//判断是否是下载模板
    private String template;
    
    
    public void setTemplate(String template) {
        this.template = template;
    }

    public String download() throws Exception {
        // 创建一个要到出表的表头
        String[] heads = { "编号", "用户名", "邮箱", "年龄", "部门" };
        
        //查询出要导出的数据,先展示出全部数据
        baseQuery.setPageSize(Integer.MAX_VALUE);
        this.pageList = employeeService.findByQuery(baseQuery);
        
        List<Employee> employees = pageList.getData();
        
        List<String[]> list = new ArrayList<>();
        if (template ==null) {
            //将 数据放入到list 中
            
            for (Employee employee : employees) {
                String[] content = new String[heads.length];
                content[0] = employee.getId().toString();
                content[1] = employee.getUsername();
                content[2] = employee.getEmail()== null? "" : employee.getEmail();
                content[3] = employee.getAge() == null? "":employee.getAge().toString();
                content[4] = employee.getDept() == null? "" :employee.getDept().getName() ;
                
                //放到list 中
                list.add(content);
            }
        }
        
        //调用BaseService 中的方法
        //把数据放到流中，，配置Struts.xml
        this.inputStream = employeeService.download(heads, list);
        return "download";
    }
    

@Override
    public InputStream download(String[] heads, List<String[]> list) throws Exception {
        // 创建一个内存对象
        SXSSFWorkbook wb = new SXSSFWorkbook();
        //创建一个Excel 表
        Sheet sheet = wb.createSheet("sheet1");
        
        //创建第0行 
        Row row = sheet.createRow(0);
        
        // 处理到处表头 第0行
        for (int i = 0; i < heads.length; i++) {
            Cell cell = row.createCell(i);
            //添加内容
            cell.setCellValue(heads[i]);
        }
        
        for (int j = 0; j < list.size(); j++) {// 行
            //创建 行
            Row row2 = sheet.createRow(j+1);
            for (int i = 0; i < heads.length; i++) {// 列
                //创建格子
                Cell cell = row2.createCell(i);
                //赋值
                cell.setCellValue(list.get(j)[i]);
            }
        }
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        wb.write(out);
        out.close();
        wb.dispose();
        return new ByteArrayInputStream(out.toByteArray());
    }

导入

public String execute() throws Exception {
        
        if (upload != null) {
            List<String[]> list = employeeService.importExcel(upload);
            //将list 中的值转为Employee对象
            
            for (String[] strings : list) {
                //创建一个Employee 对象    String[] heads = { "编号", "用户名", "邮箱", "年龄", "部门" };
                Employee employee =  new Employee();
                
                employee.setUsername(strings[1]+UUID.randomUUID().toString().substring(0, 4));
                employee.setEmail(strings[2]);
                if (StringUtils.isNotBlank(strings[3])) {
                    employee.setAge(Integer.valueOf(strings[3]));
                }
                    
                if (StringUtils.isNotBlank(strings[4])) {
                    //这里要查出部门，所以要导入DepartmentService，并且提供一个 根据名字找部门的方法
                    Department department = departmentService.findByName(strings[4]);
                    employee.setDept(department);
                }
                
                //要持久化  保存到数据库
                employeeService.save(employee);
                
            }
            
            putContextMap("ImportMsg", "成功导入"+list.size()+"条数据！");
            
        }
        
        
        return SUCCESS;
    }
/**
     * 导入Excel
     * */
    @Override
    public List<String[]> importExcel(File file) throws Exception {
        // 创建一个文件输出流,读取要导入的文件
        FileInputStream inputStream = new FileInputStream(file);
        //创建一个读取对象，在输入流中读取数据
        Workbook workbook = new XSSFWorkbook(inputStream);
        
        //获取表对象
        Sheet sheet = workbook.getSheetAt(0); //----------------------不理解
        
        //解析表对象  到list
        //定义一个List
        List<String[]> list = new ArrayList<>();
        /**
         * sheet.getLastRowNum(); 得到的是数据的总行数
         * row.getLastCellNum();获得 一行的多少列
         * */
        
        for (int i = 0; i < sheet.getLastRowNum(); i++) {
            // 获取行对象 ，注意 不要表头 从1 开始
            Row row = sheet.getRow(i+1);
            
            String[] strings = new String[row.getLastCellNum()];
            for (int j = 0; j < strings.length; j++) {
                
                //获得 格子
                Cell cell = row.getCell(j);
                strings[j] = cell.getStringCellValue();
            }
            list.add(strings);
        }
        
        
        return list;
    }