Close mail folder if no messages to produce

spring-integration-mail/src/main/java/org/springframework/integration/mail/AbstractMailReceiver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -53,6 +53,7 @@
 import org.springframework.util.Assert;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.util.MimeTypeUtils;
+import org.springframework.util.ObjectUtils;
 
 /**
  * Base class for {@link MailReceiver} implementations.
@@ -362,6 +363,7 @@ private Folder obtainFolderInstance() throws MessagingException {
 	public Object[] receive() throws jakarta.mail.MessagingException {
 		this.folderReadLock.lock(); // NOSONAR - guarded with the getReadHoldCount()
 		try {
+			Object[] messagesToReturn = null;
 			try {
 				Folder folderToCheck = getFolder();
 				if (folderToCheck == null || !folderToCheck.isOpen()) {
@@ -375,10 +377,11 @@ public Object[] receive() throws jakarta.mail.MessagingException {
 						this.folderWriteLock.unlock();
 					}
 				}
-				return convertMessagesIfNecessary(searchAndFilterMessages());
+				messagesToReturn = convertMessagesIfNecessary(searchAndFilterMessages());
+				return messagesToReturn;
 			}
 			finally {
-				if (this.autoCloseFolder) {
+				if (this.autoCloseFolder || ObjectUtils.isEmpty(messagesToReturn)) {
 					closeFolder();
 				}
 			}

spring-integration-mail/src/test/java/org/springframework/integration/mail/MailReceiverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2021 the original author or authors.
+ * Copyright 2014-2022 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.integration.mail;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
@@ -46,31 +48,37 @@
 public class MailReceiverTests {
 
 	@Test
-	public void testStoreConnect() throws Exception {
+	public void testStoreConnectAndFolderCloseWhenNoMessages() throws Exception {
 		AbstractMailReceiver receiver = new AbstractMailReceiver() {
 
 			@Override
 			protected Message[] searchForNewMessages() {
-				return null;
+				return new Message[0];
 			}
 
 		};
 		Properties props = new Properties();
 		Session session = Session.getInstance(props);
 		receiver.setSession(session);
 		receiver.setProtocol("imap");
+		receiver.setAutoCloseFolder(false);
 		Store store = session.getStore("imap");
 		store = spy(store);
 		new DirectFieldAccessor(receiver).setPropertyValue("store", store);
 		when(store.isConnected()).thenReturn(false);
 		Folder folder = mock(Folder.class);
 		when(folder.exists()).thenReturn(true);
-		when(folder.isOpen()).thenReturn(false);
+		when(folder.isOpen()).thenReturn(false, true);
 		doReturn(folder).when(store).getFolder((URLName) null);
 		doNothing().when(store).connect();
 		receiver.openFolder();
 		receiver.openFolder();
 		verify(store, times(2)).connect();
+
+		Object[] receive = receiver.receive();
+		assertThat(receive).isEmpty();
+
+		verify(folder).close(anyBoolean());
 	}
 
 }

src/reference/asciidoc/mail.adoc

@@ -140,6 +140,9 @@ This functionality is enabled with this combination of options: no `headerMapper
 The `MimeMessage` is present as the payload of the Spring message produced.
 In this case, the only header populated is the mentioned above `IntegrationMessageHeaderAccessor.CLOSEABLE_RESOURCE` for the folder which must be closed when processing of the `MimeMessage` is complete.
 
+Starting with version 5.5.11, the folder is closed automatically after `AbstractMailReceiver.receive()` if no messages received or all of them are filtered out independently of the `autoCloseFolder` flag.
+In this case there is nothing to produce downstream for possible logic around `IntegrationMessageHeaderAccessor.CLOSEABLE_RESOURCE` header.
+
 [[mail-mapping]]
 === Inbound Mail Message Mapping