Servlet 3.0, JSP 2.2 and EL 2.2 are the minimum required to deploy Petclinic

src/main/webapp/WEB-INF/web.xml

 <?xml version="1.0" encoding="ISO-8859-1"?>
-<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xmlns="http://java.sun.com/xml/ns/javaee"
+<web-app xmlns="http://java.sun.com/xml/ns/javaee"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
-http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
-         id="WebApp_ID" version="2.5">
+	      http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
+         version="3.0" metadata-complete="true">
 
     <display-name>Spring PetClinic</display-name>
     <description>Spring PetClinic sample application</description>