java上传图片前预览 控制图片尺寸大小 控制上传格式

原文：http://blog.sina.com.cn/s/blog_4d3d00180102v4yl.html

var maxH = 768;

var maxW = 1024;

function DrawImage(ImgD){

var preW = 300;

var preH = 400 ;

var image=new Image();

image.src=ImgD.src;

if(image.width > maxW || image.height > maxH){

alert("图片尺寸过大，请选择" + maxW + "*" + maxH + "的图片！");

return;

}

if(image.width>0 && image.height>0){

flag=true;

if(image.width/image.height>= preW/preH){

if(image.width>preW){

ImgD.width=preW;

ImgD.height=(image.height*preW)/image.width;

}else{

ImgD.width=image.width;

ImgD.height=image.height;

}

ImgD.alt=image.width+"×"+image.height;

}

else{

if(image.height>preH){

ImgD.height=preH;

ImgD.width=(image.width*preH)/image.height;

}else{

ImgD.width=image.width;

ImgD.height=image.height;

}

ImgD.alt=image.width+"×"+image.height;

}

}

}

function checkFormat(filePath) {

var i = filePath.lastIndexOf('.');

var len = filePath.length;

var str = filePath.substring(len,i+1);

var extName = "JPG,GIF,PNG,JPEG,BMP";

if(extName.indexOf(str.toUpperCase()) < 0) {

alert("请选择正确的图片文件!");

return false;

}

return true;

}

function FileChange(Value){

if(checkFormat(Value)){

flag=false;

document.getElementByIdx_x("uploadimage").width=10;

document.getElementByIdx_x("uploadimage").height=10;

document.getElementByIdx_x("uploadimage").alt="";

document.getElementByIdx_x("uploadimage").src=Value;

}

}