在web项目中，java导出excel有关问题

package com.test.excel;import org.apache.poi.hssf.usermodel.HSSFCellStyle; import org.apache.poi.hssf.usermodel.HSSFFont; import org.apache.poi.hssf.usermodel.HSSFRichTextString; import org.apache.poi.hssf.usermodel.HSSFWorkbook; import org.apache.poi.hssf.usermodel.HSSFSheet; import org.apache.poi.hssf.usermodel.HSSFRow; import org.apache.poi.hssf.usermodel.HSSFCell; import org.apache.poi.hssf.util.CellRangeAddress; import org.apache.poi.hssf.util.Region; import org.apache.poi.ss.usermodel.CellStyle; import org.apache.poi.ss.usermodel.RichTextString;import com.test.db.DB;import com.test.serch.Xin;import com.test.serch.Xlist;import java.io.File;import java.io.FileInputStream;import java.io.FileOutputStream; import java.io.InputStream;import java.io.OutputStream;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import javax.servlet.http.HttpServlet; public class excel extends HttpServlet {         public static String outputFile = "c:\\test.xls";     @SuppressWarnings({ "deprecation", "unchecked" })    public boolean excel()  throws SQLException     {        /*         *          * 创建excel表格         *          *          *          */         HSSFWorkbook wb = new HSSFWorkbook();//创建一个工作间          HSSFSheet sheet = wb.createSheet("sheet1");//创建一个sheet          HSSFRow row = sheet.createRow(0);//创建一行          HSSFCell cell = row.createCell((short) 0);//创建这行的第一个元素.从0开始          cell.setCellValue("序号");//写入内容          cell = row.createCell((short) 1);          cell.setCellValue("书名");          cell = row.createCell((short) 2);          cell.setCellValue("数量");          /*           *            * 将数据库的信息存到链表里面           *            *            *            *            */          ArrayList<Xin> X=new  ArrayList();            ResultSet rs=null;             Xin nu=new Xin();              String  sql="select * from book" ;             DB sqle=new DB();            rs= sqle.db(sql);        while(rs.next())        {             Xin x=new Xin();               x.setXid(rs.getString(1));               x.setXname(rs.getString(2));                x.setXnumber(rs.getInt(5)-rs.getInt(6));              X.add(x);        }        System.out.println("链表长度"+ X.size());                                        /*           *            *            *  循环遍历链表取出来值放到相应的excel表格的行列中；           *             *  取值方法：         先得到链表的第i个位置一组，然后在把这组相应的内容get出来           *            *            *            *            */          for(int i = 0 ; i < X.size() ; i++)          {           Xin x = X.get(i);           row = sheet.createRow(i+1);           cell = row.createCell((short) 0);           cell.setCellValue(x.getXid());           cell = row.createCell((short) 1);           cell.setCellValue(x.getXname());           cell = row.createCell((short) 2);           cell.setCellValue(x.getXnumber());          }                    /*           *            *            *            * 内容填好后，生成该文件，并给它相应的地址位置！           *            *            *            *            */         File file = new File("c:\\abc.xls");          //创建一个File 拿来当缓存用.也就是先将内存中的excel写入File中.然后再将File转换成输出流          try {           //OutputStream out = new FileOutputStream("abc.xls");           FileOutputStream out = new FileOutputStream(outputFile);            wb.write(out);//写入File           out.flush();         // 操作结束，关闭文件         out.close();         System.out.println("文件生成...");         return true;          } catch (Exception e) {          System.out.println(e.toString());          return false;          }                                         }}