如何在不使用event.preventDefault（）的情况下上传文件;

Question

$(document).ready(function () {
    $("#sendmail").click(function (event) {

        //stop submit the form, we will post it manually.
        event.preventDefault();
       // for (i = 0; i < mails.length; i++) {
        // Get form
        var form = $('#fileUploadForm')[0];

        // Create an FormData object
        var data = new FormData(form);

        // If you want to add an extra field for the FormData
        data.append("email12", mails[0]);

        // disabled the submit button
        $("#btnSubmit").prop("disabled", true);

        $.ajax({
            type: "POST",
            enctype: 'multipart/form-data',
            url: "EmailController",
            data: data,
            processData: false,
            contentType: false,
            cache: false,
            timeout: 600000,
            success: function (data) {

                $("#result").text(data);
                console.log("SUCCESS : ", data);
                $("#btnSubmit").prop("disabled", false);

            },
            error: function (e) {

                $("#result").text(e.responseText);
                console.log("ERROR : ", e);
                $("#btnSubmit").prop("disabled", false);

            }
        });
       // }
    });
});

在此代码中使用event.preventDefault（）它成功运行但我不想阻止按钮的默认操作...如果我不使用event.prevntDefault（）方法然后我得到错误

  java.io.IOException:                org.apache.tomcat.util.http.fileupload.FileUploadBase$IOFileUploadException: Processing of multipart/form-data request failed. Stream ended unexpectedly
at org.apache.catalina.connector.Request.parseParts(Request.java:2793)
at org.apache.catalina.connector.Request.parseParameters(Request.java:3083)
at org.apache.catalina.connector.Request.getParameter(Request.java:1151)
at org.apache.catalina.connector.RequestFacade.getParameter(RequestFacade.java:384

如何解决此问题。