[SPR-8387] Initial draft of the new DelegatingSmartContextLoader.

org.springframework.test/src/main/java/org/springframework/test/context/ContextLoaderUtils.java

@@ -50,7 +50,9 @@ abstract class ContextLoaderUtils {
 
 	private static final Log logger = LogFactory.getLog(ContextLoaderUtils.class);
 
-	private static final String DEFAULT_CONTEXT_LOADER_CLASS_NAME = "org.springframework.test.context.support.GenericXmlContextLoader";
+	// private static final String DEFAULT_CONTEXT_LOADER_CLASS_NAME =
+	// "org.springframework.test.context.support.GenericXmlContextLoader";
+	private static final String DEFAULT_CONTEXT_LOADER_CLASS_NAME = "org.springframework.test.context.support.DelegatingSmartContextLoader";
 
 
 	private ContextLoaderUtils() {

org.springframework.test/src/main/java/org/springframework/test/context/support/DelegatingSmartContextLoader.java

@@ -0,0 +1,143 @@
+/*
+ * 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.test.context.support;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.springframework.context.ApplicationContext;
+import org.springframework.test.context.ContextConfigurationAttributes;
+import org.springframework.test.context.ContextLoader;
+import org.springframework.test.context.MergedContextConfiguration;
+import org.springframework.test.context.SmartContextLoader;
+
+/**
+ * TODO Document DelegatingSmartContextLoader.
+ * 
+ * @author Sam Brannen
+ * @since 3.1
+ * @see SmartContextLoader
+ * @see GenericXmlContextLoader
+ * @see AnnotationConfigContextLoader
+ */
+public class DelegatingSmartContextLoader implements SmartContextLoader {
+
+	private static final Log logger = LogFactory.getLog(DelegatingSmartContextLoader.class);
+
+	private final List<? extends SmartContextLoader> candidates = Arrays.asList(new GenericXmlContextLoader(),
+		new AnnotationConfigContextLoader());
+
+
+	// --- SmartContextLoader --------------------------------------------------
+
+	/**
+	 * TODO Document generatesDefaults() implementation.
+	 */
+	public boolean generatesDefaults() {
+		for (SmartContextLoader loader : candidates) {
+			if (loader.generatesDefaults()) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	/**
+	 * TODO Document processContextConfiguration() implementation.
+	 */
+	public void processContextConfiguration(ContextConfigurationAttributes configAttributes) {
+		for (SmartContextLoader loader : candidates) {
+			if (logger.isDebugEnabled()) {
+				logger.debug(String.format("Delegating to loader [%s] to process context configuration [%s].",
+					loader.getClass().getName(), configAttributes));
+			}
+
+			// TODO Implement processContextConfiguration().
+			//
+			// If the original locations and classes are not empty, there's no
+			// need to bother with default generation checks; just let each
+			// loader process the configuration.
+			//
+			// Otherwise, if a loader claims to generate defaults, let it
+			// process the configuration, and then verify that it actually did
+			// generate defaults.
+			//
+			// If it generated defaults, there's no need to delegate to
+			// additional candidates. So:
+			// 1) stop iterating
+			// 2) mark the current loader as the winning candidate (?)
+			// 3) log an info message.
+
+			loader.processContextConfiguration(configAttributes);
+		}
+	}
+
+	/**
+	 * TODO Document loadContext(MergedContextConfiguration) implementation.
+	 */
+	public ApplicationContext loadContext(MergedContextConfiguration mergedConfig) throws Exception {
+
+		for (SmartContextLoader loader : candidates) {
+			if (logger.isDebugEnabled()) {
+				logger.debug(String.format("Delegating to loader [%s] to load context from [%s].",
+					loader.getClass().getName(), mergedConfig));
+			}
+
+			// TODO Implement loadContext(MergedContextConfiguration).
+			//
+			// Ask each loader if it _can_ load a context from the mergedConfig.
+			// If a loader can, let it; otherwise, continue iterating over all
+			// remaining candidates.
+			//
+			// If no candidate can load a context from the mergedConfig, throw
+			// an exception.
+		}
+
+		// TODO Implement delegation logic.
+		//
+		// Proof of concept: ensuring that hard-coded delegation to
+		// GenericXmlContextLoader works "as is".
+		return candidates.get(0).loadContext(mergedConfig);
+	}
+
+	// --- ContextLoader -------------------------------------------------------
+
+	/**
+	 * {@code DelegatingSmartContextLoader} does not support the
+	 * {@link ContextLoader#processLocations(Class, String...)} method. Call
+	 * {@link #processContextConfiguration(ContextConfigurationAttributes)} instead.
+	 * @throws UnsupportedOperationException
+	 */
+	public String[] processLocations(Class<?> clazz, String... locations) {
+		throw new UnsupportedOperationException("DelegatingSmartContextLoader does not support the ContextLoader API. "
+				+ "Call processContextConfiguration(ContextConfigurationAttributes) instead.");
+	}
+
+	/**
+	 * {@code DelegatingSmartContextLoader} does not support the
+	 * {@link ContextLoader#loadContext(String...) } method. Call
+	 * {@link #loadContext(MergedContextConfiguration)} instead.
+	 * @throws UnsupportedOperationException
+	 */
+	public ApplicationContext loadContext(String... locations) throws Exception {
+		throw new UnsupportedOperationException("DelegatingSmartContextLoader does not support the ContextLoader API. "
+				+ "Call loadContext(MergedContextConfiguration) instead.");
+	}
+
+}

org.springframework.test/src/test/java/org/springframework/test/context/ContextLoaderUtilsTests.java

@@ -27,8 +27,8 @@ import java.util.List;
 import org.junit.Test;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.test.context.support.AnnotationConfigContextLoader;
+import org.springframework.test.context.support.DelegatingSmartContextLoader;
 import org.springframework.test.context.support.GenericPropertiesContextLoader;
-import org.springframework.test.context.support.GenericXmlContextLoader;
 
 /**
  * Unit tests for {@link ContextLoaderUtils}.
@@ -120,7 +120,7 @@ public class ContextLoaderUtilsTests {
 			mergedConfig,
 			testClass,
 			new String[] { "classpath:/org/springframework/test/context/ContextLoaderUtilsTests$BareAnnotations-context.xml" },
-			EMPTY_CLASS_ARRAY, GenericXmlContextLoader.class);
+			EMPTY_CLASS_ARRAY, DelegatingSmartContextLoader.class);
 	}
 
 	@Test
@@ -129,7 +129,7 @@ public class ContextLoaderUtilsTests {
 		MergedContextConfiguration mergedConfig = ContextLoaderUtils.buildMergedContextConfiguration(testClass, null);
 
 		assertMergedContextConfiguration(mergedConfig, testClass, new String[] { "classpath:/foo.xml" },
-			new Class<?>[] { FooConfig.class }, GenericXmlContextLoader.class);
+			new Class<?>[] { FooConfig.class }, DelegatingSmartContextLoader.class);
 	}
 
 	@Test