springmvc中使用文件下载功能

Posted 2022-04-16 darange

项目代码：https://github.com/PeiranZhang/springmvc-fileupload

使用文件下载步骤

• 对请求处理方法使用void或null作为返回类型，并在方法中添加HttpServletResponse参数
• 将响应的内容类型设为文件的内容类型
• 添加一个名为Content-Disposition的HTTP响应标题，并赋值attachment; filename= fileName，这里的fileName是默认文件名，应该出现在File Download（文件下载）对话框中。它通常与文件同名，但是也并非一定如此。（可选）

例子：下载服务器上的pdf文件

指定用户、密码登录表单之后，设置session，然后才可以下载文件:/WEB-INF/data/secret.pdf

Controller代码

@Controller
public class ResourceController 

private static final Log logger = LogFactory.getLog(ResourceController.class);

/**
 * @param login @ModelAttribute 注解接受表单中的login对象
 * @param session
 * @param model
 * @return
 */
@RequestMapping(value="/login")
public String login(@ModelAttribute Login login, HttpSession session, Model model) 
    System.out.println(login);
    //与jsp中的标签绑定
    model.addAttribute("login", new Login());
    if ("paul".equals(login.getUserName()) &&
            "secret".equals(login.getPassword())) 
        //设置session
        session.setAttribute("loggedIn", Boolean.TRUE);
        return "Main";
     else 
        return "LoginForm";
    


@RequestMapping(value="/resource_download")
public String downloadResource(HttpSession session, HttpServletRequest request,
        HttpServletResponse response) 
    if (session == null || 
            session.getAttribute("loggedIn") == null) 
        return "LoginForm";
    
    String dataDirectory = request.
            getServletContext().getRealPath("/WEB-INF/data");
    System.out.println(dataDirectory);
    File file = new File(dataDirectory, "secret.pdf");
    if (file.exists()) 
        //设置响应类型，这里是下载pdf文件
        response.setContentType("application/pdf");
        //设置Content-Disposition，设置attachment，浏览器会激活文件下载框；filename指定下载后默认保存的文件名
        //不设置Content-Disposition的话，文件会在浏览器内打卡，比如txt、img文件
        response.addHeader("Content-Disposition",
                "attachment; filename=secret.pdf");
        byte[] buffer = new byte[1024];
        FileInputStream fis = null;
        BufferedInputStream bis = null;
        // if using Java 7, use try-with-resources
        try 
            fis = new FileInputStream(file);
            bis = new BufferedInputStream(fis);
            OutputStream os = response.getOutputStream();
            int i = bis.read(buffer);
            while (i != -1) 
                os.write(buffer, 0, i);
                i = bis.read(buffer);
            
         catch (IOException ex) 
            // do something, 
            // probably forward to an Error page
         finally 
            if (bis != null) 
                try 
                    bis.close();
                 catch (IOException e) 
                
            
            if (fis != null) 
                try 
                    fis.close();
                 catch (IOException e) 
                
            
        
    
    return null;

LoginForm.jsp

Main.jsp

结果

例子：浏览器内显示图片。图片放在WEN-INF目录下面，可以禁止直接请求

Controller代码

@Controller
public class ImageController 

private static final Log logger = LogFactory.getLog(ImageController.class);

@RequestMapping(value="/image_get/id", method = RequestMethod.GET)
public void getImage(@PathVariable String id, 
        HttpServletRequest request, 
        HttpServletResponse response, 
        @RequestHeader String referer) 
    //referer记录了该请求是从哪个链接过来的，可以用来判断请求是否合法
    if (referer != null) 
        System.out.println(referer);
        String imageDirectory = request.getServletContext().
                getRealPath("/WEB-INF/image");
        File file = new File(imageDirectory, 
                id + ".jpg");
        if (file.exists()) 
            response.setContentType("image/jpg");
            //不设置Content-Disposition的，图像在浏览器内打卡
            byte[] buffer = new byte[1024];
            FileInputStream fis = null;
            BufferedInputStream bis = null;
            // if you're using Java 7, use try-with-resources
            try 
                fis = new FileInputStream(file);
                bis = new BufferedInputStream(fis);
                OutputStream os = response.getOutputStream();
                int i = bis.read(buffer);
                while (i != -1) 
                    os.write(buffer, 0, i);
                    i = bis.read(buffer);
                
             catch (IOException ex) 
                // do something here
             finally 
                if (bis != null) 
                    try 
                        bis.close();
                     catch (IOException e) 
                        
                    
                
                if (fis != null) 
                    try 
                        fis.close();
                     catch (IOException e) 
                        
                    
                
            
        
    

html文件

结果

直接请求html文件，html里面的img标签的src记录了请求地址，发出请求，后台控制，将图片的内容输出到浏览器上

参考

• 《JSP、Servlet和SpringMVC学习指南》