通过HttpServer向Prometheus暴露端点

@Spi
public interface MeterRegistryFactory {
    public MeterRegistry createMeterRegistry();
}

@SpiMeta(name = "promMeterRegistryFactory")
public class PrometheusMeterRegistryFactory implements MeterRegistryFactory {
    private static final PrometheusMeterRegistry prometheusRegistry = new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);

    static {
        try {
            final int port = NumberUtils.toInt(System.getProperty("pepper.port"), 9146);
            //创建一个Http服务
            HttpServer server = HttpServer.create(new InetSocketAddress(port), 0);
            //服务设置一个针对/metrics路径请求的监听，并设置处理器HttpHandler
            server.createContext("/metrics", httpExchange -> {
                //由PrometheusMeterRegistry抓取数据，它会将抓取的数据按Prometheus所需要的格式处理好
                String response = prometheusRegistry.scrape();
                //接下来有httpExchange将数据返回给Prometheus服务器
                httpExchange.sendResponseHeaders(200, response.getBytes().length);
                try (OutputStream os = httpExchange.getResponseBody()) {
                    os.write(response.getBytes());
                }
            });
            //开启一个线程来处理Prometheus服务器抓取数据的请求
            new Thread(server::start).start();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public MeterRegistry createMeterRegistry() {
        return prometheusRegistry;
    }
}