Polish "Hide loader classes from Tomcat's ServletContext resource paths"

See gh-17538

spring-boot-tests/spring-boot-integration-tests/spring-boot-server-tests/src/test/java/com/example/ResourceHandlingApplication.java

@@ -18,6 +18,8 @@ package com.example;
 
 import java.io.IOException;
 import java.net.URL;
+import java.util.LinkedHashSet;
+import java.util.Set;
 
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServlet;
@@ -38,31 +40,62 @@ import org.springframework.context.annotation.Bean;
 @SpringBootApplication
 public class ResourceHandlingApplication {
 
+	@Bean
+	public ServletRegistrationBean<?> resourceServletRegistration() {
+		ServletRegistrationBean<?> registration = new ServletRegistrationBean<HttpServlet>(new GetResourceServlet());
+		registration.addUrlMappings("/servletContext");
+		return registration;
+	}
+
+	@Bean
+	public ServletRegistrationBean<?> resourcePathsServletRegistration() {
+		ServletRegistrationBean<?> registration = new ServletRegistrationBean<HttpServlet>(
+				new GetResourcePathsServlet());
+		registration.addUrlMappings("/resourcePaths");
+		return registration;
+	}
+
 	public static void main(String[] args) {
 		new SpringApplicationBuilder(ResourceHandlingApplication.class).properties("server.port:0")
 				.listeners(new WebServerPortFileWriter("target/server.port")).run(args);
 	}
 
-	@Bean
-	public ServletRegistrationBean<?> resourceServletRegistration() {
-		ServletRegistrationBean<?> registration = new ServletRegistrationBean<HttpServlet>(new HttpServlet() {
+	private static final class GetResourcePathsServlet extends HttpServlet {
 
-			@Override
-			protected void doGet(HttpServletRequest req, HttpServletResponse resp)
-					throws ServletException, IOException {
-				URL resource = getServletContext().getResource(req.getQueryString());
-				if (resource == null) {
-					resp.sendError(404);
-				}
-				else {
-					resp.getWriter().println(resource);
-					resp.getWriter().flush();
+		@Override
+		protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+			collectResourcePaths("/").forEach(resp.getWriter()::println);
+			resp.getWriter().flush();
+		}
+
+		private Set<String> collectResourcePaths(String path) {
+			Set<String> allResourcePaths = new LinkedHashSet<>();
+			Set<String> pathsForPath = getServletContext().getResourcePaths(path);
+			if (pathsForPath != null) {
+				for (String resourcePath : pathsForPath) {
+					allResourcePaths.add(resourcePath);
+					allResourcePaths.addAll(collectResourcePaths(resourcePath));
 				}
 			}
+			return allResourcePaths;
+		}
+
+	}
+
+	private static final class GetResourceServlet extends HttpServlet {
+
+		@Override
+		protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
+			URL resource = getServletContext().getResource(req.getQueryString());
+			if (resource == null) {
+				resp.sendError(404);
+			}
+			else {
+				resp.getWriter().println(resource);
+				resp.getWriter().flush();
+			}
+		}
 
-		});
-		registration.addUrlMappings("/servletContext");
-		return registration;
 	}
 
 }