文件上传下载

上传路径：src/main/webapp/uploads

上传

package example.controller;

import java.io.File;
import java.io.IOException;
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;

@WebServlet("/UploadServlet")
public class UploadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    // 设置上传目录
    private static final String UPLOAD_DIRECTORY = "uploads";

    // 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

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 检查请求是否为多部分内容
        if (!ServletFileUpload.isMultipartContent(request)) {
            response.getWriter().println("Error: Form must have enctype=multipart/form-data.");
            return;
        }

        // 配置上传参数
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setSizeThreshold(MEMORY_THRESHOLD);
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));

        ServletFileUpload upload = new ServletFileUpload(factory);
        upload.setFileSizeMax(MAX_FILE_SIZE);
        upload.setSizeMax(MAX_REQUEST_SIZE);

        // 构造上传路径
        String uploadPath = 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();
        }

        try {
            // 解析请求的内容
            @SuppressWarnings("unchecked")
            List<FileItem> formItems = upload.parseRequest(request);

            if (formItems != null && formItems.size() > 0) {
                for (FileItem item : formItems) {
                    // 处理非表单字段
                    if (!item.isFormField()) {
                        String fileName = new File(item.getName()).getName();
                        String filePath = uploadPath + File.separator + fileName;
                        File storeFile = new File(filePath);

                        // 保存文件到磁盘
                        item.write(storeFile);

                        request.setAttribute("message", "文件上传成功: " + fileName);
                        request.setAttribute("fileName",fileName);
                    }
                }
            }
        } catch (Exception ex) {
            request.setAttribute("message", "错误信息: " + ex.getMessage());
        }

        // 转发到 JSP 显示消息
        getServletContext().getRequestDispatcher("/msg.jsp").forward(request, response);
    }
}

下载

package example.controller;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
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("/download")
public class FileDownloadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    // 设置文件上传路径（webapp/uploads）
    private static final String UPLOAD_DIRECTORY = "uploads";

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        // 动态解析 webapp/uploads 的路径
        String uploadPath = getServletContext().getRealPath("/") + UPLOAD_DIRECTORY;

        // 获取请求的文件名
        String fileName = request.getParameter("file");
        if (fileName == null || fileName.isEmpty()) {
            response.getWriter().println("File parameter is missing");
            return;
        }

        // 构造文件的完整路径
        File file = new File(uploadPath + File.separator + fileName);

        // 检查文件是否存在
        if (!file.exists()) {
            response.getWriter().println("File not found: " + fileName);
            return;
        }

        // 设置响应的内容类型
        response.setContentType(getServletContext().getMimeType(file.getName()));
        response.setContentLength((int) file.length());
        response.setHeader("Content-Disposition", "inline; filename=\"" + fileName + "\"");

        // 读取文件并写入到响应输出流
        try (FileInputStream fis = new FileInputStream(file);
             OutputStream os = response.getOutputStream()) {
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = fis.read(buffer)) != -1) {
                os.write(buffer, 0, bytesRead);
            }
        }
    }
}