GH-9416: Extract BaseMessageBuilder for easier message extensions

Fixes: #9416
Issue link: #9416

The `MessageBuilderFactory` bean could be used a central place to provide custom `Message`
implementation into the application.
For example, the `GenericMessage.toString()` can be overridden to remove or mask sensitive
information from the payload or headers.

* Extract a `BaseMessageBuilder` from the `MessageBuilder` class to simplify
a custom `MessageBuilderFactory` implementation
* Test and document new feature and its purpose

spring-integration-core/src/main/java/org/springframework/integration/IntegrationMessageHeaderAccessor.java

@@ -108,7 +108,7 @@ public IntegrationMessageHeaderAccessor(@Nullable Message<?> message) {
 	 * @see #isReadOnly(String)
 	 */
 	public void setReadOnlyHeaders(String... readOnlyHeaders) {
-		Assert.noNullElements(readOnlyHeaders, "'readOnlyHeaders' must not be contain null items.");
+		Assert.noNullElements(readOnlyHeaders, "'readOnlyHeaders' must not contain null items.");
 		if (!ObjectUtils.isEmpty(readOnlyHeaders)) {
 			this.readOnlyHeaders = new HashSet<>(Arrays.asList(readOnlyHeaders));
 		}

spring-integration-core/src/main/java/org/springframework/integration/support/BaseMessageBuilder.java

@@ -0,0 +1,335 @@
+/*
+ * Copyright 2024 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.integration.support;
+
+import java.util.Arrays;
+import java.util.Date;
+import java.util.List;
+import java.util.Map;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.integration.IntegrationMessageHeaderAccessor;
+import org.springframework.lang.Nullable;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.MessageChannel;
+import org.springframework.messaging.MessageHeaders;
+import org.springframework.messaging.support.ErrorMessage;
+import org.springframework.messaging.support.GenericMessage;
+import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
+
+/**
+ * The {@link AbstractIntegrationMessageBuilder} extension for the default logic to build message.
+ * The {@link MessageBuilder} is fully based on this class.
+ * This abstract class can be used for creating custom {@link Message} instances.
+ * For that purpose its {@link #build()} method has to be overridden.
+ * The custom {@link Message} type could be used, for example, to hide sensitive information
+ * from payload and headers when message is logged.
+ * For this goal there would be enough to override {@link GenericMessage#toString()}
+ * and filter out (or mask) those headers which container such sensitive information.
+ *
+ * @param <T> the payload type.
+ * @param <B> the target builder class type.
+ *
+ * @author Artem Bilan
+ *
+ * @since 6.4
+ *
+ * @see MessageBuilder
+ * @see MessageBuilderFactory
+ */
+public abstract class BaseMessageBuilder<T, B extends BaseMessageBuilder<T, B>>
+		extends AbstractIntegrationMessageBuilder<T> {
+
+	private static final Log LOGGER = LogFactory.getLog(BaseMessageBuilder.class);
+
+	private final T payload;
+
+	private final IntegrationMessageHeaderAccessor headerAccessor;
+
+	@Nullable
+	private final Message<T> originalMessage;
+
+	private volatile boolean modified;
+
+	private String[] readOnlyHeaders;
+
+	protected BaseMessageBuilder(T payload, @Nullable Message<T> originalMessage) {
+		Assert.notNull(payload, "payload must not be null");
+		this.payload = payload;
+		this.originalMessage = originalMessage;
+		this.headerAccessor = new IntegrationMessageHeaderAccessor(originalMessage);
+		if (originalMessage != null) {
+			this.modified = (!this.payload.equals(originalMessage.getPayload()));
+		}
+	}
+
+	@Override
+	public T getPayload() {
+		return this.payload;
+	}
+
+	@Override
+	public Map<String, Object> getHeaders() {
+		return this.headerAccessor.toMap();
+	}
+
+	@Nullable
+	@Override
+	public <V> V getHeader(String key, Class<V> type) {
+		return this.headerAccessor.getHeader(key, type);
+	}
+
+	/**
+	 * Set the value for the given header name. If the provided value is {@code null}, the header will be removed.
+	 * @param headerName The header name.
+	 * @param headerValue The header value.
+	 * @return this MessageBuilder.
+	 */
+	@Override
+	public B setHeader(String headerName, @Nullable Object headerValue) {
+		this.headerAccessor.setHeader(headerName, headerValue);
+		return _this();
+	}
+
+	/**
+	 * Set the value for the given header name only if the header name is not already associated with a value.
+	 * @param headerName The header name.
+	 * @param headerValue The header value.
+	 * @return this MessageBuilder.
+	 */
+	@Override
+	public B setHeaderIfAbsent(String headerName, Object headerValue) {
+		this.headerAccessor.setHeaderIfAbsent(headerName, headerValue);
+		return _this();
+	}
+
+	/**
+	 * Removes all headers provided via array of 'headerPatterns'. As the name suggests the array
+	 * may contain simple matching patterns for header names. Supported pattern styles are:
+	 * {@code xxx*}, {@code *xxx}, {@code *xxx*} and {@code xxx*yyy}.
+	 * @param headerPatterns The header patterns.
+	 * @return this MessageBuilder.
+	 */
+	@Override
+	public B removeHeaders(String... headerPatterns) {
+		this.headerAccessor.removeHeaders(headerPatterns);
+		return _this();
+	}
+
+	/**
+	 * Remove the value for the given header name.
+	 * @param headerName The header name.
+	 * @return this MessageBuilder.
+	 */
+	@Override
+	public B removeHeader(String headerName) {
+		if (!this.headerAccessor.isReadOnly(headerName)) {
+			this.headerAccessor.removeHeader(headerName);
+		}
+		else if (LOGGER.isInfoEnabled()) {
+			LOGGER.info("The header [" + headerName + "] is ignored for removal because it is is readOnly.");
+		}
+		return _this();
+	}
+
+	/**
+	 * Copy the name-value pairs from the provided Map. This operation will overwrite any existing values. Use
+	 * {@link #copyHeadersIfAbsent(Map)} to avoid overwriting values. Note that the 'id' and 'timestamp' header values
+	 * will never be overwritten.
+	 * @param headersToCopy The headers to copy.
+	 * @return this MessageBuilder.
+	 * @see MessageHeaders#ID
+	 * @see MessageHeaders#TIMESTAMP
+	 */
+	@Override
+	public B copyHeaders(@Nullable Map<String, ?> headersToCopy) {
+		this.headerAccessor.copyHeaders(headersToCopy);
+		return _this();
+	}
+
+	/**
+	 * Copy the name-value pairs from the provided Map. This operation will not override any existing values.
+	 * @param headersToCopy The headers to copy.
+	 * @return this MessageBuilder.
+	 */
+	@Override
+	public B copyHeadersIfAbsent(@Nullable Map<String, ?> headersToCopy) {
+		if (headersToCopy != null) {
+			for (Map.Entry<String, ?> entry : headersToCopy.entrySet()) {
+				String headerName = entry.getKey();
+				if (!this.headerAccessor.isReadOnly(headerName)) {
+					this.headerAccessor.setHeaderIfAbsent(headerName, entry.getValue());
+				}
+			}
+		}
+		return _this();
+	}
+
+	@SuppressWarnings("unchecked")
+	@Override
+	@Nullable
+	protected List<List<Object>> getSequenceDetails() {
+		return (List<List<Object>>) this.headerAccessor.getHeader(IntegrationMessageHeaderAccessor.SEQUENCE_DETAILS);
+	}
+
+	@Override
+	@Nullable
+	protected Object getCorrelationId() {
+		return this.headerAccessor.getCorrelationId();
+	}
+
+	@Override
+	protected Object getSequenceNumber() {
+		return this.headerAccessor.getSequenceNumber();
+	}
+
+	@Override
+	protected Object getSequenceSize() {
+		return this.headerAccessor.getSequenceSize();
+	}
+
+	@Override
+	public B pushSequenceDetails(Object correlationId, int sequenceNumber, int sequenceSize) {
+		super.pushSequenceDetails(correlationId, sequenceNumber, sequenceSize);
+		return _this();
+	}
+
+	@Override
+	public B popSequenceDetails() {
+		super.popSequenceDetails();
+		return _this();
+	}
+
+	@Override
+	public B setExpirationDate(@Nullable Long expirationDate) {
+		super.setExpirationDate(expirationDate);
+		return _this();
+	}
+
+	@Override
+	public B setExpirationDate(@Nullable Date expirationDate) {
+		super.setExpirationDate(expirationDate);
+		return _this();
+	}
+
+	@Override
+	public B setCorrelationId(Object correlationId) {
+		super.setCorrelationId(correlationId);
+		return _this();
+	}
+
+	@Override
+	public B setReplyChannel(MessageChannel replyChannel) {
+		super.setReplyChannel(replyChannel);
+		return _this();
+	}
+
+	@Override
+	public B setReplyChannelName(String replyChannelName) {
+		super.setReplyChannelName(replyChannelName);
+		return _this();
+	}
+
+	@Override
+	public B setErrorChannel(MessageChannel errorChannel) {
+		super.setErrorChannel(errorChannel);
+		return _this();
+	}
+
+	@Override
+	public B setErrorChannelName(String errorChannelName) {
+		super.setErrorChannelName(errorChannelName);
+		return _this();
+	}
+
+	@Override
+	public B setSequenceNumber(Integer sequenceNumber) {
+		super.setSequenceNumber(sequenceNumber);
+		return _this();
+	}
+
+	@Override
+	public B setSequenceSize(Integer sequenceSize) {
+		super.setSequenceSize(sequenceSize);
+		return _this();
+	}
+
+	@Override
+	public B setPriority(Integer priority) {
+		super.setPriority(priority);
+		return _this();
+	}
+
+	/**
+	 * Specify a list of headers which should be considered as read only
+	 * and prohibited from being populated in the message.
+	 * @param readOnlyHeaders the list of headers for {@code readOnly} mode.
+	 * Defaults to {@link MessageHeaders#ID} and {@link MessageHeaders#TIMESTAMP}.
+	 * @return the current {@link BaseMessageBuilder}
+	 * @see IntegrationMessageHeaderAccessor#isReadOnly(String)
+	 */
+	public B readOnlyHeaders(@Nullable String... readOnlyHeaders) {
+		this.readOnlyHeaders = readOnlyHeaders != null ? Arrays.copyOf(readOnlyHeaders, readOnlyHeaders.length) : null;
+		if (readOnlyHeaders != null) {
+			this.headerAccessor.setReadOnlyHeaders(readOnlyHeaders);
+		}
+		return _this();
+	}
+
+	/**
+	 * Return an original message instance if it is not modified and does not have read-only headers.
+	 * If payload is an instance of {@link Throwable}, then an {@link ErrorMessage} is built.
+	 * Otherwise, a new instance of {@link GenericMessage} is produced.
+	 * This method can be overridden to provide any custom message implementations.
+	 * @return the message instance
+	 * @see #getPayload()
+	 * @see #getHeaders()
+	 */
+	@Override
+	@SuppressWarnings("unchecked")
+	public Message<T> build() {
+		if (!this.modified && !this.headerAccessor.isModified() && this.originalMessage != null
+				&& !containsReadOnly(this.originalMessage.getHeaders())) {
+
+			return this.originalMessage;
+		}
+		if (payload instanceof Throwable throwable) {
+			return (Message<T>) new ErrorMessage(throwable, getHeaders());
+		}
+		return new GenericMessage<>(payload, getHeaders());
+	}
+
+	private boolean containsReadOnly(MessageHeaders headers) {
+		if (!ObjectUtils.isEmpty(this.readOnlyHeaders)) {
+			for (String readOnly : this.readOnlyHeaders) {
+				if (headers.containsKey(readOnly)) {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
+	@SuppressWarnings("unchecked")
+	private B _this() {
+		return (B) this;
+	}
+
+}