ajax上传文件到本地

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import java.io.File;
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.annotation.WebServlet;
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;

/**
* Servlet implementation class CoreServlet
*/
@WebServlet(asyncSupported = true, urlPatterns = { "/CoreServlet" })
public class CoreServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* @see HttpServlet#HttpServlet()
*/
public CoreServlet() {
super();
// TODO Auto-generated constructor stub
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doPost(request, response);
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
response.setContentType("text/html; charset=utf-8");
//获得磁盘文件条目工厂
DiskFileItemFactory factory = new DiskFileItemFactory();
//获取文件需要上传到的路径
String path = this.getServletContext().getRealPath("/temp");

//如果没以下两行设置的话，上传大的 文件 会占用 很多内存，
//设置暂时存放的 存储室 , 这个存储室，可以和 最终存储文件 的目录不同
/**
* 原理 它是先存到 暂时存储室，然后在真正写到 对应目录的硬盘上，
* 按理来说 当上传一个文件时，其实是上传了两份，第一个是以 .tem 格式的
* 然后再将其真正写到 对应目录的硬盘上
*/
factory.setRepository(new File(path));
//设置 缓存的大小，当上传文件的容量超过该缓存时，直接放到 暂时存储室
factory.setSizeThreshold(1024*1024) ;

//高水平的API文件上传处理
ServletFileUpload upload = new ServletFileUpload(factory);

try {
//可以上传多个文件
List<FileItem> list = (List<FileItem>)upload.parseRequest(request);

for(FileItem item : list)
{
//获取表单的属性名字
String name = item.getFieldName();

//如果获取的 表单信息是普通的 文本 信息
if(item.isFormField())
{
//获取用户具体输入的字符串 ，名字起得挺好，因为表单提交过来的是 字符串类型的
String value = item.getString() ;

request.setAttribute(name, value);
}
//对传入的非 简单的字符串进行处理 ，比如说二进制的 图片，电影这些
else
{
/**
* 以下三步，主要获取 上传文件的名字
*/
//获取路径名
String value = item.getName() ;
//索引到最后一个反斜杠
int start = value.lastIndexOf("\\");
//截取 上传文件的 字符串名字，加1是 去掉反斜杠，
String filename = value.substring(start+1);

request.setAttribute(name, filename);

//真正写到磁盘上
//它抛出的异常 用exception 捕捉

//item.write( new File(path,filename) );//第三方提供的

//手动写的
OutputStream out = new FileOutputStream(new File(path,filename));

InputStream in = item.getInputStream() ;

int length = 0 ;
byte [] buf = new byte[1024] ;

System.out.println("获取上传文件的总共的容量："+item.getSize());

// in.read(buf) 每次读到的数据存放在   buf 数组中
while( (length = in.read(buf) ) != -1)
{
//在   buf 数组中 取出数据 写到 （输出流）磁盘上
out.write(buf, 0, length);

}
in.close();
out.close();
response.getWriter().write("{'success':true}");
}
}

} catch (FileUploadException e) {
// TODO Auto-generated catch block
response.getWriter().write("捕捉到异常：" + e.getMessage());
e.printStackTrace();
}
catch (Exception e) {
// TODO Auto-generated catch block
response.getWriter().write("捕捉到异常：" + e.getMessage());
e.printStackTrace();
//e.printStackTrace();
}

}

}
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<span style="font-family:Microsoft YaHei;font-size:18px;background-color: rgb(204, 204, 204);">以上部分为后台代码，需要两个jar包，commons-fileupload,commons-io</span>

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<span style="font-family:Microsoft YaHei;font-size:18px;background-color: rgb(204, 204, 204);">以下是前端页面代码</span>

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<pre name="code" class="html"><span style="font-family:Microsoft YaHei;font-size:18px;background-color: rgb(204, 204, 204);"><!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>上传文件</title>
<script type="text/javascript">
function uploadFile() {
var xmlhttp;
if (window.XMLHttpRequest) {// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
} else {// code for IE6, IE5
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}

xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById('myDiv').innerHTML=xmlhttp.responseText;
}
}
var formdata = new FormData(document.getElementById('form1'));
xmlhttp.open("POST", "./CoreServlet", true);
xmlhttp.send(formdata);
}
</script>
</head>
<body>

<form id="form1" enctype="multipart/form-data">
选择要上传的文件：<input type="file" name="file" /><br>
<button type="button" onclick="uploadFile()">发送</button>
</form>
<br>

<div id="myDiv"><h2></h2></div>
</body>
</html></span>

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