// JavaScript Document
jQuery.extend({

    createUploadIframe: function(id, uri)
 {
   //create frame
            var frameId = ‘jUploadFrame‘ + id;
            
            if(window.ActiveXObject) {
                //var io = document.createElement(‘<iframe id="‘ + frameId + ‘" name="‘ + frameId + ‘" />‘);
                if(jQuery.browser.version=="9.0" || jQuery.browser.version=="10.0"){  
                    var io = document.createElement(‘iframe‘);  
                    io.id = frameId;  
                    io.name = frameId;  
                }else if(jQuery.browser.version=="6.0" || jQuery.browser.version=="7.0" || jQuery.browser.version=="8.0"){  
                    var io = document.createElement(‘<iframe id="‘ + frameId + ‘" name="‘ + frameId + ‘" />‘);  
                    if(typeof uri== ‘boolean‘){
                        io.src = ‘javascript:false‘;
                    }
                    else if(typeof uri== ‘string‘){
                        io.src = uri;
                    }
                }
            }else {
                var io = document.createElement(‘iframe‘);
                io.id = frameId;
                io.name = frameId;
            }
            io.style.position = ‘absolute‘;
            io.style.top = ‘-1000px‘;
            io.style.left = ‘-1000px‘;

            document.body.appendChild(io);

            return io;   
    },
    createUploadForm: function(id, fileElementId, data)
 {
  //create form 
  var formId = ‘jUploadForm‘ + id;
  var fileId = ‘jUploadFile‘ + id;
  var form = jQuery(‘<form  action="" method="POST" name="‘ + formId + ‘" id="‘ + formId + ‘" enctype="multipart/form-data"></form>‘); 
  var oldElement = jQuery(‘#‘ + fileElementId);
  var newElement = jQuery(oldElement).clone();
  jQuery(oldElement).attr(‘id‘, fileId);
  jQuery(oldElement).before(newElement);
  jQuery(oldElement).appendTo(form);
  
  //add data
  if(data) { 
    for (var i in data) { 
        $(‘<input type="hidden" name="‘ + i + ‘" value="http://www.mamicode.com/‘ + data[i] + ‘" />‘).appendTo(form); 
    } 
  }
  //set attributes
  jQuery(form).css(‘position‘, ‘absolute‘);
  jQuery(form).css(‘top‘, ‘-1200px‘);
  jQuery(form).css(‘left‘, ‘-1200px‘);
  jQuery(form).appendTo(‘body‘);  
  return form;
    },

    ajaxFileUpload: function(s) {
        // TODO introduce global settings, allowing the client to modify them for all requests, not only timeout  
        s = jQuery.extend({}, jQuery.ajaxSettings, s);
        var id = s.id;        
        //var id = s.fileElementId;        
        var form = jQuery.createUploadForm(id, s.fileElementId,s.data);
        var io = jQuery.createUploadIframe(id, s.secureuri);
        var frameId = ‘jUploadFrame‘ + id;
        var formId = ‘jUploadForm‘ + id;  
        
        if( s.global && ! jQuery.active++ ){
            // Watch for a new set of requests
            jQuery.event.trigger( "ajaxStart" );
        }            
        var requestDone = false;
        // Create the request object
        var xml = {};   
        if( s.global ){
         jQuery.event.trigger("ajaxSend", [xml, s]);
        }            
        
        var uploadCallback = function(isTimeout){  
            // Wait for a response to come back 
            var io = document.getElementById(frameId);
            try{    
                if(io.contentWindow){
                    xml.responseText = io.contentWindow.document.body?io.contentWindow.document.body.innerHTML:null;
                    xml.responseXML = io.contentWindow.document.XMLDocument?io.contentWindow.document.XMLDocument:io.contentWindow.document;
                }else if(io.contentDocument){
                    xml.responseText = io.contentDocument.document.body?io.contentDocument.document.body.innerHTML:null;
                    xml.responseXML = io.contentDocument.document.XMLDocument?io.contentDocument.document.XMLDocument:io.contentDocument.document;
                }      
            }catch(e){
                jQuery.handleError(s, xml, null, e);
            }
            if( xml || isTimeout == "timeout"){    
                requestDone = true;
                var status;
                try {
                    status = isTimeout != "timeout" ? "success" : "error";
                    // Make sure that the request was successful or notmodified
                    if( status != "error" ){
                        // process the data (runs the xml through httpData regardless of callback)
                        var data =http://www.mamicode.com/ jQuery.uploadHttpData( xml, s.dataType );                        
                        if( s.success ){
                            // ifa local callback was specified, fire it and pass it the data
                            s.success( data, status );
                        };                 
                        if( s.global ){
                            // Fire the global callback
                            jQuery.event.trigger( "ajaxSuccess", [xml, s] );
                        };                            
                    } else{
                     jQuery.handleError(s, xml, status);
                    }
                        
                } catch(e){
                    status = "error";
                    jQuery.handleError(s, xml, status, e);
                };                
                if( s.global ){
                    // The request was completed
                    jQuery.event.trigger( "ajaxComplete", [xml, s] );
                };

                // Handle the global AJAX counter
                if(s.global && ! --jQuery.active){
                 jQuery.event.trigger("ajaxStop");
                };
                if(s.complete){
                  s.complete(xml, status);
                };                 

                jQuery(io).unbind();
                setTimeout(function(){
                try{
                    jQuery(io).remove();
                    jQuery(form).remove(); 
                }catch(e){
                      jQuery.handleError(s, xml, null, e);
                }}, 100);
                xml = null;
            };
        }
        // Timeout checker
        if( s.timeout > 0 ){
            setTimeout(function(){if(!requestDone ){uploadCallback( "timeout" );}}, s.timeout);
        }
        try{
            var form = jQuery(‘#‘ + formId);
            jQuery(form).attr(‘action‘, s.url);
            jQuery(form).attr(‘method‘, ‘POST‘);
            jQuery(form).attr(‘target‘, frameId);
            if(form.encoding){
                form.encoding = ‘multipart/form-data‘;    
            }else{    
                form.enctype = ‘multipart/form-data‘;
            }   
            jQuery(form).submit();

        } catch(e){   
            jQuery.handleError(s, xml, null, e);
        }
        /*if(window.attachEvent){
            document.getElementById(frameId).attachEvent(‘onload‘, uploadCallback);
        }
        else{
            document.getElementById(frameId).addEventListener(‘load‘, uploadCallback, false);
        }   */
        jQuery(‘#‘ + frameId).load(uploadCallback);
        return {abort: function () {}}; 

    },

    uploadHttpData: function( r, type ) {
        var data = http://www.mamicode.com/!type;
        data = type == "xml" || data ? r.responseXML : r.responseText;
        // ifthe type is "script", eval it in global context
        if( type == "script" ){
         jQuery.globalEval( data );
        }
            
        // Get the JavaScript object, ifJSON is used.
        if( type == "json" ){
            data = r.responseText;  
            var start = data.indexOf(">");  
            if(start != -1) {  
              var end = data.indexOf("<", start + 1);  
              if(end != -1) {  
                data = data.substring(start + 1, end);  
               }  
            }  
            eval( "data = "http://www.mamicode.com/+ data);  
        }
            
        // evaluate scripts within html
        if( type == "html" ){
         jQuery("<div>").html(data).evalScripts();
        }
            
        return data;
    },
    /*handleError: function( s, xml, status, e ) {
        // If a local callback was specified, fire it
        if ( s.error )
            s.error( xml, status, e );

        // Fire the global callback
        if ( s.global )
            jQuery.event.trigger( "ajaxError", [xml, s, e] );
    }*/
    handleError: function( s, xhr, status, e ) {
        // If a local callback was specified, fire it
        if ( s.error ) {
            s.error.call( s.context || s, xhr, status, e );
        }
        // Fire the global callback
        if ( s.global ) {
            (s.context ? jQuery(s.context) : jQuery.event).trigger("ajaxError", [xhr, s, e] );
        }
    }
});

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Ajax File Uploader Plugin For Jquery</title>
<script type="text/javascript" src="http://www.mamicode.com/jquery.js"></script>
<script type="text/javascript" src="http://www.mamicode.com/ajaxfileupload.js"></script>
<script type="text/javascript">
    function ajaxFileUpload() {
        $.ajaxFileUpload({
            url : ‘upload‘,
            secureuri : false,
            fileElementId : ‘fileToUpload‘,
            dataType : ‘json‘,
            data : {username : $("#username").val()},
            success : function(data, status) {
                $(‘#viewImg‘).attr(‘src‘,data.picUrl);
            },
            error : function(data, status, e) {
                alert(‘上传出错‘);
            }
        })

        return false;

    }
</script>
</head>

<body>
    <h1>选择图片后,点击按钮上传</h1>
    <input id="fileToUpload" type="file" size="45" name="fileToUpload"
        class="input">
    <button class="button" onclick="ajaxFileUpload()">上传</button>
    <br>
    <img id="viewImg">
</body>
</html>

package upload;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Date;
import java.util.List;

import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
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 具体步骤： 1）获得磁盘文件条目工厂 DiskFileItemFactory 要导包 2） 利用 request 获取 真实路径
 * ，供临时文件存储，和 最终文件存储 ，这两个存储位置可不同，也可相同 3）对 DiskFileItemFactory 对象设置一些 属性
 * 4）高水平的API文件上传处理 ServletFileUpload upload = new ServletFileUpload(factory);
 * 目的是调用 parseRequest（request）方法 获得 FileItem 集合list ，
 * 
 * 5）在 FileItem 对象中 获取信息， 遍历， 判断 表单提交过来的信息 是否是 普通文本信息 另做处理 6） 第一种. 用第三方 提供的
 * item.write( new File(path,filename) ); 直接写到磁盘上 第二种. 手动处理
 * 
 */
public class UploadProcessorServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    // 保存文件的目录
    private static String PATH_FOLDER = "/";
    // 存放临时文件的目录
    private static String TEMP_FOLDER = "/";
    
    
    @Override
    public void init(ServletConfig config) throws ServletException {
        ServletContext servletCtx = config.getServletContext();
        // 初始化路径
        // 保存文件的目录
        PATH_FOLDER = servletCtx.getRealPath("/upload");
        // 存放临时文件的目录,存放xxx.tmp文件的目录
        TEMP_FOLDER = servletCtx.getRealPath("/uploadTemp");
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8"); // 设置编码
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");
        // 获得磁盘文件条目工厂
        DiskFileItemFactory factory = new DiskFileItemFactory();
        
        // 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(TEMP_FOLDER));
        // 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 {
            // 提交上来的信息都在这个list里面
            // 这意味着可以上传多个文件
            // 请自行组织代码
            List<FileItem> list = upload.parseRequest(request);
            // 获取上传的文件
            FileItem item = getUploadFileItem(list);
            // 获取文件名
            String filename = getUploadFileName(item);
            // 保存后的文件名
            String saveName = new Date().getTime() + filename.substring(filename.lastIndexOf("."));
            // 保存后图片的浏览器访问路径
            String picUrl = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+request.getContextPath()+"/upload/"+saveName;

            System.out.println("存放目录:" + PATH_FOLDER);
            System.out.println("文件名:" + filename);
            System.out.println("浏览器访问路径:" + picUrl);

            // 真正写到磁盘上
            item.write(new File(PATH_FOLDER, saveName)); // 第三方提供的
            
            PrintWriter writer = response.getWriter();
            
            writer.print("{");
            writer.print("msg:\"文件大小:"+item.getSize()+",文件名:"+filename+"\"");
            writer.print(",picUrl:\"" + picUrl + "\"");
            writer.print("}");
            
            writer.close();
        
        } catch (FileUploadException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }
    
    private FileItem getUploadFileItem(List<FileItem> list) {
        for (FileItem fileItem : list) {
            if(!fileItem.isFormField()) {
                return fileItem;
            }
        }
        return null;
    }
    
    private String getUploadFileName(FileItem item) {
        // 获取路径名
        String value =http://www.mamicode.com/ 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);
        
        return filename;
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
     *      response)
     */
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        this.doGet(request, response);
    }

}