基于Spring实现文件上传功能-创新互联

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，
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;

@Controller
public class FileUploadController {

 private final StorageService storageService;

 @Autowired
 public FileUploadController(StorageService storageService) {
  this.storageService = storageService;
 }

 @GetMapping("/")
 public String listUploadedFiles(Model model) throws IOException {
  
  List 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 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();
 }

}