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借助commons

一、文件上传的原理分析

    1、文件上传的必要前提

      a、表单的method必须是post

      b、表单的enctype属性必须是multipart/form-data类型的。

      enctype默认值:application/x-www-form-urlencoded

      作用:告知服务器,请求正文的MIME类型

      application/x-www-form-urlencoded   :   username=abc&password=123

      ServletRequest.getParameter(String name);该方法是专门读取该类型的方法

      

      multipart/form-data:

      借助commons

    2、借助commons-fileupload组件实现文件的上传

      a、拷贝jar包:commons-fileupload.jar   commons-io.jar 

      b、实现原理

      借助commons

    3、乱码问题

      a、普通字段的乱码

        FileItem.getString(String charset);编码要和客户端一致

      b、上传的中文文件名乱码

        request.setCharacterEncoding("UTF-8");编码要和客户端一致

    4、具体实现

          

前台upload.jsp代码如下<%@ 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>    <meta http-equiv="pragma" content="no-cache">  <meta http-equiv="cache-control" content="no-cache">  <meta http-equiv="expires" content="0">  <!--  <link rel="stylesheet" type="text/css" href="styles.css">  --> </head> <body>  <form action="${pageContext.request.contextPath}/servlet/UploadServlet3" method="post" enctype="multipart/form-data">    name:<input name="name"/><br/>    file1:<input type="file" name="f1"/><br/>    file2:<input type="file" name="f2"/><br/>    <input type="submit" value="上传">  </form> </body></html>后台servlet代码package com.itheima.servlet;import java.io.File;import java.io.IOException;import java.io.PrintWriter;import java.io.UnsupportedEncodingException;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.FileUploadBase;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.FilenameUtils;//详解public class UploadServlet3 extends HttpServlet {  public void doGet(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {    request.setCharacterEncoding("UTF-8");    response.setContentType("text/html;charset=UTF-8");    PrintWriter out = response.getWriter();    System.out.print(request.getRemoteAddr());    boolean isMultipart = ServletFileUpload.isMultipartContent(request);    if(!isMultipart){      throw new RuntimeException("请检查您的表单的enctype属性,确定是multipart/form-data");    }    DiskFileItemFactory dfif = new DiskFileItemFactory();    ServletFileUpload parser = new ServletFileUpload(dfif);    //    parser.setFileSizeMax(3*1024*1024);//设置单个文件上传的大小   // parser.setSizeMax(6*1024*1024);//多文件上传时总大小限制        List<FileItem> items = null;    try {      items = parser.parseRequest(request);    }catch(FileUploadBase.FileSizeLimitExceededException e) {      out.write("上传文件超出了3M");      return;    }catch(FileUploadBase.SizeLimitExceededException e){      out.write("总文件超出了6M");      return;    }catch (FileUploadException e) {      e.printStackTrace();      throw new RuntimeException("解析上传内容失败,请重新试一下");    }        //处理请求内容    if(items!=null){      for(FileItem item:items){        if(item.isFormField()){          processFormField(item);        }else{          processUploadField(item);        }      }    }        out.write("上传成功!");  }  private void processUploadField(FileItem item) {    try {      String fileName = item.getName();                  //用户没有选择上传文件时      if(fileName!=null&&!fileName.equals("")){        fileName = UUID.randomUUID().toString()+"_"+FilenameUtils.getName(fileName);                //扩展名        String extension = FilenameUtils.getExtension(fileName);        //MIME类型        String contentType = item.getContentType();                if(contentType.startsWith("image/")){                //分目录存储:日期解决  //      Date now = new Date();  //      DateFormat df = new SimpleDateFormat("yyyy-MM-dd");  //        //      String childDirectory = df.format(now);                        //按照文件名的hashCode计算存储目录        String childDirectory = makeChildDirectory(getServletContext().getRealPath("/WEB-INF/files/"),fileName);                String storeDirectoryPath = getServletContext().getRealPath("/WEB-INF/files/"+childDirectory);        File storeDirectory = new File(storeDirectoryPath);        if(!storeDirectory.exists()){          storeDirectory.mkdirs();        }        System.out.println(fileName);        item.write(new File(storeDirectoryPath+File.separator+fileName));//删除临时文件        }      }    } catch (Exception e) {      throw new RuntimeException("上传失败,请重试");    }      }  //计算存放的子目录  private String makeChildDirectory(String realPath, String fileName) {    int hashCode = fileName.hashCode();    int dir1 = hashCode&0xf;// 取1~4位    int dir2 = (hashCode&0xf0)>>4;//取5~8位        String directory = ""+dir1+File.separator+dir2;    File file = new File(realPath,directory);    if(!file.exists())      file.mkdirs();        return directory;  }  private void processFormField(FileItem item) {    String fieldName = item.getFieldName();//字段名    String fieldValue;    try {      fieldValue = item.getString("UTF-8");    } catch (UnsupportedEncodingException e) {      throw new RuntimeException("不支持UTF-8编码");    }    System.out.println(fieldName+"="+fieldValue);  }  public void doPost(HttpServletRequest request, HttpServletResponse response)      throws ServletException, IOException {    doGet(request, response);  }}

    5、关于临时文件问题

    a、DiskFileItemFactory

      public void setRepository(File repository):设置临时文件的存放目录

      public void setSizeThreshold(int sizeThreshold):设置缓存的大小

    b、     

      文件上传时,自己用IO流处理,一定要在流关闭后删除临时文件。FileItem.delete()

      建议使用:FileItem.writer(File f).会自动删除临时文件。

    6、限制文件的大小

    a、 

      ServletFileUpload.setFileSizeMax(3*1024*1024);//设置单个文件上传的大小

    b、

      ServletFileUpload.setSizeMax(6*1024*1024);//多文件上传时总大小限制




原标题:借助commons

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