(要求的最终答案和更正的答案)
您的servlet过滤器应用得太晚了。
可能的适当顺序web.xml
如下
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/j2ee/dtds/web-app_2.3.dtd">
<web-app>
<!--CharsetFilter start-->
<filter>
<filter-name>Charset Filter</filter-name>
<filter-class>CharsetFilter</filter-class>
<init-param>
<param-name>requestEncoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<!-- The rest is ommited -->