With parameters such as key=value&another+key=another+value you should first split on &, then split on =, and only then urldecode the resulting parts. Otherwise, you could get this:

input: key=tom%26jerry
urldecode (too early!) key=tom&jerry
split on &: ["key=tom", "jerry"]
split on =: [["key", "tom"], ["jerry"]]

instead of as it should have been:

input: key=tom%26jerry
split on &: ["key=tom%26jerry"]
split on =: [["key", "tom%26jerry"]]
urldecode the parts: [["key", "tom&jerry"]]