文件上传实战-优快云博客

本文链接：https://blog.youkuaiyun.com/wangyanming123/article/details/52613853

1。文件上传的必要前提：
a、表单的method必须是post
b、表单的enctype属性必须是multipart/form-data类型的。
enctype默认值：application/x-www-form-urlencoded
作用：告知服务器，请求正文的MIME类型
c、表单中提供type=”file”类型的上传组件
2。文件上传原理。
这里写图片描述
3。文件上传案例1：
a.导包：
commons-fileupload-1.3.1.jar
commons-io-2.2.jar
b. upload.jsp文件：

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>文件上传</title>
  </head>

  <body>
    <form action="${pageContext.request.contextPath}/servlet/UploadServlet2" method="post" enctype="multipart/form-data">
        name:<input name="name"/><br>
        file1:<input type="file" name="f1"/><br>
        file2:<input type="file" name="f2"/><br>
        <input type="submit" value="上传">
    </form>
  </body>
</html>

c. web.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <servlet>
    <servlet-name>UploadServlet2</servlet-name>
    <servlet-class>com.itheima.servlet.UploadServlet2</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>UploadServlet2</servlet-name>
    <url-pattern>/servlet/UploadServlet2</url-pattern>
  </servlet-mapping>

</web-app>

d. UploadServlet2.java文件：

package com.itheima.servlet;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.FilenameUtils;
//借助commons-fileupload实现文件上传的简单案例
public class UploadServlet2 extends HttpServlet {

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

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();

        //判断用户提交的正文类型是不是multipart/form-data
        boolean isMultipart = ServletFileUpload.isMultipartContent(request);
        if(!isMultipart){
            throw new RuntimeException("请检查您的表单的enctype属性，确定是multipart/form-data");
        }
        //创建DiskFileItemFactory
        DiskFileItemFactory dfif = new DiskFileItemFactory();
        dfif.setRepository(new File("d:/"));
        ServletFileUpload parser = new ServletFileUpload(dfif);

        List<FileItem> items = null;
        //解析请求内容
        try {
            items = parser.parseRequest(request);
        } catch (FileUploadException e) {
            throw new RuntimeException("解析上传内容失败，请重新试一下");
        }

        //处理请求内容
        if(items!=null){
            for(FileItem item:items){
                if(item.isFormField()){
                    //普通表单字段
                    processFormField(item);
                }else{
                    //上传字段
                    processUploadField(item);
                }
            }
        }

        out.write("上传成功！");
    }
    //上传字段
    private void processUploadField(FileItem item) {
        try {
            InputStream in = item.getInputStream();//输入流
            String fileName = item.getName();//上传文件的文件名   C:\Users\wzhting\Desktop\a.txt   a.txt
            //截取文件名
//      fileName = fileName.substring(fileName.lastIndexOf("\\")+1);
            if(fileName!=null){
                fileName = FilenameUtils.getName(fileName);
            }

            //把文件存到服务器的某个目录中
            String storeDirectoryPath = getServletContext().getRealPath("/files");
            File storeDirectory = new File(storeDirectoryPath);
            if(!storeDirectory.exists()){
                storeDirectory.mkdirs();
            }

            //构建输出流
//          OutputStream out = new FileOutputStream(storeDirectoryPath+File.separator+fileName);
//          int len = -1;
//          byte b[] = new byte[1024];
//          while((len=in.read(b))!=-1){
//              out.write(b, 0, len);
//          }
//          in.close();
//          out.close();
//          item.delete();//删除临时文件

            item.write(new File(storeDirectoryPath+File.separator+fileName));

        } catch (Exception e) {
            throw new RuntimeException("上传失败,请重试");
        }

    }
    //普通表单字段
    private void processFormField(FileItem item) {
        String fieldName = item.getFieldName();//字段名
        String fieldValue = item.getString();
        System.out.println(fieldName+"="+fieldValue);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request, response);
    }

}

文件上传案例（1）