本文实例为大家分享了java实现文件上传下载的具体代码，供大家参考，具体内容如下

一.上传

1.前端：

<form method="post" action="FileUpload" enctype="multipart/form-data">　　<input type="file" name="uploadFile" />　　<br/>　　<input type="submit" value="上传" /></form>

2.后台：

import java.io.File;import java.io.IOException;import java.io.PrintWriter;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.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;import dao.FileDao;@WebServlet("/FileUpload")public class FileUpload extends HttpServlet { private static final long serialVersionUID = 1L; // 上传配置 private static final int MEMORY_THRESHOLD = 1024 * 1024 * 3; // 3MB private static final int MAX_FILE_SIZE = 1024 * 1024 * 40; // 40MB private static final int MAX_REQUEST_SIZE = 1024 * 1024 * 50; // 50MB public FileUpload() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); response.setContentType("text/html;charset=UTF-8"); PrintWriter out = response.getWriter(); if (!ServletFileUpload.isMultipartContent(request)) { // 如果不是则停止 out.println("Error: 表单必须包含 enctype=multipart/form-data"); out.flush(); return; } // 配置上传参数 DiskFileItemFactory factory = new DiskFileItemFactory(); // 设置内存临界值 - 超过后将产生临时文件并存储于临时目录中 factory.setSizeThreshold(MEMORY_THRESHOLD); // 设置临时存储目录 factory.setRepository(new File(System.getProperty("java.io.tmpdir"))); ServletFileUpload upload = new ServletFileUpload(factory); // 设置最大文件上传值 upload.setFileSizeMax(MAX_FILE_SIZE); // 设置最大请求值 (包含文件和表单数据) upload.setSizeMax(MAX_REQUEST_SIZE); // 中文处理 upload.setHeaderEncoding("UTF-8"); String uploadPath = request.getServletContext().getRealPath("/files"); File uploadDir = new File(uploadPath); if (!uploadDir.exists()) { uploadDir.mkdir(); } try { // 解析请求的内容提取文件数据 List<FileItem> formItems = upload.parseRequest(request); if (formItems != null && formItems.size() > 0) { // 迭代表单数据 for (FileItem item : formItems) { // 处理不在表单中的字段 if (!item.isFormField()) { String fileName = new File(item.getName()).getName(); String filePath = uploadPath + File.separator + fileName; File storeFile = new File(filePath); // 在控制台输出文件的上传路径// System.out.println(filePath); // 保存文件到硬盘 if(storeFile.exists()) { out.println("上传失败，文件已存在！"); }else { item.write(storeFile); out.println("文件上传成功!"); } } } } } catch (Exception ex) { response.getWriter().println("文件上传成功!"); } } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}

二.下载

1.下载链接：

FileDownload?filename="+URLEncoder.encode(filename,"utf-8")　--------- 需要对URL中的中文参数进行编码，否则会出现乱码

2.后台：

import java.io.File;import java.io.FileInputStream;import java.io.IOException;import java.io.PrintWriter;import java.net.URLEncoder;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("/FileDownload")public class FileDownload extends HttpServlet { private static final long serialVersionUID = 1L; public FileDownload() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("UTF-8"); response.setCharacterEncoding("UTF-8"); PrintWriter out = response.getWriter(); String dirPath = request.getServletContext().getRealPath("/files"); String filename = URLEncoder.encode(request.getParameter("filename"),"utf-8"); //需要对URL中的中文参数进行编码，否则出现乱码 response.getWriter().println(filename); String filepath = dirPath + File.separator + filename; response.setContentType("APPLICATION/OCTET-STREAM"); response.setHeader("Content-Disposition", "attachment; filename=\"" + filename + "\""); FileInputStream fileInputStream = new FileInputStream(filepath); int i = 0; while ((i = fileInputStream.read()) != -1) { out.write(i); } fileInputStream.close(); out.close(); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。