SpringBoot接口 - 如何实现接口限流之单实例

在以SpringBoot开发Restful接口时，当流量超过服务极限能力时，系统可能会出现卡死、崩溃的情况，所以就有了降级和限流。在接口层如何做限流呢？ 本文主要回顾限流的知识点，并实践单实例限流的一种思路。

• SpringBoot接口 - 如何实现接口限流之单实例
  • 准备知识点
    • 为什么要限流
    • 限流有哪些常见思路？
  • 实现思路
    • 定义RateLimit注解
    • 定义AOP
    • 自定义相关异常
    • 统一结果返回封装
    • controller接口
    • 接口测试
    • 上述实现方案的槽点
  • 示例源码

# 准备知识点

主要的知识点，请参考架构之高并发：限流, 这里小结下。

# 为什么要限流

每个系统都有服务的上线，所以当流量超过服务极限能力时，系统可能会出现卡死、崩溃的情况，所以就有了降级和限流。限流其实就是：当高并发或者瞬时高并发时，为了保证系统的稳定性、可用性，系统以牺牲部分请求为代价或者延迟处理请求为代价，保证系统整体服务可用。

# 限流有哪些常见思路？

• 从算法上看

令牌桶(Token Bucket)、漏桶(leaky bucket)和计数器算法是最常用的三种限流的算法。

• 单实例

应用级限流方式只是单应用内的请求限流，不能进行全局限流。

1. 限流总资源数
2. 限流总并发/连接/请求数
3. 限流某个接口的总并发/请求数
4. 限流某个接口的时间窗请求数
5. 平滑限流某个接口的请求数
6. Guava RateLimiter

• 分布式

我们需要分布式限流和接入层限流来进行全局限流。

1. redis+lua实现中的lua脚本
2. 使用Nginx+Lua实现的Lua脚本
3. 使用 OpenResty 开源的限流方案
4. 限流框架，比如Sentinel实现降级限流熔断

# 实现思路

主要思路：AOP拦截自定义的RateLimit注解，在AOP中通过Guava RateLimiter; Guava RateLimiter提供了令牌桶算法实现：平滑突发限流(SmoothBursty)和平滑预热限流(SmoothWarmingUp)实现。

# 定义RateLimit注解

package tech.pdai.ratelimit.guava.config.ratelimit;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;/*** @author pdai*/
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface RateLimit {int limit() default 10;}

# 定义AOP

package tech.pdai.ratelimit.guava.config.ratelimit;import java.lang.reflect.Method;
import java.util.concurrent.ConcurrentHashMap;import com.google.common.util.concurrent.RateLimiter;
import lombok.extern.slf4j.Slf4j;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Pointcut;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.stereotype.Component;/*** @author pdai*/
@Slf4j
@Aspect
@Component
public class RateLimitAspect {private final ConcurrentHashMap<String, RateLimiter> EXISTED_RATE_LIMITERS = new ConcurrentHashMap<>();@Pointcut("@annotation(tech.pdai.ratelimit.guava.config.ratelimit.RateLimit)")public void rateLimit() {}@Around("rateLimit()")public Object around(ProceedingJoinPoint point) throws Throwable {MethodSignature signature = (MethodSignature) point.getSignature();Method method = signature.getMethod();RateLimit annotation = AnnotationUtils.findAnnotation(method, RateLimit.class);// get rate limiterRateLimiter rateLimiter = EXISTED_RATE_LIMITERS.computeIfAbsent(method.getName(), k -> RateLimiter.create(annotation.limit()));// processif (rateLimiter!=null && rateLimiter.tryAcquire()) {return point.proceed();} else {throw new RuntimeException("too many requests, please try again later...");}}
}

# 自定义相关异常

package tech.pdai.ratelimit.guava.config.exception;import lombok.extern.slf4j.Slf4j;/*** business exception, besides normal exception.** @author pdai*/
@Slf4j
public class BusinessException extends RuntimeException {/*** Constructs a new exception with {@code null} as its detail message. The cause is not initialized, and may* subsequently be initialized by a call to {@link #initCause}.*/public BusinessException() {super();}/*** Constructs a new exception with the specified detail message. The cause is not initialized, and may subsequently* be initialized by a call to {@link #initCause}.** @param message the detail message. The detail message is saved for later retrieval by the {@link #getMessage()}*                method.*/public BusinessException(final String message) {super(message);}/*** Constructs a new exception with the specified detail message and cause.* <p>* Note that the detail message associated with {@code cause} is <i>not</i> automatically incorporated in this* exception's detail message.** @param message the detail message (which is saved for later retrieval by the {@link #getMessage()} method).* @param cause   the cause (which is saved for later retrieval by the {@link #getCause()} method). (A <tt>null</tt>*                value is permitted, and indicates that the cause is nonexistent or unknown.)* @since 1.4*/public BusinessException(final String message, final Throwable cause) {super(message, cause);}/*** Constructs a new exception with the specified cause and a detail message of* <tt>(cause==null ? null : cause.toString())</tt> (which typically contains the class and detail message of* <tt>cause</tt>). This constructor is useful for exceptions that are little more than wrappers for other* throwables (for example, {@link java.security.PrivilegedActionException}).** @param cause the cause (which is saved for later retrieval by the {@link #getCause()} method). (A <tt>null</tt>*              value is permitted, and indicates that the cause is nonexistent or unknown.)* @since 1.4*/public BusinessException(final Throwable cause) {super(cause);}/*** Constructs a new exception with the specified detail message, cause, suppression enabled or disabled, and* writable stack trace enabled or disabled.** @param message            the detail message.* @param cause              the cause. (A {@code null} value is permitted, and indicates that the cause is nonexistent or*                           unknown.)* @param enableSuppression  whether or not suppression is enabled or disabled* @param writableStackTrace whether or not the stack trace should be writable* @since 1.7*/protected BusinessException(final String message, final Throwable cause, boolean enableSuppression,boolean writableStackTrace) {super(message, cause, enableSuppression, writableStackTrace);}}

异常的处理

package tech.pdai.ratelimit.guava.config.exception;import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.RestControllerAdvice;
import tech.pdai.ratelimit.guava.config.response.ResponseResult;
import tech.pdai.ratelimit.guava.config.response.ResponseStatus;/*** @author pdai*/
@Slf4j
@RestControllerAdvice
public class GlobalExceptionHandler {/*** handle business exception.** @param businessException business exception* @return ResponseResult*/@ResponseBody@ExceptionHandler(BusinessException.class)public ResponseResult<BusinessException> processBusinessException(BusinessException businessException) {log.error(businessException.getLocalizedMessage());return ResponseResult.fail(null, businessException.getLocalizedMessage()==null? ResponseStatus.HTTP_STATUS_500.getDescription():businessException.getLocalizedMessage());}/*** handle other exception.** @param exception exception* @return ResponseResult*/@ResponseBody@ExceptionHandler(Exception.class)public ResponseResult<Exception> processException(Exception exception) {log.error(exception.getLocalizedMessage(), exception);return ResponseResult.fail(null, ResponseStatus.HTTP_STATUS_500.getDescription());}
}

# 统一结果返回封装

package tech.pdai.ratelimit.guava.config.response;import java.io.Serializable;import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;@NoArgsConstructor
@AllArgsConstructor
@Data
@Builder
public class ResponseResult<T> {/*** response timestamp.*/private long timestamp;/*** response code, 200 -> OK.*/private String status;/*** response message.*/private String message;/*** response data.*/private T data;/*** response success result wrapper.** @param <T> type of data class* @return response result*/public static <T> ResponseResult<T> success() {return success(null);}/*** response success result wrapper.** @param data response data* @param <T>  type of data class* @return response result*/public static <T> ResponseResult<T> success(T data) {return ResponseResult.<T>builder().data(data).message(ResponseStatus.SUCCESS.getDescription()).status(ResponseStatus.SUCCESS.getResponseCode()).timestamp(System.currentTimeMillis()).build();}/*** response error result wrapper.** @param message error message* @param <T>     type of data class* @return response result*/public static <T extends Serializable> ResponseResult<T> fail(String message) {return fail(null, message);}/*** response error result wrapper.** @param data    response data* @param message error message* @param <T>     type of data class* @return response result*/public static <T> ResponseResult<T> fail(T data, String message) {return ResponseResult.<T>builder().data(data).message(message).status(ResponseStatus.FAIL.getResponseCode()).timestamp(System.currentTimeMillis()).build();}}

# controller接口

package tech.pdai.ratelimit.guava.controller;import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import tech.pdai.ratelimit.guava.config.ratelimit.RateLimit;
import tech.pdai.ratelimit.guava.config.response.ResponseResult;/*** @author pdai*/
@Slf4j
@RestController
public class RateLimitTestController {@RateLimit@GetMapping("/limit")public ResponseResult<String> limit() {log.info("limit");return ResponseResult.success();}@RateLimit(limit = 5)@GetMapping("/limit1")public ResponseResult<String> limit1() {log.info("limit1");return ResponseResult.success();}@GetMapping("/nolimit")public ResponseResult<String> noRateLimiter() {log.info("no limit");return ResponseResult.success();}}

# 接口测试

@SneakyThrows
public static void test(int clientSize) {CountDownLatch downLatch = new CountDownLatch(clientSize);ExecutorService fixedThreadPool = Executors.newFixedThreadPool(clientSize);IntStream.range(0, clientSize).forEach(i ->fixedThreadPool.submit(() -> {RestTemplate restTemplate = new RestTemplate();restTemplate.getForObject("http://localhost:8080/limit1", ResponseResult.class);downLatch.countDown();}));downLatch.await();fixedThreadPool.shutdown();
}

测试结果

2021-10-01 15:22:47.171  INFO 30092 --- [nio-8080-exec-4] t.p.r.g.c.RateLimitTestController        : limit1
2021-10-01 15:22:47.171  INFO 30092 --- [nio-8080-exec-8] t.p.r.g.c.RateLimitTestController        : limit1
2021-10-01 15:22:47.171  INFO 30092 --- [nio-8080-exec-5] t.p.r.g.c.RateLimitTestController        : limit1
2021-10-01 15:22:47.187  INFO 30092 --- [nio-8080-exec-9] t.p.r.g.c.RateLimitTestController        : limit1
2021-10-01 15:22:47.187  INFO 30092 --- [nio-8080-exec-2] t.p.r.g.c.RateLimitTestController        : limit1
2021-10-01 15:22:47.187  INFO 30092 --- [io-8080-exec-10] t.p.r.g.c.RateLimitTestController        : limit1
2021-10-01 15:22:47.202 ERROR 30092 --- [nio-8080-exec-7] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.202 ERROR 30092 --- [nio-8080-exec-6] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.221 ERROR 30092 --- [nio-8080-exec-1] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.222 ERROR 30092 --- [nio-8080-exec-5] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [nio-8080-exec-6] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [nio-8080-exec-8] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [nio-8080-exec-3] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [io-8080-exec-12] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [io-8080-exec-14] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [io-8080-exec-13] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.225 ERROR 30092 --- [io-8080-exec-15] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.240 ERROR 30092 --- [io-8080-exec-11] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.240 ERROR 30092 --- [nio-8080-exec-4] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...
2021-10-01 15:22:47.256 ERROR 30092 --- [nio-8080-exec-2] t.p.r.g.c.e.GlobalExceptionHandler       : too many requests, please try again later...

# 上述实现方案的槽点

注意

必须要说明一下，上述实现方式只是单实例下一种思路而已，如果细细的看，上面的代码存在一些槽点。

1. 首先, EXISTED_RATE_LIMITERS.computeIfAbsent(method.getName(), k -> RateLimiter.create(annotation.limit())) 这行代码中 method.getName()表明是对方法名进行限流的，其实并不合适，应该需要至少加上类名；
2. 其次, 如果首次运行时访问的请求是一次性涌入的，即EXISTED_RATE_LIMITERS还是空的时候并发请求@RateLimit接口，那么RateLimiter.create(annotation.limit())是会重复创建并加入到EXISTED_RATE_LIMITERS的，这是明显的bug；
3. 再者, 上述实现方式按照方法名去限定请求量，对于很多情况下至少需要支持按照IP和方法名，或者其它自定义的方式进行限流。
4. 其它一些场景支持的参数抽象和封装等