说明

本文针对prometheus官方的spring cloud集成client
maven 依赖如下:

<dependency>
            <groupId>io.prometheus</groupId>
            <artifactId>simpleclient_spring_boot</artifactId>
            <version>0.0.26</version>
        </dependency>

Metrics 输出

首先从metrics输出入手,http://localhost:8080/prometheus
在工程中使用注解 @EnablePrometheusEndpoint 的时候,程序启用配置,通过注册MvcEndpoint,暴露出访问路径为”prometheus”的http请求服务.
关键代码片段:
注解

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import({PrometheusEndpointConfiguration.class})
public @interface EnablePrometheusEndpoint {
}

配置类,配置PrometheusMvcEndpoint

@Configuration
class PrometheusEndpointConfiguration {
    PrometheusEndpointConfiguration() {
    }

    @Bean
    public PrometheusEndpoint prometheusEndpoint() {
        return new PrometheusEndpoint(CollectorRegistry.defaultRegistry);
    }

    @Bean
    @ConditionalOnBean({PrometheusEndpoint.class})
    @ConditionalOnEnabledEndpoint("prometheus")
    public PrometheusMvcEndpoint prometheusEndpointFix(PrometheusEndpoint prometheusEndpoint) {
        return new PrometheusMvcEndpoint(prometheusEndpoint);
    }
}

创建PrometheusEndpoint

@ConfigurationProperties("endpoints.prometheus")
class PrometheusEndpoint extends AbstractEndpoint<String> {
    private final CollectorRegistry collectorRegistry;

    PrometheusEndpoint(CollectorRegistry collectorRegistry) {
        super("prometheus");
        this.collectorRegistry = collectorRegistry;
    }

    public String invoke() {
        return this.writeRegistry(Collections.emptySet());
    }

    public String writeRegistry(Set<String> metricsToInclude) {
        try {
            StringWriter e = new StringWriter();
            TextFormat.write004(e, this.collectorRegistry.filteredMetricFamilySamples(metricsToInclude));
            return e.toString();
        } catch (IOException var3) {
            throw new RuntimeException("Writing metrics failed", var3);
        }
    }
}

最终由writeRegistry输出metrics信息.
进去查看,发现实际上是将搜集器注册中心(CollectorRegistry)中所有的搜集器(Collector)中的信息, 描述到Enumeration中,再由TextFormat将Enumeration以text格式输出.

Metrics 搜集

创建搜集器时,搜集器被注册到CollectorRegistry.
创建搜集器Counter,并注册.

public static final Counter requestTotal = Counter.build().name("NAME").labelNames("label1", "label2").help
            ("total request counter of api").register();

注册Counter:

public C register() {
            return this.register(CollectorRegistry.defaultRegistry);
        }

        public C register(CollectorRegistry registry) {
            SimpleCollector sc = this.create();
            registry.register(sc);
            return sc;
        }

搜集器本身提供计数方法,和描述方法.
计数方法记录数据的增加, 描述方法用于输出metrics时将记录数据转换成便于描述的metrics信息.
Counter 源码:

public class Counter extends SimpleCollector<Counter.Child> implements Describable {
    Counter(Counter.Builder b) {
        super(b);
    }

    public static Counter.Builder build(String name, String help) {
        return (Counter.Builder)((Counter.Builder)(new Counter.Builder()).name(name)).help(help);
    }

    public static Counter.Builder build() {
        return new Counter.Builder();
    }

    protected Counter.Child newChild() {
        return new Counter.Child();
    }
    //计数器加1
    public void inc() {
        this.inc(1.0D);
    }

    public void inc(double amt) {
        ((Counter.Child)this.noLabelsChild).inc(amt);
    }

    public double get() {
        return ((Counter.Child)this.noLabelsChild).get();
    }
    //将数据转换成Metric
    public List<MetricFamilySamples> collect() {
        ArrayList samples = new ArrayList(this.children.size());
        Iterator var2 = this.children.entrySet().iterator();

        while(var2.hasNext()) {
            Entry c = (Entry)var2.next();
            samples.add(new Sample(this.fullname, this.labelNames, (List)c.getKey(), ((Counter.Child)c.getValue()).get()));
        }

        return this.familySamplesList(Type.COUNTER, samples);
    }

    public List<MetricFamilySamples> describe() {
        return Collections.singletonList(new CounterMetricFamily(this.fullname, this.help, this.labelNames));
    }

    public static class Child {
        private final DoubleAdder value = new DoubleAdder();

        public Child() {
        }

        public void inc() {
            this.inc(1.0D);
        }

        public void inc(double amt) {
            if(amt < 0.0D) {
                throw new IllegalArgumentException("Amount to increment must be non-negative.");
            } else {
                this.value.add(amt);
            }
        }

        public double get() {
            return this.value.sum();
        }
    }

    public static class Builder extends io.prometheus.client.SimpleCollector.Builder<Counter.Builder, Counter> {
        public Builder() {
        }

        public Counter create() {
            return new Counter(this);
        }
    }
}