Police searched his car and in front of the passenger seat where he was sitting there was a cardboard box containing a further 2.4kg of synthetic cannabis, the summary said.
Johnson told police the box was his.
His lawyer, Martin Hine, told Judge Alayne Wills that Johnson was not a synthetic cannabis user but people he associated with used the drug. He said that upon learning about the dangers of the drug he had intended to dispose of it.
"They were on their way to destroy it when they were stopped by police."
Judge Wills said she found Mr Hine's submission difficult to accept given he was charged with possession with intention to sell.
She told Johnson Parliament was taking this offending seriously and was increasing the penalties.
She said Johnson had proven previously he was not a good candidate for an electronically monitored sentence.
She said he also pleaded guilty to a charge of failing to comply with prison release conditions relating to a previous sentence and for that she sentenced him to one month prison to be served concurrently.
Just after Judge Wills handed down the sentence, Johnson turned to the public gallery and raised his fists in the air and said "yo f**k yo".
About 10 people in the public gallery stood and raised their fists chanting the same gang slogan.
Police prosecutor Sergeant Tere Rei ran from the front of the court to the public gallery yelling at the men to "get out". Court security staff ushered the men out of the court.
After they left, Judge Wills asked defence counsel to in future indicate if they believed such an incident would occur so court security staff could be prepared.
"This courtroom is not to be used as a forum for this sort of behaviour and I want to encourage counsel to identify that."
The charge:
Possession for sale/supply of non approved psychoactive product
Maximum sentence:
Two years' imprisonment or a fine of $500,000
