ajax上傳文件到本地

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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");
		//獲得磁盤文件條目工廠
		DiskFileItemFactory factory = new DiskFileItemFactory();
		//獲取文件需要上傳到的路徑
		String path = this.getServletContext().getRealPath("/temp");
		
		
		//如果沒以下兩行設置的話，上傳大的 文件 會佔用 很多內存，
		//設置暫時存放的 存儲室 , 這個存儲室，可以和 最終存儲文件 的目錄不同
		/**
		 * 原理 它是先存到 暫時存儲室，然後在真正寫到 對應目錄的硬盤上， 
		 * 按理來說 當上傳一個文件時，其實是上傳了兩份，第一個是以 .tem 格式的 
		 * 然後再將其真正寫到 對應目錄的硬盤上
		 */
		factory.setRepository(new File(path));
		//設置 緩存的大小，當上傳文件的容量超過該緩存時，直接放到 暫時存儲室
		factory.setSizeThreshold(1024*1024) ;
		
		//高水平的API文件上傳處理
		ServletFileUpload upload = new ServletFileUpload(factory);
		
		
		try {
			//可以上傳多個文件
			List<FileItem> list = (List<FileItem>)upload.parseRequest(request);
			
			for(FileItem item : list)
			{
				//獲取表單的屬性名字
				String name = item.getFieldName();
				
				//如果獲取的 表單信息是普通的 文本 信息
				if(item.isFormField())
				{					
					//獲取用戶具體輸入的字符串 ，名字起得挺好，因爲表單提交過來的是 字符串類型的
					String value = item.getString() ;
					
					request.setAttribute(name, value);
				}
				//對傳入的非 簡單的字符串進行處理 ，比如說二進制的 圖片，電影這些
				else
				{
					/**
					 * 以下三步，主要獲取 上傳文件的名字
					 */
					//獲取路徑名
					String value = item.getName() ;
					//索引到最後一個反斜槓
					int start = value.lastIndexOf("\\");
					//截取 上傳文件的 字符串名字，加1是 去掉反斜槓，
					String filename = value.substring(start+1);
					
					request.setAttribute(name, filename);
					
					//真正寫到磁盤上
					//它拋出的異常 用exception 捕捉
					
					//item.write( new File(path,filename) );//第三方提供的
					
					//手動寫的
					OutputStream out = new FileOutputStream(new File(path,filename));
					
					InputStream in = item.getInputStream() ;
					
					int length = 0 ;
					byte [] buf = new byte[1024] ;
					
					System.out.println("獲取上傳文件的總共的容量："+item.getSize());

					// in.read(buf) 每次讀到的數據存放在   buf 數組中
					while( (length = in.read(buf) ) != -1)
					{
						//在   buf 數組中 取出數據 寫到 （輸出流）磁盤上
						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("捕捉到異常：" + e.getMessage());
			e.printStackTrace();
		}
		catch (Exception e) {
			// TODO Auto-generated catch block
			response.getWriter().write("捕捉到異常：" + 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);">以上部分爲後臺代碼，需要兩個jar包，commons-fileupload,commons-io</span>

<span style="font-family:Microsoft YaHei;font-size:18px;background-color: rgb(204, 204, 204);">-----------------------------------------------------------------這個不是分割線-------------------------------------------------------------------</span>

<span style="font-family:Microsoft YaHei;font-size:18px;background-color: rgb(204, 204, 204);">以下是前端頁面代碼</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>上傳文件</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">
		選擇要上傳的文件：<input type="file" name="file" /><br>
		<button type="button" onclick="uploadFile()">發送</button>
	</form>
	<br>
	
	<div id="myDiv"><h2></h2></div>
</body>
</html></span>

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