Why the JSP Page encoding directive should be the first line in JSP?

Question

I mean the following directive

<%@ page contentType="text/html; charset=UTF-8" %> 

I have lots of JSPs. I wrote this line in a common file that was already included in all JSPs. But that didn't help, I could see browser using different encoding than what I specified in above directive.

I had to manually wrote that directive as the first line to solve the problem.

I am asking this question in context of problem raised in this article

Answer 1

问题是，在该指令之前的任何内容都将其输出写入到浏览器的输出流中 - 并且编码指定该流如何将页面的String内容转换为字节，因此必须在在写入任何内容之前创建流。

Answer 2

Java运行时如何知道该文件是一个JSP，从而编译和处理它，而不是像纯文本一样推送到客户端？