Use StringJoiner where possible to simplify String joining

spring-context/src/main/java/org/springframework/validation/DefaultMessageCodesResolver.java

@@ -22,6 +22,7 @@ import java.util.Collection;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
+import java.util.StringJoiner;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.StringUtils;
@@ -242,11 +243,10 @@ public class DefaultMessageCodesResolver implements MessageCodesResolver, Serial
 		 * null elements altogether.
 		 */
 		public static String toDelimitedString(String... elements) {
-			StringBuilder rtn = new StringBuilder();
+			StringJoiner rtn = new StringJoiner(CODE_SEPARATOR);
 			for (String element : elements) {
 				if (StringUtils.hasLength(element)) {
-					rtn.append(rtn.length() == 0 ? "" : CODE_SEPARATOR);
-					rtn.append(element);
+					rtn.add(element);
 				}
 			}
 			return rtn.toString();

spring-core/src/main/java/org/springframework/core/convert/support/CollectionToStringConverter.java

@@ -19,6 +19,7 @@ package org.springframework.core.convert.support;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.Set;
+import java.util.StringJoiner;
 
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
@@ -64,18 +65,13 @@ final class CollectionToStringConverter implements ConditionalGenericConverter {
 		if (sourceCollection.isEmpty()) {
 			return "";
 		}
-		StringBuilder sb = new StringBuilder();
-		int i = 0;
+		StringJoiner sj = new StringJoiner(DELIMITER);
 		for (Object sourceElement : sourceCollection) {
-			if (i > 0) {
-				sb.append(DELIMITER);
-			}
 			Object targetElement = this.conversionService.convert(
 					sourceElement, sourceType.elementTypeDescriptor(sourceElement), targetType);
-			sb.append(targetElement);
-			i++;
+			sj.add(String.valueOf(targetElement));
 		}
-		return sb.toString();
+		return sj.toString();
 	}
 
 }

spring-messaging/src/main/java/org/springframework/messaging/handler/AbstractMessageCondition.java

@@ -18,6 +18,7 @@ package org.springframework.messaging.handler;
 
 import java.util.Collection;
 import java.util.Iterator;
+import java.util.StringJoiner;
 
 import org.springframework.lang.Nullable;
 
@@ -51,16 +52,11 @@ public abstract class AbstractMessageCondition<T extends AbstractMessageConditio
 
 	@Override
 	public String toString() {
-		StringBuilder builder = new StringBuilder("[");
-		for (Iterator<?> iterator = getContent().iterator(); iterator.hasNext();) {
-			Object expression = iterator.next();
-			builder.append(expression.toString());
-			if (iterator.hasNext()) {
-				builder.append(getToStringInfix());
-			}
+		StringJoiner joiner = new StringJoiner(getToStringInfix(), "[", "]");
+		for (Object expression : getContent()) {
+			joiner.add(expression.toString());
 		}
-		builder.append("]");
-		return builder.toString();
+		return joiner.toString();
 	}
 
 

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

@@ -22,6 +22,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
+import java.util.StringJoiner;
 
 import org.springframework.core.io.InputStreamResource;
 import org.springframework.core.io.Resource;
@@ -210,13 +211,9 @@ public abstract class HttpRange {
 	 */
 	public static String toString(Collection<HttpRange> ranges) {
 		Assert.notEmpty(ranges, "Ranges Collection must not be empty");
-		StringBuilder builder = new StringBuilder(BYTE_RANGE_PREFIX);
-		for (Iterator<HttpRange> iterator = ranges.iterator(); iterator.hasNext(); ) {
-			HttpRange range = iterator.next();
-			builder.append(range);
-			if (iterator.hasNext()) {
-				builder.append(", ");
-			}
+		StringJoiner builder = new StringJoiner(", ", BYTE_RANGE_PREFIX, "");
+		for (HttpRange range : ranges) {
+			builder.add(range.toString());
 		}
 		return builder.toString();
 	}

spring-web/src/main/java/org/springframework/web/util/HierarchicalUriComponents.java

@@ -26,6 +26,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
+import java.util.StringJoiner;
 import java.util.function.BiFunction;
 import java.util.function.UnaryOperator;
 
@@ -916,14 +917,10 @@ final class HierarchicalUriComponents extends UriComponents {
 
 		@Override
 		public String getPath() {
-			StringBuilder pathBuilder = new StringBuilder();
-			pathBuilder.append(PATH_DELIMITER);
-			for (Iterator<String> iterator = this.pathSegments.iterator(); iterator.hasNext(); ) {
-				String pathSegment = iterator.next();
-				pathBuilder.append(pathSegment);
-				if (iterator.hasNext()) {
-					pathBuilder.append(PATH_DELIMITER);
-				}
+			String delimiter = String.valueOf(PATH_DELIMITER);
+			StringJoiner pathBuilder = new StringJoiner(delimiter, delimiter, "");
+			for (String pathSegment : this.pathSegments) {
+				pathBuilder.add(pathSegment);
 			}
 			return pathBuilder.toString();
 		}