Jakarta EE 11.0.0 · 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, 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

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 `ServletRequest` object contains the client's request request, ServletResponse the `ServletResponse` object contains the filter's response response, FilterChain the `FilterChain` for invoking the next filter or the resource 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 a `FilterConfig` object containing the filter's configuration and initialization parameters 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. Implementation Specification The default implementation takes no action.

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.

Implementation Specification

The default implementation takes no action.

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: 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. Parameters request:ServletRequest the `ServletRequest` object contains the client's request response:ServletResponse the `ServletResponse` object contains the filter's response chain:FilterChain the `FilterChain` for invoking the next filter or the resource Exceptions IOException: if an I/O related error has occurred during the processing ServletException: if an exception occurs that interferes with the filter's normal operation See Also `UnavailableException`

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:

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.

Parameters

request:ServletRequest: the ServletRequest object contains the client's request
response:ServletResponse: the ServletResponse object contains the filter's response
chain:FilterChain: the FilterChain for invoking the next filter or the resource

Exceptions

IOException:: if an I/O related error has occurred during the processing
ServletException:: if an exception occurs that interferes with the filter's normal operation

See Also

UnavailableException

init back to summary

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 container will ensure that actions performed in the `init` method will be visible to any threads that subsequently call the `doFilter` method according to the rules in JSR-133 (i.e. there is a 'happens before' relationship between `init` and `doFilter`). 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 Implementation Specification The default implementation takes no action. Parameters filterConfig:FilterConfig a `FilterConfig` object containing the filter's configuration and initialization parameters Exceptions ServletException: if an exception has occurred that interferes with the filter's normal operation

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 container will ensure that actions performed in the init method will be visible to any threads that subsequently call the doFilter method according to the rules in JSR-133 (i.e. there is a 'happens before' relationship between init and doFilter).

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

Implementation Specification

The default implementation takes no action.

Parameters

filterConfig:FilterConfig: a FilterConfig object containing the filter's configuration and initialization parameters

Exceptions

ServletException:: if an exception has occurred that interferes with the filter's normal operation

public Interface Filter

Method Summary

Method Detail