndpoint(List, Method, Object)}.
 	 */
+	@Deprecated
 	public MultiMethodKafkaListenerEndpoint(List<Method> methods, Object bean) {
 		this(methods, null, bean);
 	}
@@ -66,6 +72,15 @@ public MultiMethodKafkaListenerEndpoint(List<Method> methods, @Nullable Method d
 		setBean(bean);
 	}
 
+	/**
+	 * Set a payload validator.
+	 * @param validator the validator.
+	 * @since 2.5.11
+	 */
+	public void setValidator(Validator validator) {
+		this.validator = validator;
+	}
+
 	@Override
 	protected HandlerAdapter configureListenerAdapter(MessagingMessageListenerAdapter<K, V> messageListener) {
 		List<InvocableHandlerMethod> invocableHandlerMethods = new ArrayList<InvocableHandlerMethod>();
@@ -79,7 +94,7 @@ protected HandlerAdapter configureListenerAdapter(MessagingMessageListenerAdapte
 			}
 		}
 		DelegatingInvocableHandler delegatingHandler = new DelegatingInvocableHandler(invocableHandlerMethods,
-				defaultHandler, getBean(), getResolver(), getBeanExpressionContext(), getBeanFactory());
+				defaultHandler, getBean(), getResolver(), getBeanExpressionContext(), getBeanFactory(), this.validator);
 		return new HandlerAdapter(delegatingHandler);
 	}
 

spring-kafka/src/main/java/org/springframework/kafka/listener/adapter/DelegatingInvocableHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 the original author or authors.
+ * Copyright 2016-2021 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.
@@ -39,11 +39,15 @@
 import org.springframework.kafka.support.KafkaUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.converter.MessageConverter;
 import org.springframework.messaging.handler.HandlerMethod;
 import org.springframework.messaging.handler.annotation.Header;
 import org.springframework.messaging.handler.annotation.SendTo;
+import org.springframework.messaging.handler.annotation.support.PayloadMethodArgumentResolver;
 import org.springframework.messaging.handler.invocation.InvocableHandlerMethod;
 import org.springframework.util.Assert;
+import org.springframework.validation.Validator;
 
 
 /**
@@ -63,6 +67,9 @@ public class DelegatingInvocableHandler {
 
 	private final ConcurrentMap<Class<?>, InvocableHandlerMethod> cachedHandlers = new ConcurrentHashMap<>();
 
+	private final ConcurrentMap<InvocableHandlerMethod, MethodParameter> payloadMethodParameters =
+			new ConcurrentHashMap<>();
+
 	private final InvocableHandlerMethod defaultHandler;
 
 	private final Map<InvocableHandlerMethod, Expression> handlerSendTo = new HashMap<>();
@@ -77,17 +84,22 @@ public class DelegatingInvocableHandler {
 
 	private final ConfigurableListableBeanFactory beanFactory;
 
+	private final PayloadValidator validator;
+
 	/**
 	 * Construct an instance with the supplied handlers for the bean.
 	 * @param handlers the handlers.
 	 * @param bean the bean.
 	 * @param beanExpressionResolver the expression resolver.
 	 * @param beanExpressionContext the expression context.
+	 * @deprecated in favor of
+	 * {@link #DelegatingInvocableHandler(List, InvocableHandlerMethod, Object, BeanExpressionResolver, BeanExpressionContext, BeanFactory, Validator)}
 	 */
+	@Deprecated
 	public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers, Object bean,
 			BeanExpressionResolver beanExpressionResolver, BeanExpressionContext beanExpressionContext) {
 
-		this(handlers, null, bean, beanExpressionResolver, beanExpressionContext);
+		this(handlers, null, bean, beanExpressionResolver, beanExpressionContext, null, null);
 	}
 
 	/**
@@ -97,13 +109,16 @@ public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers, Object
 	 * @param bean the bean.
 	 * @param beanExpressionResolver the resolver.
 	 * @param beanExpressionContext the context.
+	 * @deprecated in favor of
+	 * {@link #DelegatingInvocableHandler(List, InvocableHandlerMethod, Object, BeanExpressionResolver, BeanExpressionContext, BeanFactory, Validator)}
 	 * @since 2.1.3
 	 */
+	@Deprecated
 	public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers,
 			@Nullable InvocableHandlerMethod defaultHandler,
 			Object bean, BeanExpressionResolver beanExpressionResolver, BeanExpressionContext beanExpressionContext) {
 
-		this(handlers, defaultHandler, bean, beanExpressionResolver, beanExpressionContext, null);
+		this(handlers, defaultHandler, bean, beanExpressionResolver, beanExpressionContext, null, null);
 	}
 
 	/**
@@ -114,13 +129,35 @@ public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers,
 	 * @param beanExpressionResolver the resolver.
 	 * @param beanExpressionContext the context.
 	 * @param beanFactory the bean factory.
-	 * @since 2.1.11
+	 * @deprecated in favor of
+	 * {@link #DelegatingInvocableHandler(List, InvocableHandlerMethod, Object, BeanExpressionResolver, BeanExpressionContext, BeanFactory, Validator)}
+	 * @since 2.5.11
 	 */
+	@Deprecated
 	public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers,
 			@Nullable InvocableHandlerMethod defaultHandler,
 			Object bean, BeanExpressionResolver beanExpressionResolver, BeanExpressionContext beanExpressionContext,
 			@Nullable BeanFactory beanFactory) {
 
+		this(handlers, defaultHandler, bean, beanExpressionResolver, beanExpressionContext, beanFactory, null);
+	}
+
+	/**
+	 * Construct an instance with the supplied handlers for the bean.
+	 * @param handlers the handlers.
+	 * @param defaultHandler the default handler.
+	 * @param bean the bean.
+	 * @param beanExpressionResolver the resolver.
+	 * @param beanExpressionContext the context.
+	 * @param beanFactory the bean factory.
+	 * @param validator the validator.
+	 * @since 2.5.11
+	 */
+	public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers,
+			@Nullable InvocableHandlerMethod defaultHandler,
+			Object bean, BeanExpressionResolver beanExpressionResolver, BeanExpressionContext beanExpressionContext,
+			@Nullable BeanFactory beanFactory, @Nullable Validator validator) {
+
 		this.handlers = new ArrayList<>();
 		for (InvocableHandlerMethod handler : handlers) {
 			this.handlers.add(wrapIfNecessary(handler));
@@ -132,6 +169,7 @@ public DelegatingInvocableHandler(List<InvocableHandlerMethod> handlers,
 		this.beanFactory = beanFactory instanceof ConfigurableListableBeanFactory
 				? (ConfigurableListableBeanFactory) beanFactory
 				: null;
+		this.validator = validator == null ? null : new PayloadValidator(validator);
 	}
 
 	private InvocableHandlerMethod wrapIfNecessary(InvocableHandlerMethod handler) {
@@ -166,6 +204,12 @@ public Object getBean() {
 	public Object invoke(Message<?> message, Object... providedArgs) throws Exception { //NOSONAR
 		Class<? extends Object> payloadClass = message.getPayload().getClass();
 		InvocableHandlerMethod handler = getHandlerForPayload(payloadClass);
+		if (this.validator != null) {
+			MethodParameter parameter = this.payloadMethodParameters.get(handler);
+			if (parameter != null) {
+				this.validator.validate(message, parameter, message.getPayload());
+			}
+		}
 		Object result;
 		if (handler instanceof MetadataAwareInvocableHandlerMethod) {
 			Object[] args = new Object[providedArgs.length + 1];
@@ -279,23 +323,29 @@ protected boolean matchHandlerMethod(Class<? extends Object> payloadClass, Invoc
 			if ((methodParameter.getParameterAnnotations().length == 0
 					|| !methodParameter.hasParameterAnnotation(Header.class))
 					&& methodParameter.getParameterType().isAssignableFrom(payloadClass)) {
+				if (this.validator != null) {
+					this.payloadMethodParameters.put(handler, methodParameter);
+				}
 				return true;
 			}
 		}
 
-		boolean foundCandidate = false;
+		MethodParameter foundCandidate = null;
 		for (int i = 0; i < parameterAnnotations.length; i++) {
 			MethodParameter methodParameter = new MethodParameter(method, i);
 			if ((methodParameter.getParameterAnnotations().length == 0
 					|| !methodParameter.hasParameterAnnotation(Header.class))
 					&& methodParameter.getParameterType().isAssignableFrom(payloadClass)) {
-				if (foundCandidate) {
+				if (foundCandidate != null) {
 					throw new KafkaException("Ambiguous payload parameter for " + method.toGenericString());
 				}
-				foundCandidate = true;
+				foundCandidate = methodParameter;
 			}
 		}
-		return foundCandidate;
+		if (foundCandidate != null && this.validator != null) {
+			this.payloadMethodParameters.put(handler, foundCandidate);
+		}
+		return foundCandidate != null;
 	}
 
 	/**
@@ -325,4 +375,32 @@ private static final class MetadataAwareInvocableHandlerMethod extends Invocable
 
 	}
 
+	private static final class PayloadValidator extends PayloadMethodArgumentResolver {
+
+		PayloadValidator(Validator validator) {
+			super(new MessageConverter() { // Required but never used
+
+				@Override
+				@Nullable
+				public Message<?> toMessage(Object payload, @Nullable
+				MessageHeaders headers) {
+					return null;
+				}
+
+				@Override
+				@Nullable
+				public Object fromMessage(Message<?> message, Class<?> targetClass) {
+					return null;
+				}
+
+			}, validator);
+		}
+
+		@Override
+		public void validate(Message<?> message, MethodParameter parameter, Object target) { // NOSONAR - public
+			super.validate(message, parameter, target);
+		}
+
+	}
+
 }