Sri Lanka is far away. It's quite natural to wonder about health issues and precautions to take to avoid any potential health problems.
In fact, Sri Lanka doesn't pose any particular health problem. No specific vaccination is needed to visit this beautiful island. Nevertheless it's wise to make sure that you're up to date with all your standard vaccinations.
If you prefer to be cautious, you can get vaccinated against Hepatitis A and typhoid. If you're thinking of going on a more adventurous trip (sleeping in the bush, visiting very remote places...) you can also take an antimalarial preventative treatment, but the risks of contracting malaria are extremely low.
In order to stay healthy for the duration of your trip, make sure you don't drink tap water, don't take ice in your drinks and avoid milk or frozen products. These are of course general health rules that apply in a number of countries. You won't have to worry at your hotel or in upscale restaurants.