URL decoding: UnsupportedEncodingException in Java

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 ...)

In your special case - no, it won't be thrown. Unless you execute your code in a Java runtime that does not support "UTF-8".

That's because of the odd choice to make UnsupportedEncodingException checked. No, it won't be thrown.

I usually do as follows:

} catch (UnsupportedEncodingException e) {
  throw new AssertionError("UTF-8 not supported");
}