refactor IPRange

src/main/java/com/alibaba/druid/support/http/util/IPRange.java

@@ -257,18 +257,19 @@ public class IPRange {
     }
 
     public static String toDecimalString(String inBinaryIpAddress) {
-        String decimalip = new String();
+        StringBuilder decimalip = new StringBuilder();
         String[] binary = new String[4];
 
         for (int i = 0, c = 0; i < 32; i = i + 8, c++) {
             binary[c] = inBinaryIpAddress.substring(i, i + 8);
             int octet = Integer.parseInt(binary[c], 2);
-            decimalip = decimalip + Integer.toString(octet);
+            decimalip.append(octet);
             if (c < 3) {
-                decimalip = decimalip + ".";
+                
+                decimalip.append('.');
             }
         }
-        return decimalip;
+        return decimalip.toString();
     }
 
     // -------------------------------------------------------------------------