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实现文件上传和下载

news 2025/8/5 8:25:45

文件上传的前端页面：

multiple表示支持一次上传多个文件

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>上传文件</title>
</head>
<body>
<form action="/getFiles" enctype="multipart/form-data" method="post"><input type="file" name="file" id="file" multiple><br /><button type="submit">上传</button>
</form>
</body>
</html>

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 {@Overrideprotected 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namePart 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 = "<a href=\"/download?file=" + name + "\">下载图片</a>";resp.getWriter().write("<h3>上传成功</h3>" + downloadLink);}catch (IOException e){e.printStackTrace();resp.getWriter().write("<h3>上传失败</h3>");}}@Overrideprotected 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 {@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {}@Overrideprotected 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<Part> 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 + "<a href='http://127.0.0.1/download?file=" + name + "'>下载" + name.substring(0,name.lastIndexOf(".")) + "</a><br>";message = message + "<p>" + name + "上传成功</p>";}else {message = message + "<p>" + name + "上传失败，文件格式不支持</p>";}}String html = "<html><body>";html += message;html += "<p>下载地址：</p>";html += downloadLink;html += "</body></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 {@Overrideprotected 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("<table>");html.append("<tr>").append("<th>序号</th>").append("<th>文件名</th>").append("<th>文件大小</th>").append("<th>修改时间</th><th>操作</th></tr>");//遍历这个目录for (int i = 1; i <= files.length; i++) {File f = files[i - 1];html.append("<td>").append(i).append("</td>");html.append("<td>").append(f.getName()).append("</td>");html.append("<td>").append(FileUtils.getSize(f.length())).append("</td>");html.append("<td>").append(FileUtils.getTime(f.lastModified())).append("</td>");String downloadLink = "/download?file=" + f.getName();html.append("<td><a").append(" href=").append(downloadLink).append(">下载</a>").append("</td>").append("</tr>");}html.append("</table>");resp.getWriter().write(html.toString());}else {resp.getWriter().write("<h3>服务端上传目录为空</h3>");}}
}

下载文件的前端页面

<!DOCTYPE html>
<html lang="en">
<head><meta charset="UTF-8"><title>Title</title>
</head>
<body>
<a href="/download?file=2.jpg">下载</a>
</body>
</html>

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 {@Overrideprotected 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();}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {}
}

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