文件上传时,MultipartFile.transferTo() 方法报 FileNotFoundException

Spring Upload File 报错FileNotFoundException

环境:
    Springboot 2.0.4
    JDK1.8
    内嵌 Apache Tomcat/8.5.32

1、前端代码

前端上传网页表单,enctype 和 input 的type=file 即可,使用单文件上传举例:

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

2、后端代码

@RestController
@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 saveFile = new File(path + "/" + fileName);
        if (!saveFile.getParentFile().exists()) { 
            saveFile.getParentFile().mkdirs();
        }
        try {
            file.transferTo(saveFile); // 保存文件
            return "true";
        } catch (Exception e) {
            e.printStackTrace();
            return "false";
        }
    }
}

3、问题分析与解决

按照上面配置运行时,在保存文件 file.transferTo(saveFile) 报错

3.1 问题原因分析:

saveFile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。

3.2 问题解决

transferTo 传入参数 定义为绝对路径
@RestController
@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";
        }
    }
}
也可以 file.getBytes() 获得字节数组,OutputStream.write(byte[] bytes)自己写到输出流中。

4、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;
    }
}

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