html img不显示图片怎么办

$(document).ready(function(){

var airportId = getUrlValue("airportId");

if(airportId==null || typeof(airportId) == "undefined"){

return false;

}

data = {

'airportId' : airportId ,

}

Kelp.jsonPost(

"../func/web/getActivityPointsMap",data,function(result){

if(result.re== 1 || result.re == "1" ){

var form = result.data.airportInfoMapForm;

iWidth = form.imageWidth;

iHeight = form.imageHeight;

dWidth = form.width;

imgW = iWidth*imageScale

imgH = iHeight*imageScale;

cellWidth = form.cellWidth * iWidth/dWidth;

var attachId = form.imageAttachId;

}

else{

alert(result.data);

window.history.go(-1);

return false;

}

//使画布大小对应机场图片大小

canvas.width = iWidth+XO;

canvas.height = iHeight+YO;

//创建新的图片对象

var img = new Image();

/* var img = document.getElementById('img'); */

img.src = "<%=request.getContextPath()%>/fileDownload?attachId=" + attachId;

//浏览器加载图片完毕后再绘制图片

img.onload = function(){

var w = XO+ imgW;

var h = YO +imgH;

ctx.drawImage(img,XO,YO,imgW,imgH);//限制图片的宽高，此处没有imgW和imgH则会显示为图片的实际宽高

//画网格线

drawLine();

};  

});

})