setcharacterencodingfilter.java

一套完整的档案管理系统

/*
* XP Forum
* 
* Copyright (c) 2002-2003 RedSoft Group. All rights reserved.
*
*/
package com.stsc.struts.filters;

import javax.servlet.*;
import java.io.IOException;

/**
* <p>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 <a href="mailto:[e-mail]">John Wong</a>
*
* @version $Id: SetCharacterEncodingFilter.java,v 1.1 2002/04/10 13:59:27 johnwong Exp $
*/
public class SetCharacterEncodingFilter implements Filter {

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


    /**
    * The default character encoding to set for requests that pass through
    * this filter.
    */
    protected String encoding = null;
    
    
    /**
    * The filter configuration object we are associated with. If this value
    * is null, this filter instance is not currently configured.
    */
    protected FilterConfig filterConfig = null;
    
    
    /**
    * Should a character encoding specified by the client be ignored?
    */
    protected boolean ignore = true;


    // --------------------------------------------------------- Public Methods
    
    
    /**
    * Take this filter out of service.
    */
    public 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 result 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 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 encoding = selectEncoding(request);
            if (encoding != null)
                request.setCharacterEncoding(encoding);
        }
        
        // Pass control on to the next filter
        chain.doFilter(request, response);
    
    }
    
    
    /**
    * Place this filter into service.
    *
    * @param filterConfig The filter configuration object
    */
    public void init(FilterConfig filterConfig) throws ServletException {
    
        this.filterConfig = filterConfig;
        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.
    *
    * @param request The servlet request we are processing
    */
    protected String selectEncoding(ServletRequest request) {
    
        return (this.encoding);
    
    }

}