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BAEL-8410 - Guide to Prometheus Java Client (#17823)
* BAEL-7255 - Implementing GraphQL Mutation without Returning Data * BAEL-7615 - Implement the Builder Pattern in Java 8 * BAEL-7615 - Implement the Builder Pattern in Java 8 * BAEL-7615 - review * BAEL-7780 - A Guide to Micrometer in Quarkus * fix build * fix build * editor review * editor review * fix build * typo * Revert "typo" This reverts commit fabb043. * typo * add version * add version * BAEL-8091 - Getting started with MongoDB and Quarkus * BAEL-8301 - How to Consume REST API in Quarkus * BAEL-7615 - Implement the Builder Pattern in Java 8 * BAEL-7615 - review * BAEL-7780 - A Guide to Micrometer in Quarkus * fix build * fix build * editor review * editor review * typo * Revert "typo" This reverts commit fabb043. * typo * BAEL-8301 - How to Consume REST API in Quarkus * BAEL-8301 - How to Consume REST API in Quarkus * BAEL-8301 - How to Consume REST API in Quarkus * BAEL-8301 - How to Consume REST API in Quarkus * comment module * fix build * downgrade version * downgrade version * format & added tests * format 2 * format 4 * BAEL-8410 - Guide to Prometheus Java Client * BAEL-8410 - rename test
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‎metrics/pom.xml

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<artifactId>spectator-api</artifactId>
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<version>${spectator-api.version}</version>
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</dependency>
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<dependency>
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<groupId>io.prometheus</groupId>
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<artifactId>prometheus-metrics-core</artifactId>
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<version>1.0.0</version>
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</dependency>
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<dependency>
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<groupId>io.prometheus</groupId>
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<artifactId>prometheus-metrics-instrumentation-jvm</artifactId>
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<version>1.0.0</version>
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</dependency>
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<dependency>
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<groupId>io.prometheus</groupId>
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<artifactId>prometheus-metrics-exporter-httpserver</artifactId>
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<version>1.0.0</version>
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</dependency>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-api</artifactId>
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<version>5.11.0-M2</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<properties>

‎metrics/src/main/java/com/baeldung/metrics/prometheus/PrometheusApp.java

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package com.baeldung.metrics.prometheus;
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import java.io.IOException;
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import java.util.Random;
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import io.prometheus.metrics.core.metrics.Counter;
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import io.prometheus.metrics.core.metrics.Gauge;
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import io.prometheus.metrics.core.metrics.Histogram;
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import io.prometheus.metrics.core.metrics.Info;
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import io.prometheus.metrics.core.metrics.StateSet;
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import io.prometheus.metrics.core.metrics.Summary;
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import io.prometheus.metrics.exporter.httpserver.HTTPServer;
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import io.prometheus.metrics.instrumentation.jvm.JvmMetrics;
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public class PrometheusApp {
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public static void main(String[] args) throws InterruptedException, IOException {
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JvmMetrics.builder().register();
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HTTPServer server = HTTPServer.builder()
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.port(9400)
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.buildAndStart();
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Counter requestCounter = Counter.builder()
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.name("http_requests_total")
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.help("Total number of HTTP requests")
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.labelNames("method", "status")
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.register();
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requestCounter.labelValues("GET", "200").inc();
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Gauge memoryUsage = Gauge.builder()
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.name("memory_usage_bytes")
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.help("Current memory usage in bytes")
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.register();
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memoryUsage.set(5000000);
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Histogram requestLatency = Histogram.builder()
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.name("http_request_latency_seconds")
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.help("Tracks HTTP request latency in seconds")
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.labelNames("method")
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.register();
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Random random = new Random();
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for (int i = 0; i < 100; i++) {
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double latency = 0.1 + (3 * random.nextDouble());
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requestLatency.labelValues("GET").observe(latency);
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}
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Summary requestDuration = Summary.builder()
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.name("http_request_duration_seconds")
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.help("Tracks the duration of HTTP requests in seconds")
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.quantile(0.5, 0.05)
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.quantile(0.9, 0.01)
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.register();
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for (int i = 0; i < 100; i++) {
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double duration = 0.05 + (2 * random.nextDouble());
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requestDuration.observe(duration);
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}
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Info appInfo = Info.builder()
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.name("app_info")
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.help("Application version information")
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.labelNames("version", "build")
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.register();
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appInfo.addLabelValues("1.0.0", "12345");
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StateSet stateSet = StateSet.builder()
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.name("feature_flags")
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.help("Feature flags")
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.labelNames("env")
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.states("feature1")
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.register();
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stateSet.labelValues("dev").setFalse("feature1");
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System.out.println("HTTPServer listening on http://localhost:" + server.getPort() + "/metrics");
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Thread.currentThread().join();
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}
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}

‎metrics/src/test/java/com/baeldung/metrics/prometheus/PrometheusAppUnitTest.java

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package com.baeldung.metrics.prometheus;
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import static org.junit.jupiter.api.Assertions.*;
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import java.io.BufferedReader;
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import java.io.IOException;
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import java.io.InputStreamReader;
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import java.net.HttpURLConnection;
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import java.net.URL;
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import org.junit.jupiter.api.AfterEach;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import io.prometheus.metrics.core.metrics.Counter;
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import io.prometheus.metrics.core.metrics.Gauge;
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import io.prometheus.metrics.core.metrics.Histogram;
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import io.prometheus.metrics.core.metrics.Info;
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import io.prometheus.metrics.core.metrics.StateSet;
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import io.prometheus.metrics.core.metrics.Summary;
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import io.prometheus.metrics.exporter.httpserver.HTTPServer;
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import io.prometheus.metrics.instrumentation.jvm.JvmMetrics;
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import io.prometheus.metrics.model.registry.PrometheusRegistry;
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class PrometheusAppUnitTest {
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private Counter requestCounter;
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private Gauge memoryUsage;
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private Histogram requestLatency;
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private Summary requestDuration;
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private Info appInfo;
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private StateSet stateSet;
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private HTTPServer httpServer;
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@BeforeEach
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void setUp() throws IOException {
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// Initialize JVM Metrics
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JvmMetrics.builder().register();
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// Initialize HTTP Server
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httpServer = HTTPServer.builder().port(9400).buildAndStart();
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// Initialize all the metrics within the new registry
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requestCounter = Counter.builder()
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.name("http_requests_total")
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.help("Total number of HTTP requests")
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.labelNames("method", "status")
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.register();
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memoryUsage = Gauge.builder()
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.name("memory_usage_bytes")
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.help("Current memory usage in bytes")
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.register();
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requestLatency = Histogram.builder()
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.name("http_request_latency_seconds")
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.help("Tracks HTTP request latency in seconds")
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.labelNames("method")
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.register();
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requestDuration = Summary.builder()
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.name("http_request_duration_seconds")
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.help("Tracks the duration of HTTP requests in seconds")
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.quantile(0.5, 0.05)
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.quantile(0.9, 0.01)
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.register();
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appInfo = Info.builder()
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.name("app_info")
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.help("Application version information")
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.labelNames("version", "build")
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.register();
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stateSet = StateSet.builder()
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.name("feature_flags")
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.help("Feature flags")
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.labelNames("env")
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.states("feature1")
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.register();
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}
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@AfterEach
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void tearDown() {
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if (httpServer != null) {
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httpServer.stop(); // Stop the server after each test
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}
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PrometheusRegistry.defaultRegistry.unregister(requestCounter);
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PrometheusRegistry.defaultRegistry.unregister(memoryUsage);
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PrometheusRegistry.defaultRegistry.unregister(requestLatency);
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PrometheusRegistry.defaultRegistry.unregister(requestDuration);
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PrometheusRegistry.defaultRegistry.unregister(appInfo);
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PrometheusRegistry.defaultRegistry.unregister(stateSet);
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}
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@Test
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void givenCounter_whenIncremented_thenMetricExposedCorrectly() throws IOException {
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// given
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requestCounter.labelValues("GET", "200").inc();
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// when
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String metrics = fetchMetricsFromEndpoint();
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// then
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assertTrue(metrics.contains("http_requests_total{method=\"GET\",status=\"200\"}"));
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}
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@Test
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void givenGauge_whenSet_thenMetricExposedCorrectly() throws IOException {
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// given
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memoryUsage.set(5000000);
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// when
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String metrics = fetchMetricsFromEndpoint();
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// then
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assertTrue(metrics.contains("memory_usage_bytes 5000000"));
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}
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@Test
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void givenHistogram_whenObserved_thenMetricExposedCorrectly() throws IOException {
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// given
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requestLatency.labelValues("GET").observe(0.25);
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// when
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String metrics = fetchMetricsFromEndpoint();
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// then
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assertTrue(metrics.contains("http_request_latency_seconds"));
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assertTrue(metrics.contains("http_request_latency_seconds_sum"));
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assertTrue(metrics.contains("http_request_latency_seconds_count"));
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}
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@Test
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void givenSummary_whenObserved_thenMetricExposedCorrectly() throws IOException {
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// given
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requestDuration.observe(0.15);
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// when
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String metrics = fetchMetricsFromEndpoint();
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// then
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assertTrue(metrics.contains("http_request_duration_seconds"));
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assertTrue(metrics.contains("http_request_duration_seconds_sum"));
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assertTrue(metrics.contains("http_request_duration_seconds_count"));
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}
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@Test
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void givenInfo_whenSet_thenMetricExposedCorrectly() throws IOException {
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// given
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appInfo.addLabelValues("1.0.0", "12345");
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// when
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String metrics = fetchMetricsFromEndpoint();
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// then
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assertTrue(metrics.contains("app_info{build=\"12345\",version=\"1.0.0\"} 1"));
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}
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@Test
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void givenStateSet_whenSetFalse_thenMetricExposedCorrectly() throws IOException {
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// given
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stateSet.labelValues("dev").setFalse("feature1");
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// when
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String metrics = fetchMetricsFromEndpoint();
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// then
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assertTrue(metrics.contains("feature_flags{env=\"dev\",feature_flags=\"feature1\"} 0"));
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}
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private String fetchMetricsFromEndpoint() throws IOException {
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URL url = new URL("http://localhost:9400/metrics");
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HttpURLConnection connection = (HttpURLConnection) url.openConnection();
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connection.setRequestMethod("GET");
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connection.setConnectTimeout(5000);
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connection.setReadTimeout(5000);
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BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
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String inputLine;
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StringBuilder content = new StringBuilder();
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while ((inputLine = in.readLine()) != null) {
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content.append(inputLine).append("\n");
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}
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in.close();
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connection.disconnect();
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return content.toString();
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}
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}

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