It is not a breed trait, nor something so common that I'd say boxers are any more at risk than most other breeds. But some dogs are certainly prone to it, and some of those are boxers.
Factors that contribute to the development of UTIs are diet and lifestlye. Feeding a high quality diet that does not include things like wheat, corn, beet pulp, molasses or soy is helpful (so check the ingredient list on the food you feed, and check treats as well). Lifestyle is a factor if you happen to crate your dog for long periods. Not urinating for extended periods just gives bacteria a chance to multiply - it is better if the dog drinks a lot of water and urinates frequently. If you don't have the choice about being away from home for long periods, then a dog walker or doggy daycare are good options.
In supplements, cranberry extract and plain natural yoghurt can be helpful, as can natural apple cider vinegar (just a capful or so added to drinking water).
Btw: Please take the time now to introduce yourself to the community in the introductions forum. Per the site rules, that is supposed to be the first post you make on this site, and before participating to the rest of the forums.