https://tomcat.apache.org/: jakarta.servlet package
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* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jakarta.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, 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
Since: Servlet 2.3
/**
* 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. <br>
* <br>
* Filters perform filtering in the <code>doFilter</code> 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.
* <p>
* Filters are configured in the deployment descriptor of a web application
* <p>
* Examples that have been identified for this design are<br>
* 1) Authentication Filters <br>
* 2) Logging and Auditing Filters <br>
* 3) Image conversion Filters <br>
* 4) Data compression Filters <br>
* 5) Encryption Filters <br>
* 6) Tokenizing Filters <br>
* 7) Filters that trigger resource access events <br>
* 8) XSL/T filters <br>
* 9) Mime-type chain Filter <br>
*
* @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
The default implementation is a NO-OP.
Params: - filterConfig – The configuration information associated with the
filter instance being initialised
Throws: - ServletException – if the initialisation fails
/**
* 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.
* <p>
* The web container cannot place the filter into service if the init method
* either:
* <ul>
* <li>Throws a ServletException</li>
* <li>Does not return within a time period defined by the web
* container</li>
* </ul>
* The default implementation is a NO-OP.
*
* @param filterConfig The configuration information associated with the
* filter instance being initialised
*
* @throws ServletException if the initialisation fails
*/
public default 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:-
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.
Params: - request – The request to process
- response – The response associated with the request
- chain – Provides access to the next filter in the chain for this
filter to pass the request and response to for further
processing
Throws: - IOException – if an I/O error occurs during this filter's
processing of the request
- ServletException – if the processing fails for any other reason
/**
* The <code>doFilter</code> 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.
* <p>
* A typical implementation of this method would follow the following
* pattern:- <br>
* 1. Examine the request<br>
* 2. Optionally wrap the request object with a custom implementation to
* filter content or headers for input filtering <br>
* 3. Optionally wrap the response object with a custom implementation to
* filter content or headers for output filtering <br>
* 4. a) <strong>Either</strong> invoke the next entity in the chain using
* the FilterChain object (<code>chain.doFilter()</code>), <br>
* 4. b) <strong>or</strong> not pass on the request/response pair to the
* next entity in the filter chain to block the request processing<br>
* 5. Directly set headers on the response after invocation of the next
* entity in the filter chain.
*
* @param request The request to process
* @param response The response associated with the request
* @param chain Provides access to the next filter in the chain for this
* filter to pass the request and response to for further
* processing
*
* @throws IOException if an I/O error occurs during this filter's
* processing of the request
* @throws ServletException if the processing fails for any other reason
*/
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.
The default implementation is a NO-OP.
/**
* 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. <br>
* <br>
*
* 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.
*/
public default void destroy() {}
}