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# Registry Export Processors
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Processors that configure and expose metrics through various registry endpoints, providing different formats and protocols for metrics consumption by monitoring systems.
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## Capabilities
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### RegistryBuildItem
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Build item representing a configured meter registry endpoint that will be exposed by the application.
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```java { .api }
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/**
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 * Build item representing a configured meter registry endpoint
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 */
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public final class RegistryBuildItem extends MultiBuildItem {
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    /**
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     * Create a registry build item with name and path
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     * @param name The name identifier of the registry
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     * @param path The HTTP path where the registry will be exposed
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     */
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    public RegistryBuildItem(String name, String path);
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    /**
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     * Get the registry name
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     * @return The name identifier of this registry
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     */
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    public String name();
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    /**
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     * Get the registry path
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     * @return The HTTP path where this registry is exposed
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     */
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    public String path();
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}
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```
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### Prometheus Registry Processor
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Configures Prometheus meter registry and creates HTTP endpoints for Prometheus metrics scraping.
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```java { .api }
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/**
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 * Deployment processor for Prometheus registry configuration
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 */
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@BuildSteps
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public class PrometheusRegistryProcessor {
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    /**
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     * Creates Prometheus registry provider
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     * @param config Micrometer configuration
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     * @param additionalBeans Producer for additional bean build items
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     * @return MicrometerRegistryProviderBuildItem for Prometheus registry
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     */
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    @BuildStep
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    public MicrometerRegistryProviderBuildItem createPrometheusRegistry(
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        MicrometerConfig config,
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        BuildProducer<AdditionalBeanBuildItem> additionalBeans
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    );
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    /**
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     * Registers OpenTelemetry exemplar sampler provider when tracing is enabled
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     * @param additionalBeans Producer for additional bean build items
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     */
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    @BuildStep(onlyIf = TraceEnabled.class)
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    public void registerOpentelemetryExemplarSamplerProvider(
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        BuildProducer<AdditionalBeanBuildItem> additionalBeans
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    );
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    /**
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     * Registers empty exemplar provider when tracing is disabled
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     * @param additionalBeans Producer for additional bean build items
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     */
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    @BuildStep(onlyIfNot = TraceEnabled.class)
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    public void registerEmptyExamplarProvider(
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        BuildProducer<AdditionalBeanBuildItem> additionalBeans
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    );
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    /**
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     * Creates Prometheus metrics endpoints
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     * @param routes Producer for route build items
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     * @param registries Producer for registry build items
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     * @param mConfig Micrometer configuration
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     * @param nonApplicationRootPathBuildItem Non-application root path configuration
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     * @param managementBuildTimeConfig Management interface build-time configuration
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     * @param launchModeBuildItem Launch mode build item
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     * @param recorder Prometheus recorder for runtime operations
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     */
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    @BuildStep
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    @Record(value = ExecutionTime.STATIC_INIT)
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    public void createPrometheusRoute(
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        BuildProducer<RouteBuildItem> routes,
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        BuildProducer<RegistryBuildItem> registries,
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        MicrometerConfig mConfig,
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        NonApplicationRootPathBuildItem nonApplicationRootPathBuildItem,
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        ManagementInterfaceBuildTimeConfig managementBuildTimeConfig,
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        LaunchModeBuildItem launchModeBuildItem,
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        PrometheusRecorder recorder
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    );
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    // Enablement conditions
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    public static class PrometheusEnabled implements BooleanSupplier;
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    public static class TraceEnabled implements BooleanSupplier;
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}
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```
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**Usage Examples:**
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```java
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// Prometheus registry provides metrics at /q/metrics endpoint by default
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// Example HTTP request to get Prometheus metrics:
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// GET /q/metrics
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// Content-Type: text/plain; version=0.0.4; charset=utf-8
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// Example Prometheus metrics output:
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# HELP http_server_requests_seconds Duration of HTTP server request handling
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# TYPE http_server_requests_seconds summary
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http_server_requests_seconds{method="GET",outcome="SUCCESS",status="200",uri="/api/users",quantile="0.5",} 0.002
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http_server_requests_seconds{method="GET",outcome="SUCCESS",status="200",uri="/api/users",quantile="0.95",} 0.005
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http_server_requests_seconds_count{method="GET",outcome="SUCCESS",status="200",uri="/api/users",} 42.0
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http_server_requests_seconds_sum{method="GET",outcome="SUCCESS",status="200",uri="/api/users",} 0.123
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```
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### JSON Registry Processor
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Configures JSON meter registry and creates HTTP endpoints for JSON-formatted metrics output.
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```java { .api }
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/**
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 * Deployment processor for JSON registry configuration
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 */
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@BuildSteps
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public class JsonRegistryProcessor {
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    /**
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     * Initializes JSON registry and endpoints
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     * @param config Micrometer configuration
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     * @param registryProviders Producer for registry provider build items
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     * @param routes Producer for route build items
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     * @param additionalBeans Producer for additional bean build items
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     * @param registries Producer for registry build items
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     * @param nonApplicationRootPathBuildItem Non-application root path configuration
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     * @param managementBuildTimeConfig Management interface build-time configuration
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     * @param launchModeBuildItem Launch mode build item
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     * @param recorder JSON recorder for runtime operations
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     */
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    @BuildStep
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    @Record(ExecutionTime.STATIC_INIT)
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    public void initializeJsonRegistry(
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        MicrometerConfig config,
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        BuildProducer<MicrometerRegistryProviderBuildItem> registryProviders,
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        BuildProducer<RouteBuildItem> routes,
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        BuildProducer<AdditionalBeanBuildItem> additionalBeans,
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        BuildProducer<RegistryBuildItem> registries,
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        NonApplicationRootPathBuildItem nonApplicationRootPathBuildItem,
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        ManagementInterfaceBuildTimeConfig managementBuildTimeConfig,
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        LaunchModeBuildItem launchModeBuildItem,
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        JsonRecorder recorder
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    );
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    // Enablement condition
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    public static class JsonRegistryEnabled implements BooleanSupplier;
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}
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```
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**Usage Examples:**
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```java
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// JSON registry provides metrics at /q/metrics/json endpoint by default
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// Example HTTP request to get JSON metrics:
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// GET /q/metrics/json
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// Content-Type: application/json
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// Example JSON metrics output:
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{
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  "names": ["http.server.requests", "jvm.memory.used", "system.cpu.usage"],
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  "measurements": [
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    {
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      "statistic": "COUNT",
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      "value": 42.0
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    },
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    {
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      "statistic": "TOTAL_TIME", 
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      "value": 0.123
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    }
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  ],
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  "availableTags": [
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    {
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      "tag": "method",
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      "values": ["GET", "POST", "PUT", "DELETE"]
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    },
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    {
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      "tag": "status", 
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      "values": ["200", "404", "500"]
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    }
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  ]
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}
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```
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### Registry Constants and Utilities
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```java { .api }
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// Prometheus registry class constants
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public static final String REGISTRY_CLASS_NAME = "io.micrometer.prometheus.PrometheusMeterRegistry";
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public static final Class<?> REGISTRY_CLASS; // Lazily loaded class reference
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// Registry configuration utilities
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public static boolean isPrometheusEnabled() {
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    return ConfigProvider.getConfig()
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        .getOptionalValue("quarkus.micrometer.export.prometheus.enabled", Boolean.class)
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        .orElse(true);
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}
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public static boolean isJsonRegistryEnabled() {
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    return ConfigProvider.getConfig()
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        .getOptionalValue("quarkus.micrometer.export.json.enabled", Boolean.class)
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        .orElse(false);
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}
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```
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### Custom Registry Integration
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```java
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// Example: Adding a custom registry export processor
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@BuildSteps
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public class CustomRegistryProcessor {
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    @BuildStep(onlyIf = CustomRegistryEnabled.class)
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    MicrometerRegistryProviderBuildItem createCustomRegistry() {
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        return new MicrometerRegistryProviderBuildItem(CustomMeterRegistry.class);
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    }
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    @BuildStep(onlyIf = CustomRegistryEnabled.class)
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    @Record(ExecutionTime.RUNTIME_INIT)
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    List<RouteBuildItem> createCustomEndpoints(
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        List<RegistryBuildItem> registries,
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        CustomRegistryRecorder recorder
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    ) {
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        return List.of(
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            RouteBuildItem.builder()
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                .route("/q/metrics/custom")
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                .handler(recorder.createCustomHandler())
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                .build()
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        );
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    }
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    @BuildStep(onlyIf = CustomRegistryEnabled.class)
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    RegistryBuildItem registerCustomEndpoint() {
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        return new RegistryBuildItem("custom", "/q/metrics/custom");
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    }
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    public static class CustomRegistryEnabled implements BooleanSupplier {
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        @Override
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        public boolean getAsBoolean() {
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            return ConfigProvider.getConfig()
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                .getOptionalValue("quarkus.micrometer.export.custom.enabled", Boolean.class)
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                .orElse(false);
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        }
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    }
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}
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```
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### OpenTelemetry Integration
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The Prometheus processor includes special support for OpenTelemetry exemplars when tracing is enabled:
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```java { .api }
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/**
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 * OpenTelemetry exemplar integration when both Prometheus and tracing are enabled
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 */
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@BuildStep(onlyIf = {PrometheusEnabled.class, TraceEnabled.class})
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UnremovableBeanBuildItem registerOpentelemetryExemplarSamplerProvider() {
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    return UnremovableBeanBuildItem.beanClassNames(
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        "io.quarkus.micrometer.runtime.export.exemplars.OpenTelemetryExemplarSamplerProvider"
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    );
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}
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```
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**Configuration Examples:**
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```properties
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# Enable Prometheus metrics (enabled by default)
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quarkus.micrometer.export.prometheus.enabled=true
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# Customize Prometheus endpoint path
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quarkus.micrometer.export.prometheus.path=/custom-metrics
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# Enable JSON metrics export
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quarkus.micrometer.export.json.enabled=true
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# Enable OpenTelemetry exemplars for Prometheus
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quarkus.micrometer.export.prometheus.enable-exemplars=true
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# Configure registry-specific settings
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quarkus.micrometer.export.prometheus.step=PT1M
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quarkus.micrometer.export.prometheus.descriptions=true
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```