A filter is a Java class that is called to process client requests or the server’s response. You can use filters to modify the request header or the content of a servlet request or response. Chapter 3, “Using Filters and Event Listeners,” describes how to create filters.
You can map filters to a URL or a servlet name. When a filter is mapped to a URL (path-mapped), the filter applies to every servlet and JSP in the Web application. When a filter is mapped to a servlet name (servlet-mapped), it applies to a single servlet or JSP. The path-mapped filters are executed first, followed by the servlet-mapped filters.
