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Recommended order is metadata, not a lock. Every listed chapter is directly available.

Java Foundations

J00availableJava from zero J01availableValues & flow J02availableEquality & hash J03availablePolymorphism J04availableGenerics & collections

JVM & Concurrency

J05availableExceptions & resources J06availableClassloading & bytecode J07availableHeap & GC evidence J08availableThreads & the JMM

Spring request to database

S00availableRequest system atlas S01availableRequest cost X-ray S02availableJava objects & Spring DI S03availableContainer internals S04availableWeb boundary S05availablePersistence S06availableConcurrency

S01·Spring request to database·implemented

Move work across controller, service, and database

Edit one reviewed work-placement patch, predict its cost, run it, and compare immutable receipts.

REAL_HIBERNATE_POSTGRESQLCAPTURED_RECEIPTNOT_OBSERVEDabout 45 min

Outcomes

• Identify where rows are reduced.
• Distinguish database, JVM, and serialization work.
• Reject latency claims outside the captured receipt.

Recommended context

• s00-request-system-atlas

Endpoint family / fixed variants

• /api/labs/request-xray

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Request cost X-ray available.