java/org/apache/catalina/filters/SetCharacterEncodingFilter.java

/*
* 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 {

    private static final Log log =
        LogFactory.getLog(SetCharacterEncodingFilter.class);


    // ----------------------------------------------------- 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
     */
    protected String selectEncoding(ServletRequest request) {
        return this.encoding;
    }
}