🐛 修复使用Guava限流时并发问题

[ISSUE#55](https://github.com/xkcoding/spring-boot-demo/issues/55)，感谢[@Git950715](https://github.com/Git950715)

spring-boot-demo-ratelimit-guava/README.md

@@ -135,7 +135,7 @@ public @interface RateLimiter {
 @Aspect
 @Component
 public class RateLimiterAspect {
-    private static final com.google.common.util.concurrent.RateLimiter RATE_LIMITER = com.google.common.util.concurrent.RateLimiter.create(Double.MAX_VALUE);
+    private static final ConcurrentMap<String, com.google.common.util.concurrent.RateLimiter> RATE_LIMITER_CACHE = new ConcurrentHashMap<>();
 
     @Pointcut("@annotation(com.xkcoding.ratelimit.guava.annotation.RateLimiter)")
     public void rateLimit() {
@@ -150,11 +150,14 @@ public class RateLimiterAspect {
         RateLimiter rateLimiter = AnnotationUtils.findAnnotation(method, RateLimiter.class);
         if (rateLimiter != null && rateLimiter.qps() > RateLimiter.NOT_LIMITED) {
             double qps = rateLimiter.qps();
-            log.debug("【{}】的QPS设置为: {}", method.getName(), qps);
-            // 重新设置 QPS
-            RATE_LIMITER.setRate(qps);
+            if (RATE_LIMITER_CACHE.get(method.getName()) == null) {
+                // 初始化 QPS
+                RATE_LIMITER_CACHE.put(method.getName(), com.google.common.util.concurrent.RateLimiter.create(qps));
+            }
+
+            log.debug("【{}】的QPS设置为: {}", method.getName(), RATE_LIMITER_CACHE.get(method.getName()).getRate());
             // 尝试获取令牌
-            if (!RATE_LIMITER.tryAcquire(rateLimiter.timeout(), rateLimiter.timeUnit())) {
+            if (RATE_LIMITER_CACHE.get(method.getName()) != null && !RATE_LIMITER_CACHE.get(method.getName()).tryAcquire(rateLimiter.timeout(), rateLimiter.timeUnit())) {
                 throw new RuntimeException("手速太快了，慢点儿吧~");
             }
         }

spring-boot-demo-ratelimit-guava/src/main/java/com/xkcoding/ratelimit/guava/aspect/RateLimiterAspect.java

@@ -11,6 +11,8 @@ import org.springframework.core.annotation.AnnotationUtils;
 import org.springframework.stereotype.Component;
 
 import java.lang.reflect.Method;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 /**
  * <p>
@@ -24,7 +26,7 @@ import java.lang.reflect.Method;
 @Aspect
 @Component
 public class RateLimiterAspect {
-    private static final com.google.common.util.concurrent.RateLimiter RATE_LIMITER = com.google.common.util.concurrent.RateLimiter.create(Double.MAX_VALUE);
+    private static final ConcurrentMap<String, com.google.common.util.concurrent.RateLimiter> RATE_LIMITER_CACHE = new ConcurrentHashMap<>();
 
     @Pointcut("@annotation(com.xkcoding.ratelimit.guava.annotation.RateLimiter)")
     public void rateLimit() {
@@ -39,11 +41,14 @@ public class RateLimiterAspect {
         RateLimiter rateLimiter = AnnotationUtils.findAnnotation(method, RateLimiter.class);
         if (rateLimiter != null && rateLimiter.qps() > RateLimiter.NOT_LIMITED) {
             double qps = rateLimiter.qps();
-            log.debug("【{}】的QPS设置为: {}", method.getName(), qps);
-            // 重新设置 QPS
-            RATE_LIMITER.setRate(qps);
+            if (RATE_LIMITER_CACHE.get(method.getName()) == null) {
+                // 初始化 QPS
+                RATE_LIMITER_CACHE.put(method.getName(), com.google.common.util.concurrent.RateLimiter.create(qps));
+            }
+
+            log.debug("【{}】的QPS设置为: {}", method.getName(), RATE_LIMITER_CACHE.get(method.getName()).getRate());
             // 尝试获取令牌
-            if (!RATE_LIMITER.tryAcquire(rateLimiter.timeout(), rateLimiter.timeUnit())) {
+            if (RATE_LIMITER_CACHE.get(method.getName()) != null && !RATE_LIMITER_CACHE.get(method.getName()).tryAcquire(rateLimiter.timeout(), rateLimiter.timeUnit())) {
                 throw new RuntimeException("手速太快了，慢点儿吧~");
             }
         }