Spring获取Http响应时间和状态原理

spring-actuate是spring的监控模块，默认开启很监控下，其中就有个http的响应时间和状态。

在maven的pom中引入

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
<version>1.5.3.RELEASE</version>
</dependency>

启动项目，访问 http://localhost:prot/metrics 可以看到的结果中

“counter.status.200.metrics”:24 表示/metrics接口响应200状态24次

“gauge.response.metrics”:2.0 表示/metrics接口响应时间为2ms

之后通过字符串替换，将key改成自己想要的格式

那么actuate又是如何获取到接口的响应时间和状态？

在sprint-actuate里有个MetricsFilter类，继承了OncePerRequestFilter，从名字上可以看出，这个拦截器会在每次请求执行一次，在请求处理前记录开始时间，请求处理后记录结束时间和响应状态

final class MetricsFilter extends OncePerRequestFilter {
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws ServletException, IOException {
StopWatch stopWatch = this.createStopWatchIfNecessary(request);
String path = (new UrlPathHelper()).getPathWithinApplication(request);
int status = HttpStatus.INTERNAL_SERVER_ERROR.value();

try {
chain.doFilter(request, response);
status = this.getStatus(response);
} finally {
if (!request.isAsyncStarted()) {
if (response.isCommitted()) {
status = this.getStatus(response);
}

stopWatch.stop();
request.removeAttribute(ATTRIBUTE_STOP_WATCH);
this.recordMetrics(request, path, status, stopWatch.getTotalTimeMillis());
}

}

}

...
}

最后，处理时长会存为Gauge类型，响应状态次数会存为Counter类型，Gauge存在实现了GaugeService接口的类中，Counter存在实现了CounterService接口的类中。这些类会在MetricsFilter实例化的时候传入

MetricsFilter(CounterService counterService, GaugeService gaugeService, MetricFilterProperties properties) {
this.counterService = counterService;
this.gaugeService = gaugeService;
this.properties = properties;
}

http://docs.spring.io/spring-boot/docs/current-SNAPSHOT/reference/htmlsingle/#production-ready 官方文档