Tomcat 10.1.19 · jakarta.servlet.Filter · APIdia, the JavaDoc alternative

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, 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

Modifier and Type	Method and Description
public default void	destroy() Called by the web container to indicate to a filter that it is being taken out of service.
public void	doFilter(ServletRequest The request to process request, ServletResponse The response associated with the request response, FilterChain Provides access to the next filter in the chain for this filter to pass the request and response to for further processing 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.
public default void	init(FilterConfig The configuration information associated with the filter instance being initialised filterConfig) Called by the web container to indicate to a filter that it is being placed into service.

Method Detail

destroy	back to summary
public default void destroy() 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. The default implementation is a NO-OP.

destroy

back to summary

public default void destroy()

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. The default implementation is a NO-OP.

doFilter back to summary

doFilter	back to summary
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, 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:- 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 the filter chain. Parameters request:ServletRequest The request to process response:ServletResponse The response associated with the request chain:FilterChain Provides access to the next filter in the chain for this filter to pass the request and response to for further processing Exceptions IOException: if an I/O error occurs during this filter's processing of the request ServletException: if the processing fails for any other reason

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, 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:-
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 the filter chain.

Parameters

request:ServletRequest: The request to process
response:ServletResponse: The response associated with the request
chain:FilterChain: Provides access to the next filter in the chain for this filter to pass the request and response to for further processing

Exceptions

IOException:: if an I/O error occurs during this filter's processing of the request
ServletException:: if the processing fails for any other reason

init	back to summary
public default void init(FilterConfig filterConfig) throws ServletException 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 The default implementation is a NO-OP. Parameters filterConfig:FilterConfig The configuration information associated with the filter instance being initialised Exceptions ServletException: if the initialisation fails

init

back to summary

public default void init(FilterConfig filterConfig) throws ServletException

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

The default implementation is a NO-OP.

Parameters

filterConfig:FilterConfig: The configuration information associated with the filter instance being initialised

Exceptions

ServletException:: if the initialisation fails

public Interface Filter

Method Summary

Method Detail