servlet 表单加上multipart/form-data后request.getParameter获取NULL(已解决)

先上结论（可能不对，因为这是根据实践猜测而来，欢迎指正）

表单改为multipart/form-data传值后，数据就不能通过普通的request.getParameter获取。

文件和文件名通过FileItem对象来获取，普通表单数据其实也包含在内。

先获取所有的items

List<FileItem> formItems = upload.parseRequest(request);

遍历items，Listz中包含表单中所有的input，按你jsp中form表单写的顺序放的

for (FileItem item : formItems)

循环中用到item的三个函数

item.isFormField()//判断本次遍历的item中是普通input控件的还是file控件，即判断type

item.getFieldName()//获取本次遍历的item中input控件的name值，用它结合if判断是否遍历到了自己想要的控件

item.getString()//获取本次遍历的item中input控件传来的值，参数填编码如item.getString("UTF-8")，取值的函数

好了，说完原理，上源码

package com.lxz.servlet;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

import javax.servlet.ServletException;
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 com.lxz.dao.VideoDao;
import com.lxz.viso.Video;

/**
* Servlet implementation class Video_RegisterServlet
*/
public class Video_RegisterServlet extends HttpServlet {
   private static final long serialVersionUID = 1L;

    private static final String UPLOAD_DIRECTORY = "upload";

    // 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


    /**
     * @see HttpServlet#HttpServlet()
     */
    public Video_RegisterServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

   /**
   * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
   */
   protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       request.setCharacterEncoding("UTF-8");
       response.setContentType("text/html; charset=UTF-8");


       String video_desc = request.getParameter("video_desc");

       String course_name = request.getParameter("course_name");//改了这里


       if (!ServletFileUpload.isMultipartContent(request)) {
                // 如果不是则停止
                PrintWriter writer = response.getWriter();
                writer.println("Error: 表单必须包含 enctype=multipart/form-data");
                writer.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 = 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();
        }
        VideoDao videodao = new VideoDao();
       Video video = new Video();
        String filePath;
        File storeFile;
        try {
            // 解析请求的内容提取文件数据
            @SuppressWarnings("unchecked")
            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.getFieldName().equals("video_desc"))//是否遍历到name=video_desc的input
                   video_desc = item.getString("UTF-8");//遍历到了，获取其值

                   if(item.getFieldName().equals("course_name"))
                   course_name = item.getString("UTF-8");

                    if (!item.isFormField()) {//前面有个感叹号
                        String fileName = new File(item.getName()).getName();

                        //检验是否存在相同文件名
                       video.setCourse_name(course_name);
                       video.setVideo_desc(video_desc);
                       video.setVideo_name(fileName);
                       //video.setVideo_path(uploadPath);
                       if(videodao.searchVideos(video))
                       {
                           request.setAttribute("msg", "已存在视频名称");
                           //已存在视频名称
                       }else{
                           videodao.addVideo(video);
                            filePath = uploadPath + File.separator + fileName;
                            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
                            item.write(storeFile);
                            request.setAttribute("msg","文件上传成功!");
                       }

                    }
                }
            }
        } catch (Exception ex) {
            request.setAttribute("msg","错误信息: " + ex.getMessage());
        }
       request.getRequestDispatcher("v_register.jsp").forward(request, response);

   }

   /**
   * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
   */
   protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
       // TODO Auto-generated method stub
       doGet(request, response);
   }

}

servlet 表单加上multipart/form-data后request.getParameter获取NULL(已解决)

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