How to create a metric in Spring-boot?

Question

How to create a metric in SpringBoot2.1.4.RELEASE?

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

Answer 1

If you're using spring-boot-starter-actuator, a bean of type MeterRegistry will be created. Once autowired, this allows you to create several metrics, such as counters, gauges and metrics. Each of these have a fluent builder you can use that allows you to set them up, for example:

Counters

A Counter can be used for simple incrementing metrics, for example, the amount of times a method has been called.

Counter customCounter = Counter
    .builder("my.custom.metric.counter")
    .register(meterRegistry);

By using customCounter.increment() you can increase the value.

Gauges

A Gauge on the other hand is a dynamic/live value that should be measured directly. An example of this is the size of a connection pool:

 Gauge
      .builder("my.custom.metric.gauge", () -> connectionPool.size())
      .register(meterRegistry);

The builder allows you to pass a Supplier to measure whatever you want.

Timers

As the name mentions, this can be used to measure the time it takes do something, for example:

Timer customTimer = Timer
     .builder("my.custom.metric.timer")
     .register(meterRegistry);

By using the customTimer.record(() -> myMethod()), you can add a metric about how long it takes to invoke myMethod().

---

You should be able to access these metrics when running the application. If you want to see them through HTTP, you can enable the metrics endpoint like this:

management.endpoints.web.exposure.include=metrics # Enable metrics endpoint

After that, you should be able to visit http://localhost:8080/actuator to see the list of enabled endpoints, which should contain http://localhost:8080/actuator/metrics.

This API should return a list of available metrics, which can be accessed as http://localhost:8080/actuator/metrics/my.custom.metric.counter.

Answer 2

You can use micrometer:

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
        <dependency>
            <groupId>io.micrometer</groupId>
            <artifactId>micrometer-registry-prometheus</artifactId>
        </dependency>

This will give you the end-point: /actuator/prometheus