文件上传下载

一.上传

1.前端：

<form method="post" action="FileUpload" enctype="multipart/form-data">
　　<input type="file" /> 
　　<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 = request.getParameter("filename");
//        System.out.println(filename);
        String filepath = dirPath + File.separator + filename;
        //设置返回的数据类型
        response.setContentType("APPLICATION/OCTET-STREAM");
        //设置请求头，并告诉浏览器文件的名字（filename）。其中文件的名字需要经过编码，否则会出现乱码
        response.setHeader("Content-Disposition", "attachment; filename="" + URLEncoder.encode(filename,"utf-8") + """);

        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);
    }
}