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);
            }
        }