/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (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 javax.servlet.http;

import java.io.IOException;

import javax.servlet.FilterChain;
import javax.servlet.GenericFilter;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

/**
 * Provides a base class that implements the Filter interface and ensures that the Request and Response are of type
 * HttpServletRequest and HttpServletResponse respectively.
 */
public abstract class HttpFilter extends GenericFilter {

    private static final long serialVersionUID = 1L;

    /**
     * {@inheritDoc} This implementation tests the request and response to see if they are instances of
     * {@link HttpServletRequest} and {@link HttpServletResponse} respectively. If they are then they are passed to
     * {@link #doFilter(HttpServletRequest, HttpServletResponse, FilterChain)}. If not, a {@link ServletException} is
     * thrown.
     *
     * @throws ServletException If either the request or response are not of the expected types or any other error
     *                              occurs
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        if (!(request instanceof HttpServletRequest)) {
            throw new ServletException(request + " not HttpServletRequest");
        }
        if (!(response instanceof HttpServletResponse)) {
            throw new ServletException(response + " not HttpServletResponse");
        }
        doFilter((HttpServletRequest) request, (HttpServletResponse) response, chain);
    }


    /**
     * 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. This default
     * implementation simply calls the next filter 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
     */
    protected void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        chain.doFilter(request, response);
    }
}
