Java上传下载

2021-05-12 11:03:40
633次极悦

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

1.创建工程

将所需要的两个开发包导入到工程项目中如图：

2.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="<%=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="<%=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>
    <%--
    <%
        //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:\\project\WebRoot\hello.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：