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<Map<String, String>> data = new ArrayList<>();

        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 = 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<String, String>() {{
                            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

<web-app xmlns="http://java.sun.com/xml/ns/j2ee" version="2.4">
    <servlet>
        <servlet-name>uploadServlet</servlet-name>
        <servlet-class>stu.servlet.UploadServlet</servlet-class>
    </servlet>
    <servlet>
        <servlet-name>downloadServlet</servlet-name>
        <servlet-class>stu.servlet.DownloadServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>uploadServlet</servlet-name>
        <url-pattern>/uploadServlet</url-pattern>
    </servlet-mapping>
    <servlet-mapping>
        <servlet-name>downloadServlet</servlet-name>
        <url-pattern>/downloadServlet</url-pattern>
    </servlet-mapping>
</web-app>

五、上传的jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>$Title$</title>
</head>
<body>
<h1>文件上传</h1>
<form method="post" action="/uploadServlet" enctype="multipart/form-data">
    选择一个文件:
    <input type="file" name="uploadFile"/>
    <br/><br/>
    <input type="submit" value="上传"/>
</form>
</body>
</html>

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" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
${message}
<h1>文件列表</h1>
<table>
    <tbody>
    <tr>
        <td>文件</td>
        <td>下载</td>
    </tr>
    <c:forEach items="${list}" var="item">
        <tr>
            <td>${item.name}</td>
            <td><a href="/downloadServlet?path=${item.path}">下载</a></td>
        </tr>
    </c:forEach>
    </tbody>
</table>
</body>
</html>