encodingfilter.java

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/*
 * $Header: /home/cvs/jakarta-tomcat-4.0/webapps/examples/WEB-INF/classes/filters/SetCharacterEncodingFilter.java,v 1.2 2001/10/17 22:53:19 craigmcc Exp $
 * $Revision: 1.2 $
 * $Date: 2001/10/17 22:53:19 $
 *
 * ====================================================================
 *
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 1999-2001 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
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 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Tomcat", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact [e-mail].
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 * 5. Products derived from this software may not be called "Apache"
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 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
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 * [Additional notices, if required by prior licensing conditions]
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package jaoso.framework.web.filter;

import java.io.IOException;

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


/**
 * <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 "true".
 * </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>
 *
 * @author Craig McClanahan
 * @version $Revision: 1.2 $ $Date: 2001/10/17 22:53:19 $
 */
public class EncodingFilter implements Filter {

    //~ Instance fields ========================================================

    /**
     * The filter configuration object we are associated with.  If this value
     * is null, this filter instance is not currently configured.
     */
    private FilterConfig filterConfig = null;

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

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

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

    //~ Methods ================================================================

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

    /**
     * Take this filter out of service.
     */
    public final void destroy() {

        this.encoding = null;
        this.filterConfig = null;
    }

    /**
     * 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
     */
    public final void doFilter(final ServletRequest request,
        final ServletResponse response, final FilterChain chain)
        throws IOException, ServletException {

        // Conditionally select and set the character encoding to be used
        if (ignore || (request.getCharacterEncoding() == null)) {

            String encoding1 = selectEncoding(request);

            if (encoding1 != null) {

                request.setCharacterEncoding(encoding1);
            }
        }

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

    /**
     * Place this filter into service.
     *
     * @param arg0 The filter configuration object
         * @exception ServletException error
     */
    public final void init(final FilterConfig arg0) throws ServletException {

        this.filterConfig = arg0;
        this.encoding = filterConfig.getInitParameter("encoding");

        String value = filterConfig.getInitParameter("ignore");

        if (value == null) {

            this.ignore = true;
        } else if (value.equalsIgnoreCase("true")) {

            this.ignore = true;
        } else if (value.equalsIgnoreCase("yes")) {

            this.ignore = true;
        } else {

            this.ignore = false;
        }
    }

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

    /**
     * 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.
     * </p>
     *
     * @param request The servlet request we are processing
         * @return string
     */
    protected final String selectEncoding(final ServletRequest request) {

        return (this.encoding);
    }
}