Draft candidate

Signed-off-by: chickenchickenlove <[email protected]>

Author: chickenchickenlove

spring-kafka/src/main/java/org/springframework/kafka/support/AbstractKafkaHeaderMapper.java

@@ -23,6 +23,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
@@ -79,6 +80,12 @@ public abstract class AbstractKafkaHeaderMapper implements KafkaHeaderMapper {
 
 	private Charset charset = StandardCharsets.UTF_8;
 
+	private final List<HeaderMatcher> matchersForListValue = new ArrayList<>();
+
+	private final Set<String> cachedHeadersForListValue = new LinkedHashSet<>();
+
+	private final Set<String> cachedHeadersForSingleValue = new LinkedHashSet<>();
+
 	/**
 	 * Construct a mapper that will match the supplied patterns (outbound) and all headers
 	 * (inbound). For outbound mapping, certain internal framework headers are never
@@ -97,6 +104,18 @@ public AbstractKafkaHeaderMapper(String... patterns) {
 	 * @param patterns the patterns.
 	 */
 	protected AbstractKafkaHeaderMapper(boolean outbound, String... patterns) {
+		this(outbound, new ArrayList<>(), patterns);
+	}
+
+	/**
+	 * Construct a mapper that will match the supplied patterns (outbound) and all headers
+	 * (inbound). For outbound mapping, certain internal framework headers are never
+	 * mapped.
+	 * @param outbound true for an outbound mapper.
+	 * @param patternsForListValue the patterns for multiple values at the same key.
+	 * @param patterns the patterns.
+	 */
+	protected AbstractKafkaHeaderMapper(boolean outbound, List<String> patternsForListValue, String... patterns) {
 		Assert.notNull(patterns, "'patterns' must not be null");
 		this.outbound = outbound;
 		if (outbound) {
@@ -123,6 +142,11 @@ protected AbstractKafkaHeaderMapper(boolean outbound, String... patterns) {
 		for (String pattern : patterns) {
 			this.matchers.add(new SimplePatternBasedHeaderMatcher(pattern));
 		}
+
+		for (String patternForListValue : patternsForListValue) {
+			this.matchersForListValue.add(new SimplePatternBasedHeaderMatcher(patternForListValue));
+		}
+
 	}
 
 	/**
@@ -287,6 +311,34 @@ private String mapRawIn(String header, byte[] value) {
 		return null;
 	}
 
+	/**
+	 * Check whether the header value should be mapped to multiple values.
+	 * @param headerName the header name.
+	 * @return True for multiple values at the same key.
+	 */
+	protected boolean isHeaderForListValue(String headerName) {
+		if (this.matchersForListValue.isEmpty()) {
+			return false;
+		}
+
+		if (this.cachedHeadersForSingleValue.contains(headerName)) {
+			return false;
+		}
+
+		if (this.cachedHeadersForListValue.contains(headerName)) {
+			return true;
+		}
+
+		for (HeaderMatcher headerMatcher : this.matchersForListValue) {
+			if (headerMatcher.matchHeader(headerName)) {
+				this.cachedHeadersForListValue.add(headerName);
+				return true;
+			}
+		}
+		this.cachedHeadersForSingleValue.add(headerName);
+		return false;
+	}
+
 	/**
 	 * A matcher for headers.
 	 * @since 2.3

spring-kafka/src/main/java/org/springframework/kafka/support/DefaultKafkaHeaderMapper.java

@@ -19,6 +19,7 @@
 import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
@@ -103,6 +104,23 @@ public DefaultKafkaHeaderMapper() {
 		this(JacksonUtils.enhancedObjectMapper());
 	}
 
+	/**
+	 * Construct an instance with the default object mapper and default header patterns
+	 * for outbound headers; all inbound headers are mapped. The default pattern list is
+	 * {@code "!id", "!timestamp" and "*"}. In addition, most of the headers in
+	 * {@link KafkaHeaders} are never mapped as headers since they represent data in
+	 * consumer/producer records.
+	 * @see #DefaultKafkaHeaderMapper(ObjectMapper)
+	 * @param patternsForListValue
+	 */
+	public DefaultKafkaHeaderMapper(List<String> patternsForListValue) {
+		this(JacksonUtils.enhancedObjectMapper(),
+			 patternsForListValue,
+			 "!" + MessageHeaders.ID,
+			 "!" + MessageHeaders.TIMESTAMP,
+			 "*");
+	}
+
 	/**
 	 * Construct an instance with the provided object mapper and default header patterns
 	 * for outbound headers; all inbound headers are mapped. The patterns are applied in
@@ -149,11 +167,32 @@ public DefaultKafkaHeaderMapper(String... patterns) {
 	 * @see org.springframework.util.PatternMatchUtils#simpleMatch(String, String)
 	 */
 	public DefaultKafkaHeaderMapper(ObjectMapper objectMapper, String... patterns) {
-		this(true, objectMapper, patterns);
+		this(true, objectMapper, new ArrayList<>(), patterns);
+	}
+
+	/**
+	 * Construct an instance with the provided object mapper and the provided header
+	 * patterns for outbound headers; all inbound headers are mapped. The patterns are
+	 * applied in order, stopping on the first match (positive or negative). Patterns are
+	 * negated by preceding them with "!". The patterns will replace the default patterns;
+	 * you generally should not map the {@code "id" and "timestamp"} headers. Note: most
+	 * of the headers in {@link KafkaHeaders} are never mapped as headers since they
+	 * represent data in consumer/producer records.
+	 * @param objectMapper the object mapper.
+	 * @param patternsForListValue the patterns for multiple values at the same key.
+	 * @param patterns the patterns.
+	 * @see org.springframework.util.PatternMatchUtils#simpleMatch(String, String)
+	 */
+	public DefaultKafkaHeaderMapper(ObjectMapper objectMapper, List<String> patternsForListValue, String... patterns) {
+		this(true, objectMapper, patternsForListValue, patterns);
 	}
 
 	private DefaultKafkaHeaderMapper(boolean outbound, ObjectMapper objectMapper, String... patterns) {
-		super(outbound, patterns);
+		this(outbound, objectMapper, new ArrayList<>(), patterns);
+	}
+
+	private DefaultKafkaHeaderMapper(boolean outbound, ObjectMapper objectMapper, List<String> patternsForListValue, String... patterns) {
+		super(outbound, patternsForListValue, patterns);
 		Assert.notNull(objectMapper, "'objectMapper' must not be null");
 		Assert.noNullElements(patterns, "'patterns' must not have null elements");
 		this.objectMapper = objectMapper;
@@ -340,7 +379,22 @@ else if (!(headerName.equals(JSON_TYPES)) && matchesForInbound(headerName)) {
 	 */
 
 	protected void handleHeader(String headerName, Header header, final Map<String, Object> headers) {
-		headers.put(headerName, headerValueToAddIn(header));
+		if (!this.isHeaderForListValue(headerName)) {
+			headers.put(headerName, headerValueToAddIn(header));
+		}
+		else {
+			Object values = headers.getOrDefault(headerName, new ArrayList<>());
+
+			if (values instanceof List) {
+				@SuppressWarnings("unchecked")
+				List<Object> castedValues = (List<Object>) values;
+				castedValues.add(headerValueToAddIn(header));
+				headers.put(headerName, castedValues);
+			}
+			else {
+				headers.put(headerName, headerValueToAddIn(header));
+			}
+		}
 	}
 
 	private void populateJsonValueHeader(Header header, String requestedType, Map<String, Object> headers) {

spring-kafka/src/main/java/org/springframework/kafka/support/SimpleKafkaHeaderMapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2022 the original author or authors.
+ * Copyright 2018-2025 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.
@@ -17,7 +17,9 @@
 package org.springframework.kafka.support;
 
 import java.nio.ByteBuffer;
+import java.util.ArrayList;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
@@ -77,7 +79,11 @@ public SimpleKafkaHeaderMapper(String... patterns) {
 	}
 
 	private SimpleKafkaHeaderMapper(boolean outbound, String... patterns) {
-		super(outbound, patterns);
+		this(outbound, new ArrayList<>(), patterns);
+	}
+
+	private SimpleKafkaHeaderMapper(boolean outbound, List<String> patternsForListValue, String... patterns) {
+		super(outbound, patternsForListValue, patterns);
 	}
 
 	/**
@@ -111,7 +117,21 @@ public void toHeaders(Headers source, Map<String, Object> target) {
 					target.put(headerName, ByteBuffer.wrap(header.value()).getInt());
 				}
 				else {
-					target.put(headerName, headerValueToAddIn(header));
+					if (!this.isHeaderForListValue(headerName)) {
+						target.put(headerName, headerValueToAddIn(header));
+					}
+					else {
+						Object values = target.getOrDefault(headerName, new ArrayList<>());
+						if (values instanceof List) {
+							@SuppressWarnings("unchecked")
+							List<Object> castedValues = (List<Object>) values;
+							castedValues.add(headerValueToAddIn(header));
+							target.put(headerName, castedValues);
+						}
+						else {
+							target.put(headerName, headerValueToAddIn(header));
+						}
+					}
 				}
 			}
 		});

spring-kafka/src/test/java/org/springframework/kafka/support/MultiValueKafkaHeaderMapperTest.java renamed to spring-kafka/src/test/java/org/springframework/kafka/support/DefaultKafkaHeaderMapperForMultiValueTest.java

@@ -44,9 +44,9 @@
 import org.springframework.kafka.retrytopic.RetryTopicConfigurationBuilder;
 import org.springframework.kafka.retrytopic.RetryTopicConfigurationSupport;
 import org.springframework.kafka.retrytopic.RetryTopicHeaders;
-import org.springframework.kafka.support.MultiValueKafkaHeaderMapperTest.Config.MultiValueTestListener;
-import org.springframework.kafka.support.MultiValueKafkaHeaderMapperTest.RetryTopicConfigurations.FirstTopicListener;
-import org.springframework.kafka.support.MultiValueKafkaHeaderMapperTest.RetryTopicConfigurations.MyCustomDltProcessor;
+import org.springframework.kafka.support.DefaultKafkaHeaderMapperForMultiValueTest.Config.MultiValueTestListener;
+import org.springframework.kafka.support.DefaultKafkaHeaderMapperForMultiValueTest.RetryTopicConfigurations.FirstTopicListener;
+import org.springframework.kafka.support.DefaultKafkaHeaderMapperForMultiValueTest.RetryTopicConfigurations.MyCustomDltProcessor;
 import org.springframework.kafka.support.converter.MessagingMessageConverter;
 import org.springframework.kafka.test.EmbeddedKafkaBroker;
 import org.springframework.kafka.test.context.EmbeddedKafka;
@@ -71,10 +71,10 @@
 @SpringJUnitConfig
 @DirtiesContext
 @EmbeddedKafka(partitions = 1, topics = {
-		MultiValueKafkaHeaderMapperTest.TEST_TOPIC,
-		MultiValueKafkaHeaderMapperTest.RETRY_TOPIC
+		DefaultKafkaHeaderMapperForMultiValueTest.TEST_TOPIC,
+		DefaultKafkaHeaderMapperForMultiValueTest.RETRY_TOPIC
 })
-class MultiValueKafkaHeaderMapperTest {
+class DefaultKafkaHeaderMapperForMultiValueTest {
 
 	public final static String TEST_TOPIC = "multi-value.tests";
 
@@ -211,10 +211,8 @@ public KafkaListenerContainerFactory<?> kafkaListenerContainerFactory() {
 			ConcurrentKafkaListenerContainerFactory<Integer, String> factory =
 					new ConcurrentKafkaListenerContainerFactory<>();
 
-			MultiValueKafkaHeaderMapper headerMapper = new MultiValueKafkaHeaderMapper();
-
-			// Add Test
-			headerMapper.addSingleValueHeader(SINGLE_VALUE_HEADER);
+			// For Test
+			DefaultKafkaHeaderMapper headerMapper = new DefaultKafkaHeaderMapper(List.of(MULTI_VALUE_HEADER1, MULTI_VALUE_HEADER2));
 			MessagingMessageConverter converter = new MessagingMessageConverter(headerMapper);
 
 			factory.setConsumerFactory(consumerFactory());