本篇介绍以html表单提交数据为例，讲述content-type头
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>测试表单提交Post</title>
</head>
<body>
<form action="post.php" method="post">
<input type="text" name='username'>
<input type="text" name='password'>
<input type="submit">
</form>
</body>
</html>这种最常见的表单，它的请求头为：
POST /test/httpPost/post.php HTTP/1.1 Host: localhost Connection: keep-alive Content-Length: 27 Cache-Control: max-age=0 Origin: http://localhost Upgrade-Insecure-Requests: 1 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36 Content-Type: application/x-www-form-urlencoded Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,/;q=0.8 Referer: http://localhost/test/httpPost/index.html Accept-Encoding: gzip, deflate Accept-Language: zh-CN,zh;q=0.8 Cookie: pgv_pvi=8193968128
请求体：
username=zzzz&password=tttt
这里需要注意的是，请求体里的值是经过url encode的
另一种比较复杂的http请求是这样的
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>测试表单提交Post</title>
</head>
<body>
<form action="post.php" method="post" enctype="multipart/form-data">
<input type="text" name='username'>
<input type="text" name='password'>
<input type="file" name='picture'>
<input type="submit">
</form>
</body>
</html>申明了content-type的值为multipart/form-data
这种http post请求头为： POST /test/httpPost/post.php HTTP/1.1 Host: localhost Connection: keep-alive Origin: http://localhost User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.106 Safari/537.36 Content-Type: multipart/form-data; boundary=—-WebKitFormBoundaryo8HMWnZkFmHAvcTX 声明为这种类型时，后面的boundary参数指定每个参数之间的分隔符 请求体为： ——WebKitFormBoundaryo8HMWnZkFmHAvcTX Content-Disposition: form-data; name=”username” aaa ——WebKitFormBoundaryo8HMWnZkFmHAvcTX Content-Disposition: form-data; name=”password” bbb ——WebKitFormBoundaryo8HMWnZkFmHAvcTX Content-Disposition: form-data; name=”picture”; filename=”1488794518kqnZP.jpg” Content-Type: image/jpeg ——WebKitFormBoundaryo8HMWnZkFmHAvcTX– 注意这时候的值没有经过url encode