WebStatFilter support exclustions

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

@@ -1,5 +1,6 @@
 package com.alibaba.druid.util;
 
+import javax.servlet.ServletContext;
 import javax.servlet.http.HttpServletRequest;
 
 public class DruidWebUtils {
@@ -18,4 +19,26 @@ public class DruidWebUtils {
 
         return ip;
     }
+    
+    private static String getContextPath_2_5(ServletContext context) {
+        String contextPath = context.getContextPath();
+
+        if (contextPath == null || contextPath.length() == 0) {
+            contextPath = "/";
+        }
+
+        return contextPath;
+    }
+
+    public static String getContextPath(ServletContext context) {
+        if (context.getMajorVersion() == 2 && context.getMinorVersion() < 5) {
+            return null;
+        }
+
+        try {
+            return getContextPath_2_5(context);
+        } catch (NoSuchMethodError error) {
+            return null;
+        }
+    }
 }