GH-10083: Apply Nullability to stream module

Related to: #10083

* Use `@Nullable` on `ByteStreamReadingMessageSource.doReceive()` return type

Signed-off-by: Tran Ngoc Nhan <[email protected]>

Author: ngocnhan-tran1996

spring-integration-stream/src/main/java/org/springframework/integration/stream/ByteStreamReadingMessageSource.java

@@ -22,6 +22,8 @@
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.integration.endpoint.AbstractMessageSource;
 import org.springframework.messaging.MessagingException;
 
@@ -73,7 +75,7 @@ public String getComponentType() {
 	}
 
 	@Override
-	protected byte[] doReceive() {
+	protected byte @Nullable [] doReceive() {
 		try {
 			byte[] bytes;
 			int bytesRead = 0;

spring-integration-stream/src/main/java/org/springframework/integration/stream/CharacterStreamReadingMessageSource.java

@@ -24,6 +24,8 @@
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
 import org.springframework.integration.endpoint.AbstractMessageSource;
@@ -48,7 +50,7 @@ public class CharacterStreamReadingMessageSource extends AbstractMessageSource<S
 
 	private final boolean blockToDetectEOF;
 
-	private ApplicationEventPublisher applicationEventPublisher;
+	private @Nullable ApplicationEventPublisher applicationEventPublisher;
 
 	/**
 	 * Construct an instance with the provider reader.
@@ -116,7 +118,7 @@ public String getComponentType() {
 	}
 
 	@Override
-	public String doReceive() {
+	public @Nullable String doReceive() {
 		try {
 			this.lock.lock();
 			try {

spring-integration-stream/src/main/java/org/springframework/integration/stream/CharacterStreamWritingMessageHandler.java

@@ -24,6 +24,8 @@
 import java.io.UnsupportedEncodingException;
 import java.io.Writer;
 
+import org.jspecify.annotations.Nullable;
+
 import org.springframework.integration.handler.AbstractMessageHandler;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessagingException;
@@ -80,7 +82,7 @@ public static CharacterStreamWritingMessageHandler stdout() {
 	 * @param charsetName The charset name.
 	 * @return A stdout handler.
 	 */
-	public static CharacterStreamWritingMessageHandler stdout(String charsetName) {
+	public static CharacterStreamWritingMessageHandler stdout(@Nullable String charsetName) {
 		return createTargetForStream(System.out, charsetName);
 	}
 
@@ -101,11 +103,11 @@ public static CharacterStreamWritingMessageHandler stderr() {
 	 * @param charsetName The charset name.
 	 * @return A stderr handler.
 	 */
-	public static CharacterStreamWritingMessageHandler stderr(String charsetName) {
+	public static CharacterStreamWritingMessageHandler stderr(@Nullable String charsetName) {
 		return createTargetForStream(System.err, charsetName);
 	}
 
-	private static CharacterStreamWritingMessageHandler createTargetForStream(OutputStream stream, String charsetName) {
+	private static CharacterStreamWritingMessageHandler createTargetForStream(OutputStream stream, @Nullable String charsetName) {
 		if (charsetName == null) {
 			return new CharacterStreamWritingMessageHandler(new OutputStreamWriter(stream));
 		}

spring-integration-stream/src/main/java/org/springframework/integration/stream/config/package-info.java

@@ -1,4 +1,5 @@
 /**
  * Provides classes for configuration - parsers, namespace handlers.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.stream.config;

spring-integration-stream/src/main/java/org/springframework/integration/stream/package-info.java

@@ -1,4 +1,5 @@
 /**
  * Base package for stream support.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.stream;