Honor ProtocolResolvers in GenericApplicationContext

When the ProtocolResolver SPI was introduced in Spring Framework 4.3,
support for protocol resolvers was added in DefaultResourceLoader's
getResource() implementation; however, GenericApplicationContext's
overridden getResource() implementation was not updated accordingly.

Prior to this commit, if a GenericApplicationContext was configured
with a custom ResourceLoader, registered protocol resolvers were
ignored.

This commit ensures that protocol resolvers are honored in
GenericApplicationContext even if a custom ResourceLoader is used.

Closes gh-28703

Author: sbrannen

spring-context/src/main/java/org/springframework/context/support/GenericApplicationContext.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -33,6 +33,7 @@
 import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.ApplicationContext;
+import org.springframework.core.io.ProtocolResolver;
 import org.springframework.core.io.Resource;
 import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.io.support.ResourcePatternResolver;
@@ -86,6 +87,7 @@
  *
  * @author Juergen Hoeller
  * @author Chris Beams
+ * @author Sam Brannen
  * @since 1.1.2
  * @see #registerBeanDefinition
  * @see #refresh()
@@ -216,13 +218,23 @@ public void setResourceLoader(ResourceLoader resourceLoader) {
 	//---------------------------------------------------------------------
 
 	/**
-	 * This implementation delegates to this context's ResourceLoader if set,
-	 * falling back to the default superclass behavior else.
-	 * @see #setResourceLoader
+	 * This implementation delegates to this context's {@code ResourceLoader} if set,
+	 * falling back to the default superclass behavior otherwise.
+	 * <p>As of Spring Framework 5.3.22, this method also honors registered
+	 * {@linkplain #getProtocolResolvers() protocol resolvers} when a custom
+	 * {@code ResourceLoader} has been set.
+	 * @see #setResourceLoader(ResourceLoader)
+	 * @see #addProtocolResolver(ProtocolResolver)
 	 */
 	@Override
 	public Resource getResource(String location) {
 		if (this.resourceLoader != null) {
+			for (ProtocolResolver protocolResolver : getProtocolResolvers()) {
+				Resource resource = protocolResolver.resolve(location, this);
+				if (resource != null) {
+					return resource;
+				}
+			}
 			return this.resourceLoader.getResource(location);
 		}
 		return super.getResource(location);
@@ -231,7 +243,7 @@ public Resource getResource(String location) {
 	/**
 	 * This implementation delegates to this context's ResourceLoader if it
 	 * implements the ResourcePatternResolver interface, falling back to the
-	 * default superclass behavior else.
+	 * default superclass behavior otherwise.
 	 * @see #setResourceLoader
 	 */
 	@Override

spring-context/src/test/java/org/springframework/context/support/GenericApplicationContextTests.java

@@ -24,15 +24,28 @@
 import org.springframework.beans.factory.support.RootBeanDefinition;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
+import org.springframework.core.io.ByteArrayResource;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.core.io.FileSystemResource;
+import org.springframework.core.io.FileSystemResourceLoader;
+import org.springframework.core.io.FileUrlResource;
+import org.springframework.core.io.ProtocolResolver;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
 import org.springframework.core.metrics.jfr.FlightRecorderApplicationStartup;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
+import static org.assertj.core.api.InstanceOfAssertFactories.type;
 
 /**
+ * Tests for {@link GenericApplicationContext}.
+ *
  * @author Juergen Hoeller
  * @author Chris Beams
+ * @author Sam Brannen
  */
 class GenericApplicationContextTests {
 
@@ -209,6 +222,39 @@ void configureApplicationStartupOnBeanFactory() {
 		assertThat(context.getBeanFactory().getApplicationStartup()).isEqualTo(applicationStartup);
 	}
 
+	@Test
+	void getResourceWithDefaultResourceLoader() {
+		assertGetResourceSemantics(null, ClassPathResource.class);
+	}
+
+	@Test
+	void getResourceWithCustomResourceLoader() {
+		assertGetResourceSemantics(new FileSystemResourceLoader(), FileSystemResource.class);
+	}
+
+	private void assertGetResourceSemantics(ResourceLoader resourceLoader, Class<? extends Resource> defaultResouceType) {
+		if (resourceLoader != null) {
+			context.setResourceLoader(resourceLoader);
+		}
+
+		String pingLocation = "ping:foo";
+		String fileLocation = "file:foo";
+
+		Resource resource = context.getResource(pingLocation);
+		assertThat(resource).isInstanceOf(defaultResouceType);
+		resource = context.getResource(fileLocation);
+		assertThat(resource).isInstanceOf(FileUrlResource.class);
+
+		context.addProtocolResolver(new PingPongProtocolResolver());
+
+		resource = context.getResource(pingLocation);
+		assertThat(resource).asInstanceOf(type(ByteArrayResource.class))
+			.extracting(bar -> new String(bar.getByteArray(), UTF_8))
+			.isEqualTo("pong:foo");
+		resource = context.getResource(fileLocation);
+		assertThat(resource).isInstanceOf(FileUrlResource.class);
+	}
+
 
 	static class BeanA {
 
@@ -236,4 +282,15 @@ public void setApplicationContext(ApplicationContext applicationContext) {
 
 	static class BeanC {}
 
+	static class PingPongProtocolResolver implements ProtocolResolver {
+
+		@Override
+		public Resource resolve(String location, ResourceLoader resourceLoader) {
+			if (location.startsWith("ping:")) {
+				return new ByteArrayResource(("pong:" + location.substring(5)).getBytes(UTF_8));
+			}
+			return null;
+		}
+	}
+
 }

spring-core/src/main/java/org/springframework/core/io/DefaultResourceLoader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -32,7 +32,8 @@
 
 /**
  * Default implementation of the {@link ResourceLoader} interface.
- * Used by {@link ResourceEditor}, and serves as base class for
+ *
+ * <p>Used by {@link ResourceEditor}, and serves as base class for
  * {@link org.springframework.context.support.AbstractApplicationContext}.
  * Can also be used standalone.
  *
@@ -114,6 +115,7 @@ public void addProtocolResolver(ProtocolResolver resolver) {
 	 * Return the collection of currently registered protocol resolvers,
 	 * allowing for introspection as well as modification.
 	 * @since 4.3
+	 * @see #addProtocolResolver(ProtocolResolver)
 	 */
 	public Collection<ProtocolResolver> getProtocolResolvers() {
 		return this.protocolResolvers;