问题
Why is %2526 used instead of %26 to encode an &?
Im invoking a URL to an external site and when I encode the & as %2526 the parameters are passed correctly but when I just use %26 they are not.
回答1:
If you url-encode an ampersand you get %26. If you url-encode %26 you get %2526. Thus, it is url-encoded twice.
回答2:
%25 is the percent character, so %2526 URLDecoded results in
%26
which URLDecoded results in
&
For some reason, the call you make seems to require doubly percent encoded input. Without knowing more about what you're doing, it's impossible to know why, but I guess all is in order.
回答3:
Apparently it gets decoded twice in the process, first from %2526 to %26 and then from %26 to &.
You shouldn't dwell too long on the why; if this works, just use it like this.
回答4:
& is indeed encoded as %26.
You can test it creating an HTML file, opening it in a browser, inputing symbols you need to test and looking at the resulting URL in browser:
<form>
<input type='text' name='qwe'>
<input type='submit'>
</form>
回答5:
If the URL is used in return URL or value of another query string, the Reserved and Excluded characters should be doubled encoded. & is single-encoded as %26 and double-encoded as %2526.
来源：https://stackoverflow.com/questions/9292865/what-is-url-encoding-2526