Filterr filter ************* for Web containers
Configuration in the 1--web.xml file (note the request name)
The filter is called before the servlet, and multiple filter configurations are performed in the order in which the filter-mapping is configured, such as: Two filter with the request name and servlet with the requested name
When the client makes a request for the request name, it first invokes the configured filter, calls the latter filter, and finally calls the servlet, if there is a JSP with the same name as the request, then this is the JSP that is called at the end of the
Thus, we can design a simple IP address filter, according to the user's IP address for the site access control.
The request between 2--filter and filter, response can be deferred, that is, the request of the first filter set the property, then the second filter can be obtained, the final servlet can be obtained;
(Of course, you need to use the filter chain to pass the OH)
Three ways to 3--filter filters:
Initialize the init () Web container to start, call this method when initializing filter to initialize the parameters used by the filter, or other required parameters, for example: Initialize Filterconfig
Filter Processing DoFilter ()The Dofilter (Request,response) method of the filter chain Filterchain can be called after the response processing of the request continues to invoke the following filter, servlet, or JSP page
Destroy Destroy ()The user frees the resources that the filter occupies
The 4--filterconfig interface has four methods defined, each of which can be obtained
Getfiltername () returns the name of the filter defined in the Web. XML deployment File
Getservletcontext () returns the servlet context where the caller is located ServletContext
Getinitparameter (Java.lang.Stringname) returns the string form of the filter initialization parameter value, returning the Null.name initialization parameter name when the argument does not exist
Getinitparameternames () returns the filter all initialization parameter names in enumeration form, and returns null if there are no initialization parameters.
5--Create filter steps:
Step One: Create a class that implements the filter interface and implement its three methods: Init, Dofilter, and destroy
Step Two: Write the filtering behavior in the Dofilter method. Three of these parameters are ServletRequest, Servletresponse, and Filterchain, respectively,
The first two can be strongly converted to HttpServletRequest and HttpServletResponse use,
The third parameter is used to activate the next related filter.
If no other filter is associated with a servlet or JSP page, the servlet or JSP page is activated.
Step three: Configure Web. xml
Step four: Request a Test
Filterr Filters for Web containers
