基于Spring实现文件上传功能

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(); }}