1. 背景
最近在爬取某个站点时，发现在POST数据时，使用的数据格式是request payload，有别于之前常见的 POST数据格式(Form data)。而使用Form data数据的提交方式时，无法提交成功。
1.1. Http请求中Form Data 和 Request Payload的区别
AJAX Post请求中常用的两种传参数的形式：form data 和 request payload
1.1.1. Form data
get请求的时候，我们的参数直接反映在url里面，形式为key1=value1&key2=value2形式，比如：
/ns?word=NBA&tn=news&from=news&cl=2&rn=20&ct=1
而如果是post请求，那么表单参数是在请求体中，也是以key1=value1&key2=value2的形式在请求体中。通过chrome的开发者工具可以看到，如下：
RequestURL:http://127.0.0.1:8080/test/test.do
Request Method:POST
Status Code:200 OK
Request Headers
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding:gzip,deflate,sdch
Accept-Language:zh-CN,zh;q=0.8,en;q=0.6
AlexaToolbar-ALX_NS_PH:AlexaToolbar/alxg-3.2
Cache-Control:max-age=0
Connection:keep-alive
Content-Length:25
Content-Type:application/x-www-form-urlencoded
Cookie:JSESSIONID=74AC93F9F572980B6FC10474CD8EDD8D
Host:127.0.0.1:8080
Origin:http://127.0.0.1:8080
Referer:http://127.0.0.1:8080/test/index.jsp
User-Agent:Mozilla/5.0 (Windows NT 6.1)AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.149 Safari/537.36
Form Data
name:mikan
address:street
Response Headers
Content-Length:2
Date:Sun, 11 May 11:05:33 GMT
Server:Apache-Coyote/1.1
这里要注意post请求的Content-Type为application/x-www-form-urlencoded(默认的)，参数是在请求体中，即上面请求中的Form Data。
前端代码：提交数据
xhr.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xhr.send("name=foo&value=bar");
后端代码：接收提交的数据。在servlet中，可以通过request.getParameter(name)的形式来获取表单参数。
/**
* 获取httpRequest的参数
*
* @param request
* @param name
* @return
*/
protected String getParameterValue(HttpServletRequest request, String name) {
return StringUtils.trimToEmpty(request.getParameter(name));
}
1.1.2. Request payload
如果使用原生AJAX POST请求的话，那么请求在chrome的开发者工具的表现如下，主要是参数在
Remote Address:192.168.234.240:80
Request URL:/qimage/upload.htm
Request Method:POST
Status Code:200 OK
Request Headers
Accept:application/json, text/javascript, */*; q=0.01
Accept-Encoding:gzip,deflate,sdch
Accept-Language:zh-CN,zh;q=0.8,en;q=0.6
Connection:keep-alive
Content-Length:151
Content-Type:application/json;charset=UTF-8
Cookie:JSESSIONID=E08388788943A651924CA0A10C7ACAD0
Host:
Origin:
Referer:/qimage/customerlist.htm?menu=19
User-Agent:Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.114 Safari/537.36
X-Requested-With:XMLHttpRequest
Request Payload
[{widthEncode:NNNcaXN, heightEncode:NNNN5NN, displayUrl:09/03/66I5P266rtT86oKq6,…}]
Response Headers
Connection:keep-alive
Content-Encoding:gzip
Content-Type:application/json;charset=UTF-8
Date:Thu, 04 Sep 06:49:44 GMT
Server:nginx/1.4.7
Transfer-Encoding:chunked
Vary:Accept-Encoding
