2025 年 Java 面试宝典社招春招秋招实操全攻略

// 使用Record类定义API响应结构（Java 17+）
public record ApiResponse<T>(
    boolean success,
    T data,
    String message
) {}

// 模式匹配优化类型检查
public void process(Object obj) {
    if (obj instanceof String str && str.length() > 5) {
        System.out.println("String length: " + str.length());
    } else if (obj instanceof Integer num) {
        System.out.println("Number: " + num);
    }
}

// 密封接口定义状态
public sealed interface OrderStatus 
    permits Pending, Processing, Completed, Cancelled {}

// 具体实现类
public final class Pending implements OrderStatus {}
public final class Processing implements OrderStatus {}
// ...其他状态实现

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-consul-discovery</artifactId>
</dependency>

spring:
  cloud:
    consul:
      host: localhost
      port: 8500
      discovery:
        service-name: product-service

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

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service  # 负载均衡到user-service
          predicates:
            - Path=/api/users/**
          filters:
            - StripPrefix=2  # 去除路径前缀

// 查询多个用户并合并结果
Flux<User> fetchUsers(List<Long> userIds) {
    return Flux.fromIterable(userIds)
               .flatMap(userId -> userRepository.findById(userId))  // 并行查询
               .filter(user -> user.getAge() > 18)
               .map(user -> new UserDTO(user.getId(), user.getName()));
}

// 单个结果异步处理
Mono<Order> createOrder(OrderRequest request) {
    return inventoryService.checkStock(request.getProductId())
           .flatMap(available -> {
                if (available) {
                    return orderRepository.save(new Order(request));
                } else {
                    return Mono.error(new StockException("库存不足"));
                }
           });
}

@RestController
@RequestMapping("/api/products")
public class ProductController {
    private final ProductService productService;

    public ProductController(ProductService productService) {
        this.productService = productService;
    }

    @GetMapping
    public Flux<Product> getAllProducts() {
        return productService.findAll();
    }

    @PostMapping
    public Mono<Product> createProduct(@RequestBody Mono<Product> productMono) {
        return productMono.flatMap(productService::save);
    }
}

# 构建阶段
FROM maven:3.8.6-openjdk-17 AS builder
WORKDIR /app
COPY pom.xml .
RUN mvn dependency:go-offline
COPY src ./src
RUN mvn package -DskipTests

# 运行阶段
FROM openjdk:17-jdk-alpine
WORKDIR /app
COPY --from=builder /app/target/my-app.jar .
EXPOSE 8080
CMD ["java", "-jar", "my-app.jar"]

apiVersion: apps/v1
kind: Deployment
metadata:
  name: product-service
spec:
  replicas: 3
  selector:
    matchLabels:
      app: product-service
  template:
    metadata:
      labels:
        app: product-service
    spec:
      containers:
      - name: product-service
        image: my-registry/product-service:1.0.0
        ports:
        - containerPort: 8080
        env:
        - name: DB_URL
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: url

public interface UserRepository extends JpaRepository<User, Long> {
    // 方法命名查询
    List<User> findByAgeGreaterThan(int age);

    // 使用Projection返回部分字段
    @Query("SELECT u.id, u.name FROM User u WHERE u.age > :age")
    List<UserSummary> findSummaryByAge(@Param("age") int age);

    interface UserSummary {
        Long getId();
        String getName();
    }
}

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

// 服务层使用缓存
@Service
public class ProductService {
    @Cacheable("products")
    public Product getProductById(Long id) {
        // 从数据库查询
        return productRepository.findById(id).orElseThrow();
    }

    @CacheEvict(value = "products", key = "#product.id")
    public Product updateProduct(Product product) {
        return productRepository.save(product);
    }
}

java -XX:MaxRAMPercentage=75.0 \
     -XX:+UseG1GC \
     -XX:G1HeapRegionSize=16M \
     -XX:InitiatingHeapOccupancyPercent=30 \
     -jar my-app.jar

<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-registry-prometheus</artifactId>
</dependency>

@ExtendWith(MockitoExtension.class)
class UserServiceTest {
    @Mock
    private UserRepository userRepository;

    @InjectMocks
    private UserService userService;

    @Test
    void shouldReturnUserById() {
        // 准备测试数据
        User mockUser = new User(1L, "John");
        when(userRepository.findById(1L)).thenReturn(Optional.of(mockUser));

        // 执行测试
        User result = userService.getUserById(1L);

        // 验证结果
        assertEquals("John", result.getName());
        verify(userRepository, times(1)).findById(1L);
    }
}

@SpringBootTest
@AutoConfigureMockMvc
class OrderControllerIT {
    @Container
    private static final PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:14")
        .withDatabaseName("testdb")
        .withUsername("test")
        .withPassword("test");

    static {
        postgres.start();
        System.setProperty("spring.datasource.url", postgres.getJdbcUrl());
        System.setProperty("spring.datasource.username", postgres.getUsername());
        System.setProperty("spring.datasource.password", postgres.getPassword());
    }

    @Autowired
    private MockMvc mockMvc;

    @Test
    void shouldCreateOrder() throws Exception {
        // 测试订单创建API
        mockMvc.perform(post("/api/orders")
                .contentType(MediaType.APPLICATION_JSON)
                .content("{\"productId\": 1, \"quantity\": 2}"))
            .andExpect(status().isCreated());
    }
}

@Configuration
@EnableWebSecurity
public class SecurityConfig {
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http
            .authorizeRequests()
                .antMatchers("/api/public/**").permitAll()
                .anyRequest().authenticated()
                .and()
            .oauth2ResourceServer()
                .jwt();
        return http.build();
    }
}

@RestController
@RequestMapping("/api/admin")
public class AdminController {
    @PreAuthorize("hasRole('ADMIN')")
    @DeleteMapping("/users/{id}")
    public void deleteUser(@PathVariable Long id) {
        // 删除用户逻辑
    }
}

name: Java CI with Maven
on:
  push:
    branches: [ main ]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - name: Set up JDK 17
        uses: actions/setup-java@v3
        with:
          java-version: '17'
          distribution: 'temurin'
      - name: Build with Maven
        run: mvn clean package
      - name: Push to Docker Hub
        uses: docker/build-push-action@v5
        with:
          context: .
          push: true
          tags: myusername/myapp:${{ github.sha }}