实现文件上传和下载

文件上传的前端页面：

multiple表示支持一次上传多个文件

    
    



  

  上传

上传单个文件的servlet代码：

@MultipartConfig该注解表示这个servlet支持文件上传

package servlet;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.File;
import java.io.IOException;

@WebServlet("/upload")
//location中写的是默认指定上传的路径，如果要是下面不写路径，就默认上传到这个路径
@MultipartConfig(location="E:\\temp")
public class UploadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置编码格式，防止乱码
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //上传文件的逻辑
        //对应html里面写的name
        Part file = req.getPart("file");
        //获取上传文件的名称
        String fileName = file.getSubmittedFileName();
        String name = fileName;
        System.out.println("上传文件的名称：" + fileName);
        //html中定义的name属性的值
        System.out.println(file.getName());
        String dir = "E:\\upload";
        fileName = dir + File.separator + fileName;
        File file1 = new File(fileName);
        if(!file1.getParentFile().exists()){
            file1.getParentFile().mkdirs();
        }
        System.out.println(fileName);
      try {
          file.write(fileName);
          String downloadLink = "下载图片";
          resp.getWriter().write("
上传成功
" + downloadLink);
      }catch (IOException e){
          e.printStackTrace();
          resp.getWriter().write("
上传失败
");
      }
    }

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

    }
}

支持一次上传多个文件的servlet代码实例：

package servlet;

import utils.Constant;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.File;
import java.io.IOException;
import java.util.Collection;
@WebServlet("/uploadfiles")
@MultipartConfig
public class UploadFilesServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置编码格式
        req.setCharacterEncoding("utf-8");
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        //获取要上传的多个文件
        Collection parts = req.getParts();
        String downloadLink = "";
        String message = "";
        for (Part part : parts) {
            //获取文件类型
            String type = part.getContentType();
            //获取要上传的文件名
            String name = part.getSubmittedFileName();
            if(Constant.ALLOW_TYPES.contains(type)){
                String fileName = Constant.UPLOAD_PATH + File.separator + name;
                File file = new File(fileName);
                if(!file.getParentFile().exists()){
                    //目标目录不存在就去创建
                    file.getParentFile().mkdirs();
                }
                part.write(fileName);
                downloadLink = downloadLink + "下载" + name.substring(0,name.lastIndexOf(".")) + "
";
                message = message + "
" + name + "上传成功
";
            }else {
                message = message + "
" + name + "上传失败，文件格式不支持
";
            }
        }
        String html = "";
        html += message;
        html += "
下载地址：
";
        html += downloadLink;
        html += "";
        resp.getWriter().write(html);
    }
}

展示文件列表：

package servlet;

import utils.Constant;
import utils.FileUtils;

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

@WebServlet("/list")
public class FileListServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        File file = new File(Constant.UPLOAD_PATH);
        File[] files = file.listFiles(f -> f.isFile());
        resp.setCharacterEncoding("utf-8");
        resp.setContentType("text/html;charset=utf-8");
        if(files != null && files.length > 0){
            StringBuilder html = new StringBuilder("");
            html.append("").append("").append("").append("").append("");
            //遍历这个目录
            for (int i = 1; i <= files.length; i++) {
                File f = files[i - 1];
                html.append("");
                html.append("");
                html.append("");
                html.append("");
                String downloadLink = "/download?file=" + f.getName();
                html.append("").append("");
            }
            html.append("
序号
文件名
文件大小
修改时间
操作
").append(i).append("
").append(f.getName()).append("
").append(FileUtils.getSize(f.length())).append("
").append(FileUtils.getTime(f.lastModified())).append("
下载").append("
");
            resp.getWriter().write(html.toString());
        }else {
            resp.getWriter().write("
服务端上传目录为空
");
        }
    }
}

下载文件的前端页面

    
    


下载

下载文件的servlet：

package servlet;

import utils.Constant;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
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;
@WebServlet("/download")
public class DownLoadServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //告诉浏览器要响应的是二进制流
        resp.setContentType("application/octet-stream");
        //获取本次下载的文件名称
        String file = req.getParameter("file");
        //设置以附件的形式下载，指定下载的文件名是原来的文件名
        resp.setHeader("content-disposition","attachment;filename=" + file);
        //要下载的文件的完整路径
        String path = Constant.UPLOAD_PATH + File.separator + file;
        //先用输入流读进来
        FileInputStream in = new FileInputStream(path);
        //获取响应的输出流
        ServletOutputStream out = resp.getOutputStream();
        //将文件的内容写入到输出流
        in.transferTo(out);
        out.flush();
        out.close();
        in.close();

    }

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

    }
}