Skip registering Caffeine meters when statistics are not enabled

This commit also fixes and improves GuavaCacheMetricsTest and CaffeineCacheMetricsTest.

Closes micrometer-metricsgh-5408

micrometer-core/src/main/java/io/micrometer/core/instrument/binder/cache/CacheMeterBinder.java

@@ -40,6 +40,8 @@ public abstract class CacheMeterBinder<C> implements MeterBinder {
 
     private static final String DESCRIPTION_CACHE_GETS = "The number of times cache lookup methods have returned a cached (hit) or uncached (newly loaded or null) value (miss).";
 
+    static final long UNSUPPORTED = -1L;
+
     private final WeakReference<C> cacheRef;
 
     private final Iterable<Tag> tags;
@@ -75,16 +77,20 @@ public final void bindTo(MeterRegistry registry) {
             }).tags(tags).tag("result", "miss").description(DESCRIPTION_CACHE_GETS).register(registry);
         }
 
-        FunctionCounter.builder("cache.gets", cache, c -> hitCount())
-            .tags(tags)
-            .tag("result", "hit")
-            .description(DESCRIPTION_CACHE_GETS)
-            .register(registry);
+        if (hitCount() != UNSUPPORTED) {
+            FunctionCounter.builder("cache.gets", cache, c -> hitCount())
+                .tags(tags)
+                .tag("result", "hit")
+                .description(DESCRIPTION_CACHE_GETS)
+                .register(registry);
+        }
 
-        FunctionCounter.builder("cache.puts", cache, c -> putCount())
-            .tags(tags)
-            .description("The number of entries added to the cache")
-            .register(registry);
+        if (putCount() != UNSUPPORTED) {
+            FunctionCounter.builder("cache.puts", cache, c -> putCount())
+                .tags(tags)
+                .description("The number of entries added to the cache")
+                .register(registry);
+        }
 
         if (evictionCount() != null) {
             FunctionCounter.builder("cache.evictions", cache, c -> {
@@ -108,7 +114,8 @@ public final void bindTo(MeterRegistry registry) {
 
     /**
      * @return Get requests that resulted in a "hit" against an existing cache entry.
-     * Monotonically increasing hit count.
+     * Monotonically increasing hit count. Returns -1 if the cache implementation does not
+     * support this.
      */
     protected abstract long hitCount();
 
@@ -134,6 +141,7 @@ public final void bindTo(MeterRegistry registry) {
      * The put mechanism is unimportant - this count applies to entries added to the cache
      * according to a pre-defined load function such as exists in Guava/Caffeine caches as
      * well as manual puts. Note that Guava/Caffeine caches don't count manual puts.
+     * Returns -1 if the cache implementation does not support this.
      * @return Total number of entries added to the cache. Monotonically increasing count.
      */
     protected abstract long putCount();

micrometer-core/src/main/java/io/micrometer/core/instrument/binder/cache/CaffeineCacheMetrics.java

@@ -65,7 +65,7 @@ public CaffeineCacheMetrics(C cache, String cacheName, Iterable<Tag> tags) {
 
         if (!cache.policy().isRecordingStats()) {
             log.warn(
-                    "The cache '{}' is not recording statistics, so their values will be zero. Call 'Caffeine#recordStats()' prior to building the cache for metrics to be recorded.",
+                    "The cache '{}' is not recording statistics. No meters except 'cache.size' will be registered. Call 'Caffeine#recordStats()' prior to building the cache for metrics to be recorded.",
                     cacheName);
         }
     }
@@ -176,6 +176,10 @@ protected long putCount() {
     @Override
     protected void bindImplementationSpecificMetrics(MeterRegistry registry) {
         C cache = getCache();
+        if (cache == null || !cache.policy().isRecordingStats()) {
+            return;
+        }
+
         FunctionCounter.builder("cache.eviction.weight", cache, c -> c.stats().evictionWeight())
             .tags(getTagsWithCacheName())
             .description("The sum of weights of evicted entries. This total does not include manual invalidations.")
@@ -206,6 +210,10 @@ protected void bindImplementationSpecificMetrics(MeterRegistry registry) {
     private Long getOrDefault(Function<C, Long> function, @Nullable Long defaultValue) {
         C cache = getCache();
         if (cache != null) {
+            if (!cache.policy().isRecordingStats()) {
+                return null;
+            }
+
             return function.apply(cache);
         }
 
@@ -215,6 +223,10 @@ private Long getOrDefault(Function<C, Long> function, @Nullable Long defaultValu
     private long getOrDefault(ToLongFunction<C> function, long defaultValue) {
         C cache = getCache();
         if (cache != null) {
+            if (!cache.policy().isRecordingStats()) {
+                return UNSUPPORTED;
+            }
+
             return function.applyAsLong(cache);
         }
 

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/cache/CaffeineCacheMetricsTest.java

@@ -23,12 +23,13 @@
 import io.micrometer.core.instrument.MeterRegistry;
 import io.micrometer.core.instrument.Tags;
 import io.micrometer.core.instrument.TimeGauge;
+import io.micrometer.core.instrument.search.MeterNotFoundException;
 import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
 import org.junit.jupiter.api.Test;
 
 import java.util.concurrent.TimeUnit;
 
-import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.*;
 
 /**
  * Tests for {@link CaffeineCacheMetrics}.
@@ -103,21 +104,34 @@ void returnCacheSize() {
 
     @Test
     void returnHitCount() {
+        MeterRegistry meterRegistry = new SimpleMeterRegistry();
+        metrics.bindTo(meterRegistry);
+
         cache.put("a", "1");
         cache.get("a");
         cache.get("a");
 
         assertThat(metrics.hitCount()).isEqualTo(cache.stats().hitCount()).isEqualTo(2);
+        assertThat(meterRegistry.get("cache.gets").tag("result", "hit").functionCounter().count()).isEqualTo(2);
     }
 
     @Test
     void returnHitCountWithoutRecordStats() {
         LoadingCache<String, String> cache = Caffeine.newBuilder().build(key -> "");
+        CaffeineCacheMetrics<String, String, Cache<String, String>> metrics = new CaffeineCacheMetrics<>(cache,
+                "testCache", expectedTag);
+
+        MeterRegistry meterRegistry = new SimpleMeterRegistry();
+        metrics.bindTo(meterRegistry);
+
         cache.put("a", "1");
         cache.get("a");
         cache.get("a");
 
-        assertThat(metrics.hitCount()).isEqualTo(cache.stats().hitCount()).isEqualTo(0);
+        assertThat(cache.stats().hitCount()).isEqualTo(0);
+        assertThat(metrics.hitCount()).isEqualTo(CaffeineCacheMetrics.UNSUPPORTED);
+        assertThatExceptionOfType(MeterNotFoundException.class)
+            .isThrownBy(() -> meterRegistry.get("cache.gets").tag("result", "hit").functionCounter());
     }
 
     @Test

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/cache/GuavaCacheMetricsTest.java

@@ -103,11 +103,15 @@ void returnCacheSize() {
 
     @Test
     void returnHitCount() throws ExecutionException {
+        MeterRegistry meterRegistry = new SimpleMeterRegistry();
+        metrics.bindTo(meterRegistry);
+
         cache.put("a", "1");
         cache.get("a");
         cache.get("a");
 
         assertThat(metrics.hitCount()).isEqualTo(cache.stats().hitCount()).isEqualTo(2);
+        assertThat(meterRegistry.get("cache.gets").tag("result", "hit").functionCounter().count()).isEqualTo(2);
     }
 
     @Test
@@ -117,12 +121,18 @@ public String load(String key) {
                 return "";
             }
         });
+        GuavaCacheMetrics<String, String, Cache<String, String>> metrics = new GuavaCacheMetrics<>(cache, "testCache",
+                expectedTag);
+
+        MeterRegistry meterRegistry = new SimpleMeterRegistry();
+        metrics.bindTo(meterRegistry);
 
         cache.put("a", "1");
         cache.get("a");
         cache.get("a");
 
         assertThat(metrics.hitCount()).isEqualTo(cache.stats().hitCount()).isEqualTo(0);
+        assertThat(meterRegistry.get("cache.gets").tag("result", "hit").functionCounter().count()).isEqualTo(0);
     }
 
     @Test