3 个接口分别是 Filter、FilterChain 和 FilterConfig。的问题，谢谢。

我怎么有这些src??
例如
package javax.servlet;import java.io.IOException;// Referenced classes of package javax.servlet:
//            ServletException, FilterConfig, ServletRequest, ServletResponse, 
//            FilterChainpublic interface Filter
{    public abstract void init(FilterConfig filterconfig)
        throws ServletException;    public abstract void doFilter(ServletRequest servletrequest, ServletResponse servletresponse, FilterChain filterchain)
        throws IOException, ServletException;    public abstract void destroy();
}