Fix parsing of spring.autoconfigure.exclude property

This commits makes sure that `AutoConfigureImportSelector` properly
parses comma separated lists that contain additional spaces.

Closes gh-8220

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/AutoConfigurationImportSelector.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
@@ -222,8 +223,8 @@ public class AutoConfigurationImportSelector
 				String name = entry.getKey();
 				Object value = entry.getValue();
 				if (name.isEmpty() || name.startsWith("[") && value != null) {
-					excludes.addAll(
-							StringUtils.commaDelimitedListToSet(String.valueOf(value)));
+					excludes.addAll(new HashSet<String>(Arrays.asList(StringUtils
+							.tokenizeToStringArray(String.valueOf(value), ","))));
 				}
 			}
 			return excludes;

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/AutoConfigurationImportSelectorTests.java

@@ -130,11 +130,15 @@ public class AutoConfigurationImportSelectorTests {
 		this.environment.setProperty("spring.autoconfigure.exclude",
 				FreeMarkerAutoConfiguration.class.getName() + ","
 						+ MustacheAutoConfiguration.class.getName());
-		String[] imports = selectImports(BasicEnableAutoConfiguration.class);
-		assertThat(imports).hasSize(getAutoConfigurationClassNames().size() - 2);
-		assertThat(this.importSelector.getLastEvent().getExclusions()).contains(
-				FreeMarkerAutoConfiguration.class.getName(),
-				MustacheAutoConfiguration.class.getName());
+		testSeveralPropertyExclusionsAreApplied();
+	}
+
+	@Test
+	public void severalPropertyExclusionsAreAppliedWithExtraSpaces() {
+		this.environment.setProperty("spring.autoconfigure.exclude",
+				FreeMarkerAutoConfiguration.class.getName() + " , "
+						+ MustacheAutoConfiguration.class.getName() + " ");
+		testSeveralPropertyExclusionsAreApplied();
 	}
 
 	@Test
@@ -143,6 +147,10 @@ public class AutoConfigurationImportSelectorTests {
 				FreeMarkerAutoConfiguration.class.getName());
 		this.environment.setProperty("spring.autoconfigure.exclude[1]",
 				MustacheAutoConfiguration.class.getName());
+		testSeveralPropertyExclusionsAreApplied();
+	}
+
+	private void testSeveralPropertyExclusionsAreApplied() {
 		String[] imports = selectImports(BasicEnableAutoConfiguration.class);
 		assertThat(imports).hasSize(getAutoConfigurationClassNames().size() - 2);
 		assertThat(this.importSelector.getLastEvent().getExclusions()).contains(