能帮我解释一下这段jsp程序吗？
String   MM_authorizedUsers= "guest ";
String   MM_authFailedURL= "noright.jsp ";
boolean   MM_grantAccess=false;
if   (session.getValue( "MM_Username ")   !=   null   &&   !session.getValue( "MM_Username ").equals( " "))   {
    if   (false   ||   (session.getValue( "MM_UserAuthorization ")== " ")   ||  
                    (MM_authorizedUsers.indexOf((String)session.getValue( "MM_UserAuthorization "))   > =0))   {
        MM_grantAccess   =   true;
    }
}
if   (!MM_grantAccess)   {
    String   MM_qsChar   =   "? ";
    if   (MM_authFailedURL.indexOf( "? ")   > =   0)   MM_qsChar   =   "& ";
    String   MM_referrer   =   request.getRequestURI();
    if   (request.getQueryString()   !=   null)   MM_referrer   =   MM_referrer   +   "? "   +   request.getQueryString();
    MM_authFailedURL   =   MM_authFailedURL   +   MM_qsChar   +   "accessdenied= "   +   java.net.URLEncoder.encode(MM_referrer);
    response.sendRedirect(response.encodeRedirectURL(MM_authFailedURL));
    return;
}

------解决方案--------------------
根据get的请求值重新构建URL地址
------解决方案--------------------
验证登录用户的访问权限，如果没有权限访问，则返回到一个错误界面