为什么输出的汉字为问号

package com.immoc.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ComputerServlet extends HttpServlet{

	public void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		String n=request.getParameter("n");
		int i=Integer.parseInt(n);
		int sum=0;
		for(int j=0;j<=i;j++) {
			sum=j+sum;
		}
		String a="<h1 style='color:red'>"+n+"以内自然数之和为："+sum+"</h1><hr/>";
		System.out.println("返回浏览器的响应数据为："+a);
		PrintWriter out=response.getWriter();
		out.println(a);
	}
}
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns="http://xmlns.jcp.org/xml/ns/javaee" 
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>ServletProj</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
  	<servlet-name>ComputerServlet</servlet-name>
  	<servlet-class>com.immoc.servlet.ComputerServlet</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>ComputerServlet</servlet-name>
  	<url-pattern>/ComputerServlet</url-pattern>
  </servlet-mapping>
</web-app>

输出的结果汉字就为问号了，在xml文件中有设置enconding="UTF-8"