regex optimization (#305)

Author: productivityindustries

aws-xray-recorder-sdk-aws-sdk-core/src/main/java/com/amazonaws/xray/utils/StringTransform.java

@@ -15,16 +15,18 @@
 
 package com.amazonaws.xray.utils;
 
+import java.util.regex.Pattern;
+
 /**
  * @deprecated For internal use only.
  */
 @Deprecated
 @SuppressWarnings("checkstyle:HideUtilityClassConstructor")
 public class StringTransform {
-    private static final String REGEX = "([a-z])([A-Z]+)";
+    private static final Pattern REGEX = Pattern.compile("([a-z])([A-Z]+)");
     private static final String REPLACE = "$1_$2";
 
     public static String toSnakeCase(String camelCase) {
-        return camelCase.replaceAll(REGEX, REPLACE).toLowerCase();
+        return REGEX.matcher(camelCase).replaceAll(REPLACE).toLowerCase();
     }
 }