SpringBoot文件上传异常处理

@RestController
@RequestMapping(path = "/file")
public class FileUploadRest {

    /**
     * 保存上传的文件
     *
     * @param file
     * @return
     */
    private String saveFileToLocal(MultipartFile file) {
        try {
            String name = "/tmp/out_" + System.currentTimeMillis() + file.getName();
            FileOutputStream writer = new FileOutputStream(new File(name));
            writer.write(file.getBytes());
            writer.flush();
            writer.close();
            return name;
        } catch (Exception e) {
            e.printStackTrace();
            return e.getMessage();
        }
    }

    @PostMapping(path = "upload")
    public String upload(@RequestParam("file") MultipartFile file) {
        String ans = saveFileToLocal(file);
        return ans;
    }
}

public List<FileItem> parseRequest(RequestContext ctx)
        throws FileUploadException {
    List<FileItem> items = new ArrayList<>();
    boolean successful = false;
    try {
        FileItemIterator iter = getItemIterator(ctx);
        // 注意这里，文件工厂类，里面保存了临时目录的地址
        // 这个对象首次是在 org.apache.catalina.connector.Request#parseParts 方法的
        FileItemFactory fac = getFileItemFactory();
        if (fac == null) {
            throw new NullPointerException("No FileItemFactory has been set.");
        }
        while (iter.hasNext()) {
            final FileItemStream item = iter.next();
            // Don't use getName() here to prevent an InvalidFileNameException.
            final String fileName = ((FileItemIteratorImpl.FileItemStreamImpl) item).name;
            // 创建一个临时文件对象
            FileItem fileItem = fac.createItem(item.getFieldName(), item.getContentType(),
                                               item.isFormField(), fileName);
            items.add(fileItem);
            try {
                // 流的拷贝，这块代码也挺有意思，将输入流数据写入输出流
                // 后面会贴出源码，看下开源大佬们的玩法，和我们自己写的有啥区别
                Streams.copy(item.openStream(), fileItem.getOutputStream(), true);
            } catch (FileUploadIOException e) {
                throw (FileUploadException) e.getCause();
            } catch (IOException e) {
                throw new IOFileUploadException(String.format("Processing of %s request failed. %s",
                                                       MULTIPART_FORM_DATA, e.getMessage()), e);
            }
            final FileItemHeaders fih = item.getHeaders();
            fileItem.setHeaders(fih);
        }
        successful = true;
        return items;
    } catch (FileUploadIOException e) {
        throw (FileUploadException) e.getCause();
    } catch (IOException e) {
        throw new FileUploadException(e.getMessage(), e);
    } finally {
        if (!successful) {
            for (FileItem fileItem : items) {
                try {
                    fileItem.delete();
                } catch (Exception ignored) {
                    // ignored TODO perhaps add to tracker delete failure list somehow?
                }
            }
        }
    }
}

// TEMPDIR = "javax.servlet.context.tempdir";
location = ((File) context.getServletContext().getAttribute(ServletContext.TEMPDIR));

@Bean
MultipartConfigElement multipartConfigElement() {
    MultipartConfigFactory factory = new MultipartConfigFactory();
    factory.setLocation("/tmp/tomcat");
    return factory.createMultipartConfig();
}

public static long copy(InputStream inputStream,
            OutputStream outputStream, boolean closeOutputStream,
            byte[] buffer)
    throws IOException {
    OutputStream out = outputStream;
    InputStream in = inputStream;
    try {
        long total = 0;
        for (;;) {
            int res = in.read(buffer);
            if (res == -1) {
                break;
            }
            if (res > 0) {
                total += res;
                if (out != null) {
                    out.write(buffer, 0, res);
                }
            }
        }
        if (out != null) {
            if (closeOutputStream) {
                out.close();
            } else {
                out.flush();
            }
            out = null;
        }
        in.close();
        in = null;
        return total;
    } finally {
        IOUtils.closeQuietly(in);
        if (closeOutputStream) {
            IOUtils.closeQuietly(out);
        }
    }
}