下载功能

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下载保存图片

图片默认情况下, 浏览器进行内联(inline)显示, 如果需要实现下载功能, 则需要设置一个响应头 Content-Disposition

具体请参看: rfc2616的 19.5.1 章节

下载图片的原理是:

Servlet代码：

@RequestMapping(value="/download.do",
        produces="image/png")
@ResponseBody
public byte[] download(
        HttpServletResponse response)
    throws IOException {
    String file = URLEncoder.encode(
            "实例1.png", "UTF-8");
    response.setHeader(
            "Content-Disposition", 
            "attachment; filename=\""
            +file+"\"");
    byte[] bytes=readFile("D:/1.png");
    return bytes;
}

下载Excel

1. 导入Excel API

   <!-- POI 是Apache组织提供的开源 Office API -->
   <dependency>
       <groupId>org.apache.poi</groupId>
       <artifactId>poi-ooxml</artifactId>
       <version>3.17</version>
   </dependency>
   

2. 编写控制器

   @RequestMapping(value="/excel.do",
           produces="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
   @ResponseBody
   public byte[] excel(
           HttpServletResponse response)
       throws IOException {
       String file = URLEncoder.encode(
               "实例1.xlsx", "UTF-8");
       response.setHeader(
               "Content-Disposition", 
               "attachment; filename=\""
               +file+"\"");
       byte[] bytes=createExcel();
       return bytes;
   }
   
   private byte[] createExcel()
       throws IOException{
       //创建工作簿(就是Excel文件)
       XSSFWorkbook workbook =
               new XSSFWorkbook();
       //在工作簿中创建工作表
       XSSFSheet sheet=
               workbook.createSheet("演示");
       //在工作表中创建行, 参数是行号 0 1 2 3...
       XSSFRow row = sheet.createRow(0);
       //在行中创建格子, 参数列号 0 1 2 3...
       XSSFCell cell=row.createCell(0);
       //在格子中添加数据
       cell.setCellValue("Hello  World!");
       ByteArrayOutputStream out=
               new ByteArrayOutputStream();
       workbook.write(out);
       workbook.close();
       out.close();
       byte[] bytes=out.toByteArray();
       return bytes;
   }
   

3. 编写客户端:

   <h2>下载</h2>
   <p>
       <a href="download.do">下载图片</a> 
       <a href="excel.do">下载Excel</a> 
   </p>

添加用户列表导出功能

1. 编写控制器:

   @RequestMapping(value="/export.do",
           produces="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
   @ResponseBody
   public byte[] export(
           HttpServletResponse response)
       throws IOException {
       String file = URLEncoder.encode(
               "用户列表.xlsx", "UTF-8");
       response.setHeader(
               "Content-Disposition", 
               "attachment; filename=\""
               +file+"\"");
       byte[] bytes=usersExcel();
       return bytes;
   }
   
   private byte[] usersExcel() 
       throws IOException {
       XSSFWorkbook workbook = 
               new XSSFWorkbook();
       XSSFSheet sheet = 
               workbook.createSheet("用户列表");
       //创建表头
       XSSFRow header=sheet.createRow(0);
       header.createCell(0).setCellValue("编号");
       header.createCell(1).setCellValue("姓名");
       header.createCell(2).setCellValue("电话");
       header.createCell(3).setCellValue("邮箱");
       //将用户信息填充到excel表格中
       List<User> list=userDAO.findAll();
       int n = 1;
       for(User user:list){
           XSSFRow row=sheet.createRow(n++);
           row.createCell(0).setCellValue(
                   user.getId());
           row.createCell(1).setCellValue(
                   user.getUsername());
           row.createCell(2).setCellValue(
                   user.getPhone());
           row.createCell(3).setCellValue(
                   user.getEmail());
       }
       //将Excel数据保存到 byte[] 数组中
       ByteArrayOutputStream out=
               new ByteArrayOutputStream();
       workbook.write(out);
       workbook.close();
       out.close();
       byte[] bytes=out.toByteArray();
       return bytes; 
   }