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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