我正在尝试通过将Micrometer.io与Spring Boot 2.0.0.RELEASE结合使用来生成Prometheus指标。

当我尝试将List的大小显示为Gauge时，它一直显示NaN。 在文档中说：

严格引用要使用量规测量的状态对象是您的责任。

我尝试了一些不同的方法，但无法解决问题。这是我的一些试用代码。

import io.micrometer.core.instrument.*;
import io.swagger.backend.model.Product;
import io.swagger.backend.service.ProductService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;

@RestController
@RequestMapping("metrics")
public class ExampleController {

    private AtomicInteger atomicInteger = new AtomicInteger();

    private ProductService productService;
    private final Gauge productGauge;

    @Autowired
    public HelloController(ProductService productService,
                           MeterRegistry registry) {

        this.productService = productService;

        createGauge("product_gauge", productService.getProducts(), registry);
    }

    private void createGauge(String metricName, List<Product> products,
                                    MeterRegistry registry) {

        List<Product> products = productService.getProducts();

        // #1
        // this displays product_gauge as NaN
        AtomicInteger n = registry.gauge("product_gauge", new AtomicInteger(0));
        n.set(1);
        n.set(2);

        // #2
        // this also displays product_gauge as NaN
        Gauge
            .builder("product_gauge", products, List::size)
            .register(registry);

        // #3
        // this displays also NaN
        testListReference = Arrays.asList(1, 2);
        Gauge
            .builder("random_gauge", testListReference, List::size)
            .register(registry);

        // #4
        // this also displays NaN
        AtomicInteger currentHttpRequests = registry.gauge("current.http.requests", new AtomicInteger(0));
    }

    @GetMapping(path = "/product/decrement")
    public Counter decrementAndGetProductCounter() {
        // decrement the gague by one
    }
}

有没有人可以帮助解决这个问题？任何帮助，将不胜感激。