Encoding Filter实现

public class CharacterEncodingFilter 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);
　　            }
　　        }