关于使用Common-FileUpload 组件上传的疑惑

用commons-fileupload-1.3.2.jar 编写了一个简单的上传页面。设置上传单个文件大小为1MB，总大小不超过5MB。
发现，文件在1~5MB 之间可以捕获到异常，并forward 回index.jsp 显示错误信息。
但是，如果文件大于5MB 浏览器则提示“The connection was reset.”，根本无法做任何处理。
JSP 和响应的Servlet 的源码如下，工程源码链接: https://pan.baidu.com/s/1jHAQGgY 密码: 8y6t
请问这是怎么回事呢？

index.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

<head>

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

<title>Upload Page 00</title>

</head>

<body>

	<h3 style="color:red">${message }</h3>

	<form action="uploadServlet00" method="post" enctype="multipart/form-data">

		File:<input type="file" name="file"/><br />

		Desc:<input type="text" name="desc"/><br />

		<input type="submit" value="Submit"/>

	</form>

</body>

</html>

UploadServlet00.java

package com.abc.upload.servlet;



import java.io.File;

import java.io.IOException;

import java.util.Iterator;

import java.util.List;



import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;



import org.apache.commons.fileupload.FileItem;

import org.apache.commons.fileupload.disk.DiskFileItemFactory;

import org.apache.commons.fileupload.servlet.ServletFileUpload;



@WebServlet("/uploadServlet00")

public class UploadServlet00 extends HttpServlet {

	private static final long serialVersionUID = 1L;

       

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {



		// Create a factory for disk-based file items

		DiskFileItemFactory factory = new DiskFileItemFactory();



		// Set factory constraints

		factory.setSizeThreshold(1024 * 500);

		ServletContext servletContext = this.getServletConfig().getServletContext();

		// 临时文件夹设置为Tomcat 的work 目录，最终文件也保存到那里。

		File repository = (File) servletContext.getAttribute("javax.servlet.context.tempdir");

		factory.setRepository(repository);



		// Create a new file upload handler

		ServletFileUpload upload = new ServletFileUpload(factory);



		// 设置单个文件的大小，这里设置单个文件不超过1MB

		upload.setFileSizeMax(1024 * 1024);

				

		// Set overall request size constraint

		// 设置文件上传的总大小，这里设置为5MB

		upload.setSizeMax(1024 * 1024 * 5);



		try {

			// Parse the request

			// 解析客户端请求

			List<FileItem> items = upload.parseRequest(request);

			

			// Process the uploaded items

			Iterator<FileItem> iter = items.iterator();

			while (iter.hasNext()) {

				FileItem item = iter.next();

				

				// 判断是普通域还是文件域，交由不同方法处理

				if (item.isFormField()) {

					processFormField(item);

				} else {

					processUploadedFile(item);

				}

			}

			

			request.setAttribute("message", "Upload successfully!");

			

		} catch (Exception e) {

			e.printStackTrace();

			request.setAttribute("message", e.getMessage());

			

		}

		

		request.getRequestDispatcher("/index.jsp").forward(request, response);

		

	}



	private void processFormField(FileItem item) {

		// Process a regular form field

		if (item.isFormField()) {

		    String name = item.getFieldName();

		    String value = item.getString();

		    System.out.println(name + ": " + value);

		}		

	}



	private void processUploadedFile(FileItem item) throws Exception {

		// Process a file upload

		if (!item.isFormField()) {

		    String fieldName = item.getFieldName();

		    String fileName = item.getName();

		    String contentType = item.getContentType();

		    long sizeInBytes = item.getSize();

		    System.out.println(fieldName);

		    System.out.println(fileName);

		    System.out.println(contentType);

		    System.out.println(sizeInBytes);

		    

		    fileName = this.getServletContext().getAttribute("javax.servlet.context.tempdir") + "/" + fileName;

		    item.write(new File(fileName));

		}	

	}



}