[Java] [Basic] Integration

Design principles:

Single principle of responsibility:
The function of the class should be exclusive, do not chatty
The Richter replacement principle:
Wherever you use the parent class, you can switch directly to subclasses, and do not override the parent class's methods without destroying the original inheritance structure.
Dependency Inversion principle:
Reduce coupling and improve robustness for interface programming
Interface Isolation principle:
The function of the interface must be exclusive, do not chatty
Dimitri rule: Opening and closing principle:
Open for extension, close for modification

Design mode:
Singleton mode (Singleton):
A hungry man type, lazy, thread insecure,

Servlet/listener/filter:

[Java] [Basic] Integration