Query string parameters need to be decoded as per RFC 3986, Section 2.
The implementation of the URLDecoder in the JDK is slow because it takes
long and inefficient code paths, and it generates a lot more garbage
than necessary. This decoder is about 2x faster and doesn't allocate
any memory in the easy case where the decoded string is unchanged.
When the string needs to be changed, only one buffer is allocated for
the decoded string.
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