there is no such thing as "the whole Java technology".
It's always updated, third parties are creating new libraries/frameworks, ...
If you mean you want to start learning, the sticky thread on top of this forum is worth going through, it's filled with recommended books and tutorials.
Fortunately the whole of "standard" Java is defined in just two documents - the Java Language Specification and the API JavaDoc. Oracle also maintain a detailed tutorial site that covers the vast majority of the language and SE API. If you work through the whole tutorial site you'll know more Java than most professional Java programmers.
Of course, these are all moving targets as new releases of Java contain new language and the API (the latest, Java 8, in particular has new language that's a real game-changer, not to mention a whole new API for GUIs).
And, as mentioned above, there are all kinds of libraries (Apache Commons, Google etc) that extend the API in useful ways...
All you can do is start, then keep going. You'll never finish.