Among the types of functionality available to the developer needing to use filters are the following:
■ The accessing of a resource before a request to it is invoked.
■ The processing of the request for a resource before it is invoked.
■ The modification of request headers and data by wrapping the request in customized versions of the request object.
■ The modification of response headers and response data by providing customized versions of the response object.
■ The interception of an invocation of a resource after its call.
■ Actions on a servlet, on groups of servlets, or static content by zero, one, or more filters in a specifiable order.
仅翻译如下两句即可
■ The accessing of a resource before a request to it is invoked.
■ The processing of the request for a resource before it is invoked.