From 98ad8633bd22e28e4705ee72e73d6d862fe6e8d2 Mon Sep 17 00:00:00 2001
From: Rossen Stoyanchev <rstoyanchev@vmware.com>
Date: Mon, 1 Aug 2011 10:20:49 +0000
Subject: [PATCH] SPR-8524 Add flag to AbstractCachingViewResolver to suppress
 subsequent resolution of unresolved view names.

---
 .../view/AbstractCachingViewResolver.java     | 26 +++++++++++++-
 .../web/servlet/view/ViewResolverTests.java   | 35 +++++++++++++++++--
 2 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/view/AbstractCachingViewResolver.java b/org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/view/AbstractCachingViewResolver.java
index 0ed7464c48b..99d54547c5f 100644
--- a/org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/view/AbstractCachingViewResolver.java
+++ b/org.springframework.web.servlet/src/main/java/org/springframework/web/servlet/view/AbstractCachingViewResolver.java
@@ -42,6 +42,9 @@ public abstract class AbstractCachingViewResolver extends WebApplicationObjectSu
 	/** Whether we should cache views, once resolved */
 	private boolean cache = true;
 
+	/** Whether we should attempt to resolve views again if unresolved once */
+	private boolean cacheUnresolved = false;
+
 	/** Map from view key to View instance */
 	private final Map<Object, View> viewCache = new HashMap<Object, View>();
 
@@ -62,7 +65,27 @@ public abstract class AbstractCachingViewResolver extends WebApplicationObjectSu
 	public boolean isCache() {
 		return this.cache;
 	}
+	
+	/**
+	 * Whether a view name once resolved to {@code null} should be cached and 
+	 * automatically resolved to {@code null} subsequently.
+	 * <p>Default is "false": unresolved view names are not cached.
+	 * <p>Of specific interest is the ability for some AbstractUrlBasedView 
+	 * implementations (Freemarker, Velocity, Tiles) to check if an underlying 
+	 * resource exists via {@link AbstractUrlBasedView#checkResource(Locale)}.
+	 * With this flag set to "false", an underlying resource that re-appears 
+	 * is noticed and used. With the flag set to "true", one check is made only.
+	 */
+	public void setCacheUnresolved(boolean cacheUnresolved) {
+		this.cacheUnresolved = cacheUnresolved;
+	}
 
+	/**
+	 * Return if caching of unresolved views is enabled.
+	 */
+	public boolean isCacheUnresolved() {
+		return cacheUnresolved;
+	}
 
 	public View resolveViewName(String viewName, Locale locale) throws Exception {
 		if (!isCache()) {
@@ -72,7 +95,8 @@ public abstract class AbstractCachingViewResolver extends WebApplicationObjectSu
 			Object cacheKey = getCacheKey(viewName, locale);
 			synchronized (this.viewCache) {
 				View view = this.viewCache.get(cacheKey);
-				if (view == null) {
+				boolean isCached = this.cacheUnresolved && this.viewCache.containsKey(cacheKey);
+				if (view == null && !isCached) {
 					// Ask the subclass to create the View object.
 					view = createView(viewName, locale);
 					this.viewCache.put(cacheKey, view);
diff --git a/org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/view/ViewResolverTests.java b/org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/view/ViewResolverTests.java
index 3e5db14a59b..b14ef645265 100644
--- a/org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/view/ViewResolverTests.java
+++ b/org.springframework.web.servlet/src/test/java/org/springframework/web/servlet/view/ViewResolverTests.java
@@ -16,10 +16,18 @@
 
 package org.springframework.web.servlet.view;
 
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
 import java.util.HashMap;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
+import java.util.concurrent.atomic.AtomicInteger;
+
 import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
@@ -30,9 +38,7 @@ import javax.servlet.http.HttpServletResponse;
 import javax.servlet.jsp.jstl.core.Config;
 import javax.servlet.jsp.jstl.fmt.LocalizationContext;
 
-import static org.junit.Assert.*;
 import org.junit.Test;
-
 import org.springframework.beans.MutablePropertyValues;
 import org.springframework.beans.PropertyValue;
 import org.springframework.beans.TestBean;
@@ -497,6 +503,31 @@ public class ViewResolverTests {
 		}
 	}
 
+	@Test
+	public void testCacheUnresolved() throws Exception {
+		final AtomicInteger count = new AtomicInteger();
+		AbstractCachingViewResolver viewResolver = new AbstractCachingViewResolver() {
+			@Override
+			protected View loadView(String viewName, Locale locale) throws Exception {
+				count.incrementAndGet();
+				return null;
+			}
+		};
+
+		viewResolver.setCacheUnresolved(false);
+
+		viewResolver.resolveViewName("view", Locale.getDefault());
+		viewResolver.resolveViewName("view", Locale.getDefault());
+		
+		assertEquals(2, count.intValue());
+
+		viewResolver.setCacheUnresolved(true);
+		
+		viewResolver.resolveViewName("view", Locale.getDefault());
+		viewResolver.resolveViewName("view", Locale.getDefault());
+		
+		assertEquals(2, count.intValue());
+	}
 
 	public static class TestView extends InternalResourceView {