javax.servlet.Filter Maven / Gradle / Ivy
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package javax.servlet;
import java.io.IOException;
/**
* A filter is an object that performs
* filtering tasks on either the request to a resource (a servlet or static content), or on the response
* from a resource, or both.
*
* 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:
*
* - Authentication Filters
*
- Logging and Auditing Filters
*
- Image conversion Filters
*
- Data compression Filters
*
- Encryption Filters
*
- Tokenizing Filters
*
- Filters that trigger resource access events
*
- XSL/T filters
*
- Mime-type chain Filter
*
*
* @since Servlet 2.3
*/
public interface Filter {
/**
* Called by the web container
* to indicate to a filter that it is being placed into service.
*
* 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
*
* - Throws a ServletException
*
- Does not return within a time period defined by the web container
*
*
* @implSpec
* The default implementation takes no action.
*
* @param filterConfig a FilterConfig object containing the
* filter's configuration and initialization parameters
* @throws ServletException if an exception has occurred that interferes with
* the filter's normal operation
*/
default public void init(FilterConfig filterConfig) throws ServletException {}
/**
* 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.
* 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:
*
* - Examine the request
*
- Optionally wrap the request object with a custom implementation to
* filter content or headers for input filtering
*
- Optionally wrap the response object with a custom implementation to
* filter content or headers for output filtering
*
-
*
* - Either invoke the next entity in the chain
* using the FilterChain object
* (
chain.doFilter()),
* - or not pass on the request/response pair to
* the next entity in the filter chain to
* block the request processing
*
* - Directly set headers on the response after invocation of the
* next entity in the filter chain.
*
*
* @param request the ServletRequest object contains the client's request
* @param response the ServletResponse object contains the filter's response
* @param chain the FilterChain for invoking the next filter or the resource
* @throws IOException if an I/O related error has occurred during the processing
* @throws ServletException if an exception occurs that interferes with the
* filter's normal operation
*
* @see UnavailableException
*/
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)
throws IOException, ServletException;
/**
* Called by the web container
* to indicate to a filter that it is being
* taken out of service.
*
* 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.
*
* @implSpec
* The default implementation takes no action.
*/
default public void destroy() {}
}