浅谈MultipartFile中transferTo方法的坑

@PostMapping("/uploadFile")
public String uploadImg(@RequestParam("file") MultipartFile file, @RequestParam("equipmentId") String equipmentId) {
String baseDir = "./imgFile";  // 这里不能直接使用相对路径
  if (!file.isEmpty()) {
      String name = file.getOriginalFilename();
      String prefix = name.lastIndexOf(".") != -1 ? name.substring(name.lastIndexOf(".")) : ".jpg";
      String path = UUID.randomUUID().toString().replace("-", "") + prefix;
      try {
      	// 这里代码都是没有问题的
          File filePath = new File(baseDir, path);
          // 第一次执行代码时，路径是不存在的
          logger.info("文件保存路径：{}，是否存在：{}", filePath.getParentFile().exists(), filePath.getParent());
          if (!filePath.getParentFile().exists()) {   // 如果存放路径的父目录不存在，就创建它。
              filePath.getParentFile().mkdirs();
          }
          // 如果路径不存在，上面的代码会创建路径，此时路径即已经创建好了
          logger.info("文件保存路径：{}，是否存在：{}", filePath.getParentFile().exists(), filePath.getParent());
          // 此处使用相对路径，似乎是一个坑！
          // 相对路径：filePath
          // 绝对路径：filePath.getAbsoluteFile()
          logger.info("文件将要保存的路径：{}", filePath.getPath());
          file.transferTo(filePath);
          logger.info("文件成功保存的路径：{}", filePath.getAbsolutePath());
          return "上传成功";
      } catch (Exception e) {
          logger.error(e.getMessage());
      }
  }
  return "上传失败";
}

file.transferTo(filePath.getAbsoluteFile());

@Override
public void transferTo(File dest) throws IOException, IllegalStateException {
	this.part.write(dest.getPath());
	if (dest.isAbsolute() && !dest.exists()) {
		// Servlet 3.0 Part.write is not guaranteed to support absolute file paths:
		// may translate the given path to a relative location within a temp dir
		// (e.g. on Jetty whereas Tomcat and Undertow detect absolute paths).
		// At least we offloaded the file from memory storage; it'll get deleted
		// from the temp dir eventually in any case. And for our user's purposes,
		// we can manually copy it to the requested location as a fallback.
		FileCopyUtils.copy(this.part.getInputStream(), Files.newOutputStream(dest.toPath()));
	}
}
@Override
public void write(String fileName) throws IOException {
	File file = new File(fileName);
	if (!file.isAbsolute()) {
		file = new File(location, fileName);
	}
	try {
		fileItem.write(file);
	} catch (Exception e) {
		throw new IOException(e);
	}
}

import java.io.File;
import java.io.IOException;
public class OSMain {	
	public static void main(String[] args) {
		String path1 = "./hehe";
		String path2 = "/haha";
		File file1 = new File(path1);
		File file2 = new File(path2);		
		System.out.println("file1: " + file1 + " file1是绝对路径吗？ " + file1.isAbsolute());
		System.out.println("file2: " + file1 + " file2是绝对路径吗？ " + file2.isAbsolute());
		try {
			System.out.println(file1.getCanonicalPath());
			System.out.println(file2.getCanonicalPath());
		} catch (IOException e) {
			e.printStackTrace();
		}
	}	
}