Java Development

Instructions

Follow these practices for production-grade Java development.

Build tools:

• Maven: structure projects with pom.xml, manage dependencies via with BOMs, use lifecycle phases (validate → compile → test → package → verify → install → deploy)
• Gradle: define builds in build.gradle(.kts), configure tasks with proper inputs/outputs for caching, use version catalogs (libs.versions.toml) for centralized dependency management
• Pin all dependency versions — never use dynamic ranges in production

Spring Boot:

• Use starters (spring-boot-starter-web, spring-boot-starter-data-jpa) to pull coherent dependency sets
• Leverage auto-configuration; override only what you need via application.yml or @Configuration classes
• Use profiles (spring.profiles.active) to separate dev/staging/production configuration
• Enable Actuator (/health, /metrics, /info) for observability in deployed services

JVM tuning:

• Set explicit heap bounds: -Xms (initial) and -Xmx (max) to the same value in containers to avoid resize pauses
• Select GC based on workload: G1GC (default, balanced), ZGC (low-latency), Parallel GC (throughput-heavy batch)
• For containers, use -XX:MaxRAMPercentage=75.0 instead of fixed heap sizes

Testing:

• JUnit 5 with @Test, @ParameterizedTest, @Nested for structured test suites
• Mockito for dependency isolation: @Mock, @InjectMocks, when().thenReturn()
• Integration tests with @SpringBootTest and test slices (@WebMvcTest, @DataJpaTest)

Logging:

• SLF4J facade with Logback implementation — never use System.out.println
• Structured logging with MDC for request correlation in distributed systems
• Log levels: ERROR (failures), WARN (degraded), INFO (business events), DEBUG (diagnostics)

Docker deployment:

• Multi-stage builds: builder stage with full JDK for compilation, runtime stage with JRE-only base (eclipse-temurin:21-jre-alpine)
• Copy only the built JAR to the runtime image to minimize attack surface and image size
• Run as non-root user; set ENTRYPOINT ["java", "-jar", "app.jar"]