判断是否是ajax请求，区分返回页面值

boolean isAjax = "XMLHttpRequest".equals(req.getHeader("X-Requested-With")); 
//如果是ajax请求 
        if (isAjax) {        
             
            String jsonObject = "{\"message\":\"You are not privileged to request this resource.\",\"access-denied\":true,\"cause\":\"AUTHORIZATION_FAILURE\"}"; 
            String contentType = "application/json"; 
            resp.setContentType(contentType); 
            PrintWriter out = resp.getWriter(); 
            out.print(jsonObject); 
            out.flush(); 
            out.close(); 
            return; 
        } 
        else 
        { 
         
         String path = req.getContextPath(); 
         String basePath = req.getScheme()+"://"+req.getServerName()+":"+req.getServerPort()+path+"/"; 
         resp.sendRedirect(basePath+accessDeniedUrl); 
        } 
//全局设置 jquery_ajax事件
(function($){ 
    // 保存原有的jquery ajax; 
    var $_ajax = $.ajax; 
     
    $.ajax = function(options){ 
        var originalSuccess, 
            mySuccess, 
            success_context; 
     
        if (options.success) { 
                        // save reference to original success callback 
            originalSuccess = options.success; 
            success_context = options.context ? options.context : $; 
             
                        // 自定义callback 
            mySuccess = function(data) { 
                 
                 
                                        
                            
                            if (data['access-denied']) { 
                                  if (data.cause==='AUTHENTICATION_FAILURE') { 
                                    alert('登录超时,请重新登录.'); 
                    window.location.href = contextPath + '/'; 
                                  } else if (data.cause==='AUTHORIZATION_FAILURE') { 
                                       if (data=="noright") 
                                       { 
                                        alert('对不起，你没有访问该资源的权限.'); 
                                       } 
                    } 
                                   return; 
                         
                              
                                // call original success callback                            
                originalSuccess.apply(success_context, arguments); 
            }; 
                        // override success callback with custom implementation 
            options.success = mySuccess; 
        } 
         
                // call original ajax function with modified arguments 
        $_ajax.apply($, arguments); 
    }; 
     
})(jQuery);