sdks/java/testing/test-utils/src/main/java/org/apache/beam/sdk/testutils/metrics/CountMonitor.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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
 *
 *     http://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 org.apache.beam.sdk.testutils.metrics;

import org.apache.beam.sdk.metrics.Counter;
import org.apache.beam.sdk.metrics.Metrics;
import org.apache.beam.sdk.transforms.DoFn;

/**
 * Monitor that records number of elements flowing through a pipeline
 *
 * <p>To use: apply a monitor in a desired place in the pipeline. This will capture how many
 * elements * flew through this DoFn. Such information can be then collected and written out and
 * queried using * {@link org.apache.beam.sdk.testutils.metrics.MetricsReader}.
 */
public class CountMonitor<T> extends DoFn<T, T> {
  private Counter counter;

  public CountMonitor(String namespace, String name) {
    this.counter = Metrics.counter(namespace, name);
  }

  @ProcessElement
  public void processElement(ProcessContext context) {
    counter.inc();
    context.output(context.element());
  }
}