Update DevTools' ResourceLoader to delegate to user's custom loader

Previously, when DevTools' was used it would set the application
context's ResourceLoader and overwrite any custom ResourceLoader that
had been configured. On the rare occasion when the user had customized
the ResourceLoader this meant that the customization was lost and
certain resources would become unavailable.

This commit updates DevTools' ResourceLoader to delegate a custom
ResourceLoader if one has been configured. If one has not been
configured it delegates as before, i.e. to
WebApplicationContextResourceLoader for web applications and to
DefaultResourceLoader for all others apps.

Closes gh-8010

spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/ClassLoaderFilesResourcePatternResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -18,6 +18,7 @@ package org.springframework.boot.devtools.restart;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.lang.reflect.Field;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.util.ArrayList;
@@ -40,6 +41,7 @@ import org.springframework.core.io.support.ResourcePatternResolver;
 import org.springframework.util.AntPathMatcher;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.PathMatcher;
+import org.springframework.util.ReflectionUtils;
 import org.springframework.web.context.WebApplicationContext;
 import org.springframework.web.context.support.ServletContextResource;
 import org.springframework.web.context.support.ServletContextResourcePatternResolver;
@@ -59,7 +61,7 @@ final class ClassLoaderFilesResourcePatternResolver implements ResourcePatternRe
 	private static final String WEB_CONTEXT_CLASS = "org.springframework.web.context."
 			+ "WebApplicationContext";
 
-	private final ResourcePatternResolver delegate;
+	private final ResourcePatternResolver patternResolverDelegate;
 
 	private final PathMatcher antPathMatcher = new AntPathMatcher();
 
@@ -68,8 +70,19 @@ final class ClassLoaderFilesResourcePatternResolver implements ResourcePatternRe
 	ClassLoaderFilesResourcePatternResolver(ApplicationContext applicationContext,
 			ClassLoaderFiles classLoaderFiles) {
 		this.classLoaderFiles = classLoaderFiles;
-		this.delegate = getResourcePatternResolverFactory()
-				.getResourcePatternResolver(applicationContext);
+		this.patternResolverDelegate = getResourcePatternResolverFactory()
+				.getResourcePatternResolver(applicationContext,
+						retrieveResourceLoader(applicationContext));
+	}
+
+	private ResourceLoader retrieveResourceLoader(ApplicationContext applicationContext) {
+		Field field = ReflectionUtils.findField(applicationContext.getClass(),
+				"resourceLoader", ResourceLoader.class);
+		if (field == null) {
+			return null;
+		}
+		ReflectionUtils.makeAccessible(field);
+		return (ResourceLoader) ReflectionUtils.getField(field, applicationContext);
 	}
 
 	private ResourcePatternResolverFactory getResourcePatternResolverFactory() {
@@ -81,12 +94,12 @@ final class ClassLoaderFilesResourcePatternResolver implements ResourcePatternRe
 
 	@Override
 	public ClassLoader getClassLoader() {
-		return this.delegate.getClassLoader();
+		return this.patternResolverDelegate.getClassLoader();
 	}
 
 	@Override
 	public Resource getResource(String location) {
-		Resource candidate = this.delegate.getResource(location);
+		Resource candidate = this.patternResolverDelegate.getResource(location);
 		if (isDeleted(candidate)) {
 			return new DeletedClassLoaderFileResource(location);
 		}
@@ -96,7 +109,8 @@ final class ClassLoaderFilesResourcePatternResolver implements ResourcePatternRe
 	@Override
 	public Resource[] getResources(String locationPattern) throws IOException {
 		List<Resource> resources = new ArrayList<Resource>();
-		Resource[] candidates = this.delegate.getResources(locationPattern);
+		Resource[] candidates = this.patternResolverDelegate
+				.getResources(locationPattern);
 		for (Resource candidate : candidates) {
 			if (!isDeleted(candidate)) {
 				resources.add(candidate);
@@ -190,8 +204,9 @@ final class ClassLoaderFilesResourcePatternResolver implements ResourcePatternRe
 	private static class ResourcePatternResolverFactory {
 
 		public ResourcePatternResolver getResourcePatternResolver(
-				ApplicationContext applicationContext) {
-			return new PathMatchingResourcePatternResolver();
+				ApplicationContext applicationContext, ResourceLoader resourceLoader) {
+			return new PathMatchingResourcePatternResolver(resourceLoader == null
+					? new DefaultResourceLoader() : resourceLoader);
 		}
 
 	}
@@ -205,13 +220,14 @@ final class ClassLoaderFilesResourcePatternResolver implements ResourcePatternRe
 
 		@Override
 		public ResourcePatternResolver getResourcePatternResolver(
-				ApplicationContext applicationContext) {
+				ApplicationContext applicationContext, ResourceLoader resourceLoader) {
 			if (applicationContext instanceof WebApplicationContext) {
-				return new ServletContextResourcePatternResolver(
-						new WebApplicationContextResourceLoader(
-								(WebApplicationContext) applicationContext));
+				return new ServletContextResourcePatternResolver(resourceLoader == null
+						? new WebApplicationContextResourceLoader(
+								(WebApplicationContext) applicationContext)
+						: resourceLoader);
 			}
-			return super.getResourcePatternResolver(applicationContext);
+			return super.getResourcePatternResolver(applicationContext, resourceLoader);
 		}
 
 	}