Spring Boot 上传文件报The field file

根据异常内提示的类，可以定位到：
FileUploadBase（class FileItemStreamImpl 的构造函数）

/**
             * Creates a new instance.
             *
             * @param pName The items file name, or null.
             * @param pFieldName The items field name.
             * @param pContentType The items content type, or null.
             * @param pFormField Whether the item is a form field.
             * @param pContentLength The items content length, if known, or -1
             * @throws IOException Creating the file item failed.
             */
            FileItemStreamImpl(String pName, String pFieldName,
                    String pContentType, boolean pFormField,
                    long pContentLength) throws IOException {
                name = pName;
                fieldName = pFieldName;
                contentType = pContentType;
                formField = pFormField;
                final ItemInputStream itemStream = multi.newInputStream();
                InputStream istream = itemStream;
                if (fileSizeMax != -1) {
                    if (pContentLength != -1
                            &&  pContentLength > fileSizeMax) {
                        FileSizeLimitExceededException e =
                            new FileSizeLimitExceededException(
                                String.format("The field %s exceeds its maximum permitted size of %s bytes.",
                                        fieldName, Long.valueOf(fileSizeMax)),
                                pContentLength, fileSizeMax);
                        e.setFileName(pName);
                        e.setFieldName(pFieldName);
                        throw new FileUploadIOException(e);
                    }
                    istream = new LimitedInputStream(istream, fileSizeMax) {
                        @Override
                        protected void raiseError(long pSizeMax, long pCount)
                                throws IOException {
                            itemStream.close(true);
                            FileSizeLimitExceededException e =
                                new FileSizeLimitExceededException(
                                    String.format("The field %s exceeds its maximum permitted size of %s bytes.",
                                           fieldName, Long.valueOf(pSizeMax)),
                                    pCount, pSizeMax);
                            e.setFieldName(fieldName);
                            e.setFileName(name);
                            throw new FileUploadIOException(e);
                        }
                    };
                }
                stream = istream;
            }

发现fileSizeMax该值控制上传上限，在207行看到

    /**
     * Sets the maximum allowed size of a single uploaded file,
     * as opposed to {@link #getSizeMax()}.
     *
     * @see #getFileSizeMax()
     * @param fileSizeMax Maximum size of a single uploaded file.
     */
    public void setFileSizeMax(long fileSizeMax) {
        this.fileSizeMax = fileSizeMax;
    }

追踪后发现在Request类的parseParts方法（2863行）upload.setFileSizeMax(mce.getMaxFileSize());

mce对象是在2800行MultipartConfigElement mce = getWrapper().getMultipartConfigElement();初始化的。
通过getMultipartConfigElement()可在StandardWrapper内的1072行处发现如下代码

if (multipartConfigElement == null) {
                MultipartConfig annotation =
                        servlet.getClass().getAnnotation(MultipartConfig.class);
                if (annotation != null) {
                    multipartConfigElement =
                            new MultipartConfigElement(annotation);
                }
            }

最终发现 通过MultipartConfig注解可配置。
配置完不好使！！！
后发现可通过配置文件：

spring:
  http:
    multipart:
      maxFileSize: 10Mb
      maxRequestSize: 100Mb