data:image/jpeg;base64,===>我想取jepg
###/^data:image\/([a-z]+);.*/
反向引用 $1 就是
###Matcher matcher = Pattern.compile("(.*)/(\\w+);").matcher("data:image/jpeg;base64");
if (matcher.find()) {
String str = matcher.group(2);
System.out.println(str);
}
###// => jpeg
var imgType = 'data:image/jpeg;base64;,'.replace(/^(data:image\/)(.*?)(;.*)/, '$2')