Q:

Why URL is not decoded completely?

I am writing a java program where my url need to be decoded and I am using 
URLDecoder.decode(url,"UTF-8")

method to achieve it.But, unfortunately it is not decoding completely. For eg. above method decodes %3d to = , %2B to + but it is not decoding few chars like %3A%2F which remain unchanged even after decoding. Please tell me if I am missing something. 

A:

First, everything is working as expected. Your problem is, that the input-string is encoded twice. So simply decode it two times.
Example:

Input: %253A
Decodes as: %3A
Decodes as: :

Code:
String input = "40.2%2522%26url%3Dhttp%253A%252F%252Fr1";
String output1 = URLDecoder.decode(input, "UTF-8");
String output2 = URLDecoder.decode(output1, "UTF-8");
System.out.println(input);
System.out.println(output1);
System.out.println(output2);

Output:
40.2%2522%26url%3Dhttp%253A%252F%252Fr1
40.2%22&url=http%3A%2F%2Fr1
40.2"&url=http://r1

Note:
If it's uncertain how many times the string is encoded you could repeat decoding until result remains constant.
String input = "40.2%2522%26url%3Dhttp%253A%252F%252Fr1";
String output = input;

do {
    input = output;
    output = URLDecoder.decode(input, "UTF-8");

} while (!input.equals(output));

