Lazily start resources on demand (if necessary outside of lifecycle)

See gh-32945

Author: jhoeller

spring-web/src/main/java/org/springframework/http/client/ReactorResourceFactory.java

@@ -61,12 +61,12 @@ public class ReactorResourceFactory
 	private Supplier<ConnectionProvider> connectionProviderSupplier = () -> ConnectionProvider.create("webflux", 500);
 
 	@Nullable
-	private ConnectionProvider connectionProvider;
+	private volatile ConnectionProvider connectionProvider;
 
 	private Supplier<LoopResources> loopResourcesSupplier = () -> LoopResources.create("webflux-http");
 
 	@Nullable
-	private LoopResources loopResources;
+	private volatile LoopResources loopResources;
 
 	private boolean manageConnectionProvider = false;
 
@@ -141,16 +141,22 @@ public void setConnectionProvider(ConnectionProvider connectionProvider) {
 
 	/**
 	 * Return the configured {@link ConnectionProvider}.
+	 * <p>Lazily tries to start the resources on demand if not initialized yet.
+	 * @see #start()
 	 */
 	public ConnectionProvider getConnectionProvider() {
-		Assert.state(this.connectionProvider != null, "ConnectionProvider not initialized yet");
-		return this.connectionProvider;
+		if (this.connectionProvider == null) {
+			start();
+		}
+		ConnectionProvider connectionProvider = this.connectionProvider;
+		Assert.state(connectionProvider != null, "ConnectionProvider not initialized");
+		return connectionProvider;
 	}
 
 	/**
 	 * Use this when you don't want to participate in global resources and
 	 * you want to customize the creation of the managed {@code LoopResources}.
-	 * <p>By default, {@code LoopResources.create("reactor-http")} is used.
+	 * <p>By default, {@code LoopResources.create("webflux-http")} is used.
 	 * <p>Note that this option is ignored if {@code userGlobalResources=false} or
 	 * {@link #setLoopResources(LoopResources)} is set.
 	 * @param supplier the supplier to use
@@ -170,10 +176,16 @@ public void setLoopResources(LoopResources loopResources) {
 
 	/**
 	 * Return the configured {@link LoopResources}.
+	 * <p>Lazily tries to start the resources on demand if not initialized yet.
+	 * @see #start()
 	 */
 	public LoopResources getLoopResources() {
-		Assert.state(this.loopResources != null, "LoopResources not initialized yet");
-		return this.loopResources;
+		if (this.loopResources == null) {
+			start();
+		}
+		LoopResources loopResources = this.loopResources;
+		Assert.state(loopResources != null, "LoopResources not initialized");
+		return loopResources;
 	}
 
 	/**
@@ -220,13 +232,25 @@ public void setApplicationContext(ApplicationContext applicationContext) {
 	}
 
 
+	/**
+	 * Starts the resources if initialized outside an ApplicationContext.
+	 * This is for backwards compatibility; the preferred way is to rely on
+	 * the ApplicationContext's {@link SmartLifecycle lifecycle management}.
+	 * @see #start()
+	 */
 	@Override
 	public void afterPropertiesSet() {
 		if (this.applicationContext == null) {
 			start();
 		}
 	}
 
+	/**
+	 * Stops the resources if initialized outside an ApplicationContext.
+	 * This is for backwards compatibility; the preferred way is to rely on
+	 * the ApplicationContext's {@link SmartLifecycle lifecycle management}.
+	 * @see #stop()
+	 */
 	@Override
 	public void destroy() {
 		if (this.applicationContext == null) {

spring-web/src/test/java/org/springframework/http/client/ReactorResourceFactoryTests.java

@@ -261,4 +261,22 @@ protected void finishRefresh() {
 		assertThat(resourceFactory.isRunning()).isFalse();
 	}
 
+	@Test
+	void lazilyStartOnConnectionProviderAccess() {
+		assertThat(this.resourceFactory.isRunning()).isFalse();
+		this.resourceFactory.getConnectionProvider();
+		assertThat(this.resourceFactory.isRunning()).isTrue();
+		this.resourceFactory.stop();
+		assertThat(this.resourceFactory.isRunning()).isFalse();
+	}
+
+	@Test
+	void lazilyStartOnLoopResourcesAccess() {
+		assertThat(this.resourceFactory.isRunning()).isFalse();
+		this.resourceFactory.getLoopResources();
+		assertThat(this.resourceFactory.isRunning()).isTrue();
+		this.resourceFactory.stop();
+		assertThat(this.resourceFactory.isRunning()).isFalse();
+	}
+
 }