GH-3241: MetadataStoreSelector - compare old/new (#3242)

Resolves: https://github.com/spring-projects/spring-integration/issues/3241

 * Docs and XML namespace support.

spring-integration-core/src/main/java/org/springframework/integration/config/xml/IdempotentReceiverInterceptorParser.java

@@ -59,6 +59,8 @@ public class IdempotentReceiverInterceptorParser extends AbstractBeanDefinitionP
 		boolean hasValueStrategy = StringUtils.hasText(valueStrategy);
 		String valueExpression = element.getAttribute("value-expression");
 		boolean hasValueExpression = StringUtils.hasText(valueExpression);
+		String compareValues = element.getAttribute("compare-values");
+		boolean hasCompareValues = StringUtils.hasText(compareValues);
 
 		String endpoints = element.getAttribute("endpoint");
 
@@ -68,10 +70,10 @@ public class IdempotentReceiverInterceptorParser extends AbstractBeanDefinitionP
 		}
 
 		if (hasSelector && (hasStore || hasKeyStrategy || hasKeyExpression || hasValueStrategy // NOSONAR complexity
-				|| hasValueExpression)) {
+				|| hasValueExpression || hasCompareValues)) {
 			parserContext.getReaderContext().error("The 'selector' attribute is mutually exclusive with " +
-					"'metadata-store', 'key-strategy', 'key-expression', 'value-strategy' " +
-					"or 'value-expression'", source);
+					"'metadata-store', 'key-strategy', 'key-expression', 'value-strategy', " +
+					"'value-expression', and 'compare-values'", source);
 		}
 
 		if (hasKeyStrategy && hasKeyExpression) {
@@ -133,6 +135,7 @@ public class IdempotentReceiverInterceptorParser extends AbstractBeanDefinitionP
 			else {
 				selectorBuilder.addConstructorArgValue(new RootBeanDefinition(SimpleMetadataStore.class));
 			}
+			IntegrationNamespaceUtils.setReferenceIfAttributeDefined(selectorBuilder, element, "compare-values");
 			selectorBeanDefinition = selectorBuilder.getBeanDefinition();
 		}
 

spring-integration-core/src/main/java/org/springframework/integration/selector/MetadataStoreSelector.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2019 the original author or authors.
+ * Copyright 2014-2020 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.
@@ -16,10 +16,13 @@
 
 package org.springframework.integration.selector;
 
+import java.util.function.BiPredicate;
+
 import org.springframework.integration.core.MessageSelector;
 import org.springframework.integration.handler.MessageProcessor;
 import org.springframework.integration.metadata.ConcurrentMetadataStore;
 import org.springframework.integration.metadata.SimpleMetadataStore;
+import org.springframework.lang.Nullable;
 import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 
@@ -58,6 +61,9 @@ public class MetadataStoreSelector implements MessageSelector {
 
 	private final MessageProcessor<String> valueStrategy;
 
+	@Nullable
+	private BiPredicate<String, String> compareValues;
+
 	public MetadataStoreSelector(MessageProcessor<String> keyStrategy) {
 		this(keyStrategy, (MessageProcessor<String>) null);
 	}
@@ -79,6 +85,26 @@ public class MetadataStoreSelector implements MessageSelector {
 		this.valueStrategy = valueStrategy;
 	}
 
+	/**
+	 * Set a {@link BiPredicate} to compare old and new values in the metadata store for
+	 * the key. The first parameter is the old value; return true if we should accept this
+	 * message and replace the old value with the new value.
+	 * @param compareValues the {@link BiPredicate}.
+	 * @since 5.3
+	 */
+	public void setCompareValues(@Nullable BiPredicate<String, String> compareValues) {
+		this.compareValues = compareValues;
+	}
+
+	/**
+	 * Fluent version of {@link #setCompareValues(BiPredicate)}.
+	 * @param compareValues the {@link BiPredicate}.
+	 * @return this.
+	 */
+	public MetadataStoreSelector compareValues(@Nullable BiPredicate<String, String> compareValues) {
+		setCompareValues(compareValues);
+		return this;
+	}
 
 	@Override
 	public boolean accept(Message<?> message) {
@@ -88,7 +114,21 @@ public class MetadataStoreSelector implements MessageSelector {
 				? this.valueStrategy.processMessage(message)
 				: (timestamp == null ? "0" : Long.toString(timestamp));
 
-		return this.metadataStore.putIfAbsent(key, value) == null;
+		if (this.compareValues == null) {
+			return this.metadataStore.putIfAbsent(key, value) == null;
+		}
+		else {
+			synchronized (this) {
+				String oldValue = this.metadataStore.get(key);
+				if (oldValue == null) {
+					return this.metadataStore.putIfAbsent(key, value) == null;
+				}
+				if (this.compareValues.test(oldValue, value)) {
+					return this.metadataStore.replace(key, oldValue, value);
+				}
+				return false;
+			}
+		}
 	}
 
 }

spring-integration-core/src/main/resources/org/springframework/integration/config/spring-integration.xsd

@@ -4853,6 +4853,19 @@ The list of component name patterns you want to track (e.g.,  tracked-components
 				]]></xsd:documentation>
 				</xsd:annotation>
 			</xsd:attribute>
+			<xsd:attribute name="compare-values">
+				<xsd:annotation>
+					<xsd:appinfo>
+						<tool:annotation kind="ref">
+							<tool:expected-type type="java.util.function.BiPredicate"/>
+						</tool:annotation>
+					</xsd:appinfo>
+					<xsd:documentation><![CDATA[
+					A 'BiPredicate<String, String>' which is called if a value exists to determine whether the message
+					should be accepted and the old value replaced with the new value in the metadata store.
+				]]></xsd:documentation>
+				</xsd:annotation>
+			</xsd:attribute>
 			<xsd:attribute name="discard-channel" type="xsd:string">
 				<xsd:annotation>
 					<xsd:appinfo>