Preserve programmatically set context config locations

Prior to this fix, ContextLoader(Listener)'s would overwrite any
value set directly against a WebApplicationContext's #setConfigLocation
method. This is a likely scenario when using Spring 3.1's new
WebApplicationInitializer support.

Now a check is performed to ensure that the ContextLoader init-param
value is non-null before doing the overwriting.

Added tests to ensure that all expected precedence, overwriting and
defaulting of context config locations works as expected.

Issue: SPR-8510

org.springframework.web.servlet/src/test/java/org/springframework/web/context/ContextLoaderTests.java

@@ -61,6 +61,7 @@ import org.springframework.web.servlet.SimpleWebApplicationContext;
  * @author Sam Brannen
  * @author Chris Beams
  * @since 12.08.2003
+ * @see org.springframework.web.context.support.Spr8510Tests
  */
 public final class ContextLoaderTests {
 

org.springframework.web/src/main/java/org/springframework/web/context/ContextLoader.java

@@ -376,7 +376,10 @@ public class ContextLoader {
 
 		wac.setParent(parent);
 		wac.setServletContext(sc);
-		wac.setConfigLocation(sc.getInitParameter(CONFIG_LOCATION_PARAM));
+		String initParameter = sc.getInitParameter(CONFIG_LOCATION_PARAM);
+		if (initParameter != null) {
+			wac.setConfigLocation(initParameter);
+		}
 		customizeContext(sc, wac);
 		wac.refresh();
 	}

org.springframework.web/src/test/java/org/springframework/web/context/support/Spr8510Tests.java

@@ -0,0 +1,187 @@
+/*
+ * Copyright 2002-2011 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.web.context.support;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+import javax.servlet.ServletContextEvent;
+
+import org.junit.Test;
+import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;
+import org.springframework.mock.web.MockServletContext;
+import org.springframework.web.context.ContextLoader;
+import org.springframework.web.context.ContextLoaderListener;
+
+/**
+ * Tests the interaction between a WebApplicationContext and ContextLoaderListener with
+ * regard to config location precedence, overriding and defaulting in programmatic
+ * configuration use cases, e.g. with Spring 3.1's WebApplicationInitializer.
+ *
+ * @author Chris Beams
+ * @since 3.1
+ * @see org.springframework.web.context.ContextLoaderTests
+ */
+public class Spr8510Tests {
+
+	@Test
+	public void abstractRefreshableWAC_respectsProgrammaticConfigLocations() {
+		XmlWebApplicationContext ctx = new XmlWebApplicationContext();
+		ctx.setConfigLocation("programmatic.xml");
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+
+		MockServletContext sc = new MockServletContext();
+
+		try {
+			cll.contextInitialized(new ServletContextEvent(sc));
+			fail("expected exception");
+		} catch (Throwable t) {
+			// assert that an attempt was made to load the correct XML
+			assertTrue(t.getMessage(), t.getMessage().endsWith(
+					"Could not open ServletContext resource [/programmatic.xml]"));
+		}
+	}
+
+	/**
+	 * If a contextConfigLocation init-param has been specified for the ContextLoaderListener,
+	 * then it should take precedence. This is generally not a recommended practice, but
+	 * when it does happen, the init-param should be considered more specific than the
+	 * programmatic configuration, given that it still quite possibly externalized in
+	 * hybrid web.xml + WebApplicationInitializer cases.
+	 */
+	@Test
+	public void abstractRefreshableWAC_respectsInitParam_overProgrammaticConfigLocations() {
+		XmlWebApplicationContext ctx = new XmlWebApplicationContext();
+		ctx.setConfigLocation("programmatic.xml");
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+
+		MockServletContext sc = new MockServletContext();
+		sc.addInitParameter(ContextLoader.CONFIG_LOCATION_PARAM, "from-init-param.xml");
+
+		try {
+			cll.contextInitialized(new ServletContextEvent(sc));
+			fail("expected exception");
+		} catch (Throwable t) {
+			// assert that an attempt was made to load the correct XML
+			assertTrue(t.getMessage(), t.getMessage().endsWith(
+					"Could not open ServletContext resource [/from-init-param.xml]"));
+		}
+	}
+
+	/**
+	 * If setConfigLocation has not been called explicitly against the application context,
+	 * then fall back to the ContextLoaderListener init-param if present.
+	 */
+	@Test
+	public void abstractRefreshableWAC_fallsBackToInitParam() {
+		XmlWebApplicationContext ctx = new XmlWebApplicationContext();
+		//ctx.setConfigLocation("programmatic.xml"); // nothing set programmatically
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+
+		MockServletContext sc = new MockServletContext();
+		sc.addInitParameter(ContextLoader.CONFIG_LOCATION_PARAM, "from-init-param.xml");
+
+		try {
+			cll.contextInitialized(new ServletContextEvent(sc));
+			fail("expected exception");
+		} catch (Throwable t) {
+			// assert that an attempt was made to load the correct XML
+			assertTrue(t.getMessage().endsWith(
+					"Could not open ServletContext resource [/from-init-param.xml]"));
+		}
+	}
+
+	/**
+	 * Ensure that any custom default locations are still respected.
+	 */
+	@Test
+	public void customAbstractRefreshableWAC_fallsBackToInitParam() {
+		XmlWebApplicationContext ctx = new XmlWebApplicationContext() {
+			@Override
+			protected String[] getDefaultConfigLocations() {
+				return new String[] { "/WEB-INF/custom.xml" };
+			}
+		};
+		//ctx.setConfigLocation("programmatic.xml"); // nothing set programmatically
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+
+		MockServletContext sc = new MockServletContext();
+		sc.addInitParameter(ContextLoader.CONFIG_LOCATION_PARAM, "from-init-param.xml");
+
+		try {
+			cll.contextInitialized(new ServletContextEvent(sc));
+			fail("expected exception");
+		} catch (Throwable t) {
+			// assert that an attempt was made to load the correct XML
+			System.out.println(t.getMessage());
+			assertTrue(t.getMessage().endsWith(
+					"Could not open ServletContext resource [/from-init-param.xml]"));
+		}
+	}
+
+	/**
+	 * If context config locations have been specified neither against the application
+	 * context nor the context loader listener, then fall back to default values.
+	 */
+	@Test
+	public void abstractRefreshableWAC_fallsBackToConventionBasedNaming() {
+		XmlWebApplicationContext ctx = new XmlWebApplicationContext();
+		//ctx.setConfigLocation("programmatic.xml"); // nothing set programmatically
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+
+		MockServletContext sc = new MockServletContext();
+		// no init-param set
+		//sc.addInitParameter(ContextLoader.CONFIG_LOCATION_PARAM, "from-init-param.xml");
+
+		try {
+			cll.contextInitialized(new ServletContextEvent(sc));
+			fail("expected exception");
+		} catch (Throwable t) {
+			// assert that an attempt was made to load the correct XML
+			System.out.println(t.getMessage());
+			assertTrue(t.getMessage().endsWith(
+					"Could not open ServletContext resource [/WEB-INF/applicationContext.xml]"));
+		}
+	}
+
+	/**
+	 * Ensure that ContextLoaderListener and GenericWebApplicationContext interact nicely.
+	 */
+	@Test
+	public void genericWAC() {
+		GenericWebApplicationContext ctx = new GenericWebApplicationContext();
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+
+		ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(ctx);
+		scanner.scan("bogus.pkg");
+
+		cll.contextInitialized(new ServletContextEvent(new MockServletContext()));
+	}
+
+	/**
+	 * Ensure that ContextLoaderListener and AnnotationConfigApplicationContext interact nicely.
+	 */
+	@Test
+	public void annotationConfigWAC() {
+		AnnotationConfigWebApplicationContext ctx = new AnnotationConfigWebApplicationContext();
+
+		ctx.scan("does.not.matter");
+
+		ContextLoaderListener cll = new ContextLoaderListener(ctx);
+		cll.contextInitialized(new ServletContextEvent(new MockServletContext()));
+	}
+}