servlet上传下载

一、添加项目依赖(gradle)

dependencies {
    compile group: 'javax.servlet', name: 'javax.servlet-api', version: '3.1.0'
    compile group: 'commons-fileupload', name: 'commons-fileupload', version: '1.3.3'
    compile group: 'javax.servlet', name: 'jstl', version: '1.2'
}

二、上传servlet

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

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.*;

public class UploadServlet extends HttpServlet {
    // 上传文件存储目录
    private static final String UPLOAD_DIRECTORY = "upload";

    // 上传配置 上传文件最大值
    private static final int MAX_FILE_SIZE = 1024 * 1024 * 40; // 40MB


    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 检测是否为多媒体上传
        if (!ServletFileUpload.isMultipartContent(request)) {
            // 如果不是则停止
            PrintWriter writer = response.getWriter();
            writer.println("Error: 表单必须包含 enctype=multipart/form-data");
            writer.flush();
            return;
        }

        // 配置上传参数
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        // 设置最大文件上传值
        upload.setFileSizeMax(MAX_FILE_SIZE);
        // 中文处理
        upload.setHeaderEncoding("UTF-8");
        // 构造临时路径来存储上传的文件
        // 这个路径相对当前应用的目录
        String uploadPath = request.getServletContext().getRealPath("./") + File.separator + UPLOAD_DIRECTORY;

        // 如果目录不存在则创建
        File uploadDir = new File(uploadPath);
        if (!uploadDir.exists()) {
            uploadDir.mkdir();
        }

        List> data = new ArrayList<>();

        try {
            // 解析请求的内容提取文件数据
            List 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 = item.getName();
                        String filePath = uploadPath + File.separator + UUID.randomUUID() + 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
                        item.write(storeFile);
                        data.add(new HashMap() {{
                            put("name", fileName);
                            put("path", filePath);
                        }});
                    }
                }
            }
            request.getSession().setAttribute("list", data);
            request.setAttribute("message", "文件上传成功!");
        } catch (Exception ex) {
            request.setAttribute("message", "错误信息: " + ex.getMessage());
        }
        // 跳转到 message.jsp
        request.getServletContext().getRequestDispatcher("/message.jsp").forward(request, response);
    }
}

三、下载servlet

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;

public class DownloadServlet extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doPost(request, response);
    }


    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        String path = request.getParameter("path");
        //处理请求
        //读取要下载的文件
        File f = new File(path);
        if (f.exists()) {
            FileInputStream fis = new FileInputStream(f);
            String filename = URLEncoder.encode(f.getName(), "utf-8"); //解决中文文件名下载后乱码的问题
            byte[] b = new byte[fis.available()];
            fis.read(b);
            response.setCharacterEncoding("utf-8");
            response.setHeader("Content-Disposition", "attachment; filename=" + filename + "");
            //获取响应报文输出流对象
            ServletOutputStream out = response.getOutputStream();
            //输出
            out.write(b);
            out.flush();
            out.close();
        }

    }
}

四、配置web.xml

    
        uploadServlet
        stu.servlet.UploadServlet
    
    
        downloadServlet
        stu.servlet.DownloadServlet
    
    
        uploadServlet
        /uploadServlet
    
    
        downloadServlet
        /downloadServlet
    

五、上传的jsp

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


    


文件上传

    选择一个文件:
    
    


    

六、下载的jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>


    


${message}
文件列表

        

    

    

        
文件
        
下载
    
    

            
${item.name}
            
下载