#####一丶先引入上传下载的lib

#####二丶上传的的servlet

package com.test.action;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import java.util.List;

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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

@WebServlet("/upload")
public class FileUpLoadAction extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doPost(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		// 设置编码
		request.setCharacterEncoding("utf-8");	
		
		//对提交的数据进行处理，保存上传文件	
		boolean success = processUpload(request);
		
		if(success){
			//获取表单text控件的值
			String account = request.getAttribute("account").toString();
			System.out.println(account);
			
			//获取文件上传的原始名称
			String fileName = request.getAttribute("upfile").toString();
			System.out.println(fileName);
			
			//获取文件上传后，服务器上保存的名字
			String fileNameServer = request.getAttribute("upfileServer").toString();
			System.out.println(fileNameServer);
			request.setAttribute("upfile", fileNameServer);
			
			request.setAttribute("message", "上传成功");
		}
		request.getRequestDispatcher("/upload.jsp").forward(request, response);
	}

	private boolean processUpload(HttpServletRequest request) {
		boolean success = true;
		String message = null;
		// 获取文件需要上传到的路径
		String path = request.getServletContext().getRealPath("/upload");
		System.out.println(path);
		// 如果此文件夹不存在，则构造此文件夹
		File f = new File(path);
		if (!f.exists()) {
			f.mkdir();
		}
		// 构造出文件工厂，用于存放JSP页面中传递过来的文件
		DiskFileItemFactory factory = new DiskFileItemFactory();
		// 设置上传文件的保存路径
		factory.setRepository(f);
		// 设置缓存大小，如果文件大于缓存大小时，则先把文件放到缓存中
		factory.setSizeThreshold(1 * 1024 * 1024);

		ServletFileUpload upload = new ServletFileUpload(factory);
		// 设置可以上传文件大小的上界20MB
		upload.setSizeMax(20 * 1024 * 1024);
		try {
			// 可以上传多个文件
			List<FileItem> list = (List<FileItem>) upload.parseRequest(request);
			for (FileItem item : list) {
				// 获取表单的属性名字
				String name = item.getFieldName();

				if (item.isFormField()) {
					String value = item.getString();
					//解决乱码问题
					value = new String(value.getBytes("iso-8859-1"),"utf-8"); 
					request.setAttribute(name, value);
				} else {
					// 获得文件类型
					String contentType = item.getContentType();
					// 获得文件大小
					long fileSize = item.getSize();
					// 获取路径名
					String value = item.getName();
					// 索引到最后一个反斜杠
					int start = value.lastIndexOf("\\");
					// 截取 上传文件的 字符串名字，加1是 去掉反斜杠，
					String filename = value.substring(start + 1);

					if (filename != null && !filename.trim().equals("")) {
						// 如果上传的文件不是图片，那么不上传
						String allImgExt = ".jpg|.jpeg|.gif|.bmp|.png|";
						String extName = filename.substring(filename.indexOf("."), filename.length());
						if (allImgExt.indexOf(extName + "|") == -1) {
							message = "该文件类型不允许上传。请上传 " + allImgExt
									+ " 类型的文件，当前文件类型为" + extName;
							success = false;
							break;
						}
						request.setAttribute(name, filename);
						// 随机数产生名称
						String newName = System.currentTimeMillis() + extName;
						request.setAttribute(name + "Server", newName);
						// 将文件保存到服务器中
						InputStream in = item.getInputStream();
						// 原文件名
						// OutputStream out = new FileOutputStream(new File(path, filename));
						// 随机数文件名
						OutputStream out = new FileOutputStream(new File(path,
								newName));
						int length = 0;
						byte[] buf = new byte[1024];
						while ((length = in.read(buf)) != -1) {
							out.write(buf, 0, length);
						}
						in.close();
						out.close();
					}
				}
			}
		} catch (FileUploadException e) {
			message = "文件的内容过大，请上传小于20MB的文件" ;
			success = false;
			e.printStackTrace();
		} catch (IOException e) {
			success = false;
			e.printStackTrace();
		}
		request.setAttribute("message", message);
		return success;
	}
}

#####三丶下载的servlet

package com.test.action;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/download")
public class FileDownloadAction extends HttpServlet {
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		String id = request.getParameter("id");
		// 根据主键读取文件的真实名字 + 服务器上的名字

		processDownload("1444442288605.png", "腾讯.png", request, response);
	}

	private boolean processDownload(String fileName, String saveName,
			HttpServletRequest request, HttpServletResponse response) {
		boolean success = true;
		// 获取文件下载所在的路径
		String path = request.getServletContext().getRealPath("/upload");
		File fileLoad = new File(path, fileName); // 下载文件
		long fileLength = fileLoad.length(); // 文件大小
		byte[] buffer = new byte[1024]; // 缓冲字节数组
		try {
			response.reset();
			response.setHeader("Content-disposition", "attachment;filename=\""
					+ new String(saveName.getBytes("gb2312"), "ISO-8859-1")	+ "\"");
			response.setContentType("application/octet-stream");
			response.setHeader("Content_Length", String.valueOf(fileLength));

			OutputStream os = response.getOutputStream();
			FileInputStream in = new FileInputStream(fileLoad);
			int hasRead = 0;
			while ((hasRead = in.read(buffer)) != -1) {
				os.write(buffer, 0, hasRead);
			}
			os.flush();
			os.close();
			in.close();
		} catch (IOException e) {
			success = false;
			e.printStackTrace();
		}
		return success;
	}

}