How to Decode URL content in Java ?

The task to the reverse of URL encoding and distinct from URL parser is called Url Decoding.
It is a common requirement to implement URL encoding and decoding in Java while creating crawlers or downloaders.

Decode URL

The Decode URL following steps are given below,

The same URL can be encoded multiple times, we need to decode it until the URL cannnot be decoded further. For example, “video%252Fmp4” is the result of two encodings. Upon decoding it once, we get “video%2Fmp4”. Now the URL needs to be further decoded so that we get “video/mp4”, which is the result.
We use the decode method of a predefined Java class named URLDecoder.
The decode method of URLDecoder takes two arguments:
- The first argument defines the URL to be decoded.
- The second argument defines the decoding scheme to be used.
After decoding, the resulting decoded URL is returned.
We create two variables: prevURL, which is empty, and decodeURL, which contains the URL to be decoded.
We create an iteration that runs until prevURL!=decodeURL
Now we update prevURL to decodeURL and update decodeURL with the decoded value of the URL passed.
As you can see, prevURL!=decodeURL, so we run it again and again.
Now, prevURL=decodeURL, so the decoded URL is returned.

Sample Code

[pastacode lang=”java” manual=”import%20java.io.UnsupportedEncodingException%3B%0Aimport%20java.net.URLDecoder%3B%0A%20%0Apublic%20class%20DecodeURLExample%20%7B%0A%20%20%20%20public%20static%20void%20main(String%20a%5B%5D)%7B%0A%20%20%20%20%20%20%20%20try%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20System.out.println(URLDecoder.decode(%22special%2Bchars%253A%2B%2526%2525*%2B%22%2C%20%22UTF-8%22))%3B%0A%20%20%20%20%20%20%20%20%7D%20catch%20(UnsupportedEncodingException%20ex)%20%7B%0A%20%20%20%20%20%20%20%20%20%20%20%20ex.printStackTrace()%3B%0A%20%20%20%20%20%20%20%20%7D%0A%20%20%20%20%7D%0A%7D” message=”” highlight=”” provider=”manual”/]

Output

special chars: &%*

How to Decode URL content in Java ?