Use String.indexOf(char) when checking for the index of a single character; it executes faster.

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

@@ -227,7 +227,7 @@ public class IPAddress implements Cloneable {
             for (int i = 0; i < 3; i++) {
 
                 // get the position of the first dot
-                int index = tmp.indexOf(".");
+                int index = tmp.indexOf('.');
 
                 // if there is not a dot then the ip string representation is
                 // not compliant to the decimal-dotted notation.

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

@@ -198,7 +198,7 @@ public class IPRange {
             throw new IllegalArgumentException("Invalid IP range");
         }
 
-        int index = range.indexOf("/");
+        int index = range.indexOf('/');
         String subnetStr = null;
         if (index == -1) {
             ipAddress = new IPAddress(range);

src/main/java/com/alibaba/druid/util/MapComparator.java

@@ -62,7 +62,7 @@ public class MapComparator<K extends Object, V extends Object> implements Compar
             String keyStr = (String) key;
 
             if (keyStr.matches(".+\\[[0-9]+\\]")) {
-                Object value = map.get(keyStr.substring(0, keyStr.indexOf("[")));
+                Object value = map.get(keyStr.substring(0, keyStr.indexOf('[')));
                 if (value == null) {
                     return null;
                 }