doFilter method. Every Filter has access to
a FilterConfig object from which it can obtain its initialization parameters, 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
1) Authentication Filters
2) Logging and Auditing Filters
3) Image conversion Filters
4) Data compression Filters
5) Encryption Filters
6) Tokenizing Filters
7) Filters that trigger resource access events
8) XSL/T filters
9) Mime-type chain Filter
| Method Summary | |
|---|---|
| void |
Called by the web container to indicate to a filter that it is being taken out of service. |
| void |
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 |
Called by the web container to indicate to a filter that it is being placed into service. |
public
void
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:-
1. Examine the request
2. Optionally wrap the request object with a custom implementation to
filter content or headers for input filtering
3. Optionally wrap the response object with a custom implementation to
filter content or headers for output filtering
4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()),
4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
5. Directly set headers on the response after invocation of the next entity in ther filter chain.
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.