Do not create String instances in 'Strings' methods accepting StringBuilder (#22907)

Author: sabi0

core/src/main/java/org/elasticsearch/common/Strings.java

@@ -25,7 +25,6 @@
 import org.elasticsearch.common.io.FastStringReader;
 import org.elasticsearch.common.util.CollectionUtils;
 import org.elasticsearch.common.xcontent.ToXContent;
-import org.elasticsearch.common.xcontent.ToXContentObject;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.json.JsonXContent;
 
@@ -712,18 +711,19 @@ public static Set<String> commaDelimitedListToSet(String str) {
      * @return the delimited String
      */
     public static String collectionToDelimitedString(Iterable<?> coll, String delim, String prefix, String suffix) {
-        return collectionToDelimitedString(coll, delim, prefix, suffix, new StringBuilder());
+        StringBuilder sb = new StringBuilder();
+        collectionToDelimitedString(coll, delim, prefix, suffix, sb);
+        return sb.toString();
     }
 
-    public static String collectionToDelimitedString(Iterable<?> coll, String delim, String prefix, String suffix, StringBuilder sb) {
+    public static void collectionToDelimitedString(Iterable<?> coll, String delim, String prefix, String suffix, StringBuilder sb) {
         Iterator<?> it = coll.iterator();
         while (it.hasNext()) {
             sb.append(prefix).append(it.next()).append(suffix);
             if (it.hasNext()) {
                 sb.append(delim);
             }
         }
-        return sb.toString();
     }
 
     /**
@@ -758,20 +758,21 @@ public static String collectionToCommaDelimitedString(Iterable<?> coll) {
      * @return the delimited String
      */
     public static String arrayToDelimitedString(Object[] arr, String delim) {
-        return arrayToDelimitedString(arr, delim, new StringBuilder());
+        StringBuilder sb = new StringBuilder();
+        arrayToDelimitedString(arr, delim, sb);
+        return sb.toString();
     }
 
-    public static String arrayToDelimitedString(Object[] arr, String delim, StringBuilder sb) {
+    public static void arrayToDelimitedString(Object[] arr, String delim, StringBuilder sb) {
         if (isEmpty(arr)) {
-            return "";
+            return;
         }
         for (int i = 0; i < arr.length; i++) {
             if (i > 0) {
                 sb.append(delim);
             }
             sb.append(arr[i]);
         }
-        return sb.toString();
     }
 
     /**

modules/transport-netty4/src/test/java/org/elasticsearch/http/netty4/Netty4HttpServerTransportTests.java

@@ -109,12 +109,12 @@ public void shutdown() throws Exception {
     public void testCorsConfig() {
         final Set<String> methods = new HashSet<>(Arrays.asList("get", "options", "post"));
         final Set<String> headers = new HashSet<>(Arrays.asList("Content-Type", "Content-Length"));
-        final String suffix = randomBoolean() ? " " : ""; // sometimes have a leading whitespace between comma delimited elements
+        final String prefix = randomBoolean() ? " " : ""; // sometimes have a leading whitespace between comma delimited elements
         final Settings settings = Settings.builder()
                                       .put(SETTING_CORS_ENABLED.getKey(), true)
                                       .put(SETTING_CORS_ALLOW_ORIGIN.getKey(), "*")
-                                      .put(SETTING_CORS_ALLOW_METHODS.getKey(), collectionToDelimitedString(methods, ",", suffix, ""))
-                                      .put(SETTING_CORS_ALLOW_HEADERS.getKey(), collectionToDelimitedString(headers, ",", suffix, ""))
+                                      .put(SETTING_CORS_ALLOW_METHODS.getKey(), collectionToDelimitedString(methods, ",", prefix, ""))
+                                      .put(SETTING_CORS_ALLOW_HEADERS.getKey(), collectionToDelimitedString(headers, ",", prefix, ""))
                                       .put(SETTING_CORS_ALLOW_CREDENTIALS.getKey(), true)
                                       .build();
         final Netty4CorsConfig corsConfig = Netty4HttpServerTransport.buildCorsConfig(settings);