1. Filter Filter
1. Introduction to filter
Filter is the filtering of the client's access to resources. It is released when the conditions are met, but not when the conditions are not met, and logical processing can be performed before and after the target resource is accessed.
2. Quick start
step:
1) Write a filter class that implements the Filter interface
2) Implement methods that have not yet been implemented in the interface (focus on implementing the doFilter method)
3) Configure in web.xml (mainly configure which resources to filter)
3. Detailed API of Filter
(1) The filter life cycle and its methods related to the life cycle
The Filter interface has three methods, and these three are methods related to the life of Filter
init(Filterconfig): On behalf of the filter object initialization method, it is executed when the filter object is created
doFilter(ServletRequest,ServletResponse,FilterCha): The core method of performing filtering on behalf of the filter. If a resource has been configured to be filtered by this filter, the doFilter method will be executed every time the resource is accessed.
Destory(): Represents the filter destruction method. This method is executed when the filter object is destroyed.
The life cycle of the Filter object:
When filter is created: the filter object is created when the server starts
When is the filter destroyed: the filter is destroyed when the server shuts down
(2) Detailed AP of Filter
1）init(FilterConfig)
The parameter config represents the object of the configuration information of the Filter object, and the internal encapsulation is the configuration information of the filter.
2) destroy() method
Executed when the filter object is destroyed
3) doFilter method
doFilter(ServletRequest,ServletResponse,FilterChain)
Among the parameters:
ServletRequest/ServletResponse: Each time the doFilter method is executed, the web container is responsible for creating a request and a response object and passing it in as the parameters of doFilter. The request and the response are the request and response when accessing the service method of the target resource.
FilterChain: The filter chain object, the request can be released through the doFilter method of the object
Pay attention to the execution order of filters
4. Filter configuration
When url-pattern is configured
1) Exactly match /sertvle1
2) Directory matches /aaa/bbb/* ---- the most
/user/*: access to foreground resources to enter this filter
/admin/*: Execute this filter when accessing resources in the background
3) The extension matches *.abc *.jsp
Note: url-pattern can be replaced by servlet-name or mixed
dispatcher: the way to access (understand)
REQUEST: The default value, which means that the filter is executed when a resource is directly accessed
FORWARD: filter is only executed when forwarding
INCLUDE: Execute filter when resources are included
ERROR: jumping when an error occurs is to execute filter
Summarize the role of Filter?
1) Extraction of public code
2) The methods in request and response can be enhanced (decorator pattern/dynamic proxy)
3) Perform permission control