RPG game engine. Skill application calculations

Question

Short preface

I am a part of a small team which is entering game development. We're creating a new RPG setting with custom game system and mechanics based on dice rolls. I'm server-side java programmer, so the game engine is my responsibility.

The problem

I have a problem designing talent classes. Each character may have a set of talents. The problem is, most talents are unique and different from others. For example:
Talent Season fever gives character a stat bonus depending on the season of the year, e.g. strength +2 in Winter, dexterity +2 in Spring, etc. Which gives player an opportunity to add and swap talents because of changed stats four times a year.
Talent Fortune Wheel allows a player to roll d6 each morning and get a bonus on one of the six stats (strength, dexterity, etc.) for that day.
Talent Attuned to partner gives a player +2 on his hit roll if his character has exactly one partner in the battle. If his partner also has this talent, both of them get +4 instead. As you see mechanics of each talent are different. Question is how to universally implement all this different functionalities in Java classes.

Some technical details

I use latest version of JDK 7.
Springframework stack (spring-data, spring-mvc, spring-security, etc.)
MongoDB for persistent storage.

My ideas

The solution I came up with:

• Create a parent Talent class with generic fields and methods, like id, name, description, requirements to obtain, etc. and an abstract apply() method.
• For each talent in the game extend Talent class and add custom logic by implementing the apply() method.
• I also need some trigger mechanism (I don't really know how it would look, so please advise if you have ideas). For example, if character has some talent which gives him bonus to a melee attack in some situations (preconditions) the trigger would fire on each event of melee attack made by the player, when the trigger fires it also checks if preconditions are met and if they are it calls the apply() method of a talent.
• I have to implement scheduling for triggering or processing talents which depend on times or periods like the Season fever talent described above.

Disclaimer I have really small experience of asking questions on stack-exchange, so feel free to point out suggestions on question format and additional info required. Also, English is not my native language, so feel free to correct me if something annoys you (grammar-nazi style)

Answer 1

What CamFred said in his comments is sensible. If you want more suggestions, here's one.

Use an observer/observable pattern. Make the Talent class an Observer, and the character an Observable. Now, adding a Talent to a character is simply a matter of adding an observer. Whenever something happens that might trigger an event, you notify the observers, and they decide whether anything happens.

This is really easy to do in Java - it actually has built-in Observer- and Observable-classes that you can extend. Anyway, here's the Wikipedia page - there's even a Java example.