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java eclipse 中文件的上傳和下載示例解析

更新時(shí)間：2020年07月14日 17:30:52 作者：java小斌

這篇文章主要介紹了eclipse java中文件的上傳和下載示例解析,文件上傳，瀏覽器在上傳的過程中是將文件以流的形式提交到服務(wù)器端的。對此感興趣的小伙伴可以了解一下

文件的上傳與下載（一）

在實(shí)現(xiàn)文件上傳和下載之前我們需要做一些準(zhǔn)備工作，在Apache官網(wǎng)去下載文件上傳下載的兩個(gè)組件，下載鏈接這里給出：common-fileupload組件下載：http://commons.apache.org/proper/commons-fileupload/

common-io組件下載：http://commons.apache.org/proper/commons-io/根據(jù)自己需求下載對應(yīng)版本

一、創(chuàng)建工程

將所需要的兩個(gè)開發(fā)包導(dǎo)入到工程項(xiàng)目中如圖：

二、代碼編寫

1.前端頁面代碼

1）. 在WebRoot目錄下新建一個(gè)fileUpload.jsp頁面，用來上傳文件

<%@ 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="<%=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="styles.css">
 -->

 </head>

 <body>
 <!-- 文件上傳表單的提交方式必須是“post” 編碼類型必須為：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="上傳文件">

 </form>

 </body>
</html>

2）.新建一個(gè)fileUploadResult.jsp頁面用來顯示結(jié)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="<%=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="styles.css">
 -->

 </head>

 <body>
 <%--
 <%
  //獲取流對象
  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. 編寫上傳文件處理的Servlet代碼

1) UploadServlet.java代碼如下：

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 {


  //得到上傳文件的保存目錄，將上傳的文件放在webRoot目錄下（但是一般為了安全放在WEB-INF目錄下，不允許外界直接訪問，保證上傳的安全）
  String path = this.getServletContext().getRealPath("/upload");

  File file = new File(path);

  //判斷上傳文件的保存目錄是否存在
  if(!file.exists() && !file.isDirectory()){
   System.out.println(path + "目錄不存在，需要?jiǎng)?chuàng)建！");
   //創(chuàng)建目錄
   file.mkdir();
  }
  //消息提示
  String message = "";
  try{
   //使用Apache文件上傳組件處理文件上傳步驟：
   //1.創(chuàng)建一個(gè)DiskFileItemFactory工廠
   DiskFileItemFactory factory = new DiskFileItemFactory();
   //2.創(chuàng)建一個(gè)文件上傳解析器
   ServletFileUpload upload = new ServletFileUpload(factory);
   //解決中文亂碼
   upload.setHeaderEncoding("UTF-8");
   //3.判斷提交的數(shù)據(jù)普通表單的數(shù)據(jù)還是帶文件上傳的表單
   if(!upload.isMultipartContent(request)){
    //如果是表單數(shù)據(jù)普通表單,則按照傳統(tǒng)方式獲取數(shù)據(jù)
    return ;
   }
   //4.使用ServletFileUpload解析器解析上傳數(shù)據(jù)，解析結(jié)果返回的是一個(gè)List<FileItem>集合，每一個(gè)FileItem對應(yīng)一個(gè)Form表單的輸入項(xiàng)
   List<FileItem> list = upload.parseRequest(request);
   for(FileItem item : list){
    //如果fileItem中封裝的是普通輸入項(xiàng)的數(shù)據(jù)
    if(item.isFormField()){
     //獲取字段名字
     String name = item.getFieldName();
     //解決普通輸入項(xiàng)中中文亂碼問題
     String value = item.getString("UTF-8");//value = new String(value.getBytes("iso8859-1"),"UTF-8");
     System.out.println(name + " = " + value);
    }else{ //如果表單中提交的是上傳文件
     //獲得上傳的文件名稱
     String filename = item.getName();
     System.out.println(filename);
     if(filename == null || filename.trim().equals(" ")){
      continue;
     }
     //注意：不同的瀏覽器提交的文件名稱是不一樣的，有些瀏覽器提交的文件會(huì)帶有路徑，如“D:\\project\WebRoot\hello.jsp”，有一些是單純的文件名：hello.jsp
     //去掉獲取到文件名中的路徑名，保留單純的文件名
     filename = filename.substring(filename.lastIndexOf("\\") + 1);
     //獲取item中的上傳文件的輸入流
     InputStream in = item.getInputStream();
     //創(chuàng)建一個(gè)文件輸入流
     FileOutputStream out = new FileOutputStream(path + "\\" + filename);
     //創(chuàng)建一個(gè)緩沖區(qū)
     byte buffer[] = new byte[1024];
     //判斷輸入流中的數(shù)據(jù)是否已經(jīng)讀取完畢的標(biāo)志位
     int len = 0;
     //循環(huán)將輸入流讀入到緩沖區(qū)當(dāng)中，（len = in.read(buffer)>0）就表示in里面還有數(shù)據(jù)存在
     while((len = in.read(buffer)) > 0){
      //使用FileOutputStream輸出流將緩沖區(qū)的數(shù)據(jù)寫入到指定的目錄（path+"\\"+filename）當(dāng)中
      out.write(buffer, 0, len);
     }
     //關(guān)閉輸入流
     in.close();
     //關(guān)閉輸出流
     out.close();
     //刪除處理文件上傳生成的臨時(shí)文件
     item.delete();
     message = "文件上傳成功!";


    }
   }

  }catch(Exception e){
   message = "文件上傳失敗！";
   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>

結(jié)果：