Remove unnecessary Nullable annotations

* Set AppContext to not be nullable
* Consumer's inbound channels are never null. Update to remove nullable
* Update outbound channels so they are not nullable
* Use local variable trick to work past Nullables inability to see a new above return value
* Add contract to channelToBeanName in IntegrationGraphServer

Author: cppwfs

spring-integration-core/src/main/java/org/springframework/integration/graph/CompositeMessageHandlerNode.java

@@ -35,7 +35,7 @@ public class CompositeMessageHandlerNode extends MessageHandlerNode {
 
 	private final List<InnerHandler> handlers = new ArrayList<>();
 
-	public CompositeMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input, @Nullable String output,
+	public CompositeMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input, @Nullable String output,
 			List<InnerHandler> handlers) {
 
 		super(nodeId, name, handler, input, output);

spring-integration-core/src/main/java/org/springframework/integration/graph/DiscardingMessageHandlerNode.java

@@ -32,7 +32,7 @@ public class DiscardingMessageHandlerNode extends MessageHandlerNode {
 
 	private final @Nullable String discards;
 
-	public DiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input,
+	public DiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input,
 			@Nullable String output, @Nullable String discards) {
 
 		super(nodeId, name, handler, input, output);

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableCompositeMessageHandlerNode.java

@@ -36,7 +36,7 @@ public class ErrorCapableCompositeMessageHandlerNode extends CompositeMessageHan
 	private final @Nullable String errors;
 
 	public ErrorCapableCompositeMessageHandlerNode(int nodeId, String name, CompositeMessageHandler handler,
-			@Nullable String input, @Nullable String output, @Nullable String errors, List<InnerHandler> handlers) {
+			String input, @Nullable String output, @Nullable String errors, List<InnerHandler> handlers) {
 
 		super(nodeId, name, handler, input, output, handlers);
 		this.errors = errors;

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableDiscardingMessageHandlerNode.java

@@ -33,7 +33,7 @@ public class ErrorCapableDiscardingMessageHandlerNode extends DiscardingMessageH
 
 	private final @Nullable String errors;
 
-	public ErrorCapableDiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input,
+	public ErrorCapableDiscardingMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input,
 			@Nullable String output, @Nullable String discards, @Nullable String errors) {
 
 		super(nodeId, name, handler, input, output, discards);

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableMessageHandlerNode.java

@@ -31,7 +31,7 @@ public class ErrorCapableMessageHandlerNode extends MessageHandlerNode implement
 
 	private final @Nullable String errors;
 
-	public ErrorCapableMessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input,
+	public ErrorCapableMessageHandlerNode(int nodeId, String name, MessageHandler handler, String input,
 			@Nullable String output, @Nullable String errors) {
 
 		super(nodeId, name, handler, input, output);

spring-integration-core/src/main/java/org/springframework/integration/graph/ErrorCapableRoutingNode.java

@@ -35,7 +35,7 @@ public class ErrorCapableRoutingNode extends RoutingMessageHandlerNode implement
 
 	private final @Nullable String errors;
 
-	public ErrorCapableRoutingNode(int nodeId, String name, MessageHandler handler, @Nullable String input, @Nullable String output,
+	public ErrorCapableRoutingNode(int nodeId, String name, MessageHandler handler, String input, @Nullable String output,
 			@Nullable String errors, Collection<String> routes) {
 
 		super(nodeId, name, handler, input, output, routes);

spring-integration-core/src/main/java/org/springframework/integration/graph/IntegrationGraphServer.java

@@ -55,6 +55,7 @@
 import org.springframework.integration.support.management.MappingMessageRouterManagement;
 import org.springframework.integration.support.management.micrometer.MicrometerMetricsCaptorConfiguration;
 import org.springframework.integration.support.utils.IntegrationUtils;
+import org.springframework.lang.Contract;
 import org.springframework.messaging.MessageChannel;
 import org.springframework.messaging.MessageHandler;
 import org.springframework.messaging.PollableChannel;
@@ -81,7 +82,8 @@ public class IntegrationGraphServer implements ApplicationContextAware, Applicat
 
 	private @Nullable MicrometerNodeEnhancer micrometerEnhancer;
 
-	private @Nullable ApplicationContext applicationContext;
+	@SuppressWarnings("NullAway.Init")
+	private ApplicationContext applicationContext;
 
 	private volatile @Nullable Graph graph;
 
@@ -133,20 +135,20 @@ public void onApplicationEvent(ContextRefreshedEvent event) {
 	 * @return the graph.
 	 * @see #rebuild()
 	 */
-	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	public Graph getGraph() {
 		if (this.graph == null) {
 			this.lock.lock();
 			try {
 				if (this.graph == null) {
-					buildGraph();
+					this.graph = buildGraph();
 				}
 			}
 			finally {
 				this.lock.unlock();
 			}
 		}
-		return this.graph;
+		var graph = this.graph;
+		return graph;
 	}
 
 	/**
@@ -175,9 +177,6 @@ public Graph rebuild() {
 	 * @since 5.1
 	 */
 	protected <T> Map<String, T> getBeansOfType(Class<T> type) {
-		if (this.applicationContext == null) {
-			throw new IllegalStateException("ApplicationContext is not set");
-		}
 		return this.applicationContext.getBeansOfType(type, true, false);
 	}
 
@@ -190,11 +189,7 @@ private <T extends IntegrationNode> T enhance(T node) {
 		}
 	}
 
-	@SuppressWarnings("NullAway") // Dataflow analysis limitation
 	private Graph buildGraph() {
-		if (this.applicationContext == null) {
-			throw new IllegalStateException("ApplicationContext is not set");
-		}
 		if (this.micrometerEnhancer == null && MicrometerMetricsCaptorConfiguration.METER_REGISTRY_PRESENT) {
 			this.micrometerEnhancer = new MicrometerNodeEnhancer(this.applicationContext);
 		}
@@ -221,8 +216,9 @@ private Graph buildGraph() {
 		gateways(nodes, links, channelNodes);
 		producers(nodes, links, channelNodes);
 		consumers(nodes, links, channelNodes);
-		this.graph = new Graph(descriptor, nodes, links);
-		return this.graph;
+		var graph = new Graph(descriptor, nodes, links);
+		this.graph = graph;
+		return graph;
 	}
 
 	private Map<String, MessageChannelNode> channels(Collection<IntegrationNode> nodes) {
@@ -416,6 +412,7 @@ MessageGatewayNode gatewayNode(String name, MessagingGatewaySupport gateway) {
 			return new MessageGatewayNode(this.nodeId.incrementAndGet(), name, gateway, requestChannel, errorChannel);
 		}
 
+		@Contract("null -> null; !null -> !null")
 		private @Nullable String channelToBeanName(@Nullable MessageChannel messageChannel) {
 			return messageChannel instanceof NamedComponent namedComponent
 					? namedComponent.getBeanName()
@@ -425,6 +422,7 @@ MessageGatewayNode gatewayNode(String name, MessagingGatewaySupport gateway) {
 		MessageProducerNode producerNode(String name, MessageProducerSupport producer) {
 			String errorChannel = channelToBeanName(producer.getErrorChannel());
 			String outputChannel = channelToBeanName(producer.getOutputChannel());
+			Assert.state(outputChannel != null, "'outputChannel' must not be null");
 			return new MessageProducerNode(this.nodeId.incrementAndGet(), name, producer, outputChannel, errorChannel);
 		}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/MessageHandlerNode.java

@@ -33,21 +33,20 @@
  */
 public class MessageHandlerNode extends EndpointNode implements SendTimersAware {
 
-	private final @Nullable String input;
+	private final String input;
 
 	private @Nullable Supplier<SendTimers> sendTimers;
 
-	public MessageHandlerNode(int nodeId, String name, MessageHandler handler, @Nullable String input, @Nullable String output) {
+	public MessageHandlerNode(int nodeId, String name, MessageHandler handler, String input, @Nullable String output) {
 		super(nodeId, name, handler, output);
 		this.input = input;
 	}
 
-	public @Nullable String getInput() {
+	public String getInput() {
 		return this.input;
 	}
 
-	@Nullable
-	public SendTimers getSendTimers() {
+	public @Nullable SendTimers getSendTimers() {
 		return this.sendTimers != null ? this.sendTimers.get() : null;
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/MessageProducerNode.java

@@ -30,7 +30,7 @@
  */
 public class MessageProducerNode extends ErrorCapableEndpointNode {
 
-	public MessageProducerNode(int nodeId, String name, MessageProducerSupport producer, @Nullable String output, @Nullable String errors) {
+	public MessageProducerNode(int nodeId, String name, MessageProducerSupport producer, String output, @Nullable String errors) {
 		super(nodeId, name, producer, output, errors);
 	}
 

spring-integration-core/src/main/java/org/springframework/integration/graph/MessageSourceNode.java

@@ -35,7 +35,7 @@ public class MessageSourceNode extends ErrorCapableEndpointNode implements Recei
 
 	private @Nullable Supplier<ReceiveCounters> receiveCounters;
 
-	public MessageSourceNode(int nodeId, String name, MessageSource<?> messageSource, @Nullable String output, @Nullable String errors) {
+	public MessageSourceNode(int nodeId, String name, MessageSource<?> messageSource, String output, @Nullable String errors) {
 		super(nodeId, name, messageSource, output, errors);
 	}