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();

}