/*
 * 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 org.apache.catalina.filters;

import java.io.IOException;

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

import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;


/**
 * <p>
 * Example filter that sets the character encoding to be used in parsing the incoming request, either unconditionally or
 * only if the client did not specify a character encoding. Configuration of this filter is based on the following
 * initialization parameters:
 * </p>
 * <ul>
 * <li><strong>encoding</strong> - The character encoding to be configured for this request, either conditionally or
 * unconditionally based on the <code>ignore</code> initialization parameter. This parameter is required, so there is no
 * default.</li>
 * <li><strong>ignore</strong> - If set to "true", any character encoding specified by the client is ignored, and the
 * value returned by the <code>selectEncoding()</code> method is set. If set to "false, <code>selectEncoding()</code> is
 * called <strong>only</strong> if the client has not already specified an encoding. By default, this parameter is set
 * to "false".</li>
 * </ul>
 * <p>
 * Although this filter can be used unchanged, it is also easy to subclass it and make the <code>selectEncoding()</code>
 * method more intelligent about what encoding to choose, based on characteristics of the incoming request (such as the
 * values of the <code>Accept-Language</code> and <code>User-Agent</code> headers, or a value stashed in the current
 * user's session).
 * </p>
 */
public class SetCharacterEncodingFilter extends FilterBase {

    // Log must be non-static as loggers are created per class-loader and this
    // Filter may be used in multiple class loaders
    private final Log log = LogFactory.getLog(SetCharacterEncodingFilter.class); // must not be static


    // ----------------------------------------------------- Instance Variables

    /**
     * The default character encoding to set for requests that pass through this filter.
     */
    private String encoding = null;

    public void setEncoding(String encoding) {
        this.encoding = encoding;
    }

    public String getEncoding() {
        return encoding;
    }


    /**
     * Should a character encoding specified by the client be ignored?
     */
    private boolean ignore = false;

    public void setIgnore(boolean ignore) {
        this.ignore = ignore;
    }

    public boolean isIgnore() {
        return ignore;
    }


    // --------------------------------------------------------- Public Methods


    /**
     * Select and set (if specified) the character encoding to be used to interpret request parameters for this request.
     *
     * @param request  The servlet request we are processing
     * @param response The servlet response we are creating
     * @param chain    The filter chain we are processing
     *
     * @exception IOException      if an input/output error occurs
     * @exception ServletException if a servlet error occurs
     */
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        // Conditionally select and set the character encoding to be used
        if (ignore || (request.getCharacterEncoding() == null)) {
            String characterEncoding = selectEncoding(request);
            if (characterEncoding != null) {
                request.setCharacterEncoding(characterEncoding);
            }
        }

        // Pass control on to the next filter
        chain.doFilter(request, response);
    }


    // ------------------------------------------------------ Protected Methods

    @Override
    protected Log getLogger() {
        return log;
    }


    /**
     * Select an appropriate character encoding to be used, based on the characteristics of the current request and/or
     * filter initialization parameters. If no character encoding should be set, return <code>null</code>.
     * <p>
     * The default implementation unconditionally returns the value configured by the <strong>encoding</strong>
     * initialization parameter for this filter.
     *
     * @param request The servlet request we are processing
     *
     * @return the encoding that was configured
     */
    protected String selectEncoding(ServletRequest request) {
        return this.encoding;
    }
}
