Allow FrameworkServlet to be used as a bean

Change FrameworkServlet so that it can also be used as a bean within an
existing ApplicationContext. Primarily added to support use with
embedded servlet containers where Spring bootstraps the servlet
container, rather than the servlet container bootstrapping Spring.

Issue: SPR-10381

spring-webmvc/src/main/java/org/springframework/web/servlet/FrameworkServlet.java

@@ -21,14 +21,17 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.concurrent.Callable;
+
 import javax.servlet.ServletContext;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.servlet.http.HttpServletResponseWrapper;
 
 import org.springframework.beans.BeanUtils;
+import org.springframework.beans.BeansException;
 import org.springframework.context.ApplicationContext;
+import org.springframework.context.ApplicationContextAware;
 import org.springframework.context.ApplicationContextException;
 import org.springframework.context.ApplicationContextInitializer;
 import org.springframework.context.ApplicationListener;
@@ -122,14 +125,15 @@
  * @author Sam Brannen
  * @author Chris Beams
  * @author Rossen Stoyanchev
+ * @author Phillip Webb
  * @see #doService
  * @see #setContextClass
  * @see #setContextConfigLocation
  * @see #setContextInitializerClasses
  * @see #setNamespace
  */
 @SuppressWarnings("serial")
-public abstract class FrameworkServlet extends HttpServletBean {
+public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
 
 	/**
 	 * Suffix for WebApplicationContext namespaces. If a servlet of this class is
@@ -190,6 +194,9 @@ public abstract class FrameworkServlet extends HttpServletBean {
 	/** WebApplicationContext for this servlet */
 	private WebApplicationContext webApplicationContext;
 
+	/** If the WebApplicationContext was injected via {@link #setApplicationContext} */
+	private boolean webApplicationContextInjected = false;
+
 	/** Flag used to detect whether onRefresh has already been called */
 	private boolean refreshEventReceived = false;
 
@@ -789,6 +796,9 @@ protected void onRefresh(ApplicationContext context) {
 	 */
 	@Override
 	public void destroy() {
+		if (this.webApplicationContextInjected) {
+			return;
+		}
 		getServletContext().log("Destroying Spring FrameworkServlet '" + getServletName() + "'");
 		if (this.webApplicationContext instanceof ConfigurableApplicationContext) {
 			((ConfigurableApplicationContext) this.webApplicationContext).close();
@@ -1055,6 +1065,30 @@ protected String getUsernameForRequest(HttpServletRequest request) {
 		return (userPrincipal != null ? userPrincipal.getName() : null);
 	}
 
+	/**
+	 * Called by Spring via {@link ApplicationContextAware} to inject the current
+	 * application context. This method allows FrameworkServlets to be registered as
+	 * Spring Beans inside an existing {@link WebApplicationContext} rather than
+	 * {@link #findWebApplicationContext() finding} a
+	 * {@link org.springframework.web.context.ContextLoaderListener bootstrapped} context.
+	 *
+	 * <p>Primarily added to support use in embedded servlet containers, this method is not
+	 * intended to be called directly.
+	 *
+	 * @since 4.0
+	 */
+	public void setApplicationContext(ApplicationContext applicationContext)
+			throws BeansException {
+		if (this.webApplicationContext == null
+				&& applicationContext instanceof WebApplicationContext) {
+			if (logger.isDebugEnabled()) {
+				logger.debug("Using existing application context for "
+						+ ClassUtils.getShortName(getClass()));
+			}
+			this.webApplicationContext = (WebApplicationContext) applicationContext;
+			this.webApplicationContextInjected = true;
+		}
+	}
 
 	/**
 	 * Subclasses must implement this method to do the work of request handling,