Java中的Filter详解 --基础篇

package javax.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.
 * @since Servlet 2.3
 */
 
public interface Filter {
 
    /**
     * Called by the web container to indicate to a filter that it is
     * being placed into service.
     */
    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.
     */
    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.
     */
    public void destroy();
 
}