[BAEL-17473] - Initial commit

spring-boot-runtime/src/main/java/com/baeldung/compare/ComparisonApplication.java

@@ -0,0 +1,12 @@
+package com.baeldung.compare;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class ComparisonApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(ComparisonApplication.class, args);
+	}
+}

spring-boot-runtime/src/main/java/com/baeldung/compare/StartupEventHandler.java

@@ -0,0 +1,65 @@
+package com.baeldung.compare;
+
+import java.util.Arrays;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.function.BiFunction;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.context.event.ApplicationReadyEvent;
+import org.springframework.context.event.EventListener;
+import org.springframework.stereotype.Component;
+
+import io.micrometer.core.instrument.Meter;
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.Statistic;
+
+@Component
+public class StartupEventHandler {
+
+    // logger, constructor
+    private static Logger logger = LoggerFactory.getLogger(StartupEventHandler.class);
+    
+    public StartupEventHandler(MeterRegistry registry) {
+        this.meterRegistry = registry;
+    }
+    
+    private String[] METRICS = {
+      "jvm.memory.used", 
+      "jvm.classes.loaded", 
+      "jvm.threads.live"};
+
+    private String METRIC_MSG_FORMAT = "Startup Metric >> {}={}";
+    
+    private MeterRegistry meterRegistry;
+
+    @EventListener
+    public void getAndLogStartupMetrics(
+      ApplicationReadyEvent event) {
+        Arrays.asList(METRICS)
+          .forEach(this::getAndLogActuatorMetric);
+    }
+
+    private void getAndLogActuatorMetric(String metric) {
+        Meter meter = meterRegistry.find(metric).meter();
+        Map<Statistic, Double> stats = getSamples(meter);
+ 
+        logger.info(METRIC_MSG_FORMAT, metric, stats.get(Statistic.VALUE).longValue());
+    }
+
+    private Map<Statistic, Double> getSamples(Meter meter) {
+        Map<Statistic, Double> samples = new LinkedHashMap<>();
+        mergeMeasurements(samples, meter);
+        return samples;
+    }
+
+    private void mergeMeasurements(Map<Statistic, Double> samples, Meter meter) {
+        meter.measure().forEach((measurement) -> samples.merge(measurement.getStatistic(),
+                measurement.getValue(), mergeFunction(measurement.getStatistic())));
+    }
+
+    private BiFunction<Double, Double, Double> mergeFunction(Statistic statistic) {
+        return Statistic.MAX.equals(statistic) ? Double::max : Double::sum;
+    }    
+}