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Zhongwei Li
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skills/references/java.md
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skills/references/java.md
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# Java Architecture Patterns
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## Table of Contents
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- Common Frameworks and Patterns
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- Project Structure Conventions
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- Deployment Considerations
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- Best Practices
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## Common Frameworks and Patterns
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### Spring Boot
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**Typical Structure:**
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```
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project/
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├── src/main/java/com/company/project/
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│ ├── Application.java # Main class
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│ ├── controller/ # REST controllers
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│ ├── service/ # Business logic
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│ ├── repository/ # Data access
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│ ├── model/entity/ # JPA entities
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│ ├── model/dto/ # DTOs
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│ ├── config/ # Configuration
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│ └── exception/ # Exception handling
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├── src/main/resources/
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│ ├── application.properties
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│ └── application-{env}.properties
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├── src/test/java/
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└── pom.xml or build.gradle
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```
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**Key Characteristics:**
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- Convention over configuration
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- Auto-configuration
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- Embedded servers (Tomcat, Jetty)
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- Spring ecosystem integration
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- Dependency injection
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### Jakarta EE (formerly Java EE)
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**Key Technologies:**
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- JAX-RS for REST APIs
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- JPA for persistence
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- CDI for dependency injection
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- EJB for business logic
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- Deployed to application servers (WildFly, Payara)
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### Micronaut
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**Key Characteristics:**
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- Fast startup, low memory
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- Compile-time dependency injection
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- Native image support (GraalVM)
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- Cloud-native focus
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### Quarkus
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**Key Characteristics:**
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- Kubernetes-native
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- Fast startup, low memory
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- Developer experience focused
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- GraalVM native images
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## Project Structure Conventions
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### Spring Boot Microservice
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```
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project/
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├── src/main/java/com/company/service/
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│ ├── ServiceApplication.java
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│ ├── api/ # API layer
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│ │ ├── controller/
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│ │ └── dto/
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│ ├── domain/ # Domain layer
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│ │ ├── model/
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│ │ └── service/
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│ ├── infrastructure/ # Infrastructure
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│ │ ├── repository/
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│ │ ├── client/
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│ │ └── config/
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│ └── common/ # Shared utilities
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├── src/main/resources/
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├── src/test/
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├── pom.xml
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└── Dockerfile
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```
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### Maven Multi-Module Project
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```
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parent-project/
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├── pom.xml # Parent POM
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├── api-module/
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│ ├── pom.xml
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│ └── src/
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├── service-module/
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│ ├── pom.xml
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│ └── src/
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├── common-module/
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│ ├── pom.xml
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│ └── src/
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└── integration-tests/
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├── pom.xml
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└── src/
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```
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## Deployment Considerations
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### Build Tools
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- **Maven**: XML-based, widespread
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- **Gradle**: Groovy/Kotlin DSL, flexible, faster
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### Application Servers
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- **Spring Boot**: Embedded Tomcat/Jetty/Undertow
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- **Traditional**: WildFly, Payara, WebLogic, WebSphere
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- **Lightweight**: Tomcat, Jetty as standalone
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### Containerization
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```dockerfile
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# Multi-stage build
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FROM maven:3.9-eclipse-temurin-17 AS build
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WORKDIR /app
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COPY pom.xml .
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COPY src ./src
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RUN mvn clean package -DskipTests
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FROM eclipse-temurin:17-jre-alpine
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WORKDIR /app
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COPY --from=build /app/target/*.jar app.jar
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EXPOSE 8080
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ENTRYPOINT ["java", "-jar", "app.jar"]
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```
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### Common Deployment Platforms
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- **AWS**: Elastic Beanstalk, ECS, Lambda (with GraalVM)
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- **Google Cloud**: App Engine, Cloud Run, GKE
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- **Azure**: App Service, Container Instances, AKS
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- **Kubernetes**: Primary choice for microservices
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- **Traditional**: On-premise application servers
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## Best Practices
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### Code Organization
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**Layered Architecture:**
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- Controller → Service → Repository
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- DTOs for data transfer
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- Entities for persistence
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- Use interfaces for services
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**Package by Feature:**
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```
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com.company.project/
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├── user/
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│ ├── UserController.java
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│ ├── UserService.java
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│ ├── UserRepository.java
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│ └── User.java
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├── order/
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└── product/
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```
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### Database Integration
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**Spring Data JPA:**
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```java
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public interface UserRepository extends JpaRepository<User, Long> {
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Optional<User> findByEmail(String email);
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}
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```
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**Hibernate:** JPA implementation
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**Flyway/Liquibase:** Database migrations
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**Connection Pooling:** HikariCP (default in Spring Boot)
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### Configuration
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**Spring Boot application.properties:**
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```properties
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spring.datasource.url=${DB_URL}
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spring.jpa.hibernate.ddl-auto=validate
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server.port=${PORT:8080}
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```
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**Profiles:** application-dev.properties, application-prod.properties
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**Environment variables:** For secrets and env-specific config
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**Spring Cloud Config:** Centralized configuration
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### Security
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**Spring Security:**
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- Authentication and authorization
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- JWT support
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- OAuth2/OpenID Connect
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- Method-level security
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**Best Practices:**
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- Use BCrypt for passwords
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- Validate input with Bean Validation
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- Prevent SQL injection (use JPA)
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- CORS configuration
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- HTTPS in production
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### Error Handling
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**Spring Boot:**
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```java
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@ControllerAdvice
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public class GlobalExceptionHandler {
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@ExceptionHandler(ResourceNotFoundException.class)
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public ResponseEntity<ErrorResponse> handleNotFound(
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ResourceNotFoundException ex) {
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return ResponseEntity.status(404)
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.body(new ErrorResponse(ex.getMessage()));
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}
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}
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```
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### Testing
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**Frameworks:**
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- **JUnit 5**: Standard testing framework
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- **Mockito**: Mocking framework
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- **Spring Boot Test**: Integration testing
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- **RestAssured**: API testing
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- **TestContainers**: Database testing with containers
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**Patterns:**
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- Unit tests with Mockito
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- Integration tests with @SpringBootTest
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- Slice tests (@WebMvcTest, @DataJpaTest)
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- Test coverage with JaCoCo
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### Logging
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**SLF4J + Logback (Spring Boot default):**
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```java
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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private static final Logger log =
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LoggerFactory.getLogger(MyClass.class);
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log.info("Processing request for user {}", userId);
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```
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**Structured Logging:** Logstash encoder for JSON logs
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### API Documentation
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**OpenAPI/Swagger:**
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- springdoc-openapi for automatic generation
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- Annotations for customization
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- Swagger UI for interactive docs
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### Dependency Injection
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**Spring:**
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- Constructor injection (preferred)
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- @Autowired annotation
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- @Component, @Service, @Repository stereotypes
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- Java Config with @Configuration and @Bean
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### Common Libraries
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- **Lombok**: Reduce boilerplate
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- **MapStruct**: Object mapping
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- **Apache Commons**: Utility libraries
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- **Guava**: Google's core libraries
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- **Jackson**: JSON processing
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## Technology-Specific Patterns
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### Microservices
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**Spring Cloud:**
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- Service Discovery: Eureka
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- API Gateway: Spring Cloud Gateway
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- Config: Spring Cloud Config
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- Circuit Breaker: Resilience4j
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- Distributed Tracing: Micrometer + Zipkin
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### Messaging
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- **Spring AMQP**: RabbitMQ integration
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- **Spring Kafka**: Kafka integration
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- **Spring JMS**: JMS support
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- **AWS SQS**: Cloud messaging
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### Caching
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- **Spring Cache**: Abstraction layer
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- **Redis**: Distributed cache
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- **Caffeine**: In-memory cache
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- **Hazelcast**: Distributed cache
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### Reactive Programming
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**Spring WebFlux:**
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- Non-blocking, event-driven
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- Project Reactor
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- Better for high concurrency
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- MongoDB/Cassandra reactive support
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### GraphQL
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- **Spring for GraphQL**: Official Spring support
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- Schema-first approach
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- DataFetchers for resolvers
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### Monitoring
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- **Spring Boot Actuator**: Health checks, metrics
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- **Micrometer**: Metrics facade
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- **Prometheus**: Metrics collection
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- **Grafana**: Visualization
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- **Zipkin/Jaeger**: Distributed tracing
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- **ELK Stack**: Logging
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### Performance
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- **Connection pooling**: HikariCP
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- **Query optimization**: Proper JPA fetch strategies
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- **Caching**: Redis, Caffeine
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- **Async processing**: @Async, CompletableFuture
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- **JVM tuning**: Heap size, GC configuration
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