uploader对应的后台代码接收怎么区分第一次请求和第二次请求，我的java后台总是报错

后台报错如下:the request doesn't contain a multipart/form-data or multipart/mixed stream, content type header is application/x-www-form-urlencoded
前台js代码如下:
function uploadFile(){
var f=plus.storage.getItem("fiels_0");
outSet(f);
if(f.length<=0){
plus.nativeUI.alert("没有添加上传文件！");
return;
}
outSet("开始上传：")
var wt=plus.nativeUI.showWaiting();
var task=plus.uploader.createUpload(server,
{method:"POST"},
function(t,status){ //上传完成
if(status==200){
outLine("上传成功："+t.responseText);
wt.close();
// plus.storage.setItem("uploader",t.responseText);
// var w=plus.webview.create("uploader_ret.html","uploader_ret.html",{scrollIndicator:'none',scalable:false});
// w.addEventListener("loaded",function(){
//
// w.show("slide-in-right",300);
// },false);
}else{
outLine("上传失败："+status);
wt.close();
}
}
);
task.addData("client","HelloH5+");
task.addData("uid",getUid());
// for(var i=0;i<files.length;i++){
task.addFile(f,{key:111});
// }
task.start();
}