Gillespie and Barney played on the OSU team that won the College World Series in 2006.
"We share a lot of great memories together, and it's pretty fun to be reunited at the big league level," Gillespie said.
The outfielder batted .277 in 74 games for Triple-A Fresno before being called up to the Giants on July 5. He went hitless in nine big league at-bats before he was designated for assignment on July 9. What kind of hitter is he?
"I'm a gap-to-gap guy, like to hit doubles, occasional pop," Gillespie said. "I feel I can steal some bases. I like to think I can do the little things good."
Gillespie was with Cubs manager Dale Sveum in the Brewers' Spring Training camp when Sveum was their hitting coach.
"It seemed like he's seen me more than I thought he has," Gillespie said.
The 29-year-old is just hoping for some regular at-bats. Gillespie will likely get starts against left-handed pitchers.
"It's been up and down the last few years, and hopefully, I get a pretty good opportunity here," he said.
Rodriguez, 26, had a 4.09 ERA in 22 relief appearances with the Nationals and Cubs this season. He was acquired from Washington on June 11.
Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.