一、文件上传原理
1、文件上传的前提:
a、form表单的method必须是post
b、form表单的enctype必须是multipart/form-data(决定了POST请求方式,请求正文的数据类型)
c、form中提供input的type是file类型的文件上传域
二、利用第三方组件实现文件上传
1、commons-fileupload组件:
jar:commons-fileupload.jar
commons-io.jar
2、核心类或接口
DiskFileItemFactory:设置环境
public void setSizeThreshold(int sizeThreshold) :设置缓冲区大小。默认是10Kb。
当上传的文件超出了缓冲区大小,fileupload组件将使用临时文件缓存上传文件
public void setRepository(java.io.File repository):设置临时文件的存放目录。默认是系统的临时文件存放目录。
ServletFileUpload:核心上传类(主要作用:解析请求的正文内容)
boolean isMultipartContent(HttpServletRequest?request):判断用户的表单的enctype是否是multipart/form-data类型的。
List parseRequest(HttpServletRequest request):解析请求正文中的内容
setFileSizeMax(4*1024*1024);//设置单个上传文件的大小
upload.setSizeMax(6*1024*1024);//设置总文件大小
FileItem:代表表单中的一个输入域。
boolean isFormField():是否是普通字段
String getFieldName:获取普通字段的字段名
String getString():获取普通字段的值
InputStream getInputStream():获取上传字段的输入流
String getName():获取上传的文件名
实例:先在WEB-INF目录下建一个files文件夹,也就是文件都要上传到这里,也是避免其他人直接访问
1.获取files的真实路径
String storePath = getServletContext().getRealPath("/WEB-INF/files");
2.设置环境
DiskFileItemFactory factory = new DiskFileItemFactory();//用默认的缓存和临时文件存储的地方
3.判断表单传送方式
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boolean isMultipart = ServletFileUpload.isMultipartContent(request);
if (!isMultipart)
{
System.out.println( "上传方式错误!" );
return ;
}
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4.文件上传核心类
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ServletFileUpload upload = new ServletFileUpload(factory); 5 .解析
//解析
List<FileItem> items = upload.parseRequest(request);
for (FileItem item: items)
{
if (item.isFormField()){ //普通字段,表单提交过来的
String fieldName = item.getFieldName(); //表单信息的字段名
String fieldValue = item.getString(); //表单信息字段值
System.out.println(fieldName+ "=" +fieldValue);
} else //文件处理
{
InputStream in = item.getInputStream();
//上传文件名 C:\Users\Administrator\Desktop\a.txt
String name = item.getName(); //只需要 a.txt
String fileName = name.substring(name.lastIndexOf( "\\" )+ 1 );
//构建输出流
String storeFile = storePath+ "\\" +fileName; //上传文件的保存地址
OutputStream out = new FileOutputStream(storeFile);
byte [] b = new byte [ 1024 ];
int len = - 1 ;
while ((len=in.read(b))!=- 1 )
{
out.write(b, 0 , len);
}
in.close(); //关闭流
out.close();
}
}
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写一个表单
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<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
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 '1.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 >
< form action = "${pageContext.request.contextPath}/servlet/UploadServlet2" method = "post" enctype = "multipart/form-data" >
用户名< input type = "text" name = "username" /> < br />
< input type = "file" name = "f1" />< br />
< input type = "file" name = "f2" />< br />
< input type = "submit" value = "保存" />
</ form >
</ body >
</ html >
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写一个提交servlet:UploadServlet2
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package com.liuzhen.upload;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
//文件上传入门案例
public class UploadServlet2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置编码
request.setCharacterEncoding( "UTF-8" );
response.setContentType( "text/html;charset=UTF-8" );
try {
//上传文件的路徑
String storePath = getServletContext().getRealPath( "/WEB-INF/files" );
//设置环境
DiskFileItemFactory factory = new DiskFileItemFactory();
//判断表单传送方式 form enctype=multipart/form-data
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
if (!isMultipart)
{
System.out.println( "上传方式错误!" );
return ;
}
ServletFileUpload upload = new ServletFileUpload(factory);
//解析
List<FileItem> items = upload.parseRequest(request);
for (FileItem item: items)
{
if (item.isFormField()){ //普通字段,表单提交过来的
String fieldName = item.getFieldName(); //表单信息的字段名
String fieldValue = item.getString(); //表单信息字段值
System.out.println(fieldName+ "=" +fieldValue);
} else //文件处理
{
InputStream in = item.getInputStream();
//上传文件名 C:\Users\Administrator\Desktop\a.txt
String name = item.getName(); //只需要 a.txt
String fileName = name.substring(name.lastIndexOf( "\\" )+ 1 );
//构建输出流
String storeFile = storePath+ "\\" +fileName; //上传文件的保存地址
OutputStream out = new FileOutputStream(storeFile);
byte [] b = new byte [ 1024 ];
int len = - 1 ;
while ((len=in.read(b))!=- 1 )
{
out.write(b, 0 , len);
}
in.close(); //关闭流
out.close();
}
}
} catch (FileUploadException e) {
throw new RuntimeException(e);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
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上传的文件是在Tomcat应用中。
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持服务器之家。