Implement simpler exclusion logic for Gradle

Simplify the exclusion logic used in Gradle by implementing implicit
exclusions rather than trying to detect transitive excludes.

This commit reverts much of the code originally included to fix gh-1047
which adds far too much complexity to the build and still doesn't solve
the underlying issue.

Fixes gh-1103

spring-boot-tools/spring-boot-gradle-plugin/src/main/groovy/org/springframework/boot/gradle/exclude/ApplyExcludeRules.java

@@ -47,17 +47,19 @@ public class ApplyExcludeRules implements Action<Configuration> {
 	@Override
 	public void execute(Configuration configuration) {
 		if (!VersionManagedDependencies.CONFIGURATION.equals(configuration.getName())) {
-			configuration.getIncoming().beforeResolve(new Action<ResolvableDependencies>() {
-				@Override
-				public void execute(ResolvableDependencies resolvableDependencies) {
-					resolvableDependencies.getDependencies().all(new Action<Dependency>() {
+			configuration.getIncoming().beforeResolve(
+					new Action<ResolvableDependencies>() {
 						@Override
-						public void execute(Dependency dependency) {
-							applyExcludeRules(dependency);
+						public void execute(ResolvableDependencies resolvableDependencies) {
+							resolvableDependencies.getDependencies().all(
+									new Action<Dependency>() {
+										@Override
+										public void execute(Dependency dependency) {
+											applyExcludeRules(dependency);
+										}
+									});
 						}
 					});
-				}
-			});
 		}
 	}
 
@@ -73,13 +75,10 @@ public class ApplyExcludeRules implements Action<Configuration> {
 		org.springframework.boot.dependency.tools.Dependency managedDependency = managedDependencies
 				.find(dependency.getGroup(), dependency.getName());
 		if (managedDependency != null) {
-			if (managedDependency.getExclusions().isEmpty()) {
-				logger.debug("No exclusions rules applied for managed dependency "
-						+ dependency);
-			}
 			for (Exclusion exclusion : managedDependency.getExclusions()) {
 				addExcludeRule(dependency, exclusion);
 			}
+			addImplicitExcludeRules(dependency);
 		}
 		else {
 			logger.debug("No exclusions rules applied for non-managed dependency "
@@ -94,4 +93,21 @@ public class ApplyExcludeRules implements Action<Configuration> {
 		dependency.getExcludeRules().add(rule);
 	}
 
+	private void addImplicitExcludeRules(ModuleDependency dependency) {
+		if (isStarter(dependency)) {
+			logger.info("Adding implicit managed exclusion rules to starter "
+					+ dependency);
+			dependency.getExcludeRules().add(
+					new DefaultExcludeRule("commons-logging", "commons-logging"));
+			dependency.getExcludeRules().add(
+					new DefaultExcludeRule("commons-logging", "commons-logging-api"));
+		}
+	}
+
+	private boolean isStarter(ModuleDependency dependency) {
+		return (dependency.getGroup() != null
+				&& dependency.getGroup().equals("org.springframework.boot") && dependency
+				.getName().startsWith("spring-boot-starter"));
+	}
+
 }