一个包搞定了
先看看项目结构
package com.dragon.action;

import java.io.IOException;
import java.io.OutputStream;

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

import org.apache.poi.hssf.usermodel.HSSFCellStyle;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.Cell;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.ss.usermodel.Workbook;

public class ExcelServlet extends HttpServlet {

  /**
   * Constructor of the object.
   */
  public ExcelServlet() {
    super();
  }

  /**
   * Destruction of the servlet. <br>
   */
  public void destroy() {
    super.destroy(); // Just puts "destroy" string in log
    // Put your code here
  }

  /**
   * The doGet method of the servlet. <br>
   *
   * This method is called when a form has its tag value method equals to get.
   *
   * @param request the request send by the client to the server
   * @param response the response send by the server to the client
   * @throws ServletException if an error occurred
   * @throws IOException if an error occurred
   */
  public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {

    //  response.setContentType("text/html");
    //  PrintWriter out = response.getWriter();
    //  out.println("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">");
    //  out.println("<HTML>");
    //  out.println("  <HEAD><TITLE>A Servlet</TITLE></HEAD>");
    //  out.println("  <BODY>");
    //  out.print("    This is ");
    //  out.print(this.getClass());
    //  out.println(", using the GET method");
    //  out.println("  </BODY>");
    //  out.println("</HTML>");
    //  out.flush();
    //  out.close();
    this.doPost(request, response);
  }

  /**
   * The doPost method of the servlet. <br>
   *
   * This method is called when a form has its tag value method equals to post.
   *
   * @param request the request send by the client to the server
   * @param response the response send by the server to the client
   * @throws ServletException if an error occurred
   * @throws IOException if an error occurred
   */
  public void doPost(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    request.setCharacterEncoding("utf-8");
    response.setCharacterEncoding("utf-8");
    response.setContentType("application/vnd.ms-excel");
    OutputStream out = response.getOutputStream();
    //报头用于提供一个推荐的文件名，并强制浏览器显示保存对话框
    //attachment表示以附件方式下载。如果要在页面中打开，则改为 inline
    response.setHeader("Content-Disposition", "attachment; filename=TestExcel1.xls ");
    //创建workbook工作薄
    Workbook workbook = new HSSFWorkbook();
    //创建工作表
    Sheet sheet = workbook.createSheet("用户信息");
    //创建第二个工作薄
    Sheet sheet2 = workbook.createSheet();
    //为工作薄起名字
    workbook.setSheetName(1, "口袋里的小龙");
    //设置单元格样式
    HSSFCellStyle hssfCellStyle = (HSSFCellStyle) workbook.createCellStyle();
    hssfCellStyle.setAlignment(HSSFCellStyle.ALIGN_CENTER);//居中显示
    hssfCellStyle.setVerticalAlignment(HSSFCellStyle.VERTICAL_CENTER);//纵向居中
    //创建行
    Row row = sheet.createRow(0);
    //创建单元格
    Cell cell = row.createCell(0);
    //设置第一行第一格的值
    cell.setCellValue("姓名");
    //设置单元格的文本居中显示
    cell.setCellStyle(hssfCellStyle);
    //创建单元格
    Cell cell1 = row.createCell(1);
    //设置第一行第一格的值
    cell1.setCellValue("性别");
    cell1.setCellStyle(hssfCellStyle);
    //创建单元格
    Cell cell2 = row.createCell(2);
    //设置第一行第一格的值
    cell2.setCellValue("年龄");
    cell2.setCellStyle(hssfCellStyle);
    //创建单元格
    Cell cell3 = row.createCell(3);
    //设置第一行第一格的值
    cell3.setCellValue("家庭住址");
    cell3.setCellStyle(hssfCellStyle);
    for (int i = 1; i <= 5; i++) {
      //创建行
      Row rows = sheet.createRow(i);
      //创建单元格
      Cell cells = rows.createCell(0);
      //设置第一行第一格的值
      cells.setCellValue("张三"+i);
      //创建单元格
      Cell cell1s = rows.createCell(1);
      //设置第一行第一格的值
      cell1s.setCellValue("男");
      //创建单元格
      Cell cell2s = rows.createCell(2);
      //设置第一行第一格的值
      cell2s.setCellValue(18+i);
      //创建单元格
      Cell cell3s = rows.createCell(3);
      //设置第一行第一格的值
      cell3s.setCellValue("家庭住址"+i);
    }
    workbook.write(out);
    System.out.println("数据写入成功！");
    out.flush();
    out.close();
  }

  /**
   * Initialization of the servlet. <br>
   *
   * @throws ServletException if an error occurs
   */
  public void init() throws ServletException {
    // Put your code here
  }

}
index.jsp页面

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">

<title>My JSP 'index.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">   
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>

<body>
<form action="servlet/ExcelServlet" method="post">
<input type="submit" value="测试"></input>
</form>
</body>
</html>

亲自试试吧 poi的下载地址为： http://apache.fayea.com/poi/dev/bin/poi-bin-3.12-beta1-20150228.zip找到需要的jar包 导入项目即可