对于文件上传，浏览器在上传的过程中是将文件以流的形式提交到服务器端的，如果直接使用Servlet获取上传文件的输入流然后再解析里面的请求参数是比较麻烦，所以一般选择采用apache的开源工具common-fileupload这个文件上传组件。这个common-fileupload上传组件的jar包可以去apache官网上面下载，也可以在struts的lib文件夹下面找到，struts上传的功能就是基于这个实现的。common-fileupload是依赖于common-io这个包的，所以还需要下载这个包。
一、开发环境搭建
创建一个FileUploadAndDownLoad项目，加入Apache的commons-fileupload文件上传组件的相关Jar包，如下图所示：
二、实现文件上传
2.1、文件上传页面form.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8" ???pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body> ???<form action="/FileUpload/fileUploadServlet1" method="post" enctype="multipart/form-data"> ???????<input type="text" name="username"> ???????<input type="file" name="filename"> ???????<input type="submit" value="上传文件"> ???</form></body></html>
2.2、处理文件上传的servlet
//1.创建磁盘工厂 ???????DiskFileItemFactory factory = new DiskFileItemFactory(); ???????//2.创建文件上传的核心类 ???????ServletFileUpload upload = new ServletFileUpload(factory); ???????upload.setHeaderEncoding("UTF-8"); ???????//3.解析request---获得文件项集合 ???????List<FileItem> parseRequest = upload.parseRequest(request); ???????//4、遍历文件项集合 ???????for(FileItem item : parseRequest){ ???????????//5、判断普通表单项/文件上传项 ???????????boolean formField = item.isFormField();//判断是否为普通表单 ???????????if(formField){
//普通表单项 ???????????????String fieldName = item.getFieldName(); ???????????????String fieldValue = item.getString("UTF-8"); ???????????????System.out.println(fieldName+":"+fieldValue); ???????????}else{ ???????????????//获得上传文件的名称 ???????????????String fileName = item.getName(); ???????????????//获得上传文件的内容 ???????????????InputStream in = item.getInputStream(); ???????????????//将in中的数据拷贝服务器上 ???????????????String path =this.getServletContext().getRealPath("jpg"); ???????????????OutputStream out= new FileOutputStream(path+"/"+fileName); ???????????????int len = 0 ; ???????????????byte[] buffer =new byte[1024]; ???????????????while((len=in.read(buffer))>0){ ???????????????????out.write(buffer, 0, len); ???????????????} ???????????????in.close(); ???????????????out.close(); ???????????} ???????} ???????2.3、commons-fileupload扩展功能，中文编码，缓存工具等
//1、创建磁盘文件项工厂 ???????????//作用：设置缓存文件的大小 ?设置临时文件存储的位置 ???????????String path_temp = this.getServletContext().getRealPath("temp"); ???????????//DiskFileItemFactory factory = new DiskFileItemFactory(1024*1024, new File(path_temp)); ???????????DiskFileItemFactory factory = new DiskFileItemFactory(); ???????????factory.setSizeThreshold(1024*1024); ???????????factory.setRepository(new File(path_temp)); ???????????//2、创建文件上传的核心类 ???????????ServletFileUpload upload = new ServletFileUpload(factory); ???????????//设置上传文件的名称的编码 ???????????upload.setHeaderEncoding("UTF-8"); ???????????//ServletFileUpload的API ???????????boolean multipartContent = upload.isMultipartContent(request);//判断表单是否是文件上传的表单 ???????????if(multipartContent){ ???????????????//是文件上传的表单 ???????????????//***解析request获得文件项集合 ???????????????List<FileItem> parseRequest = upload.parseRequest(request); ???????????????if(parseRequest!=null){ ???????????????????for(FileItem item : parseRequest){ ???????????????????????//判断是不是一个普通表单项 ???????????????????????boolean formField = item.isFormField(); ???????????????????????if(formField){ ???????????????????????????//username=zhangsan ???????????????????????????String fieldName = item.getFieldName(); ???????????????????????????String fieldValue = item.getString("UTF-8");//对普通表单项的内容进行编码 ???????????????????????????????????????????????????????System.out.println(fieldName+"----"+fieldValue); ???????????????????????????????????????????????????????//当表单是enctype="multipart/form-data"时 request.getParameter相关的方法 ???????????????????????????//String parameter = request.getParameter("username"); ???????????????????????????????????????????????????}else{ ???????????????????????????//文件上传项 ???????????????????????????//文件的名 ???????????????????????????String fileName = item.getName(); ???????????????????????????//获得上传文件的内容 ???????????????????????????InputStream in = item.getInputStream(); ???????????????????????????String path_store = this.getServletContext().getRealPath("upload"); ???????????????????????????OutputStream out = new FileOutputStream(path_store+"/"+fileName); ???????????????????????????IOUtils.copy(in, out); ???????????????????????????in.close(); ???????????????????????????out.close(); ???????????????????????????????????????????????????????//删除临时文件 ???????????????????????????item.delete(); ???????????????????????????????????????????????????} ???????????????????} ???????????????} ???????????}else{ ???????????????//不是文件上传表单 ???????????????//使用原始的表单数据的获得方式 request.getParameter(); ???????????}文件上传
原文地址：https://www.cnblogs.com/zemul/p/10226257.html