在服务器端判断request 来自Ajax请求(异步)还是传统请求(同步)：

两种请求在请求的Header不同，Ajax 异步请求比传统的同步请求多了一个头参数

1、传统同步请求参数

accept? text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
accept-charset? gb2312,utf-8;q=0.7,*;q=0.7
accept-encoding? gzip,deflate
accept-language? zh-cn,zh;q=0.5
cache-control? max-age=0
connection? keep-alive
cookie? JSESSIONID=1A3BED3F593EA9747C9FDA16D309AF6B
host? 192.168.101.72:8080
keep-alive? 300
referer??http://192.168.101.72:8080/htfsweb/spring_security_login
user-agent? Mozilla/5.0 (Windows; U; Windows NT 5.1; zh-CN; rv:1.9.0.15) Gecko/2009101601 Firefox/3.0.15 (.NET CLR 3.5.30729)

2、Ajax 异步请求方式

accept? */*
accept-language? zh-cn
referer??http://192.168.101.72:8080/scm/?token=3b194bff23bf6acecea5661ac8e14c51
?x-requested-with? XMLHttpRequest
content-type? application/x-www-form-urlencoded,text/javascript
accept-encoding? gzip, deflate
user-agent? Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0; QQDownload 598; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; CIBA; .NET CLR 1.1.4322; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; InfoPath.1)
host? 192.168.101.72:8080
content-length? 233
connection? Keep-Alive
cache-control? no-cache
cookie? CSS=undefined; JSESSIONID=1B9AC25036290F7FB6823CCE1A24E541

　　可以看到 Ajax 请求多了个 x-requested-with?，可以利用它，request .getHeader("x-requested-with"); 为 null，则为传统同步请求，为 XMLHttpRequest，则为 Ajax 异步请求。