GH-10083: Apply Nullability to spring-integration-mail

Related to: #10083

Signed-off-by: Jiandong Ma <[email protected]>

Author: mjd507

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -40,6 +40,7 @@
 import jakarta.mail.Store;
 import jakarta.mail.URLName;
 import jakarta.mail.internet.MimeMessage;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.factory.DisposableBean;
 import org.springframework.expression.Expression;
@@ -78,18 +79,19 @@ public abstract class AbstractMailReceiver extends IntegrationObjectSupport impl
 	 */
 	public static final String DEFAULT_SI_USER_FLAG = "spring-integration-mail-adapter";
 
-	private final URLName url;
+	private final @Nullable URLName url;
 
 	private final ReentrantReadWriteLock folderLock = new ReentrantReadWriteLock();
 
 	private final Lock folderReadLock = this.folderLock.readLock();
 
 	private final Lock folderWriteLock = this.folderLock.writeLock();
 
-	private String protocol;
+	private @Nullable String protocol;
 
 	private int maxFetchSize = -1;
 
+	@SuppressWarnings("NullAway.Init")
 	private Session session;
 
 	private boolean shouldDeleteMessages;
@@ -98,13 +100,14 @@ public abstract class AbstractMailReceiver extends IntegrationObjectSupport impl
 
 	private Properties javaMailProperties = new Properties();
 
-	private Authenticator javaMailAuthenticator;
+	private @Nullable Authenticator javaMailAuthenticator;
 
+	@SuppressWarnings("NullAway.Init")
 	private StandardEvaluationContext evaluationContext;
 
-	private Expression selectorExpression;
+	private @Nullable Expression selectorExpression;
 
-	private HeaderMapper<MimeMessage> headerMapper;
+	private @Nullable HeaderMapper<MimeMessage> headerMapper;
 
 	private String userFlag = DEFAULT_SI_USER_FLAG;
 
@@ -116,8 +119,10 @@ public abstract class AbstractMailReceiver extends IntegrationObjectSupport impl
 
 	private boolean flaggedAsFallback = true;
 
+	@SuppressWarnings("NullAway.Init")
 	private volatile Store store;
 
+	@SuppressWarnings("NullAway.Init")
 	private volatile Folder folder;
 
 	public AbstractMailReceiver() {
@@ -129,7 +134,7 @@ public AbstractMailReceiver(URLName urlName) {
 		this.url = urlName;
 	}
 
-	public AbstractMailReceiver(String url) {
+	public AbstractMailReceiver(@Nullable String url) {
 		if (url != null) {
 			this.url = new URLName(url);
 		}
@@ -138,7 +143,7 @@ public AbstractMailReceiver(String url) {
 		}
 	}
 
-	public void setSelectorExpression(Expression selectorExpression) {
+	public void setSelectorExpression(@Nullable Expression selectorExpression) {
 		this.selectorExpression = selectorExpression;
 	}
 
@@ -359,7 +364,8 @@ protected void openFolder() throws MessagingException {
 			connectStoreIfNecessary();
 		}
 		if (this.folder == null || !this.folder.exists()) {
-			throw new IllegalStateException("no such folder [" + this.url.getFile() + "]");
+			String file = this.url != null ? this.url.getFile() : "";
+			throw new IllegalStateException("no such folder [" + file + "]");
 		}
 		if (this.folder.isOpen()) {
 			return;
@@ -637,8 +643,8 @@ public void destroy() {
 		try {
 			closeFolder();
 			MailTransportUtils.closeService(this.store);
-			this.folder = null;
-			this.store = null;
+			// this.folder = null;
+			// this.store = null;
 		}
 		finally {
 			this.folderWriteLock.unlock();
@@ -654,7 +660,7 @@ protected void onInit() {
 
 	@Override
 	public String toString() {
-		return this.url.toString();
+		return this.url != null ? this.toString() : "url not given";
 	}
 
 	Store getStore() {
@@ -674,7 +680,7 @@ private final class IntegrationMimeMessage extends MimeMessage {
 
 		private final MimeMessage source;
 
-		private final Object content;
+		private final @Nullable Object content;
 
 		IntegrationMimeMessage(MimeMessage source) throws MessagingException {
 			super(source);
@@ -727,7 +733,7 @@ public int getLineCount() throws MessagingException {
 		}
 
 		@Override
-		public Object getContent() throws IOException, MessagingException {
+		public @Nullable Object getContent() throws IOException, MessagingException {
 			if (AbstractMailReceiver.this.simpleContent) {
 				return super.getContent();
 			}

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -24,6 +24,7 @@
 import jakarta.mail.Folder;
 import jakarta.mail.Message;
 import org.aopalliance.aop.Advice;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.beans.factory.BeanClassLoaderAware;
@@ -35,7 +36,6 @@
 import org.springframework.integration.transaction.IntegrationResourceHolder;
 import org.springframework.integration.transaction.IntegrationResourceHolderSynchronization;
 import org.springframework.integration.transaction.TransactionSynchronizationFactory;
-import org.springframework.lang.Nullable;
 import org.springframework.messaging.MessagingException;
 import org.springframework.transaction.support.TransactionSynchronization;
 import org.springframework.transaction.support.TransactionSynchronizationManager;
@@ -62,18 +62,22 @@ public class ImapIdleChannelAdapter extends MessageProducerSupport implements Be
 
 	private final ImapMailReceiver mailReceiver;
 
+	@SuppressWarnings("NullAway.Init")
 	private Executor taskExecutor;
 
-	private TransactionSynchronizationFactory transactionSynchronizationFactory;
+	private @Nullable TransactionSynchronizationFactory transactionSynchronizationFactory;
 
+	@SuppressWarnings("NullAway.Init")
 	private ClassLoader classLoader;
 
+	@SuppressWarnings("NullAway.Init")
 	private ApplicationEventPublisher applicationEventPublisher;
 
 	private boolean shouldReconnectAutomatically = true;
 
-	private List<Advice> adviceChain;
+	private @Nullable List<Advice> adviceChain;
 
+	@SuppressWarnings("NullAway.Init")
 	private Consumer<Object> messageSender;
 
 	private long reconnectDelay = DEFAULT_RECONNECT_DELAY; // milliseconds
@@ -252,8 +256,8 @@ private void delayNextIdleCall() {
 		}
 	}
 
-	@Nullable
-	private static jakarta.mail.MessagingException getJakartaMailMessagingExceptionFromCause(Throwable cause) {
+	@SuppressWarnings("NullAway")
+	private static jakarta.mail.MessagingException getJakartaMailMessagingExceptionFromCause(@Nullable Throwable cause) {
 		if (cause == null) {
 			return null;
 		}

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

@@ -33,6 +33,7 @@
 import jakarta.mail.search.NotTerm;
 import jakarta.mail.search.SearchTerm;
 import org.eclipse.angus.mail.imap.IMAPFolder;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.scheduling.TaskScheduler;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
@@ -67,19 +68,20 @@ public class ImapMailReceiver extends AbstractMailReceiver {
 
 	private long cancelIdleInterval = DEFAULT_CANCEL_IDLE_INTERVAL;
 
+	@SuppressWarnings("NullAway.Init")
 	private TaskScheduler scheduler;
 
 	private boolean isInternalScheduler;
 
-	private volatile ScheduledFuture<?> pingTask;
+	private volatile @Nullable ScheduledFuture<?> pingTask;
 
 	@SuppressWarnings("this-escape")
 	public ImapMailReceiver() {
 		setProtocol(PROTOCOL);
 	}
 
 	@SuppressWarnings("this-escape")
-	public ImapMailReceiver(String url) {
+	public ImapMailReceiver(@Nullable String url) {
 		super(url);
 		if (url != null) {
 			Assert.isTrue(url.toLowerCase(Locale.ROOT).startsWith(PROTOCOL),
@@ -238,7 +240,7 @@ private Message[] nullSafeMessages(Message[] messageArray) {
 		}
 	}
 
-	private SearchTerm compileSearchTerms(Flags supportedFlags) {
+	private @Nullable SearchTerm compileSearchTerms(Flags supportedFlags) {
 		return this.searchTermStrategy.generateSearchTerm(supportedFlags, this.getFolder());
 	}
 
@@ -277,7 +279,7 @@ private class DefaultSearchTermStrategy implements SearchTermStrategy {
 		}
 
 		@Override
-		public SearchTerm generateSearchTerm(Flags supportedFlags, Folder folder) {
+		public @Nullable SearchTerm generateSearchTerm(Flags supportedFlags, Folder folder) {
 			SearchTerm searchTerm = null;
 			boolean recentFlagSupported = false;
 			if (supportedFlags != null) {
@@ -320,7 +322,7 @@ public SearchTerm generateSearchTerm(Flags supportedFlags, Folder folder) {
 			return searchTerm;
 		}
 
-		private SearchTerm applyTermsWhenNoRecentFlag(Folder folder, SearchTerm searchTerm) {
+		private SearchTerm applyTermsWhenNoRecentFlag(Folder folder, @Nullable SearchTerm searchTerm) {
 			NotTerm notFlagged;
 			if (folder.getPermanentFlags().contains(Flag.USER)) {
 				logger.debug(() -> "This email server does not support RECENT flag, but it does support " +

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.integration.mail;
 
+import org.jspecify.annotations.Nullable;
+
 /**
  * Strategy interface for receiving mail {@link jakarta.mail.Message Messages}.
  *
@@ -25,6 +27,6 @@
  */
 public interface MailReceiver {
 
-	Object[] receive() throws jakarta.mail.MessagingException;
+	Object @Nullable [] receive() throws jakarta.mail.MessagingException;
 
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -20,6 +20,8 @@
 import java.util.Queue;
 import java.util.concurrent.ConcurrentLinkedQueue;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.core.log.LogMessage;
 import org.springframework.integration.endpoint.AbstractMessageSource;
 import org.springframework.messaging.MessagingException;
@@ -54,7 +56,7 @@ public String getComponentType() {
 	}
 
 	@Override
-	protected Object doReceive() {
+	protected @Nullable Object doReceive() {
 		try {
 			Object mailMessage = this.mailQueue.poll();
 			if (mailMessage == null) {

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

@@ -16,8 +16,12 @@
 
 package org.springframework.integration.mail;
 
+import java.util.Arrays;
+import java.util.Objects;
+
 import jakarta.mail.MessagingException;
 import jakarta.mail.internet.MimeMessage;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.core.io.ByteArrayResource;
 import org.springframework.integration.handler.AbstractMessageHandler;
@@ -190,12 +194,14 @@ private void applyHeadersToMailMessage(MailMessage mailMessage, MessageHeaders h
 		}
 	}
 
-	private String[] retrieveHeaderValueAsStringArray(MessageHeaders headers, String key) {
+	private String @Nullable [] retrieveHeaderValueAsStringArray(MessageHeaders headers, String key) {
 		Object value = headers.get(key);
 		String[] returnedHeaders = null;
 		if (value != null) {
-			if (value instanceof String[]) {
-				returnedHeaders = (String[]) value;
+			if (value instanceof String[] strArr) {
+				returnedHeaders = Arrays.stream(strArr)
+						.filter(Objects::nonNull)
+						.toArray(String[]::new);
 			}
 			else if (value instanceof String) {
 				returnedHeaders = StringUtils.commaDelimitedListToStringArray((String) value);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2007-2024 the original author or authors.
+ * Copyright 2007-2025 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.
@@ -22,6 +22,7 @@
 import jakarta.mail.URLName;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.util.StringUtils;
 
@@ -44,7 +45,7 @@ public abstract class MailTransportUtils {
 	 * @see jakarta.mail.Transport
 	 * @see jakarta.mail.Store
 	 */
-	public static void closeService(Service service) {
+	public static void closeService(@Nullable Service service) {
 		if (service != null) {
 			try {
 				service.close();
@@ -61,7 +62,7 @@ public static void closeService(Service service) {
 	 * @param folder  the JavaMail Folder to close (may be <code>null</code>)
 	 * @param expunge whether all deleted messages should be expunged from the folder
 	 */
-	public static void closeFolder(Folder folder, boolean expunge) {
+	public static void closeFolder(@Nullable Folder folder, boolean expunge) {
 		if (folder != null && folder.isOpen()) {
 			try {
 				folder.close(expunge);

spring-integration-mail/src/main/java/org/springframework/integration/mail/Pop3MailReceiver.java

@@ -21,6 +21,7 @@
 import jakarta.mail.MessagingException;
 import jakarta.mail.URLName;
 import jakarta.mail.internet.MimeMessage;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.util.Assert;
 
@@ -41,7 +42,7 @@ public Pop3MailReceiver() {
 	}
 
 	@SuppressWarnings("this-escape")
-	public Pop3MailReceiver(String url) {
+	public Pop3MailReceiver(@Nullable String url) {
 		super(url);
 		if (url != null) {
 			Assert.isTrue(url.startsWith(PROTOCOL), "url must start with 'pop3'");