Java 8 + Spring + AWS

**Java 8 Features**
🔸 Lambda Expressions enable functional programming by passing behavior as a parameter  
🔸 Stream API is used for processing collections in a functional and parallel way  
🔸 Optional Class helps to avoid NullPointerException by handling null values  
🔸 Default and Static Methods allow interfaces to have method implementations  
🔸 Functional Interfaces contain a single abstract method like Predicate and Consumer  
🔸 New Date and Time API provides better date and time handling using java.time  

**Stream API Performance**
🔸 Stream API improves performance using lazy evaluation and parallel processing  
🔸 It can process large datasets efficiently using parallelStream()  

**map() vs flatMap()**
🔸 map() transforms each element in a stream  
🔸 flatMap() flattens nested structures into a single stream  

**Lambda Expressions**
🔸 Lambda expressions allow concise code by passing behavior as data  
🔸 It reduces boilerplate code and improves readability  

**Stream API Concepts**
🔸 Stream API processes data in a declarative and parallel way  
🔸 Intermediate operations include filter(), map(), sorted()  
🔸 Terminal operations include collect(), forEach(), reduce()  
🔸 Parallel processing can be achieved using parallelStream()  

**Optional Class**
🔸 Optional is used to safely handle null values  
🔸 Methods include isPresent(), ifPresent(), orElse()  

**Default and Static Methods**
🔸 Interfaces can have default implementations  
🔸 Static methods can be called directly using interface name  

**Functional Interfaces**
🔸 Functional interfaces have only one abstract method  
🔸 Examples include Predicate, Consumer, Function  

**Date and Time API**
🔸 java.time package replaces old Date and Calendar  
🔸 Classes include LocalDate, LocalTime, LocalDateTime  
🔸 Period and Duration represent time intervals  

**Other Java Enhancements**
🔸 Method references simplify lambda expressions  
🔸 Stream collectors help in transforming data  
🔸 CompletableFuture supports asynchronous programming  
🔸 Nashorn engine allows JavaScript execution (deprecated later)  

**Microservices Design**
🔸 Break monolith into small independent services  
🔸 Use API Gateway as a single entry point  
🔸 Maintain separate database per service  
🔸 Use service discovery tools like Eureka  
🔸 Implement circuit breaker for resilience  
🔸 Use REST, gRPC or messaging systems for communication  

**Microservices Data Consistency**
🔸 Eventual consistency using asynchronous events  
🔸 Saga pattern for distributed transactions  
🔸 Two-phase commit used rarely due to performance issues  

**Spring Boot in Microservices**
🔸 Auto configuration reduces boilerplate  
🔸 Embedded servers make apps self-contained  
🔸 Actuator provides monitoring features  
🔸 Easy integration with databases and cloud  

**Spring Boot Security**
🔸 Use Spring Security for authentication and authorization  
🔸 Use JWT or OAuth2 for token-based security  
🔸 Secure APIs using HTTPS and rate limiting  

**@RestController vs @Controller**
🔸 @RestController returns JSON or XML responses  
🔸 @Controller returns views  

**AWS Services Usage**
🔸 EC2 for hosting applications  
🔸 S3 for storage  
🔸 RDS for relational databases  
🔸 Lambda for serverless computing  
🔸 CloudWatch for monitoring  
🔸 API Gateway for managing APIs  

**Scaling Microservices on AWS**
🔸 Use ELB for load balancing  
🔸 Use Auto Scaling for dynamic scaling  
🔸 Use ECS or EKS for container management  

**Elastic Beanstalk vs EC2**
🔸 Elastic Beanstalk is PaaS with minimal setup  
🔸 EC2 is IaaS with full control  

**Monitoring Distributed Systems**
🔸 Use ELK stack or CloudWatch for logging  
🔸 Use Zipkin or Jaeger for tracing  
🔸 Use Prometheus and Grafana for metrics  

**Handling Failures in Microservices**
🔸 Use retry mechanisms  
🔸 Use fallback responses  
🔸 Use circuit breakers  

**Behavioral Questions**
🔸 Explain a challenging problem with solution approach and outcome  
🔸 Use Agile tools like Jira or Trello for task management  

**Lambda Expression Concept**
🔸 Lambda provides a concise way to implement functional interfaces  
🔸 Functional interface has one abstract method and multiple default or static methods  

**Common Functional Interfaces**
🔸 Runnable, Comparable, Predicate, Function, Consumer, Supplier  

**Stream API Example**
🔸 Stream API processes collections using filter(), map(), reduce(), collect()  

**Intermediate and Terminal Operations**
🔸 Intermediate operations return a new stream  
🔸 Terminal operations return final result  

**Functional Types**
🔸 Function takes input and returns result  
🔸 Consumer takes input and returns nothing  
🔸 Supplier takes no input and returns result  
🔸 Predicate returns boolean  

**Optional Methods**
🔸 of creates optional with value  
🔸 empty creates empty optional  
🔸 ofNullable handles null  
🔸 get returns value or throws exception  
🔸 orElse returns default value  
🔸 orElseGet uses supplier  
🔸 orElseThrow throws exception  

**Stream Selection Operations**
🔸 filter selects matching elements  
🔸 limit selects first n elements  
🔸 distinct removes duplicates  
🔸 skip ignores first n elements  

**Stream Reducing Operations**
🔸 min returns minimum  
🔸 max returns maximum  
🔸 count returns total elements  
🔸 collect returns result container