Use StringJoiner where possible to simplify String joining

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassParser.java

@@ -33,6 +33,7 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.StringJoiner;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -724,15 +725,11 @@ class ConfigurationClassParser {
 		 */
 		@Override
 		public String toString() {
-			StringBuilder builder = new StringBuilder("[");
-			Iterator<ConfigurationClass> iterator = iterator();
-			while (iterator.hasNext()) {
-				builder.append(iterator.next().getSimpleName());
-				if (iterator.hasNext()) {
-					builder.append("->");
+			StringJoiner joiner = new StringJoiner("->", "[", "]");
+			for (ConfigurationClass configurationClass : this) {
+				joiner.add(configurationClass.getSimpleName());
 			}
-			}
-			return builder.append(']').toString();
+			return joiner.toString();
 		}
 	}
 
@@ -946,7 +943,7 @@ class ConfigurationClassParser {
 			return new AssignableTypeFilter(clazz).match((MetadataReader) this.source, metadataReaderFactory);
 		}
 
-		public ConfigurationClass asConfigClass(ConfigurationClass importedBy) throws IOException {
+		public ConfigurationClass asConfigClass(ConfigurationClass importedBy) {
 			if (this.source instanceof Class) {
 				return new ConfigurationClass((Class<?>) this.source, importedBy);
 			}
@@ -1014,7 +1011,7 @@ class ConfigurationClassParser {
 			return result;
 		}
 
-		public Set<SourceClass> getAnnotations() throws IOException {
+		public Set<SourceClass> getAnnotations() {
 			Set<SourceClass> result = new LinkedHashSet<>();
 			for (String className : this.metadata.getAnnotationTypes()) {
 				try {

spring-core/src/main/java/org/springframework/util/ClassUtils.java

@@ -38,6 +38,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import java.util.StringJoiner;
 
 import org.springframework.lang.Nullable;
 
@@ -656,16 +657,11 @@ public abstract class ClassUtils {
 		if (CollectionUtils.isEmpty(classes)) {
 			return "[]";
 		}
-		StringBuilder sb = new StringBuilder("[");
-		for (Iterator<Class<?>> it = classes.iterator(); it.hasNext(); ) {
-			Class<?> clazz = it.next();
-			sb.append(clazz.getName());
-			if (it.hasNext()) {
-				sb.append(", ");
+		StringJoiner sj = new StringJoiner(", ", "[", "]");
+		for (Class<?> clazz : classes) {
+			sj.add(clazz.getName());
 		}
-		}
-		sb.append("]");
-		return sb.toString();
+		return sj.toString();
 	}
 
 	/**

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -39,6 +39,7 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
+import java.util.StringJoiner;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -1505,17 +1506,13 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	 * @return a combined result with comma delimitation
 	 */
 	protected String toCommaDelimitedString(List<String> headerValues) {
-		StringBuilder builder = new StringBuilder();
-		for (Iterator<String> it = headerValues.iterator(); it.hasNext();) {
-			String val = it.next();
+		StringJoiner joiner = new StringJoiner(", ");
+		for (String val : headerValues) {
 			if (val != null) {
-				builder.append(val);
-				if (it.hasNext()) {
-					builder.append(", ");
+				joiner.add(val);
 			}
 		}
-		}
-		return builder.toString();
+		return joiner.toString();
 	}
 
 	/**