面试重要程度：⭐⭐⭐⭐⭐

常见提问方式：如何设计一个高并发系统？系统架构设计需要考虑哪些因素？

预计阅读时间：35分钟

🎯 高并发系统设计核心原则

高可用性设计原则

/**
 * 高可用性架构设计
 */
@Component
public class HighAvailabilityDesign {
    
    /**
     * 系统可用性计算
     */
    public static class AvailabilityCalculator {
        
        // 可用性等级定义
        public enum AvailabilityLevel {
            BASIC(99.0, "基础级", "87.6小时/年"),
            STANDARD(99.9, "标准级", "8.76小时/年"),
            HIGH(99.99, "高可用", "52.56分钟/年"),
            ULTRA_HIGH(99.999, "超高可用", "5.26分钟/年");
            
            private final double percentage;
            private final String name;
            private final String downtime;
        }
        
        /**
         * 计算系统整体可用性（串联系统）
         */
        public double calculateSerialAvailability(List<Double> componentAvailabilities) {
            return componentAvailabilities.stream()
                .reduce(1.0, (a, b) -> a * b);
        }
        
        /**
         * 计算系统整体可用性（并联系统）
         */
        public double calculateParallelAvailability(List<Double> componentAvailabilities) {
            double unavailability = componentAvailabilities.stream()
                .map(availability -> 1.0 - availability)
                .reduce(1.0, (a, b) -> a * b);
            return 1.0 - unavailability;
        }
    }
    
    /**
     * 容错设计模式
     */
    @Component
    public static class FaultTolerancePatterns {
        
        /**
         * 故障隔离 - 舱壁模式
         */
        @Component
        public static class BulkheadPattern {
            
            // 为不同业务分配独立的线程池
            private final ExecutorService userServiceExecutor;
            private final ExecutorService orderServiceExecutor;
            
            public BulkheadPattern() {
                this.userServiceExecutor = new ThreadPoolExecutor(
                    10, 20, 60L, TimeUnit.SECONDS,
                    new LinkedBlockingQueue<>(100),
                    new ThreadFactoryBuilder().setNameFormat("user-service-%d").build()
                );
                
                this.orderServiceExecutor = new ThreadPoolExecutor(
                    15, 30, 60L, TimeUnit.SECONDS,
                    new LinkedBlockingQueue<>(200),
                    new ThreadFactoryBuilder().setNameFormat("order-service-%d").build()
                );
            }
            
            /**
             * 用户服务处理
             */
            public CompletableFuture<UserResponse> handleUserRequest(UserRequest request) {
                return CompletableFuture.supplyAsync(() -> {
                    try {
                        return processUserRequest(request);
                    } catch (Exception e) {
                        log.error("User service error", e);
                        return UserResponse.error("用户服务暂时不可用");
                    }
                }, userServiceExecutor);
            }
        }
        
        /**
         * 超时控制
         */
        @Component
        public static class TimeoutControl {
            
            /**
             * 带超时的服务调用
             */
            public <T> CompletableFuture<T> callWithTimeout(
                    Supplier<T> supplier, 
                    long timeout, 
                    TimeUnit unit) {
                
                CompletableFuture<T> future = CompletableFuture.supplyAsync(supplier);
                CompletableFuture<T> timeoutFuture = new CompletableFuture<>();
                
                ScheduledExecutorService scheduler = Executors.newSingleThreadScheduledExecutor();
                scheduler.schedule(() -> {
                    timeoutFuture.completeExceptionally(new TimeoutException("Operation timeout"));
                }, timeout, unit);
                
                return CompletableFuture.anyOf(future, timeoutFuture)
                    .thenApply(result -> (T) result);
            }
            
            /**
             * HTTP客户端超时配置
             */
            @Bean
            public RestTemplate restTemplateWithTimeout() {
                HttpComponentsClientHttpRequestFactory factory = 
                    new HttpComponentsClientHttpRequestFactory();
                
                factory.setConnectTimeout(5000);        // 连接超时5秒
                factory.setReadTimeout(10000);          // 读取超时10秒
                factory.setConnectionRequestTimeout(3000); // 请求超时3秒
                
                return new RestTemplate(factory);
            }
        }
        
        /**
         * 重试机制
         */
        @Component
        public static class RetryMechanism {
            
            /**
             * 指数退避重试
             */
            public <T> T retryWithExponentialBackoff(
                    Supplier<T> operation,
                    int maxRetries,
                    long initialDelay,
                    double multiplier) {
                
                Exception lastException = null;
                long delay = initialDelay;
                
                for (int attempt = 0; attempt <= maxRetries; attempt++) {
                    try {
                        return operation.get();
                    } catch (Exception e) {
                        lastException = e;
                        
                        if (attempt == maxRetries) {
                            break;
                        }
                        
                        try {
                            Thread.sleep(delay);
                            delay = (long) (delay * multiplier);
                        } catch (InterruptedException ie) {
                            Thread.currentThread().interrupt();
                            throw new RuntimeException("Retry interrupted", ie);
                        }
                    }
                }
                
                throw new RuntimeException("Operation failed after retries", lastException);
            }
            
            /**
             * Spring Retry注解方式
             */
            @Retryable(
                value = {Exception.class},
                maxAttempts = 3,
                backoff = @Backoff(delay = 1000, multiplier = 2)
            )
            public String callExternalService(String param) {
                return externalServiceClient.call(param);
            }
            
            @Recover
            public String recoverFromFailure(Exception e, String param) {
                log.error("External service call failed after retries", e);
                return "默认响应";
            }
        }
    }
}

高并发性设计原则

/**
 * 高并发架构设计
 */
@Component
public class HighConcurrencyDesign {
    
    /**
     * 无状态设计
     */
    @RestController
    @RequestMapping("/api/stateless")
    public static class StatelessController {
        
        @Autowired
        private UserService userService;
        
        @Autowir