public interface Filter
Filters perform filtering in the doFilter
method.
Every Filter has access to a FilterConfig object from which it can obtain
its initialization parameters, and a reference to the ServletContext which
it can use, for example, to load resources needed for filtering tasks.
Filters are configured in the deployment descriptor of a web application.
Examples that have been identified for this design are:
Modifier and Type | Method and Description |
---|---|
void |
destroy()
Called by the web container to indicate to a filter that it is being
taken out of service.
|
void |
doFilter(ServletRequest request,
ServletResponse response,
FilterChain chain)
The
doFilter method of the Filter is called by the
container each time a request/response pair is passed through the
chain due to a client request for a resource at the end of the chain. |
void |
init(FilterConfig filterConfig)
Called by the web container to indicate to a filter that it is
being placed into service.
|
void init(FilterConfig filterConfig) throws ServletException
The servlet container calls the init method exactly once after instantiating the filter. The init method must complete successfully before the filter is asked to do any filtering work.
The web container cannot place the filter into service if the init method either
ServletException
void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
doFilter
method of the Filter is called by the
container each time a request/response pair is passed through the
chain due to a client request for a resource at the end of the chain.
The FilterChain passed in to this method allows the Filter to pass
on the request and response to the next entity in the chain.
A typical implementation of this method would follow the following pattern:
chain.doFilter()
),
IOException
ServletException
void destroy()
This method is only called once all threads within the filter's doFilter method have exited or after a timeout period has passed. After the web container calls this method, it will not call the doFilter method again on this instance of the filter.
This method gives the filter an opportunity to clean up any resources that are being held (for example, memory, file handles, threads) and make sure that any persistent state is synchronized with the filter's current state in memory.
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