基于Spring实现文件上传功能

2019-11-26 11:31:57

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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。

package cn.tiny77.guide05;import java.io.IOException;import java.util.List;import java.util.stream.Collectors;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.core.io.Resource;import org.springframework.http.HttpHeaders;import org.springframework.http.ResponseEntity;import org.springframework.stereotype.Controller;import org.springframework.ui.Model;import org.springframework.web.bind.annotation.ExceptionHandler;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.PathVariable;import org.springframework.web.bind.annotation.PostMapping;import org.springframework.web.bind.annotation.RequestParam;import org.springframework.web.bind.annotation.ResponseBody;import org.springframework.web.multipart.MultipartFile;import org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder;import org.springframework.web.servlet.mvc.support.RedirectAttributes;@Controllerpublic class FileUploadController { private final StorageService storageService; @Autowired public FileUploadController(StorageService storageService) {  this.storageService = storageService; } @GetMapping("/") public String listUploadedFiles(Model model) throws IOException {    List<String> paths = storageService.loadAll().map(    path -> MvcUriComponentsBuilder.fromMethodName(FileUploadController.class,      "serveFile", path.getFileName().toString()).build().toString())    .collect(Collectors.toList());  model.addAttribute("files", paths);  return "uploadForm"; } @GetMapping("/files/{filename:.+}") @ResponseBody public ResponseEntity<Resource> serveFile(@PathVariable String filename) {  Resource file = storageService.loadAsResource(filename);  return ResponseEntity.ok().header(HttpHeaders.CONTENT_DISPOSITION,    "attachment; filename=/"" + file.getFilename() + "/"").body(file); } @PostMapping("/") public String handleFileUpload(@RequestParam("file") MultipartFile file,   RedirectAttributes redirectAttributes) {  storageService.store(file);  redirectAttributes.addFlashAttribute("message",    "You successfully uploaded " + file.getOriginalFilename() + "!");  return "redirect:/"; } @ExceptionHandler(StorageFileNotFoundException.class) public ResponseEntity<?> handleStorageFileNotFound(StorageFileNotFoundException exc) {  return ResponseEntity.notFound().build(); }}

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

package cn.tiny77.guide05;import org.springframework.core.io.Resource;import org.springframework.web.multipart.MultipartFile;import java.nio.file.Path;import java.util.stream.Stream;public interface StorageService { void init(); void store(MultipartFile file); Stream<Path> loadAll(); Path load(String filename); Resource loadAsResource(String filename); void deleteAll();}

以下是接口实现类

package cn.tiny77.guide05;import java.io.IOException;import java.net.MalformedURLException;import java.nio.file.Files;import java.nio.file.Path;import java.nio.file.Paths;import java.nio.file.StandardCopyOption;import java.util.stream.Stream;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.core.io.Resource;import org.springframework.core.io.UrlResource;import org.springframework.stereotype.Service;import org.springframework.util.FileSystemUtils;import org.springframework.util.StringUtils;import org.springframework.web.multipart.MultipartFile;@Servicepublic class FileSystemStorageService implements StorageService { private final Path rootLocation; @Autowired public FileSystemStorageService(StorageProperties properties) {  this.rootLocation = Paths.get(properties.getLocation()); } @Override public void store(MultipartFile file) {  String filename = StringUtils.cleanPath(file.getOriginalFilename());  try {   if (file.isEmpty()) {    throw new StorageException("无法保存空文件 " + filename);   }   if (filename.contains("..")) {    // This is a security check    throw new StorageException(      "无权访问该位置 "        + filename);   }   Files.copy(file.getInputStream(), this.rootLocation.resolve(filename),     StandardCopyOption.REPLACE_EXISTING);  }  catch (IOException e) {   throw new StorageException("无法保存文件 " + filename, e);  } } @Override public Stream<Path> loadAll() {  try {   return Files.walk(this.rootLocation, 1)     .filter(path -> !path.equals(this.rootLocation))     .map(path -> this.rootLocation.relativize(path));  }  catch (IOException e) {   throw new StorageException("读取文件异常", e);  } } @Override public Path load(String filename) {  return rootLocation.resolve(filename); } @Override public Resource loadAsResource(String filename) {  try {   Path file = load(filename);   Resource resource = new UrlResource(file.toUri());   if (resource.exists() || resource.isReadable()) {    return resource;   }   else {    throw new StorageFileNotFoundException(      "无法读取文件: " + filename);   }  }  catch (MalformedURLException e) {   throw new StorageFileNotFoundException("无法读取文件: " + filename, e);  } } @Override public void deleteAll() {  FileSystemUtils.deleteRecursively(rootLocation.toFile()); } @Override public void init() {  try {   Files.createDirectories(rootLocation);  }  catch (IOException e) {   throw new StorageException("初始化存储空间出错", e);  } }}

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}" rel="external nofollow" 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

package cn.tiny77.guide05;import org.springframework.boot.CommandLineRunner;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.boot.context.properties.EnableConfigurationProperties;import org.springframework.context.annotation.Bean;@SpringBootApplication@EnableConfigurationProperties(StorageProperties.class)public class Application { public static void main(String[] args) {  SpringApplication.run(Application.class, args); } @Bean CommandLineRunner init(StorageService storageService) {  return (args) -> {   storageService.deleteAll();   storageService.init();  }; }}

5、运行结果