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2. Java garbage collection mechanism, dynamic proxy, common data structure, optimization of the characteristics of each version of JVM to application server, parameter configuration of connection pool, loading mechanism of CSS style
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4. How to do the website security mechanism? Possibility to optimize the SSH protocol? java multithreading, design patterns, SPRING internal mechanism, classic scenarios of operating system deadlock, CSS loading mechanism, database optimization, differences between nosql and relational databases, common operation commands in linux