java实现文件上传下载

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);
 }
}

来源：https://www.cnblogs.com/DOLFAMINGO/p/9559185.html