Sheet index (0) is out of range (0.1) POI操作Excel异常

<s:form action="userInfo" method="post" enctype="multipart/form-data">       导入Excel文件：<s:file name="excelFile"></s:file> <br/>      <s:submit value="导入"></s:submit> </s:form>

package com.boxun.bean;import java.util.ArrayList;import java.util.List;import org.apache.poi.hssf.record.formula.functions.T;public class ExcelWorkSheet<T> {    private String sheetName;    private List<T> data = new ArrayList<T>();  //数据行    private List<String> columns; //列名    public String getSheetName() {        return sheetName;    }    public void setSheetName(String sheetName) {        this.sheetName = sheetName;    }    public List<T> getData() {        return data;    }    public void setData(List<T> data) {        this.data = data;    }    public List<String> getColumns() {        return columns;    }    public void setColumns(List<String> columns) {        this.columns = columns;    }    }

package com.boxun.action;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.InputStream;import java.util.ArrayList;import java.util.Iterator;import java.util.List;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;import org.apache.poi.xssf.usermodel.XSSFWorkbook;import com.boxun.bean.ExcelWorkSheet;import com.boxun.bean.Userinfo;import com.boxun.biz.IUserBiz;import com.opensymphony.xwork2.ActionSupport;public class UserAction extends ActionSupport {    private IUserBiz userBiz;    public void setUserBiz(IUserBiz userBiz) {        this.userBiz = userBiz;    }        private File excelFile; //上传的文件        private String excelFileFileName; //保存原始文件名        //将Excel文件解析完毕后信息存放到这个对象中    private ExcelWorkSheet<Userinfo> excelWorkSheet;        public File getExcelFile() {        return excelFile;    }    public void setExcelFile(File excelFile) {        this.excelFile = excelFile;    }    public String getExcelFileFileName() {        return excelFileFileName;    }    public void setExcelFileFileName(String excelFileFileName) {        this.excelFileFileName = excelFileFileName;    }    public ExcelWorkSheet<Userinfo> getExcelWorkSheet() {        return excelWorkSheet;    }    public void setExcelWorkSheet(ExcelWorkSheet<Userinfo> excelWorkSheet) {        this.excelWorkSheet = excelWorkSheet;    }            //判断文件类型    public Workbook createWorkBook(InputStream is) throws IOException{        if(excelFileFileName.toLowerCase().endsWith("xls")){            return new HSSFWorkbook();        }        if(excelFileFileName.toLowerCase().endsWith("xlsx")){            return new XSSFWorkbook();        }        return null;    }        public String execute() throws Exception{        Workbook book = createWorkBook(new FileInputStream(excelFile));        Sheet sheet =  book.getSheetAt(0);  //在这一行的时候报错        excelWorkSheet = new ExcelWorkSheet<Userinfo>();        //保存工作单名称        Row firstRow = sheet.getRow(0);        Iterator<Cell> iterator = firstRow.iterator();                //保存列名        List<String> cellNames = new ArrayList<String>();        while (iterator.hasNext()) {            cellNames.add(iterator.next().getStringCellValue());        }        excelWorkSheet.setColumns(cellNames);                for (int i = 1; i <= sheet.getLastRowNum(); i++) {            Row ros = sheet.getRow(i);            Userinfo user = new Userinfo();            user.setId((int)ros.getCell(0).getNumericCellValue());            user.setName(ros.getCell(1).getStringCellValue());            user.setPass(ros.getCell(2).getStringCellValue());            user.setLastname(ros.getCell(3).getStringCellValue());            user.setAddres(ros.getCell(4).getStringCellValue());            user.setRemark(ros.getCell(5).getStringCellValue());            excelWorkSheet.getData().add(user);        }        for (int i = 0; i < excelWorkSheet.getData().size(); i++) {            Userinfo info = excelWorkSheet.getData().get(i);            System.out.println(info.getLastname());        }        return SUCCESS;    }                }