最近在做一个项目需要实现异步上传图片，在网上找了很多资料后，采用了ajaxfileupload可以实现，以下是核心代码：

jsp:

<!-- 上传窗口 -->
<div id="uploadPicWindow" class="easyui-window" title="上传图片"  style="width:420px;height:220px;padding:20px;background:#fafafa;" data-options="iconCls:'icon-save',closable:true, collapsible:true,minimizable:true,maximizable:true">
<form id="picForm" action="" method="post">
<div style="margin-bottom:20px">
图片名称:
<input type="text" name="name" id="picName" class="easyui-textbox" style="width:80%" data-options="required:true,validType:'stringCheck'"/>
</div>
<br/>
<div style="margin-bottom:20px">
选择图片:
<input type="file" name="file" id="file" data-options="prompt:'Choose a file...'" style="width:80%"/>
</div>
<div id="picTip"></div>
<div id="formWindowfooterPic1" style="padding:5px;text-align:right;"> 
<a href="#" onclick="submitPic();" class="easyui-linkbutton" data-options="iconCls:'icon-save'">提交</a>
</div>
</form>
</div>

js:

//新建或编辑 保存提交
function submitPic(){
if(!$("#picForm").form('validate')){
return false;
}
var projectId = $("#projectId").val();
var name=$("#picName").val();
var type="1";//展示图片
var f = $("#file").val();
if(f==null||f==""){
$("#picTip").html("<span style='color:Red'>错误提示:上传文件不能为空,请重新选择文件</span>");
return false;
  }else{
   var extname = f.substring(f.lastIndexOf(".")+1,f.length);
   extname = extname.toLowerCase();//处理了大小写
   if(extname!= "jpeg"&&extname!= "jpg"&&extname!= "gif"&&extname!= "png"){
 $("#picTip").html("<span style='color:Red'>错误提示:格式不正确,支持的图片格式为：JPEG、GIF、PNG！</span>");
     return false;
    }
  }
 var file = document.getElementById("file").files;  
 var size = file[0].size;
 if(size>2097152){
  $("#picTip").html("<span style='color:Red'>错误提示:所选择的图片太大，图片大小最多支持2M!</span>"); 
  return false;
  }
ajaxFileUploadPic(projectId,name,type);
}

function ajaxFileUploadPic(projectId,name,type) {
$.ajaxFileUpload({
url : '${ctx}/projectPic/saveorupdate.jhtml?projectId='+projectId+'&name='+name+'&type='+type, //用于文件上传的服务器端请求地址
secureuri : false, //一般设置为false
fileElementId : 'file', //文件上传空间的id属性  <input type="file" id="file" name="file" />
type : 'post',
dataType : 'json', //返回值类型 一般设置为json
success : function(data, status) //服务器成功响应处理函数
{
 $("#picList").datagrid('reload');
     $('#uploadPicWindow').window('close');
    // alert(data.msg);
},
error : function(data, status, e)//服务器响应失败处理函数
{
 $("#picList").datagrid('reload');
     $('#uploadPicWindow').window('close');
    // alert(data.msg);
}
});
return false;
}

jQuery.extend({

    createUploadIframe: function(id, uri)
{
//create frame
            var frameId = 'jUploadFrame' + id;
            var iframeHtml = '<iframe id="' + frameId + '" name="' + frameId + '" style="position:absolute; top:-9999px; left:-9999px"';
if(window.ActiveXObject)
{
                if(typeof uri== 'boolean'){
iframeHtml += ' src="' + 'javascript:false' + '"';

                }
                else if(typeof uri== 'string'){
iframeHtml += ' src="' + uri + '"';

                }
}
iframeHtml += ' />';
jQuery(iframeHtml).appendTo(document.body);

            return jQuery('#' + frameId).get(0);
    },
    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>');
if(data)
{
for(var i in data)
{
jQuery('<input type="hidden" name="' + i + '" value="' + data[i] + '" />').appendTo(form);
}
}
var oldElement = jQuery('#' + fileElementId);
var newElement = jQuery(oldElement).clone();
jQuery(oldElement).attr('id', fileId);
jQuery(oldElement).before(newElement);
jQuery(oldElement).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 = new Date().getTime()        
var form = jQuery.createUploadForm(id, s.fileElementId, (typeof(s.data)=='undefined'?false:s.data));
var io = jQuery.createUploadIframe(id, s.secureuri);
var frameId = 'jUploadFrame' + id;
var formId = 'jUploadForm' + id;
        // Watch for a new set of requests
        if ( s.global && ! jQuery.active++ )
{
jQuery.event.trigger( "ajaxStart" );
}            
        var requestDone = false;
        // Create the request object
        var xml = {}   
        if ( s.global )
            jQuery.event.trigger("ajaxSend", [xml, s]);
        // Wait for a response to come back
        var uploadCallback = function(isTimeout)
{
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 = jQuery.uploadHttpData( xml, s.dataType );    
                        // If a local callback was specified, fire it and pass it the data
                        if ( s.success )
                            s.success( data, status );
    
                        // Fire the global callback
                        if( s.global )
                            jQuery.event.trigger( "ajaxSuccess", [xml, s] );
                    } else
                        jQuery.handleError(s, xml, status);
                } catch(e) 
{
                    status = "error";
                    jQuery.handleError(s, xml, status, e);
                }

                // The request was completed
                if( s.global )
                    jQuery.event.trigger( "ajaxComplete", [xml, s] );

                // Handle the global AJAX counter
                if ( s.global && ! --jQuery.active )
                    jQuery.event.trigger( "ajaxStop" );

                // Process result
                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(){
                // Check to see if the request is still happening
                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)
{
jQuery(form).attr('encoding', 'multipart/form-data');      
            }
            else
{
jQuery(form).attr('enctype', 'multipart/form-data');
            }
            jQuery(form).submit();

        } catch(e) 
{
            jQuery.handleError(s, xml, null, e);
        }

jQuery('#' + frameId).load(uploadCallback);
        return {abort: function () {}};

    },

    uploadHttpData: function( r, type ) {
        var data = !type;
        data = type == "xml" || data ? r.responseXML : r.responseText;
        // If the type is "script", eval it in global context
        if ( type == "script" )
            jQuery.globalEval( data );
        // Get the JavaScript object, if JSON is used.
        if ( type == "json" )
            eval( "data = " + data );
        // evaluate scripts within html
        if ( type == "html" )
            jQuery("<div>").html(data).evalScripts();

        return data;
    },
    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] );
    }
    }
 
})

注：如果出现

jQuery.handleError is not a function 

原因是，经测试handlerError只在jquery-1.4.2之前的版本中存在，jquery-1.6 和1.7中都没有这个函数了，因此在1.4.2中将这个函数复制到了ajaxFileUpload.js中，问题解决
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] );
}
},
问题2：一直得到error ，无法执行指定的success方法。通过追踪ajaxFileUpload的执行过程发现，在调用它自身的uploadHttpData函数时，当执行if（type=="json")    eval("data = "+data);
会抛出异常，导致在处理异常的时候将status = "error" 因此一直执行error方法。
上网查询，得知eval函数是用来执行一段js代码，而并不是如我所想的反解json串
eval("data = "+data);的意思是 将data 赋值给 data参数 ，但是当我返回给页面的是一个简单的字符串，比如"OK" ，时，这样写就抛出异常。最后改为 eval("data = \" "+data+" \" ");即将返回的数据用双引号引起来当作字符串，然后赋给 data 。终于成功了。。。

        @RequestMapping(value = "/saveorupdate.jhtml")
@ResponseBody
public synchronized String saveOrUpdate(HttpServletRequest request) throws IOException {
DynamicParams params = new DynamicParams(request);
String projectId = request.getParameter("projectId");
String name = request.getParameter("name");
String type = request.getParameter("type");
params.put("projectId", projectId);
params.put("name", name);
params.put("type", type);

MultipartHttpServletRequest multipartRequest = (MultipartHttpServletRequest) request;
MultipartFile file = null;
if("1".equals(type)){
file = multipartRequest.getFile("file");// 获取上传文件名
}else{
file = multipartRequest.getFile("attachFile");// 获取上传文件名
}
ProjectPic projectPic = params.convertToEntity(ProjectPic.class);
projectPicManager.save(projectPic, file.getInputStream());
return successMsg();
}