Limit your license keys per domain.

I want to implement to java client still not understand the concept of client side.

I’ve read
https://github.com/10quality/license-keys-php-client/wiki/Tutorial:-Quick-Script

when we activate the license key (then we will get activation_id) but what should we do when we get activation_id from activation.

Should i stored activation_id at client side?

i just dont want many user to use the same license key.

The premiun (paid) extension allows you to limit the license usages. You might want to check that out.