小伙伴们，你们好，我是老寇，我又回来辣，几个月不见甚是想念啊！！！
使用SpringBoot 3.3.x集成Micrometer和Prometheus，导致项目无法启动，因为集成的组件特别多，具体什么组件有问题，无法得知。但是，作为一名程序员，基本排查问题的思路，还是需要具备的！
排查问题方向
1.版本不兼容【代码冲突】
2.错误使用
因此，按照这两个方向进行排查，首先，排除 错误使用 剩下就是版本问题，因为是引入micrometer-registry-prometheus才导致项目阻塞，而对于组件，一般有两种解决方案，一种是降低版本【治标不治本】，另一种阅读源码，找出具体代码，然后改掉【治本】
所以，就有以下两种解决方案
1.降低micrometer的版本至1.11.12，但是需要注意的是spring boot 3.5会删除 PrometheusSimpleclientMetricsExportAutoConfiguration 因此，这种方式不推荐
1 <dependencies><dependency><groupId>io.micrometer</groupId><artifactId>micrometer-registry-prometheus</artifactId><version>1.11.12</version></dependency></dependencies>2.直接阅读源码，找出问题的根源，经过我debug，找出造成阻塞的代码。注意，使用ObjectProvider，会延迟加载，需要被实际调用，才会完成初始化
源码里面有这么一段注释，大致意思是：MeterRegistry依赖于Tracer,Tracer又依赖于MeterRegistry，所以通过延迟加载的方式来打破循环Since the MeterRegistry can depend on the {@link Tracer} (Exemplars) and the {@link Tracer} can depend on the MeterRegistry (recording metrics),
this {@link SpanContext} breaks the cycle by lazily loading the {@link Tracer}.
注意：ObjectProvider.getObject() 本身不会直接造成项目阻塞，但如果Bean的获取耗时过长，可能会导致调用该方法的线程被阻塞，此外，如果存在循环依赖，还会造成死锁的情况
@AutoConfiguration(before = PrometheusMetricsExportAutoConfiguration.class,after = MicrometerTracingAutoConfiguration.class)
@ConditionalOnBean(Tracer.class)
@ConditionalOnClass({ Tracer.class, SpanContext.class })
public class PrometheusExemplarsAutoConfiguration {@Bean@ConditionalOnMissingBean// 延迟加载SpanContext spanContext(ObjectProvider<Tracer> tracerProvider) {return new LazyTracingSpanContext(tracerProvider);}/*** Since the MeterRegistry can depend on the {@link Tracer} (Exemplars) and the* {@link Tracer} can depend on the MeterRegistry (recording metrics), this* {@link SpanContext} breaks the cycle by lazily loading the {@link Tracer}.*/static class LazyTracingSpanContext implements SpanContext {private final SingletonSupplier<Tracer> tracer;LazyTracingSpanContext(ObjectProvider<Tracer> tracerProvider) {this.tracer = SingletonSupplier.of(tracerProvider::getObject);}@Overridepublic String getCurrentTraceId() {Span currentSpan = currentSpan();return (currentSpan != null) ? currentSpan.context().traceId() : null;}@Overridepublic String getCurrentSpanId() {Span currentSpan = currentSpan();return (currentSpan != null) ? currentSpan.context().spanId() : null;}@Overridepublic boolean isCurrentSpanSampled() {Span currentSpan = currentSpan();if (currentSpan == null) {return false;}Boolean sampled = currentSpan.context().sampled();return sampled != null && sampled;}@Overridepublic void markCurrentSpanAsExemplar() {}private Span currentSpan() {return this.tracer.obtain().currentSpan();}}}因此，改为直接从IOC容器，获取Bean，源码改动如下
@AutoConfiguration(before = PrometheusMetricsExportAutoConfiguration.class,after = MicrometerTracingAutoConfiguration.class)
@ConditionalOnBean(Tracer.class)
@ConditionalOnClass({ Tracer.class, SpanContext.class })
public class PrometheusExemplarsAutoConfiguration {@Bean@ConditionalOnMissingBeanSpanContext spanContext() {return new TracingSpanContext();}/*** Since the MeterRegistry can depend on the {@link Tracer} (Exemplars) and the* {@link Tracer} can depend on the MeterRegistry (recording metrics), this* {@link SpanContext} breaks the cycle by lazily loading the {@link Tracer}.*/static class TracingSpanContext implements SpanContext {@Overridepublic String getCurrentTraceId() {Span currentSpan = currentSpan();return ObjectUtil.isNotNull(currentSpan) ? currentSpan.context().traceId() : null;}@Overridepublic String getCurrentSpanId() {Span currentSpan = currentSpan();return ObjectUtil.isNotNull(currentSpan) ? currentSpan.context().spanId() : null;}@Overridepublic boolean isCurrentSpanSampled() {Span currentSpan = currentSpan();if (ObjectUtil.isNull(currentSpan)) {return false;}return currentSpan.context().sampled();}@Overridepublic void markCurrentSpanAsExemplar() {}private Span currentSpan() {try {return SpringContextUtil.getBean(Tracer.class).currentSpan();}catch (Exception e) {return null;}}}}大功告成
这个问题，可是困扰了我好几周呢，中间可是折腾好久，换好多种实现，其中，不外乎换组件，换架构！终于，硬着头皮解决这个问题啦，哈哈哈~
我是老寇，我们后会有期
