翻译一下手册：
If you want to receive application/json post data in your script you can not use $_POST. $_POST does only handle form data.
如果你希望接收application/json的post数据，你不能用$_POST,$_POST仅仅用来处理表单数据

Read from php://input instead. You can use fopen or file_get_contents.
用php://input替代读取数据，使用fopen或者file_get_contents方法

Example:
举例：