Filter 字符过滤器

/**
* 中文过滤器
*/
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);
}
}