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 +1,31 @@
+/*
+ * Copyright 2025 VMware, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+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 +1,37 @@
+/*
+ * Copyright 2025 VMware, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+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/main/java/io/micrometer/core/instrument/config/filter/package-info.java

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2025 VMware, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.micrometer.core.instrument.config.filter;

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;