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/test/java/org/springframework/boot/devtools/restart/ClassLoaderFilesResourcePatternResolverTests.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.
@@ -31,17 +31,21 @@ import org.springframework.boot.devtools.restart.classloader.ClassLoaderFiles;
 import org.springframework.context.support.GenericApplicationContext;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
+import org.springframework.core.io.ResourceLoader;
 import org.springframework.mock.web.MockServletContext;
 import org.springframework.util.FileCopyUtils;
 import org.springframework.web.context.support.GenericWebApplicationContext;
 import org.springframework.web.context.support.ServletContextResource;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
 
 /**
  * Tests for {@link ClassLoaderFilesResourcePatternResolver}.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  */
 public class ClassLoaderFilesResourcePatternResolverTests {
 
@@ -71,7 +75,7 @@ public class ClassLoaderFilesResourcePatternResolverTests {
 	}
 
 	@Test
-	public void getResourceWhenHasServeletContextShouldReturnServletResource()
+	public void getResourceWhenHasServletContextShouldReturnServletResource()
 			throws Exception {
 		GenericWebApplicationContext context = new GenericWebApplicationContext(
 				new MockServletContext());
@@ -111,6 +115,27 @@ public class ClassLoaderFilesResourcePatternResolverTests {
 		assertThat(resources).isEmpty();
 	}
 
+	@Test
+	public void customResourceLoaderIsUsedInNonWebApplication() throws Exception {
+		GenericApplicationContext context = new GenericApplicationContext();
+		ResourceLoader resourceLoader = mock(ResourceLoader.class);
+		context.setResourceLoader(resourceLoader);
+		this.resolver = new ClassLoaderFilesResourcePatternResolver(context, this.files);
+		this.resolver.getResource("foo.txt");
+		verify(resourceLoader).getResource("foo.txt");
+	}
+
+	@Test
+	public void customResourceLoaderIsUsedInWebApplication() throws Exception {
+		GenericWebApplicationContext context = new GenericWebApplicationContext(
+				new MockServletContext());
+		ResourceLoader resourceLoader = mock(ResourceLoader.class);
+		context.setResourceLoader(resourceLoader);
+		this.resolver = new ClassLoaderFilesResourcePatternResolver(context, this.files);
+		this.resolver.getResource("foo.txt");
+		verify(resourceLoader).getResource("foo.txt");
+	}
+
 	private File createFile(File folder, String name) throws IOException {
 		File file = new File(folder, name);
 		FileCopyUtils.copy("test".getBytes(), file);