DelegatingFilterProxy autodetects a unique DispatcherServlet context

Issue: SPR-13191

spring-web/src/main/java/org/springframework/web/context/support/WebApplicationContextUtils.java

@@ -68,7 +68,7 @@ public abstract class WebApplicationContextUtils {
 
 
 	/**
-	 * Find the root {@link WebApplicationContext} for this web app, typically
+	 * Find the root {@code WebApplicationContext} for this web app, typically
 	 * loaded via {@link org.springframework.web.context.ContextLoaderListener}.
 	 * <p>Will rethrow an exception that happened on root context startup,
 	 * to differentiate between a failed context startup and no context at all.
@@ -86,7 +86,7 @@ public abstract class WebApplicationContextUtils {
 	}
 
 	/**
-	 * Find the root {@link WebApplicationContext} for this web app, typically
+	 * Find the root {@code WebApplicationContext} for this web app, typically
 	 * loaded via {@link org.springframework.web.context.ContextLoaderListener}.
 	 * <p>Will rethrow an exception that happened on root context startup,
 	 * to differentiate between a failed context startup and no context at all.
@@ -99,7 +99,7 @@ public abstract class WebApplicationContextUtils {
 	}
 
 	/**
-	 * Find a custom {@link WebApplicationContext} for this web app.
+	 * Find a custom {@code WebApplicationContext} for this web app.
 	 * @param sc ServletContext to find the web application context for
 	 * @param attrName the name of the ServletContext attribute to look for
 	 * @return the desired WebApplicationContext for this web app, or {@code null} if none
@@ -125,6 +125,40 @@ public abstract class WebApplicationContextUtils {
 		return (WebApplicationContext) attr;
 	}
 
+	/**
+	 * Find a unique {@code WebApplicationContext} for this web app: either the
+	 * root web app context (preferred) or a unique {@code WebApplicationContext}
+	 * among the registered {@code ServletContext} attributes (typically coming
+	 * from a single {@code DispatcherServlet} in the current web application).
+	 * <p>Note that {@code DispatcherServlet}'s exposure of its context can be
+	 * controlled through its {@code publishContext} property, which is {@code true}
+	 * by default but can be selectively switched to only publish a single context
+	 * despite multiple {@code DispatcherServlet} registrations in the web app.
+	 * @param sc ServletContext to find the web application context for
+	 * @return the desired WebApplicationContext for this web app, or {@code null} if none
+	 * @since 4.2
+	 * @see #getWebApplicationContext(ServletContext)
+	 * @see ServletContext#getAttributeNames()
+	 */
+	public static WebApplicationContext findWebApplicationContext(ServletContext sc) {
+		WebApplicationContext wac = getWebApplicationContext(sc);
+		if (wac == null) {
+			Enumeration<String> attrNames = sc.getAttributeNames();
+			while (attrNames.hasMoreElements()) {
+				String attrName = attrNames.nextElement();
+				Object attrValue = sc.getAttribute(attrName);
+				if (attrValue instanceof WebApplicationContext) {
+					if (wac != null) {
+						throw new IllegalStateException("No unique WebApplicationContext found: more than one " +
+								"DispatcherServlet registered with publishContext=true?");
+					}
+					wac = (WebApplicationContext) attrValue;
+				}
+			}
+		}
+		return wac;
+	}
+
 
 	/**
 	 * Register web-specific scopes ("request", "session", "globalSession")

spring-web/src/main/java/org/springframework/web/filter/DelegatingFilterProxy.java

@@ -249,7 +249,8 @@ public class DelegatingFilterProxy extends GenericFilterBean {
 				if (this.delegate == null) {
 					WebApplicationContext wac = findWebApplicationContext();
 					if (wac == null) {
-						throw new IllegalStateException("No WebApplicationContext found: no ContextLoaderListener registered?");
+						throw new IllegalStateException("No WebApplicationContext found: " +
+								"no ContextLoaderListener or DispatcherServlet registered?");
 					}
 					this.delegate = initDelegate(wac);
 				}
@@ -288,11 +289,12 @@ public class DelegatingFilterProxy extends GenericFilterBean {
 	 */
 	protected WebApplicationContext findWebApplicationContext() {
 		if (this.webApplicationContext != null) {
-			// the user has injected a context at construction time -> use it
+			// The user has injected a context at construction time -> use it...
 			if (this.webApplicationContext instanceof ConfigurableApplicationContext) {
-				if (!((ConfigurableApplicationContext)this.webApplicationContext).isActive()) {
-					// the context has not yet been refreshed -> do so before returning it
-					((ConfigurableApplicationContext)this.webApplicationContext).refresh();
+				ConfigurableApplicationContext cac = (ConfigurableApplicationContext) this.webApplicationContext;
+				if (!cac.isActive()) {
+					// The context has not yet been refreshed -> do so before returning it...
+					cac.refresh();
 				}
 			}
 			return this.webApplicationContext;
@@ -302,7 +304,7 @@ public class DelegatingFilterProxy extends GenericFilterBean {
 			return WebApplicationContextUtils.getWebApplicationContext(getServletContext(), attrName);
 		}
 		else {
-			return WebApplicationContextUtils.getWebApplicationContext(getServletContext());
+			return WebApplicationContextUtils.findWebApplicationContext(getServletContext());
 		}
 	}
 

spring-web/src/test/java/org/springframework/web/filter/CompositeFilterTests.java

@@ -1,6 +1,5 @@
 /*
- * Copyright 2004, 2005 Acegi Technology Pty Limited
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -44,9 +43,7 @@ public class CompositeFilterTests {
 	@Test
 	public void testCompositeFilter() throws ServletException, IOException {
 		ServletContext sc = new MockServletContext();
-
 		MockFilter targetFilter = new MockFilter();
-
 		MockFilterConfig proxyConfig = new MockFilterConfig(sc);
 
 		CompositeFilter filterProxy = new CompositeFilter();
@@ -75,7 +72,7 @@ public class CompositeFilterTests {
 		}
 
 		@Override
-		public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
+		public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) {
 			request.setAttribute("called", Boolean.TRUE);
 		}
 

spring-web/src/test/java/org/springframework/web/filter/DelegatingFilterProxyTests.java

@@ -1,6 +1,5 @@
 /*
- * Copyright 2004, 2005 Acegi Technology Pty Limited
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2015 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.
@@ -40,6 +39,7 @@ import static org.junit.Assert.*;
 /**
  * @author Juergen Hoeller
  * @author Chris Beams
+ * @author Rob Winch
  * @since 08.05.2005
  */
 public class DelegatingFilterProxyTests {
@@ -268,6 +268,128 @@ public class DelegatingFilterProxyTests {
 		assertNull(targetFilter.filterConfig);
 	}
 
+	@Test
+	public void testDelegatingFilterProxyWithFrameworkServletContext() throws ServletException, IOException {
+		ServletContext sc = new MockServletContext();
+		StaticWebApplicationContext wac = new StaticWebApplicationContext();
+		wac.setServletContext(sc);
+		wac.registerSingleton("targetFilter", MockFilter.class);
+		wac.refresh();
+		sc.setAttribute("org.springframework.web.servlet.FrameworkServlet.CONTEXT.dispatcher", wac);
+
+		MockFilter targetFilter = (MockFilter) wac.getBean("targetFilter");
+
+		MockFilterConfig proxyConfig = new MockFilterConfig(sc);
+		proxyConfig.addInitParameter("targetBeanName", "targetFilter");
+		DelegatingFilterProxy filterProxy = new DelegatingFilterProxy();
+		filterProxy.init(proxyConfig);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		filterProxy.doFilter(request, response, null);
+
+		assertNull(targetFilter.filterConfig);
+		assertEquals(Boolean.TRUE, request.getAttribute("called"));
+
+		filterProxy.destroy();
+		assertNull(targetFilter.filterConfig);
+	}
+
+	@Test
+	public void testDelegatingFilterProxyInjectedPreferred() throws ServletException, IOException {
+		ServletContext sc = new MockServletContext();
+		StaticWebApplicationContext wac = new StaticWebApplicationContext();
+		wac.setServletContext(sc);
+		wac.refresh();
+		sc.setAttribute("org.springframework.web.servlet.FrameworkServlet.CONTEXT.dispatcher", wac);
+
+		StaticWebApplicationContext injectedWac = new StaticWebApplicationContext();
+		injectedWac.setServletContext(sc);
+		String beanName = "targetFilter";
+		injectedWac.registerSingleton(beanName, MockFilter.class);
+		injectedWac.refresh();
+
+		MockFilter targetFilter = (MockFilter) injectedWac.getBean(beanName);
+
+		DelegatingFilterProxy filterProxy = new DelegatingFilterProxy(beanName, injectedWac);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		filterProxy.doFilter(request, response, null);
+
+		assertNull(targetFilter.filterConfig);
+		assertEquals(Boolean.TRUE, request.getAttribute("called"));
+
+		filterProxy.destroy();
+		assertNull(targetFilter.filterConfig);
+	}
+
+	@Test
+	public void testDelegatingFilterProxyNotInjectedWacServletAttrPreferred() throws ServletException, IOException {
+		ServletContext sc = new MockServletContext();
+		StaticWebApplicationContext wac = new StaticWebApplicationContext();
+		wac.setServletContext(sc);
+		wac.refresh();
+		sc.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, wac);
+		sc.setAttribute("org.springframework.web.servlet.FrameworkServlet.CONTEXT.dispatcher", wac);
+
+		StaticWebApplicationContext wacToUse = new StaticWebApplicationContext();
+		wacToUse.setServletContext(sc);
+		String beanName = "targetFilter";
+		String attrName = "customAttrName";
+		wacToUse.registerSingleton(beanName, MockFilter.class);
+		wacToUse.refresh();
+		sc.setAttribute(attrName, wacToUse);
+
+		MockFilter targetFilter = (MockFilter) wacToUse.getBean(beanName);
+
+		DelegatingFilterProxy filterProxy = new DelegatingFilterProxy(beanName);
+		filterProxy.setContextAttribute(attrName);
+		filterProxy.setServletContext(sc);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		filterProxy.doFilter(request, response, null);
+
+		assertNull(targetFilter.filterConfig);
+		assertEquals(Boolean.TRUE, request.getAttribute("called"));
+
+		filterProxy.destroy();
+		assertNull(targetFilter.filterConfig);
+	}
+
+	@Test
+	public void testDelegatingFilterProxyNotInjectedWithRootPreferred() throws ServletException, IOException {
+		ServletContext sc = new MockServletContext();
+		StaticWebApplicationContext wac = new StaticWebApplicationContext();
+		wac.setServletContext(sc);
+		wac.refresh();
+		sc.setAttribute("org.springframework.web.servlet.FrameworkServlet.CONTEXT.dispatcher", wac);
+		sc.setAttribute("another", wac);
+
+		StaticWebApplicationContext wacToUse = new StaticWebApplicationContext();
+		wacToUse.setServletContext(sc);
+		String beanName = "targetFilter";
+		wacToUse.registerSingleton(beanName, MockFilter.class);
+		wacToUse.refresh();
+		sc.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, wacToUse);
+
+		MockFilter targetFilter = (MockFilter) wacToUse.getBean(beanName);
+
+		DelegatingFilterProxy filterProxy = new DelegatingFilterProxy(beanName);
+		filterProxy.setServletContext(sc);
+
+		MockHttpServletRequest request = new MockHttpServletRequest();
+		MockHttpServletResponse response = new MockHttpServletResponse();
+		filterProxy.doFilter(request, response, null);
+
+		assertNull(targetFilter.filterConfig);
+		assertEquals(Boolean.TRUE, request.getAttribute("called"));
+
+		filterProxy.destroy();
+		assertNull(targetFilter.filterConfig);
+	}
+
 
 	public static class MockFilter implements Filter {