URL decoding: UnsupportedEncodingException in Java

Question

What I understand from the documentation is that UnsupportedEncodingException can only be thrown if I specify a wrong encoding as the second parameter to URLDecoder.decode(String, String) method. Is it so? I need to know cases where this exception can be thrown.

Basically, I have this code segment in one of my functions:

if (keyVal.length == 2) {     try {         value = URLDecoder.decode(             keyVal[1],             "UTF-8");     } catch (UnsupportedEncodingException e) {           // Will it ever be thrown?     } } 

Since I am explicitly mentioning "UTF-8", is there any way this exception can be thrown? Do I need to do anything in the catch block? Or, if my understanding is completely wrong, please let me know.

Answer 1

It cannot happen, unless there is something fundamentally broken in your JVM. But I think you should write this as:

try {     value = URLDecoder.decode(keyVal[1], "UTF-8"); } catch (UnsupportedEncodingException e) {     throw new AssertionError("UTF-8 is unknown");     // or 'throw new AssertionError("Impossible things are happening today. " +     //                              "Consider buying a lottery ticket!!");' } 

The cost of doing this is a few bytes of code that will "never" be executed, and one String literal that will never be used. That a small price for the protecting against the possibility that you may have misread / misunderstood the javadocs (you haven't in this case ...) or that the specs might change (they won't in this case ...)