如何使用OpenTelemetry Java API获取当前计数器值？

方案一：本地同步维护计数器值 #

由于你完全控制Counter的增减调用，最直接的方式是在调用OpenTelemetry Counter的add方法时，同步更新一个线程安全的本地变量（比如AtomicLong），直接读取这个变量就能拿到当前值。

示例代码：

import io.opentelemetry.api.metrics.Counter;
import io.opentelemetry.api.metrics.Meter;
import io.opentelemetry.api.OpenTelemetry;
import java.util.concurrent.atomic.AtomicLong;

public class CustomCounter {
    private final Counter<Long> otelCounter;
    private final AtomicLong localCounter = new AtomicLong(0);

    public CustomCounter(OpenTelemetry openTelemetry) {
        Meter meter = openTelemetry.meterBuilder("your.meter.name").build();
        otelCounter = meter.counterBuilder("your.counter.name")
                .setDescription("Custom counter")
                .setUnit("1")
                .build();
    }

    public void increment(long value) {
        otelCounter.add(value);
        localCounter.addAndGet(value);
    }

    public long getCurrentValue() {
        return localCounter.get();
    }
}

方案二：使用内存导出器（InMemoryMetricExporter）读取指标 #

OpenTelemetry Java SDK提供了InMemoryMetricExporter，可以将指标数据保存在内存中，无需发送到外部后端，你可以通过MetricReader手动或定期获取聚合后的指标值。

步骤1：添加依赖（Maven） #

<dependency>
    <groupId>io.opentelemetry</groupId>
    <artifactId>opentelemetry-sdk-metrics</artifactId>
    <version>your-otel-version</version>
</dependency>
<dependency>
    <groupId>io.opentelemetry</groupId>
    <artifactId>opentelemetry-exporter-metrics-inmemory</artifactId>
    <version>your-otel-version</version>
</dependency>

步骤2：配置并读取Counter值 #

import io.opentelemetry.api.OpenTelemetry;
import io.opentelemetry.api.metrics.Counter;
import io.opentelemetry.api.metrics.Meter;
import io.opentelemetry.exporter.metrics.inmemory.InMemoryMetricExporter;
import io.opentelemetry.sdk.metrics.SdkMeterProvider;
import io.opentelemetry.sdk.metrics.export.MetricReader;
import io.opentelemetry.sdk.metrics.export.PeriodicMetricReader;
import java.util.concurrent.TimeUnit;

public class OtelCounterReader {
    private final Counter<Long> otelCounter;
    private final InMemoryMetricExporter exporter;
    private final MetricReader reader;

    public OtelCounterReader() {
        exporter = InMemoryMetricExporter.create();
        reader = PeriodicMetricReader.builder(exporter)
                .setInterval(1, TimeUnit.SECONDS) // 定期收集，也可替换为手动读取的ManualMetricReader
                .build();

        SdkMeterProvider meterProvider = SdkMeterProvider.builder()
                .registerMetricReader(reader)
                .build();

        OpenTelemetry openTelemetry = OpenTelemetry.builder()
                .setMeterProvider(meterProvider)
                .build();

        Meter meter = openTelemetry.meterBuilder("your.meter.name").build();
        otelCounter = meter.counterBuilder("your.counter.name")
                .setDescription("Counter for testing")
                .setUnit("1")
                .build();
    }

    public void increment(long value) {
        otelCounter.add(value);
    }

    public long getCurrentCounterValue() {
        // 手动触发一次收集（若用PeriodicMetricReader也可等待自动收集）
        reader.collectAllMetrics().join();
        
        return exporter.getFinishedMetricItems().stream()
                .filter(item -> item.getName().equals("your.counter.name"))
                .findFirst()
                .map(item -> item.getSumData().getPoints().get(0).getValue().longValue())
                .orElse(0L);
    }
}

注意事项 #

• Counter的聚合类型为Sum，需从SumData中提取数值；
• 若需要完全手动控制收集时机，可使用ManualMetricReader替代PeriodicMetricReader，主动调用collect方法触发指标聚合。

内容的提问来源于stack exchange，提问作者Vasu. Tk