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Salad Lam
Salad Lam

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How to add a meter data into Spring Boot Actuator metrics endpoint

#java #springboot

Step

First, to add the following dependency

pom.xml

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<!-- for Prometheus endpoint -->
<dependency>
    <groupId>io.micrometer</groupId>
    <artifactId>micrometer-registry-prometheus</artifactId>
</dependency>
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Then to enable endpoints through web access

src/main/resources/application.properties

management.endpoints.web.exposure.include=prometheus,metrics
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Add a singleton component

@Component
public class MyMetrics implements MeterBinder {

    private final Random random = new Random();
    private final AtomicInteger counter = new AtomicInteger();

    @Override
    public void bindTo(MeterRegistry registry) {
        // can any value
        Gauge.builder("mymetrics.gauge", this, MyMetrics::getRandom)
                .description("MyMetrics gauge")
                .register(registry);

        // must the same or greater than the value last got, or reset to zero on restart
        FunctionCounter.builder("mymetrics.counter", this, MyMetrics::counterGetAndIncrement)
                .description("MyMetrics counter")
                .register(registry);
    }

    public double getRandom() {
        return random.nextDouble();
    }

    public int counterGetAndIncrement() {
        return counter.getAndIncrement();
    }

}
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Finally, metric data can be accessed through

/actuator/metrics/mymetrics.counter

{"name":"mymetrics.counter","description":"MyMetrics counter","baseUnit":null,"measurements":[{"statistic":"COUNT","value":9.0}],"availableTags":[]}
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/actuator/metrics/mymetrics.gauge

{"name":"mymetrics.gauge","description":"MyMetrics gauge","baseUnit":null,"measurements":[{"statistic":"VALUE","value":0.7618330619753056}],"availableTags":[]}
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/actuator/prometheus

# HELP mymetrics_counter_total MyMetrics counter
# TYPE mymetrics_counter_total counter
mymetrics_counter_total 8.0
# HELP mymetrics_gauge MyMetrics gauge
# TYPE mymetrics_gauge gauge
mymetrics_gauge 0.1346348968727723
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Beans

Endpoints

Endpoints are annotated with org.springframework.boot.actuate.endpoint.annotation.Endpoint, and they are beans and managed by Spring's BeanFactory.

Endpoint Class Created by
metrics org.springframework.boot.actuate.metrics.MetricsEndpoint org.springframework.boot.actuate.autoconfigure.metrics.MetricsEndpointAutoConfiguration#metricsEndpoint
prometheus org.springframework.boot.actuate.metrics.export.prometheus.PrometheusScrapeEndpoint org.springframework.boot.actuate.autoconfigure.metrics.export.prometheus.PrometheusMetricsExportAutoConfiguration.PrometheusScrapeEndpointConfiguration#prometheusEndpoint

org.springframework.boot.actuate.endpoint.web.servlet.WebMvcEndpointHandlerMapping class

This is created by org.springframework.boot.actuate.autoconfigure.endpoint.web.servlet.WebMvcEndpointManagementContextConfiguration#webEndpointServletHandlerMapping. Endpoints information is provided by org.springframework.boot.actuate.endpoint.web.annotation.WebEndpointDiscoverer.

The mapping between path and endpoints will be registered in org.springframework.boot.actuate.endpoint.web.servlet.AbstractWebMvcEndpointHandlerMapping#initHandlerMethods.

It implements org.springframework.web.servlet.HandlerMapping interface, so the instance will be registered into DispatcherServlet during instance construction.

Expose endpoints to JMX

Just add a line into src/main/resources/application.properties

spring.jmx.enabled=true
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Association of the endpoints with MBeanServer is by org.springframework.boot.actuate.autoconfigure.endpoint.jmx.JmxEndpointAutoConfiguration.

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