clean code for isBlank

apollo-core/src/main/java/com/ctrip/framework/foundation/internals/Utils.java

 package com.ctrip.framework.foundation.internals;
 
+import com.google.common.base.Strings;
+
 public class Utils {
   public static boolean isBlank(String str) {
-    if (str == null || str.length() == 0) {
-      return true;
-    }
-
-    int length = str.length();
-    for (int i = 0; i < length; i++) {
-      char ch = str.charAt(i);
-
-      if (!Character.isWhitespace(ch)) {
-        return false;
-      }
-    }
-    return true;
+    return Strings.nullToEmpty(str).trim().isEmpty();
   }
 
   public static boolean isOSWindows() {