取得 HTTP post 的 body

要取得 HTTP POST 的 body 可以使用 ServletRequest interface 的兩個方法: 

BufferedReader getReader()
          Retrieves the body of the request as character data using a BufferedReader.

ServletInputStream

getInputStream()           Retrieves the body of the request as binary data using a ServletInputStream.

getReader() 方法用於字元資料， getInputStream() 方法用於 binary data