Backend Architecture, Distributed Locks, and Session Management in Java

The document outlines a typical Java backend architecture, starting with front‑end/back‑end separation and showing deployment diagrams that illustrate how Nginx, Tomcat and other components interact.

It then introduces locking mechanisms: thread locks (synchronized), process locks, and distributed locks. Three common distributed‑lock implementations are described—database optimistic lock, Redis‑based lock, and Zookeeper‑based lock—each with detailed workflow explanations.

Redis‑based distributed lock uses commands such as SETNX, GETSET and EXPIRE. Sample Java code using Jedis is provided:

jedis.set(String key, String value, String nxxx, String expx, int time)

Two incorrect locking patterns are shown, highlighting the risk of deadlocks when expiration is not set or when client clocks are unsynchronized.

The unlocking step simply deletes the key after verifying ownership: jedis.del(lockKey) Zookeeper‑based distributed lock relies on temporary sequential znodes. The lock acquisition process involves creating a sequential node under a designated locker node, checking if it has the smallest sequence number, and watching the predecessor node for deletion to obtain the lock.

Session management in distributed systems is discussed, noting that high concurrency can cause a user’s requests to hit different servers, leading to session loss. Solutions include storing sessions in Redis, using IP‑hash load balancing, or ensuring session consistency across servers.

The article also covers related topics such as Spring cache annotations ( @Cacheable, @CachePut), database locking (optimistic vs. pessimistic), and various Java code snippets for collections, streams, and concurrency utilities.

Additional sections explain the differences between List and Set, the internal workings of HashMap (including bucket chaining, conversion to red‑black trees, and load factor), and provide example code for converting a list of objects to a map using Java streams.

Overall, the piece serves as a practical guide for Java backend developers dealing with architecture design, distributed locking, session handling, and performance‑critical code patterns.