javaweb如何实现文件上传?

要实现文件上传功能,我们需要依靠Apache组织的Commons-io.jar,
Commons-fileupload.jar两个jar包来实现,(有许多版本,我给大家仅提供一个版本)或者去官网下载最新版本:http://commons.apache.org/;
链接:https://pan.baidu.com/s/1ImnYdtOavU0ETr7exf4JMg
提取码:npld
1.创建一个fileupdate项目,将其放在自己项目的WEB-INF/lib文件夹下,如图:

2.文件上传一般是存在服务器的upload目录下,文件名陈存在数据库中,为了防止上传文件重名,一般我们用UUID,(绝不会重复)
3.index.jsp页面的代码如下:
注意:form表单不能忘了enctype=“multipart/form-data” 此属性

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>    
    <title>文件上传</title>
  </head>
  <body>
  	<div align="center">
    <form action="UploadServlet" enctype="multipart/form-data" method="post">
    	名称：<input name="name" /> <br>
    	上传文件：<input name="img" type="file"/><br>
    	<input type="submit" value="提交" /> &nbsp;&nbsp;
    	<input type="reset" value="重置" />
    </form>
    </div>
  </body>
</html>

message.jsp代码:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <title>上传文件成功</title>
  </head>
  <body>
   	<h1 align="center">上传文件成功!</h1>
  </body>
</html>

4.UploadServlet代码:

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

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.FileUtils;


public class UploadServlet extends HttpServlet {

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

		this.doPost(request, response);
	}

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

		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		DiskFileItemFactory sf= new DiskFileItemFactory();//实例化磁盘被文件列表工厂
		String path = request.getRealPath("/upload");//得到上传文件的存放目录
		sf.setRepository(new File(path));//设置文件存放目录
		sf.setSizeThreshold(1024*1024);//设置文件上传小于1M放在内存中
		String rename = "";//文件新生成的文件名
		String fileName = "";//文件原名称
		String name = "";//普通field字段
		//从工厂得到servletupload文件上传类
		ServletFileUpload sfu = new ServletFileUpload(sf);
		
		try {
			List<FileItem> lst = sfu.parseRequest(request);//得到request中所有的元素
			for (FileItem fileItem : lst) {
				if(fileItem.isFormField()){
					if("name".equals(fileItem.getFieldName())){
						name = fileItem.getString("UTF-8");
					}
				}else{
					//获得文件名称
					fileName = fileItem.getName();
					fileName = fileName.substring(fileName.lastIndexOf("\\")+1);
					String houzhui = fileName.substring(fileName.lastIndexOf("."));
					rename = UUID.randomUUID()+houzhui;
					fileItem.write(new File(path, rename));
				}
			}
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		response.sendRedirect("message.jsp");
		out.flush();
		out.close();
	}
}

一般当你createservlet是web.xml自动配置了相关信息,如图:

运行效果如下:

目前Tomcat下面为空:

选择一张图片,如下:

OK!
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