private Integer getHttpMethod(final DocItem docItem) {
        Integer httpMethod = null;
        Optional<String> first = docItem.getHttpMethodList().stream().findFirst();
        if (first.isPresent()) {
            String method = docItem.getHttpMethodList().size() == 1 ? StringUtils.upperCase(first.get()) : ApiHttpMethodEnum.GET.getName();
            httpMethod = ApiHttpMethodEnum.getValueByName(method);
        }
        return httpMethod;
    }
add docInfo.

@param instance    instance
@param docInfoJson docInfoJson
@param callback    callback
shenyu-admin/src/main/java/org/apache/shenyu/admin/service/manager/impl/DocManagerImpl.java