Should I take my own coffee to Japan?

No. Coffee is all over the place. I don’t know where you are from, but the quality of coffee is typically better in Japan than in the US. Even Starbucks in Japan has much better quality coffee than Starbucks in the US, where it is extremely watered down. Vending machine coffee is typically not very good in my opinion, as I don’t like sugar in my coffee and it is really sweet, though the black coffee can be decent. “Aroma black” and Georgia Black (by CocaCola) are pretty good

Nobody here seems to know some of the most drunk and most easily available coffee in Japan : convenience store coffee.
Convenience stores are open 24/7 and you’ll find them everywhere: 7&11 (or 7&i Holdings), Family Mart, Lawson, Circle K, Mini-stop….

These companies spend enormous amount of money to deliver the same coffee in all their stores, so once you find one that suits your taste you should be fine.

I guess they’re not so well-known to foreigners because you won’t find them on shelves, you have to ask at the counter for one (though in Circle K shops you have to pick a small card, sort of like iTunes credit iirc). Just speak clearly and most employees will understand you and give you a glass that you fill at the machine, then you can add sugar or milk or get a straw at the counter by yourself.

Small-sized coffee usually costs 100 to 110 yens, which is cheaper than a lot of coffee cans you’ll find in vending machines.

Some of the best coffee I’ve had was in Japan. I even bought some to bring back with me Stateside. They have whole bean and ground packages readily available at grocery stores, department stores and coffee shops (i.e. Tully’s).

Ryokans generally have coffee in the room, but they vary on quality. Many places have a water boiler and basic instant coffee. Some others have one cup coffee makers (like a Verismo) with a handful of coffee pods. I don’t recall requesting coffee during any of the meals at a Ryokan, but I believe such request would be accommodated.

Coffee (コーヒー kōhī) is very readily available in Japan in a variety of forms and quality. Yes, you can find a large variety of super cheap canned coffee in vending machines and convenience stores; however I’d rather describe those as caffeinated soft drinks with coffee-ish flavor than as coffee.

Instant and filter coffee (“drip” coffee, ドリップ) is very easy to get almost anywhere; supermarkets and convenience stores sell one-cup coffee-in-filter sets you just need to add hot water to, some convenience stores sell fresh hot coffee either from a pot or a machine, “family restaurants” like Denny’s or Gusto (ガスト) offer full western style breakfasts (somewhat japanized of course) where the coffee usually comes from a machine. Most restaurants will have a standard selection of coffee on their menu, except Japanese speciality places (like sushi or udon restaurants). If this is good enough for you, you’ll be able to get by just fine.

Starbucks and a whole bunch of competing chains (Doutor, Tully’s, Beck’s, Veloce, Excelsior) are all over the place, typically at least one of them near every train station or at the local department store, except for very out-of-the-way places. You should be able to get a decent shot of coffee there in every major and mid-sized city. You can usually get your coffee hotto (hot) or aisu (cold).

Aside from those there are many independent cafés (カフェ kafe) every here and there. Some very old-fashioned places specialize in romanticized western coffee tradition (dim light, counter seats and booths) and usually carry some form of 珈琲館 kōhīkan in the name. Others are more places to socialize which incidentally sell coffee; take your pick. A lot of these places carry the same selection of coffee, Key Coffee and UCC are big brands and often part of the signage.

You may or may not get a coffee at your ryokan; unless they’re extremely old fashioned they’ll probably have something, but whether that suits your taste or not you won’t know until you try. Modern hotels usually have something to offer. At the very least you’ll be able to make a filter or instant coffee with hot water in your room.

Should you insist on a very specific sort of beans brewed just so, you may have a bit of a hard time. But as long as standard “international” coffee (black, latte/au lait, cappuccino, espresso) is fine for you, Japan has enough of it. Whatever coffee you will get will probably be pretty good for what it is; can coffee doesn’t compare to a fresh shot under any circumstances, but can be very nice with the right expectations. Standard restaurant machine coffee will be decent for what it is. Starbucks & co. are fine for what they are. You’ll be hard pressed to find a truly terrible coffee in any category.

If you plan to rely on vending machine coffee, do some research before you go. When I was in Japan, I tried two of the vending machine cold canned coffees and both were absolutely disgusting. They were extremely sweet, which might have been OK but it was all artificial sweetener, and so much of it that I could still taste the sweeteners hours later, even after throwing it away after a couple of sips. Unfortunately, I can’t remember the brands.

So, if you want to avoid industrial quantities of artificial sweetener, or if you don’t like your coffee super super sweet, you need to find out in advance what brands of canned coffee will meet your requirements. As some of the other answers say, the vending machines are ubiquitous so if there is a brand you like, they’re a great solution.

Thanks to jpatokal for pointing out the key information (and for being patient with me while I mangled it badly):

• the characters 無糖 (mutou), mean “no sugar” or “unsweetened”; ブラック (burakku) [black], often written in English, also usually implies unsweetened.

• ゼロカロリー (zero karorii [calories]) is the usual way of marking artificial sweeteners

(Fellow coffee-lover here; have only travelled a little in Japan, but based on what I’ve heard from others, my experience was fairly typical.)

tl;dr: It depends on your tastes; but you’re probably ok without.

You can get canned coffee — iced or hot, usually sweet — from vending machines on (almost literally) every street corner. It’s not fantastic, but (to my tastes) it’s certainly no worse than what you’d get at a hotel or diner in much of the US.

In reasonable-sized cities, there will be good (sometimes very good) modern international-style coffee shops, though you’ll have to look for them; they’re not as common as Starbucks etc. are in the West. (Helpfully, unlike many other Japanese businesses, these seemed to have fairly good web presence.) There are also more traditional Japanese coffee shops — I didn’t explore these much, mainly because I had trouble finding them.

If you want to brew your own, then it will probably be possible in principle to buy decent beans in most towns/cities. However, from what I could find, they were sold only in smaller shops, not supermarkets, and because of the language/cultural differences, it took me a while to get oriented enough to find them. On the other hand if pre-ground espresso is acceptable — e.g. Lavazza — then you can probably find that in supermarkets.

So I’d say: if you really need high-quality coffee every day, then either locate coffee shops online in advance, or bring your own beans. But if the non-negotiable part is the caffeine, and you’re open to trying different styles of coffee, then don’t bother; try the local way!

You can find real coffee powder (both instant and not) at supermarkets and most convenience stores, but stay away from the pre-made stuff sold at vending machines and the like. Hot water will be available in your room (probably along with cups and instant tea).

I think if I were you I would just bring my own, if it’s not too big a burden. The ones sold here may taste different from what you are used to.

You are not getting good advice. You can even find cold coffee in cans. And look for the discount “breakfest set” (the Japanese pronunciation of breakfast is a little hard to catch) of an egg, toast, and coffee, much cheaper than a la carte.

As it happens I don’t like coffee…