Core Code
Core Code Modern Dev Handbook
JAVA Contents
Java Foundations & Tooling
JDK Distributions, Version Strategy Maven vs Gradle, Standard Layout Running, Fat JAR, Manifest SLF4J, Logback, Log Levels Config with Env Vars, Profiles CLI Args, Exit Codes, Non-zero Failures Timezones, Locale Footguns Dependency Pinning, BOMs, Reproducible Builds
Core Language & Idioms
Types, Nullability, Optional Exceptions, Wrapping, Cause Chains Immutability, Records, Value Objects Encoding, Unicode, Charset Safety java.time, Clock Injection equals/hashCode, Collections Bugs Streams in Production (when/when not) Validation Patterns (DTO vs Domain)
OOP, Design & Maintainability
Packages, Modules, Boundaries SOLID (Pragmatic), Avoid Overengineering DI Concepts, Constructor Injection Domain Modeling, Aggregates Error Modeling (Result vs Exception) API Design, Backward Compatibility Refactoring, Tests as Guardrails
Collections, Generics & Functional
Choosing List/Set/Map in Production Generics, Wildcards, Invariance HashMap internals, sizing, pitfalls Lambdas, functional interfaces Stream performance, boxing, allocations Optional patterns, anti-patterns
Concurrency & Performance Basics
Executors, thread pools, sizing CompletableFuture, timeouts synchronized, ReentrantLock, contention Deadlocks, races, visibility Heap, GC basics, leak signals JFR/async-profiler basics (conceptual)
I/O, Files, Networking & HTTP Clients
NIO.2, safe file operations Buffered IO, backpressure hints Java HTTP Client, retries/timeouts TLS/keystore/truststore basics Jackson basics, safe defaults
Data Access & Transactions (JDBC + JPA)
JDBC, PreparedStatement, pooling Isolation levels, anomalies Entity design, lazy loading pitfalls N+1 detection & fixes Flyway/Liquibase basics, safe rollout
Spring Boot Web Services
Structure, layering, configs Controllers, DTOs, validation RFC7807 style errors Request ID, correlation timeouts, resilience patterns graceful shutdown, readiness/liveness
Testing, Quality Gates & CI
JUnit5, test structure Mockito, test slices Testcontainers, DB integration Consumer-driven contracts coverage + mutation (conceptual) CI steps, caching, artifacts
Observability
JSON logs, MDC, redaction Micrometer metrics basics OTel traces basics liveness/readiness, dependency checks alerting signals, SLO-ish basics
Security for Web Services
validation vs sanitization Jackson hardening patterns SSRF, allowlists, egress authn/authz, JWT basics security headers, CORS basics
Build, Release & Deployment
build profiles, reproducibility Dockerizing, distroless concepts secrets, env vars, vault-ish patterns rollbacks, migrations safety zero-downtime deploy checklist
Reliability & Incident Playbooks
retries/timeouts/idempotency rate limiting, backpressure failure modes map runbooks writing go-live checklist

liveness/readiness, dependency checks

Implement liveness and readiness health checks in Spring Boot to protect production deployments and traffic routing.
On this page

Why Health Checks Are Deployment Control

Health checks decide: - whether traffic reaches your service - whether a pod is restarted - whether rolling deploys are safe Misconfigured health checks cause outages.

Liveness vs Readiness

Liveness: Is the process alive? Readiness: Is the service ready to accept traffic? If readiness is true while DB is down, traffic hits a broken service.

Dependency Checks

Readiness should reflect critical dependencies: - database connectivity - message broker - essential downstream APIs Non-critical dependencies should not fail readiness.

Checklist

- Separate liveness and readiness - Fail readiness during shutdown - Check only critical dependencies - Avoid expensive health checks - Test behavior under dependency failure Health checks protect rolling deploys from self-inflicted outages.
alerting signals, SLO-ish basics →