Introduced FilterSupport for internal MeterFilter implementations

Signed-off-by: etki <[email protected]>

Author: etki

micrometer-core/src/main/java/io/micrometer/core/instrument/config/filter/FilterSupport.java

@@ -0,0 +1,14 @@
+package io.micrometer.core.instrument.config.filter;
+
+class FilterSupport {
+    /**
+     * At the moment of writing, it was impossible to estimate tags
+     * count from the outside of class, but quite often a temporary
+     * storage (ArrayList) had to be allocated during processing. To
+     * avoid excessive resizes, this constant is introduced to
+     * preallocate space for such a list.
+     */
+    public static final int DEFAULT_TAG_COUNT_EXPECTATION = 32;
+
+    private FilterSupport() {}
+}

micrometer-core/src/main/java/io/micrometer/core/instrument/config/filter/NoOpFilter.java

@@ -0,0 +1,19 @@
+package io.micrometer.core.instrument.config.filter;
+
+import io.micrometer.core.instrument.config.MeterFilter;
+
+/**
+ * A fallback for all factory methods that have received an input
+ * functionally equivalent to "abstain from processing".
+ *
+ * @since 1.15
+ */
+public class NoOpFilter implements MeterFilter {
+    private static final MeterFilter INSTANCE = new NoOpFilter();
+
+    private NoOpFilter() {}
+
+    public static MeterFilter create() {
+        return INSTANCE;
+    }
+}

micrometer-core/src/test/java/io/micrometer/core/instrument/MeterFilterTest.java renamed to micrometer-core/src/test/java/io/micrometer/core/instrument/config/MeterFilterTest.java

@@ -13,12 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package io.micrometer.core.instrument;
+package io.micrometer.core.instrument.config;
 
 import io.micrometer.common.lang.Nullable;
 import io.micrometer.core.Issue;
-import io.micrometer.core.instrument.config.MeterFilter;
-import io.micrometer.core.instrument.config.MeterFilterReply;
+import io.micrometer.core.instrument.Meter;
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.Tags;
 import io.micrometer.core.instrument.distribution.DistributionStatisticConfig;
 import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
 import org.assertj.core.api.Condition;