JSP POST传参为何是ISO8859_1，该如何处理

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %><% response.setCharacterEncoding("UTF-8"); %><meta http-equiv="content-type" content="text/html; charset=UTF-8" /><form action="BBB.jsp" method="post">    <input type="submit" name="submit" value="中文" /></form>

<%@ page contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %><% request.setCharacterEncoding("UTF-8"); %><meta http-equiv="content-type" content="text/html; charset=UTF-8" /><!-- 请问 #P1 为何乱码 --><p id="p1"><%=request.getParameter("submit")%></p><!-- 请问 #P2 为何要重建字符串？以前听说POST传参只需设置request编码，为什么是ISO8859_1？--><p id="p2"><%=new String(request.getParameter("submit").getBytes("ISO8859_1"), "UTF-8")%></p>