Spring 随笔05 文件上传

Posted 2020-10-05 MrQin

本小节你将建立一个可以接受HTTP multi-part 文件的服务。

你将建立一个后台服务来接收文件以及前台页面来上传文件。

要利用servlet容器上传文件，你要注册一个MultipartConfigElement类，以往需要在web.xml 中配置<multipart-config>，
而在这里，你要感谢SpringBoot，一切都为你自动配置好了。

1、新建一个文件上传的Controller：

应用已经包含一些 存储文件 和 从磁盘中加载文件 的类，他们在cn.tiny77.guide05这个包下。我们将会在FileUploadController中用到这些类。

 1 package cn.tiny77.guide05;
 2 
 3 import java.io.IOException;
 4 import java.util.List;
 5 import java.util.stream.Collectors;
 6 
 7 import org.springframework.beans.factory.annotation.Autowired;
 8 import org.springframework.core.io.Resource;
 9 import org.springframework.http.HttpHeaders;
10 import org.springframework.http.ResponseEntity;
11 import org.springframework.stereotype.Controller;
12 import org.springframework.ui.Model;
13 import org.springframework.web.bind.annotation.ExceptionHandler;
14 import org.springframework.web.bind.annotation.GetMapping;
15 import org.springframework.web.bind.annotation.PathVariable;
16 import org.springframework.web.bind.annotation.PostMapping;
17 import org.springframework.web.bind.annotation.RequestParam;
18 import org.springframework.web.bind.annotation.ResponseBody;
19 import org.springframework.web.multipart.MultipartFile;
20 import org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder;
21 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
22 
23 @Controller
24 public class FileUploadController {
25 
26     private final StorageService storageService;
27 
28     @Autowired
29     public FileUploadController(StorageService storageService) {
30         this.storageService = storageService;
31     }
32 
33     @GetMapping("/")
34     public String listUploadedFiles(Model model) throws IOException {
35         
36         List<String> paths = storageService.loadAll().map(
37                 path -> MvcUriComponentsBuilder.fromMethodName(FileUploadController.class,
38                         "serveFile", path.getFileName().toString()).build().toString())
39                 .collect(Collectors.toList());
40 
41         model.addAttribute("files", paths);
42 
43         return "uploadForm";
44     }
45 
46     @GetMapping("/files/{filename:.+}")
47     @ResponseBody
48     public ResponseEntity<Resource> serveFile(@PathVariable String filename) {
49 
50         Resource file = storageService.loadAsResource(filename);
51         return ResponseEntity.ok().header(HttpHeaders.CONTENT_DISPOSITION,
52                 "attachment; filename=\\"" + file.getFilename() + "\\"").body(file);
53     }
54 
55     @PostMapping("/")
56     public String handleFileUpload(@RequestParam("file") MultipartFile file,
57             RedirectAttributes redirectAttributes) {
58 
59         storageService.store(file);
60         redirectAttributes.addFlashAttribute("message",
61                 "You successfully uploaded " + file.getOriginalFilename() + "!");
62 
63         return "redirect:/";
64     }
65 
66     @ExceptionHandler(StorageFileNotFoundException.class)
67     public ResponseEntity<?> handleStorageFileNotFound(StorageFileNotFoundException exc) {
68         return ResponseEntity.notFound().build();
69     }
70 
71 }

 

该类用@Controller注解，因此SpringMvc可以基于它设定相应的路由。每一个@GetMapping和@PostMapping注解将绑定对应的请求参数和请求类型到特定的方法。

GET / 通过StorageService 扫描文件列表并 将他们加载到 Thymeleaf 模板中。它通过MvcUriComponentsBuilder来生成资源文件的连接地址。

GET /files/{filename} 当文件存在时候，将加载文件，并发送文件到浏览器端。通过设置返回头"Content-Disposition"来实现文件的下载。

POST / 接受multi-part文件并将它交给StorageService保存起来。

你需要提供一个服务接口StorageService来帮助Controller操作存储层。接口大致如下

 1 package cn.tiny77.guide05;
 2 
 3 import org.springframework.core.io.Resource;
 4 import org.springframework.web.multipart.MultipartFile;
 5 
 6 import java.nio.file.Path;
 7 import java.util.stream.Stream;
 8 
 9 public interface StorageService {
10 
11     void init();
12 
13     void store(MultipartFile file);
14 
15     Stream<Path> loadAll();
16 
17     Path load(String filename);
18 
19     Resource loadAsResource(String filename);
20 
21     void deleteAll();
22 
23 }

 

以下是接口实现类

  1 package cn.tiny77.guide05;
  2 
  3 import java.io.IOException;
  4 import java.net.MalformedURLException;
  5 import java.nio.file.Files;
  6 import java.nio.file.Path;
  7 import java.nio.file.Paths;
  8 import java.nio.file.StandardCopyOption;
  9 import java.util.stream.Stream;
 10 
 11 import org.springframework.beans.factory.annotation.Autowired;
 12 import org.springframework.core.io.Resource;
 13 import org.springframework.core.io.UrlResource;
 14 import org.springframework.stereotype.Service;
 15 import org.springframework.util.FileSystemUtils;
 16 import org.springframework.util.StringUtils;
 17 import org.springframework.web.multipart.MultipartFile;
 18 
 19 @Service
 20 public class FileSystemStorageService implements StorageService {
 21 
 22     private final Path rootLocation;
 23 
 24     @Autowired
 25     public FileSystemStorageService(StorageProperties properties) {
 26         this.rootLocation = Paths.get(properties.getLocation());
 27     }
 28 
 29     @Override
 30     public void store(MultipartFile file) {
 31         String filename = StringUtils.cleanPath(file.getOriginalFilename());
 32         try {
 33             if (file.isEmpty()) {
 34                 throw new StorageException("无法保存空文件 " + filename);
 35             }
 36             if (filename.contains("..")) {
 37                 // This is a security check
 38                 throw new StorageException(
 39                         "无权访问该位置 "
 40                                 + filename);
 41             }
 42             Files.copy(file.getInputStream(), this.rootLocation.resolve(filename),
 43                     StandardCopyOption.REPLACE_EXISTING);
 44         }
 45         catch (IOException e) {
 46             throw new StorageException("无法保存文件 " + filename, e);
 47         }
 48     }
 49 
 50     @Override
 51     public Stream<Path> loadAll() {
 52         try {
 53             return Files.walk(this.rootLocation, 1)
 54                     .filter(path -> !path.equals(this.rootLocation))
 55                     .map(path -> this.rootLocation.relativize(path));
 56         }
 57         catch (IOException e) {
 58             throw new StorageException("读取文件异常", e);
 59         }
 60 
 61     }
 62 
 63     @Override
 64     public Path load(String filename) {
 65         return rootLocation.resolve(filename);
 66     }
 67 
 68     @Override
 69     public Resource loadAsResource(String filename) {
 70         try {
 71             Path file = load(filename);
 72             Resource resource = new UrlResource(file.toUri());
 73             if (resource.exists() || resource.isReadable()) {
 74                 return resource;
 75             }
 76             else {
 77                 throw new StorageFileNotFoundException(
 78                         "无法读取文件: " + filename);
 79 
 80             }
 81         }
 82         catch (MalformedURLException e) {
 83             throw new StorageFileNotFoundException("无法读取文件: " + filename, e);
 84         }
 85     }
 86 
 87     @Override
 88     public void deleteAll() {
 89         FileSystemUtils.deleteRecursively(rootLocation.toFile());
 90     }
 91 
 92     @Override
 93     public void init() {
 94         try {
 95             Files.createDirectories(rootLocation);
 96         }
 97         catch (IOException e) {
 98             throw new StorageException("初始化存储空间出错", e);
 99         }
100     }
101 }

 

2、建立一个html页面

这里使用Thymeleaf模板

<html xmlns:th="http://www.thymeleaf.org">
<body>

    <div th:if="${message}">
        <h2 th:text="${message}"/>
    </div>

    <div>
        <form method="POST" enctype="multipart/form-data" action="/">
            <table>
                <tr><td>File to upload:</td><td><input type="file" name="file" /></td></tr>
                <tr><td></td><td><input type="submit" value="Upload" /></td></tr>
            </table>
        </form>
    </div>

    <div>
        <ul>
            <li th:each="file : ${files}">
                <a th:href="${file}" th:text="${file}" />
            </li>
        </ul>
    </div>

</body>
</html>

 

页面主要分为三部分分

- 顶部展示SpringMvc传过来的信息
- 一个提供用户上传文件的表单
- 一个后台提供的文件列表

3、限制上传文件的大小
在文件上传的应用中通常要设置文件大小的，想象一下后台处理的文件如果是5GB，那得多糟糕！在SpringBoot中，我们可以通过属性文件来控制。
新建一个application.properties，代码如下：
spring.http.multipart.max-file-size=128KB #文件总大小不能超过128kb
spring.http.multipart.max-request-size=128KB #请求数据的大小不能超过128kb

4、应用启动函数

 1 package cn.tiny77.guide05;
 2 
 3 import org.springframework.boot.CommandLineRunner;
 4 import org.springframework.boot.SpringApplication;
 5 import org.springframework.boot.autoconfigure.SpringBootApplication;
 6 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 7 import org.springframework.context.annotation.Bean;
 8 
 9 
10 @SpringBootApplication
11 @EnableConfigurationProperties(StorageProperties.class)
12 public class Application {
13 
14     public static void main(String[] args) {
15         SpringApplication.run(Application.class, args);
16     }
17 
18     @Bean
19     CommandLineRunner init(StorageService storageService) {
20         return (args) -> {
21             storageService.deleteAll();
22             storageService.init();
23         };
24     }
25 }

 

5、运行结果

 

 6.项目DEMO : https://github.com/qinrongjin/SpringGuide05