java eclipse 中文件的上传和下载示例解析
文件的上传与下载（一）
在实现文件上传和下载之前我们需要做一些准备工作，在Apache官网去下载文件上传下载的两个组件，下载链接这里给出：common-fileupload组件下载：http://commons.apache.org/proper/commons-fileupload/
common-io组件下载：http://commons.apache.org/proper/commons-io/根据自己需求下载对应版本
一、创建工程
将所需要的两个开发包导入到工程项目中如图：
二、代码编写
1.前端页面代码
1）. 在WebRoot目录下新建一个fileUpload.jsp页面，用来上传文件
<%@ page language='java' import='java.util.*' pageEncoding='GB18030'%><%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> <base href='https://www.haobala.com/bcjs/<%=basePath%>'> <title>My JSP ’fileUpload.jsp’ starting page</title> <meta http-equiv='pragma' content='no-cache'> <meta http-equiv='cache-control' content='no-cache'> <meta http-equiv='expires' content='0'> <meta http-equiv='keywords' content='keyword1,keyword2,keyword3'> <meta http-equiv='description' content='This is my page'> <!-- <link rel='stylesheet' type='text/css' href='https://www.haobala.com/bcjs/styles.css'> --> </head> <body> <!-- 文件上传表单的提交方式必须是“post” 编码类型必须为：enctype='multipart/form-data' --> <form action='UploadServlet' method='post' enctype='multipart/form-data'> username: <input type='text' name='username' /><br> file: <input type='file' name='file'><br> file2: <input type='file' name='file2'><br> <input type='submit' value='上传文件'> </form> </body></html>
2）.新建一个fileUploadResult.jsp页面用来显示结果信息
<%@ page language='java' import='java.util.*,java.io.*' pageEncoding='GB18030'%><%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> <base href='https://www.haobala.com/bcjs/<%=basePath%>'> <title>My JSP ’fileUploadResult.jsp’ starting page</title> <meta http-equiv='pragma' content='no-cache'> <meta http-equiv='cache-control' content='no-cache'> <meta http-equiv='expires' content='0'> <meta http-equiv='keywords' content='keyword1,keyword2,keyword3'> <meta http-equiv='description' content='This is my page'> <!-- <link rel='stylesheet' type='text/css' href='https://www.haobala.com/bcjs/styles.css'> --> </head> <body> <%-- <% //获取流对象 InputStream inputStream = request.getInputStream(); BufferedReader br = new BufferedReader(new InputStreamReader(inputStream)); String buffer = null; while((buffer = br.readLine()) != null){ out.print(buffer + '<br>'); } br.close(); inputStream.close(); %> --%> ${message}<br> EL-username : ${requestScope.username} <br> EL-file1 : ${requestScope.file }<br> EL-file2 : ${requestScope.file2}<br> </body></html>
2. 编写上传文件处理的Servlet代码
1) UploadServlet.java代码如下：
package com.Servlet;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStream;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;public class UploadServlet extends HttpServlet { /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //得到上传文件的保存目录，将上传的文件放在webRoot目录下（但是一般为了安全放在WEB-INF目录下，不允许外界直接访问，保证上传的安全） String path = this.getServletContext().getRealPath('/upload'); File file = new File(path); //判断上传文件的保存目录是否存在 if(!file.exists() && !file.isDirectory()){ System.out.println(path + '目录不存在，需要创建！'); //创建目录 file.mkdir(); } //消息提示 String message = ''; try{ //使用Apache文件上传组件处理文件上传步骤： //1.创建一个DiskFileItemFactory工厂 DiskFileItemFactory factory = new DiskFileItemFactory(); //2.创建一个文件上传解析器 ServletFileUpload upload = new ServletFileUpload(factory); //解决中文乱码 upload.setHeaderEncoding('UTF-8'); //3.判断提交的数据普通表单的数据还是带文件上传的表单 if(!upload.isMultipartContent(request)){ //如果是表单数据普通表单,则按照传统方式获取数据 return ; } //4.使用ServletFileUpload解析器解析上传数据，解析结果返回的是一个List<FileItem>集合，每一个FileItem对应一个Form表单的输入项 List<FileItem> list = upload.parseRequest(request); for(FileItem item : list){ //如果fileItem中封装的是普通输入项的数据 if(item.isFormField()){ //获取字段名字 String name = item.getFieldName(); //解决普通输入项中中文乱码问题 String value = item.getString('UTF-8');//value = new String(value.getBytes('iso8859-1'),'UTF-8'); System.out.println(name + ' = ' + value); }else{ //如果表单中提交的是上传文件 //获得上传的文件名称 String filename = item.getName(); System.out.println(filename); if(filename == null || filename.trim().equals(' ')){ continue; } //注意：不同的浏览器提交的文件名称是不一样的，有些浏览器提交的文件会带有路径，如“D:projectWebRoothello.jsp”，有一些是单纯的文件名：hello.jsp //去掉获取到文件名中的路径名，保留单纯的文件名 filename = filename.substring(filename.lastIndexOf('') + 1); //获取item中的上传文件的输入流 InputStream in = item.getInputStream(); //创建一个文件输入流 FileOutputStream out = new FileOutputStream(path + '' + filename); //创建一个缓冲区 byte buffer[] = new byte[1024]; //判断输入流中的数据是否已经读取完毕的标志位 int len = 0; //循环将输入流读入到缓冲区当中，（len = in.read(buffer)>0）就表示in里面还有数据存在 while((len = in.read(buffer)) > 0){ //使用FileOutputStream输出流将缓冲区的数据写入到指定的目录（path+''+filename）当中 out.write(buffer, 0, len); } //关闭输入流 in.close(); //关闭输出流 out.close(); //删除处理文件上传生成的临时文件 item.delete(); message = '文件上传成功!'; } } }catch(Exception e){ message = '文件上传失败！'; e.printStackTrace(); } request.setAttribute(message, message); request.getRequestDispatcher('fileUploadResult.jsp').forward(request, response); }}
2）web.xml文件中的配置
<?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>UploadServlet</servlet-name> <servlet-class>com.Servlet.UploadServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>UploadServlet</servlet-name> <url-pattern>/UploadServlet</url-pattern> </servlet-mapping></web-app>
结果：
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