Apply Nullability into XMPP module

Related to: #10083

* Add `@org.jspecify.annotations.NullMarked`  to all packages of SI-XMPP module
* Fix raised concerns about `@Nullable`

Author: artembilan

spring-integration-xmpp/src/main/java/org/springframework/integration/xmpp/config/XmppConnectionFactoryBean.java

@@ -24,12 +24,14 @@
 import org.jivesoftware.smack.roster.Roster;
 import org.jivesoftware.smack.tcp.XMPPTCPConnection;
 import org.jivesoftware.smack.tcp.XMPPTCPConnectionConfiguration;
+import org.jspecify.annotations.Nullable;
 import org.jxmpp.stringprep.XmppStringprepException;
 import org.jxmpp.util.XmppStringUtils;
 
 import org.springframework.beans.factory.BeanInitializationException;
 import org.springframework.beans.factory.config.AbstractFactoryBean;
 import org.springframework.context.SmartLifecycle;
+import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
 /**
@@ -53,21 +55,21 @@ public class XmppConnectionFactoryBean extends AbstractFactoryBean<XMPPConnectio
 
 	private final Lock lifecycleMonitor = new ReentrantLock();
 
-	private XMPPTCPConnectionConfiguration connectionConfiguration;
+	private @Nullable XMPPTCPConnectionConfiguration connectionConfiguration;
 
-	private String resource; // server will generate resource if not provided
+	private @Nullable String resource; // server will generate resource if not provided
 
-	private String user;
+	private @Nullable String user;
 
-	private String password;
+	private @Nullable String password;
 
-	private String serviceName;
+	private @Nullable String serviceName;
 
-	private String host;
+	private @Nullable String host;
 
 	private int port = 5222; // NOSONAR magic number
 
-	private Roster.SubscriptionMode subscriptionMode = Roster.getDefaultSubscriptionMode();
+	private Roster.@Nullable SubscriptionMode subscriptionMode = Roster.getDefaultSubscriptionMode();
 
 	private boolean autoStartup = true;
 
@@ -128,7 +130,7 @@ public void setPort(int port) {
 	 * Can be {@code null}.
 	 * @see Roster#setSubscriptionMode(Roster.SubscriptionMode)
 	 */
-	public void setSubscriptionMode(Roster.SubscriptionMode subscriptionMode) {
+	public void setSubscriptionMode(Roster.@Nullable SubscriptionMode subscriptionMode) {
 		this.subscriptionMode = subscriptionMode;
 	}
 
@@ -141,6 +143,7 @@ public Class<? extends XMPPConnection> getObjectType() {
 	protected XMPPConnection createInstance() throws XmppStringprepException {
 		XMPPTCPConnectionConfiguration connectionConfig = this.connectionConfiguration;
 		if (connectionConfig == null) {
+			Assert.notNull(this.user, "The 'user' property is required'");
 			XMPPTCPConnectionConfiguration.Builder builder =
 					XMPPTCPConnectionConfiguration.builder()
 							.setHost(this.host)

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

@@ -1,4 +1,5 @@
 /**
  * Contains parser classes for the XMPP namespace support.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xmpp.config;

spring-integration-xmpp/src/main/java/org/springframework/integration/xmpp/core/AbstractXmppConnectionAwareEndpoint.java

@@ -30,6 +30,7 @@
  */
 public abstract class AbstractXmppConnectionAwareEndpoint extends MessageProducerSupport {
 
+	@SuppressWarnings("NullAway.Init")
 	private XMPPConnection xmppConnection;
 
 	private boolean initialized;

spring-integration-xmpp/src/main/java/org/springframework/integration/xmpp/core/AbstractXmppConnectionAwareMessageHandler.java

@@ -30,6 +30,7 @@
  */
 public abstract class AbstractXmppConnectionAwareMessageHandler extends AbstractMessageHandler {
 
+	@SuppressWarnings("NullAway.Init")
 	private XMPPConnection xmppConnection;
 
 	private volatile boolean initialized;
@@ -53,7 +54,7 @@ protected boolean isInitialized() {
 
 	@Override
 	protected void onInit() {
-		BeanFactory beanFactory = this.getBeanFactory();
+		BeanFactory beanFactory = getBeanFactory();
 		if (this.xmppConnection == null && beanFactory != null) {
 			this.xmppConnection =
 					beanFactory.getBean(XmppContextUtils.XMPP_CONNECTION_BEAN_NAME, XMPPConnection.class);

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

@@ -1,4 +1,5 @@
 /**
  * Provides classes shared across all XMPP components.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xmpp.core;

spring-integration-xmpp/src/main/java/org/springframework/integration/xmpp/inbound/ChatMessageListeningEndpoint.java

@@ -24,6 +24,7 @@
 import org.jivesoftware.smack.filter.StanzaFilter;
 import org.jivesoftware.smack.packet.ExtensionElement;
 import org.jivesoftware.smack.packet.Stanza;
+import org.jspecify.annotations.Nullable;
 
 import org.springframework.expression.EvaluationContext;
 import org.springframework.expression.Expression;
@@ -52,10 +53,11 @@ public class ChatMessageListeningEndpoint extends AbstractXmppConnectionAwareEnd
 
 	private XmppHeaderMapper headerMapper = new DefaultXmppHeaderMapper();
 
-	private Expression payloadExpression;
+	private @Nullable Expression payloadExpression;
 
-	private StanzaFilter stanzaFilter;
+	private @Nullable StanzaFilter stanzaFilter;
 
+	@SuppressWarnings("NullAway.Init")
 	private EvaluationContext evaluationContext;
 
 	public ChatMessageListeningEndpoint() {
@@ -110,10 +112,7 @@ protected void doStart() {
 
 	@Override
 	protected void doStop() {
-		XMPPConnection xmppConnection = getXmppConnection();
-		if (xmppConnection != null) {
-			xmppConnection.removeAsyncStanzaListener(this.stanzaListener);
-		}
+		getXmppConnection().removeAsyncStanzaListener(this.stanzaListener);
 	}
 
 	private class ChatMessagePublishingStanzaListener implements StanzaListener {

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

@@ -2,4 +2,5 @@
  * Provides XMPP inbound Endpoint implementations that extend
  * {@link org.springframework.integration.xmpp.core.AbstractXmppConnectionAwareEndpoint}.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xmpp.inbound;

spring-integration-xmpp/src/main/java/org/springframework/integration/xmpp/outbound/ChatMessageSendingMessageHandler.java

@@ -26,6 +26,7 @@
 import org.jivesoftware.smack.provider.ExtensionElementProvider;
 import org.jivesoftware.smack.util.PacketParserUtils;
 import org.jivesoftware.smack.xml.XmlPullParser;
+import org.jspecify.annotations.Nullable;
 import org.jxmpp.jid.Jid;
 import org.jxmpp.jid.impl.JidCreate;
 
@@ -56,7 +57,7 @@ public class ChatMessageSendingMessageHandler extends AbstractXmppConnectionAwar
 
 	private XmppHeaderMapper headerMapper = new DefaultXmppHeaderMapper();
 
-	private ExtensionElementProvider<? extends ExtensionElement> extensionProvider;
+	private @Nullable ExtensionElementProvider<? extends ExtensionElement> extensionProvider;
 
 	public ChatMessageSendingMessageHandler() {
 	}
@@ -94,22 +95,21 @@ protected void handleMessageInternal(Message<?> message) {
 		try {
 			Object payload = message.getPayload();
 			MessageBuilder xmppMessageBuilder;
-			if (payload instanceof org.jivesoftware.smack.packet.Message) {
-				xmppMessage = (org.jivesoftware.smack.packet.Message) payload;
-				xmppMessageBuilder = xmppMessage.asBuilder();
+			if (payload instanceof org.jivesoftware.smack.packet.Message smackMessage) {
+				xmppMessageBuilder = smackMessage.asBuilder();
 			}
 			else {
 				String to = message.getHeaders().get(XmppHeaders.TO, String.class);
 				Assert.state(StringUtils.hasText(to), () -> "The '" + XmppHeaders.TO + "' header must not be null");
 				xmppMessageBuilder = buildXmppMessage(payload, to);
 			}
 
-			if (this.headerMapper != null) {
-				this.headerMapper.fromHeadersToRequest(message.getHeaders(), xmppMessageBuilder);
-			}
+			this.headerMapper.fromHeadersToRequest(message.getHeaders(), xmppMessageBuilder);
 			XMPPConnection xmppConnection = getXmppConnection();
-			if (!xmppConnection.isConnected() && xmppConnection instanceof AbstractXMPPConnection) {
-				((AbstractXMPPConnection) xmppConnection).connect();
+			if (!xmppConnection.isConnected() &&
+					xmppConnection instanceof AbstractXMPPConnection abstractXMPPConnection) {
+
+				abstractXMPPConnection.connect();
 			}
 			xmppMessage = xmppMessageBuilder.build();
 			xmppConnection.sendStanza(xmppMessage);

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

@@ -3,4 +3,5 @@
  * These components extend
  * {@link org.springframework.integration.xmpp.core.AbstractXmppConnectionAwareMessageHandler}
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xmpp.outbound;

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

@@ -1,4 +1,5 @@
 /**
  * Root package of the Spring Integration XMPP Module.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xmpp;

spring-integration-xmpp/src/main/java/org/springframework/integration/xmpp/support/DefaultXmppHeaderMapper.java

@@ -25,6 +25,7 @@
 import org.jivesoftware.smack.packet.MessageBuilder;
 import org.jivesoftware.smackx.jiveproperties.JivePropertiesManager;
 import org.jivesoftware.smackx.jiveproperties.packet.JivePropertiesExtension;
+import org.jspecify.annotations.Nullable;
 import org.jxmpp.jid.Jid;
 import org.jxmpp.stringprep.XmppStringprepException;
 
@@ -86,8 +87,8 @@ protected Map<String, Object> extractStandardHeaders(MessageBuilder source) {
 	}
 
 	@Override
-	protected Map<String, Object> extractUserDefinedHeaders(MessageBuilder source) {
-		Map<String, Object> headers = new HashMap<>();
+	protected Map<String, @Nullable Object> extractUserDefinedHeaders(MessageBuilder source) {
+		Map<String, @Nullable Object> headers = new HashMap<>();
 		JivePropertiesExtension jpe = JivePropertiesExtension.from(source.build());
 		if (jpe == null) {
 			return headers;

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

@@ -3,4 +3,5 @@
  * {@link org.springframework.integration.xmpp.support.XmppHeaderMapper} implementation
  * in this package.
  */
+@org.jspecify.annotations.NullMarked
 package org.springframework.integration.xmpp.support;