Cache resolved error template view names

Fixes gh-5933

Author: philwebb

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/DefaultErrorViewResolver.java

@@ -18,8 +18,10 @@
 
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -66,6 +68,10 @@ public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {
 		SERIES_VIEWS = Collections.unmodifiableMap(views);
 	}
 
+	private static final int CACHE_LIMIT = 1024;
+
+	private static final Object UNRESOLVED = new Object();
+
 	private ApplicationContext applicationContext;
 
 	private final ResourceProperties resourceProperties;
@@ -74,6 +80,30 @@ public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {
 
 	private int order = Ordered.LOWEST_PRECEDENCE;
 
+	/**
+	 * resolved template views, returning already cached instances without a global lock.
+	 */
+	private final Map<Object, Object> resolved = new ConcurrentHashMap<Object, Object>(
+			CACHE_LIMIT);
+
+	/**
+	 * Map from view name resolve template view, synchronized when accessed.
+	 */
+	@SuppressWarnings("serial")
+	private final Map<Object, Object> cache = new LinkedHashMap<Object, Object>(
+			CACHE_LIMIT, 0.75f, true) {
+
+		@Override
+		protected boolean removeEldestEntry(Map.Entry<Object, Object> eldest) {
+			if (size() > CACHE_LIMIT) {
+				DefaultErrorViewResolver.this.resolved.remove(eldest.getKey());
+				return true;
+			}
+			return false;
+		}
+
+	};
+
 	/**
 	 * Create a new {@link DefaultErrorViewResolver} instance.
 	 * @param applicationContext the source application context
@@ -120,11 +150,25 @@ private ModelAndView resolve(String viewName, Map<String, Object> model) {
 	}
 
 	private ModelAndView resolveTemplate(String viewName, Map<String, Object> model) {
+		Object resolved = this.resolved.get(viewName);
+		if (resolved == null) {
+			synchronized (this.cache) {
+				resolved = resolveTemplateViewName(viewName);
+				resolved = (resolved == null ? UNRESOLVED : resolved);
+				this.resolved.put(viewName, resolved);
+				this.cache.put(viewName, resolved);
+			}
+		}
+		return (resolved == UNRESOLVED ? null
+				: new ModelAndView((String) resolved, model));
+	}
+
+	private String resolveTemplateViewName(String viewName) {
 		for (TemplateAvailabilityProvider templateAvailabilityProvider : this.templateAvailabilityProviders) {
 			if (templateAvailabilityProvider.isTemplateAvailable("error/" + viewName,
 					this.applicationContext.getEnvironment(),
 					this.applicationContext.getClassLoader(), this.applicationContext)) {
-				return new ModelAndView("error/" + viewName, model);
+				return "error/" + viewName;
 			}
 		}
 		return null;

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/DefaultErrorViewResolverTests.java

@@ -47,6 +47,7 @@
 import static org.mockito.Matchers.any;
 import static org.mockito.Matchers.eq;
 import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 
@@ -198,6 +199,21 @@ public void resolveWhenExactResourceMatchAndSeriesTemplateMatchShouldFavorResour
 		assertThat(response.getContentType()).isEqualTo(MediaType.TEXT_HTML_VALUE);
 	}
 
+	@Test
+	public void resolveShouldCacheTemplate() throws Exception {
+		given(this.templateAvailabilityProvider.isTemplateAvailable(eq("error/4xx"),
+				any(Environment.class), any(ClassLoader.class),
+				any(ResourceLoader.class))).willReturn(true);
+		for (int i = 0; i < 10; i++) {
+			ModelAndView resolved = this.resolver.resolveErrorView(this.request,
+					HttpStatus.NOT_FOUND, this.model);
+			assertThat(resolved.getViewName()).isEqualTo("error/4xx");
+		}
+		verify(this.templateAvailabilityProvider, times(1)).isTemplateAvailable(
+				eq("error/4xx"), any(Environment.class), any(ClassLoader.class),
+				any(ResourceLoader.class));
+	}
+
 	@Test
 	public void orderShouldBeLowest() throws Exception {
 		assertThat(this.resolver.getOrder()).isEqualTo(Ordered.LOWEST_PRECEDENCE);