A Spring PublicMetrics ExpositionHook for Prometheus

dependency.gradle

compile 'io.prometheus:client:0.0.8'
compile 'com.matttproud.accepts:accepts:0.0.2'
compile 'args4j:args4j:2.0.16'

ExampleMetricsService.groovy

package de.gesellix.example

import com.matttproud.accepts.Accept
import com.matttproud.accepts.Parser
import io.prometheus.client.Prometheus
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.web.bind.annotation.RequestMapping
import org.springframework.web.bind.annotation.ResponseStatus
import org.springframework.web.bind.annotation.RestController

import javax.annotation.PostConstruct
import javax.servlet.http.HttpServletRequest
import javax.servlet.http.HttpServletResponse

import static org.springframework.http.HttpStatus.OK
import static org.springframework.web.bind.annotation.RequestMethod.GET

@RestController
class ExampleMetricsService {

  @Autowired
  SpringBootMetricsExpositionHook springBootMetricsExpositionHook

  @PostConstruct
  def init() {
    Prometheus.defaultInitialize()
    Prometheus.defaultAddPreexpositionHook(springBootMetricsExpositionHook)
  }

  @RequestMapping(value = "/prom", method = GET)
  @ResponseStatus(OK)
  def metrics(HttpServletRequest request, HttpServletResponse response) throws IOException {
    boolean dispensed = false
    try {
      for (final Accept spec : Parser.parse(request)) {
        if ("application".equals(spec.getType()) && "vnd.google.protobuf".equals(spec.getSubtype())) {
          final Map<String, String> params = spec.getParams()
          if ("io.prometheus.client.MetricFamily".equals(params.get("proto"))
              && "delimited".equals(params.get("encoding"))) {
            dumpProto(response)
            dispensed = true
            break
          }
        }
      }
    }
    catch (final IllegalArgumentException ignore) {
    }
    finally {
      dispensed || dumpJson(response)
    }
  }

  def dumpJson(final HttpServletResponse resp) throws IOException {
    resp.setContentType("application/json; schema=\"prometheus/telemetry\"; version=0.0.2")
    Prometheus.defaultDumpJson(resp.getWriter())
  }

  def dumpProto(final HttpServletResponse resp) throws IOException {
    resp.setContentType("application/vnd.google.protobuf; proto=\"io.prometheus.client.MetricFamily\"; encoding=\"delimited\"")
    final BufferedOutputStream buf = new BufferedOutputStream(resp.getOutputStream())
    Prometheus.defaultDumpProto(buf)
    buf.close()
  }
}

SpringBootMetricsExpositionHook.groovy

package de.gesellix.example

import io.prometheus.client.Prometheus
import io.prometheus.client.metrics.Gauge
import org.springframework.beans.factory.annotation.Autowired
import org.springframework.boot.actuate.endpoint.PublicMetrics
import org.springframework.boot.actuate.endpoint.VanillaPublicMetrics
import org.springframework.boot.actuate.metrics.Metric
import org.springframework.boot.actuate.metrics.reader.MetricReader
import org.springframework.boot.actuate.metrics.repository.InMemoryMetricRepository
import org.springframework.stereotype.Component

import javax.annotation.PostConstruct

@Component
class SpringBootMetricsExpositionHook implements Prometheus.ExpositionHook {

  @Autowired
  def MetricReader metricRepository = new InMemoryMetricRepository()
  def PublicMetrics metrics

  def static final Gauge publicMetrics = Gauge.newBuilder()
      .namespace("spring")
      .name("metrics")
      .labelNames("name")
      .documentation("All Spring public metrics")
      .build()


  @PostConstruct
  def init() {
    metrics = new VanillaPublicMetrics(metricRepository)
  }

  @Override
  void run() {
    for (Metric<? extends Number> metric : metrics.metrics()) {
      publicMetrics.newPartial()
          .labelPair("name", metric.getName())
          .apply()
          .set(metric.getValue().doubleValue())
    }
  }
}