The case is an appeal from a District Court ruling which found Slater could not claim the source protection allowed to journalists under the Evidence Act.
Slater said bloggers had challenged the traditional view of a news organisation, with bloggers labelled as "parasites and plagiarists".
"Many journalists have gone out of their way to attack me," he said.
But he said views on newly arrived online media should be contrasted against the changes traditional media had undergone over the last century.
"The rules... do not say you have to be this massive corporate. It doesn't preclude other people setting up or running media organisations themselves. My website has broken numerous stories."
Among stories cited by Slater was the revelation Auckland Mayor Len Brown was having an extra-marital affair.
"I deal with informants and sources and people who want to provide confidential information on a daily basis."
Mr Blomfield's lawyer Matt Karim said the definition of journalist was an integral factor in the case. Other jurisdictions require the person claiming such status to be paid for the work they do, he said.
In Mr Slater's case, Mr Karim said the question of journalistic status had to be taken from August 2011 when he began accepting information for which he was now claiming protection.
He said in the year prior, Mr Slater had blogged about being on the sickness benefit.
He had also written about how his blog was an outlet for coping with a mental health issue, he said.
"The website was an outlet which he utilised to deal with his depression."
Mr Karim said there were also comments from Mr Slater during 2011 in which he had rejected the description of "journalist", preferring in one case to be known as a "partisan blogger".
Julian Miles QC, who was called by the court to lend his expertise, said the key question was whether an informant believed the person they supplied information to would use and protect it in a journalist way. Someone with no track record would not inspire the confidence of informants, he said.
The case continues.