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. <br><br>
* The web container cannot place the filter into service if the init method either<br>
* 1.Throws a ServletException <br>
* 2.Does not return within a time period defined by the web container
*/
public void init(FilterConfig filterConfig) throws ServletException;
/**
* 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.
**/
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. <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.
*/
public void destroy();
}
public interface FilterChain {
/**
* Causes the next filter in the chain to be invoked, or if the calling filter is the last filter
* in the chain, causes the resource at the end of the chain to be invoked.
*
* @param request the request to pass along the chain.
* @param response the response to pass along the chain.
*
* @since 2.3
*/
public void doFilter ( ServletRequest request, ServletResponse response ) throws IOException, ServletException;
}
public interface FilterConfig {
/**
* Returns the filter-name of this filter as defined in the deployment descriptor.
*/
public String getFilterName();
/**
* Returns a reference to the {@link ServletContext} in which the caller
* is executing.
*
*
* @return a {@link ServletContext} object, used
* by the caller to interact with its servlet
* container
*
* @see ServletContext
*
*/
public ServletContext getServletContext();
/**
* Returns a <code>String</code> containing the value of the
* named initialization parameter, or <code>null</code> if
* the parameter does not exist.
*
* @param name a <code>String</code> specifying the name
* of the initialization parameter
*
* @return a <code>String</code> containing the value
* of the initialization parameter
*
*/
public String getInitParameter(String name);
/**
* Returns the names of the filter's initialization parameters
* as an <code>Enumeration</code> of <code>String</code> objects,
* or an empty <code>Enumeration</code> if the filter has
* no initialization parameters.
*
* @return an <code>Enumeration</code> of <code>String</code>
* objects containing the names of the filter's
* initialization parameters
*
*
*
*/
public Enumeration getInitParameterNames();
}