Comprehensive Java Backend Interview Guide: Redis, Spring Boot, Annotations, Git, Exceptions, Java 8, HashMap, Docker, and CI/CD

Recent trends in Chinese manufacturing firms such as Midea, DJI and Haier enforce strict no‑overtime policies, partly due to the EU 2024 “Ban Forced Labour” law.

Redis cache problems : cache avalanche occurs when many keys expire simultaneously or Redis fails, causing massive DB load; cache breakdown happens when a hot key expires and many requests hit the DB; cache penetration occurs when requested data is absent from both cache and DB. Solutions include randomizing expiration times, using mutex locks, background cache refresh, limiting illegal requests, caching null values, and employing Bloom filters.

Spring Boot initialization : the @SpringBootApplication class’s main method creates a SpringApplication instance, triggers SpringApplicationRunListeners , loads ConfigurableEnvironment , creates ConfigurableApplicationContext , and finally refreshes the context to instantiate beans and apply auto‑configuration.

@SpringBootApplication
public class Application{
    public static void main(String[] args){
        SpringApplication.run(Application.class, args);
    }
}

Common Spring annotations : @Component , @ComponentScan , @Controller , @RestController , @Repository , @Bean , dependency‑injection annotations ( @Autowired , @Resource , @Qualifier ), configuration annotations ( @Value , @ConfigurationProperties ), web mapping annotations ( @RequestMapping , @GetMapping , @PostMapping , @PutMapping , @DeleteMapping ), and others such as @Transactional and @Scheduled .

MyBatis characteristics : SQL‑centric, XML‑based dynamic statements, reduces boilerplate compared with JDBC, works with any JDBC‑compatible database, integrates smoothly with Spring, and provides ORM‑style mapping tags.

Git workflow : typical commands are git pull , git add . , git commit -m "msg" , git push . To undo a commit use git reset --soft HEAD^ (keeps changes staged) or git reset --mixed HEAD^ (keeps changes only in the working tree).

Java exception hierarchy : Throwable → Error (serious VM problems) and Exception , which splits into checked (non‑runtime) exceptions that must be declared or caught, and unchecked RuntimeException subclasses.

Java 8 new features (selected): lambda expressions, functional interfaces, Stream API, Optional , method references, default and static interface methods, parallel array sorting, repeatable annotations, type annotations, and CompletableFuture for asynchronous programming.

Lambda expression examples show the concise syntax (a, b) -> a + b compared with anonymous inner classes, and usage in collections with list.stream().filter(x -> x % 2 == 0).collect(Collectors.toList()) .

public class AnonymousClassExample{
    public static void main(String[] args){
        Thread t1 = new Thread(new Runnable(){
            @Override
            public void run(){
                System.out.println("Running using anonymous class");
            }
        });
        t1.start();
    }
}

public class LambdaExample{
    public static void main(String[] args){
        Thread t1 = new Thread(() -> System.out.println("Running using lambda expression"));
        t1.start();
    }
}

HashMap implementation : pre‑JDK 8 uses an array of buckets with linked lists; when a bucket’s list exceeds 8 entries it is transformed into a red‑black tree (reverted to a list when size drops below 6), improving lookup from O(n) to O(log n).

Docker isolation : relies on Linux namespaces for view isolation (PID, network, mount, IPC) and cgroups for resource limits (CPU, memory, I/O).

Jenkins CI/CD : Jenkins automates continuous integration (code checkout, Maven build, unit tests, quality checks, artifact generation) and continuous deployment (automatic release to test, pre‑release, and production environments, with monitoring and rollback).

The interview experience notes a friendly Haier interview atmosphere and includes several practical code snippets throughout the guide.