servlet上傳下載

一、新增專案依賴(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、上傳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 {
    // 上傳檔案儲存目錄
    private static final String UPLOAD_DIRECTORY = "upload";

    // 上傳配置 上傳檔案最大值
    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 {
        // 檢測是否為多媒體上傳
        if (!ServletFileUpload.isMultipartContent(request)) {
            // 如果不是則停止
            PrintWriter writer = response.getWriter();
            writer.println("Error: 表單必須包含 enctype=multipart/form-data");
            writer.flush();
            return;
        }

        // 配置上傳引數
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        // 設定最大檔案上傳值
        upload.setFileSizeMax(MAX_FILE_SIZE);
        // 中文處理
        upload.setHeaderEncoding("UTF-8");
        // 構造臨時路徑來儲存上傳的檔案
        // 這個路徑相對當前應用的目錄
        String uploadPath = request.getServletContext().getRealPath("./") + File.separator + UPLOAD_DIRECTORY;

        // 如果目錄不存在則建立
        File uploadDir = new File(uploadPath);
        if (!uploadDir.exists()) {
            uploadDir.mkdir();
        }

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

        try {
            // 解析請求的內容提取檔案資料
            List<FileItem> formItems = upload.parseRequest(request);
            if (formItems != null && formItems.size() > 0) {
                // 迭代表單資料
                for (FileItem item : formItems) {
                    // 處理不在表單中的欄位
                    if (!item.isFormField()) {
                        String fileName = item.getName();
                        String filePath = uploadPath + File.separator + UUID.randomUUID() + fileName;
                        File storeFile = new File(filePath);
                        // 在控制檯輸出檔案的上傳路徑
                        System.out.println(filePath);
                        // 儲存檔案到硬碟
                        item.write(storeFile);
                        data.add(new HashMap<String, String>() {{
                            put("name", fileName);
                            put("path", filePath);
                        }});
                    }
                }
            }
            request.getSession().setAttribute("list", data);
            request.setAttribute("message", "檔案上傳成功!");
        } catch (Exception ex) {
            request.setAttribute("message", "錯誤資訊: " + ex.getMessage());
        }
        // 跳轉到 message.jsp
        request.getServletContext().getRequestDispatcher("/message.jsp").forward(request, response);
    }
}

三、下載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");
        //處理請求
        //讀取要下載的檔案
        File f = new File(path);
        if (f.exists()) {
            FileInputStream fis = new FileInputStream(f);
            String filename = URLEncoder.encode(f.getName(), "utf-8"); //解決中文檔名下載後亂碼的問題
            byte[] b = new byte[fis.available()];
            fis.read(b);
            response.setCharacterEncoding("utf-8");
            response.setHeader("Content-Disposition", "attachment; filename=" + filename + "");
            //獲取響應報文輸出流物件
            ServletOutputStream out = response.getOutputStream();
            //輸出
            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、上傳的jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>$Title$</title>
</head>
<body>
<h1>檔案上傳</h1>
<form method="post" action="/uploadServlet" enctype="multipart/form-data">
    選擇一個檔案:
    <input type="file" name="uploadFile"/>
    <br/><br/>
    <input type="submit" value="上傳"/>
</form>
</body>
</html>

六、下載的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>
${message}
<h1>檔案列表</h1>
<table>
    <tbody>
    <tr>
        <td>檔案</td>
        <td>下載</td>
    </tr>
    <c:forEach items="${list}" var="item">
        <tr>
            <td>${item.name}</td>
            <td><a href="/downloadServlet?path=${item.path}">下載</a></td>
        </tr>
    </c:forEach>
    </tbody>
</table>
</body>
</html>