MultipartFile.transferTo(dest) 报 FileNotFoundException

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Spring Upload file 报错FileNotFoundException

环境：

    Springboot 2.0.4
    JDK8
    内嵌 Apache Tomcat/8.5.32

表单，enctype 和 input 的type=file 即可，例子使用单文件上传

<form enctype="multipart/form-data" method="POST"
	action="/file/fileUpload">
	图片<input type="file" name="file" />
	<input type="submit" value="上传" />
</form>

@Controller
@RequestMapping("/file")
public class UploadFileController {
	@Value("${file.upload.path}")
	private String path = "upload/";

	@RequestMapping(value = "fileUpload", method = RequestMethod.POST)
	@ResponseBody
	public String fileUpload(@RequestParam("file") MultipartFile file) {
		if (file.isEmpty()) {
			return "false";
		}
		String fileName = file.getOriginalFilename();
		File dest = new File(path + "/" + fileName);
		if (!dest.getParentFile().exists()) { 
			dest.getParentFile().mkdirs();
		}
		try {
			file.transferTo(dest); // 保存文件
			return "true";
		} catch (Exception e) {
			e.printStackTrace();
			return "false";
		}
	}
}

运行在保存文件 file.transferTo(dest) 报错
问题
dest 是相对路径，指向 upload/doc20170816162034_001.jpg
file.transferTo 方法调用时，判断如果是相对路径，则使用temp目录，为父目录
因此，实际保存位置为 C:\Users\xxxx\AppData\Local\Temp\tomcat.372873030384525225.8080\work\Tomcat\localhost\ROOT\upload\doc20170816162034_001.jpg

一则，位置不对，二则没有父目录存在，因此产生上述错误。

    解决办法
    transferTo 传入参数 定义为绝对路径

@Controller
@RequestMapping("/file")
public class UploadFileController {
	@Value("${file.upload.path}")
	private String path = "upload/";

	@RequestMapping(value = "fileUpload", method = RequestMethod.POST)
	@ResponseBody
	public String fileUpload(@RequestParam("file") MultipartFile file) {
		if (file.isEmpty()) {
			return "false";
		}
		String fileName = file.getOriginalFilename();
		File dest = new File(new File(path).getAbsolutePath()+ "/" + fileName);
		if (!dest.getParentFile().exists()) { 
			dest.getParentFile().mkdirs();
		}
		try {
			file.transferTo(dest); // 保存文件
			return "true";
		} catch (Exception e) {
			e.printStackTrace();
			return "false";
		}
	}
}

    另外也可以 file.getBytes() 获得字节数组，OutputStream.write(byte[] bytes)自己写到输出流中。

补充方法
application.properties 中增加配置项
spring.servlet.multipart.location= # Intermediate location of uploaded files.

关于上传文件的访问

    增加一个自定义的ResourceHandler把目录公布出去

// 写一个Java Config 
@Configuration
public class webMvcConfig implements org.springframework.web.servlet.config.annotation.WebMvcConfigurer{
	// 定义在application.properties
	@Value("${file.upload.path}")
	private String path = "upload/";
	public void addResourceHandlers(ResourceHandlerRegistry registry) {
		String p = new File(path).getAbsolutePath() + File.separator;//取得在服务器中的绝对路径
		System.out.println("Mapping /upload/** from " + p);
		registry.addResourceHandler("/upload/**") // 外部访问地址
			.addResourceLocations("file:" + p)// springboot需要增加file协议前缀
			.setCacheControl(CacheControl.maxAge(30, TimeUnit.MINUTES));// 设置浏览器缓存30分钟
	}
}

application.properties 中 file.upload.path=upload/

实际存储目录
D:/upload/2019/03081625111.jpg

访问地址（假设应用发布在http://www.a.com/）
http://www.a.com/upload/2019/03081625111.jpg

    在Controller中增加一个RequestMapping，把文件输出到输出流中

@RestController
@RequestMapping("/file")
public class UploadFileController {
	@Autowired
	protected HttpServletRequest request;
	@Autowired
	protected HttpServletResponse response;
	@Autowired
	protected ConversionService conversionService;

	@Value("${file.upload.path}")
	private String path = "upload/";	

	@RequestMapping(value="/view", method = RequestMethod.GET)
	public Object view(@RequestParam("id") Integer id){
		// 通常上传的文件会有一个数据表来存储，这里返回的id是记录id
		UploadFile file = conversionService.convert(id, UploadFile.class);// 这步也可以写在请求参数中
		if(file==null){
			throw new RuntimeException("没有文件");
		}
		
		File source= new File(new File(path).getAbsolutePath()+ "/" + file.getPath());
		response.setContentType(contentType);

		try {
			FileCopyUtils.copy(new FileInputStream(source), response.getOutputStream());
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}
}