1、简介
Spring Boot Actuator 是一个为生产环境准备（Production-ready Features）的功能，提供了对生产环境的管理和监控功能。使用只需要添加一个依赖就可以了。
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
该功能由两子个项目组成，他的功能实现与配置都独立与spring-boot项目。
2、实现
它通过向web 容器注册自己的servlet 来实现，在actuator 项目中定义为Endpoint（servlet）, Endpoint实现类与请求的 URL向匹配。Operation与HTTP 方法对应，并且绑定Endpoint实现类的method。如何与SpringMVC DispatcherServlet 相兼容，见下文配置部分。
1、注册servlet
org.springframework.boot.actuate.endpoint.web.ServletEndpointRegistrar
actuator 项目注册逻辑：
public class ServletEndpointRegistrar implements ServletContextInitializer {
public void onStartup(ServletContext servletContext) throws ServletException {
this.servletEndpoints.forEach((servletEndpoint) -> register(servletContext, servletEndpoint));
}
private void register(ServletContext servletContext, ExposableServletEndpoint endpoint) {
String name = endpoint.getEndpointId().toLowerCaseString() + "-actuator-endpoint";
String path = this.basePath + "/" + endpoint.getRootPath();
String urlMapping = path.endsWith("/") ? path + "*" : path + "/*";
EndpointServlet endpointServlet = endpoint.getEndpointServlet();
Dynamic registration = servletContext.addServlet(name, endpointServlet.getServlet());
registration.addMapping(urlMapping);
registration.setInitParameters(endpointServlet.getInitParameters());
registration.setLoadOnStartup(endpointServlet.getLoadOnStartup());
logger.info("Registered '" + path + "' to " + name);
}
}
actuator-autoconfigure
判断有没有DispatcherServlet，DispatcherServlet 会影响注册的servlet 匹配路径，实现了与DispatcherServlet 兼容配置。
ServletEndpointManagementContextConfiguration
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(DispatcherServlet.class)
public static class WebMvcServletEndpointManagementContextConfiguration {
@Bean
public ServletEndpointRegistrar servletEndpointRegistrar(WebEndpointProperties properties,
ServletEndpointsSupplier servletEndpointsSupplier, DispatcherServletPath dispatcherServletPath) {
return new ServletEndpointRegistrar(dispatcherServletPath.getRelativePath(properties.getBasePath()),
servletEndpointsSupplier.getEndpoints());
}
}
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(ResourceConfig.class)
@ConditionalOnMissingClass("org.springframework.web.servlet.DispatcherServlet")
public static class JerseyServletEndpointManagementContextConfiguration {
@Bean
public ServletEndpointRegistrar servletEndpointRegistrar(WebEndpointProperties properties,
ServletEndpointsSupplier servletEndpointsSupplier, JerseyApplicationPath jerseyApplicationPath) {
return new ServletEndpointRegistrar(jerseyApplicationPath.getRelativePath(properties.getBasePath()),
servletEndpointsSupplier.getEndpoints());
}
}
实例化ServletEndpointRegistrar 依赖的ServletEndpointsSupplier。
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
static class WebEndpointServletConfiguration {
@Bean
@ConditionalOnMissingBean(ServletEndpointsSupplier.class)
ServletEndpointDiscoverer servletEndpointDiscoverer(ApplicationContext applicationContext,
ObjectProvider<PathMapper> endpointPathMappers,
ObjectProvider<EndpointFilter<ExposableServletEndpoint>> filters) {
return new ServletEndpointDiscoverer(applicationContext,
endpointPathMappers.orderedStream().collect(Collectors.toList()),
filters.orderedStream().collect(Collectors.toList()));
}
}
ServletEndpointDiscoverer 会扫描SpringContext 里面被@Endpoint 注解的bean 定义。
private Collection<EndpointBean> createEndpointBeans() {
.....
String[] beanNames = BeanFactoryUtils.beanNamesForAnnotationIncludingAncestors(this.applicationContext,
Endpoint.class);
.....
return byId.values();
}
将EndpointBean 转换为ExposableEndpoint 然后在获取 EndpointServlet，这样就能注册到容器的中去。简言之，一个被@Endpoint注解的类，会被当成一个Servlet 注册到容器中。url 路径有默认值。
2、方法调用
通过http 请求的url 匹配（请求路径+请求方法）到对应的servlet ，由servlet 实现类调用到类里面具体的某一个方法。中间还有参数匹配与参数转换等等。。
3、HealthEndpoint
HealthEndpoint 是一个特殊的Endpoint，他对所有实现了HealthContributor 接口的bean 的聚合功能。
3.1 HealthEndpoint 类
请求health 接口时候会从 HealthContributorRegistry 注册中心返回匹配的HealthContributor ，然后调用getHealth方法。如果匹配到多个HealthContributor，将会聚合结果返回。
@Endpoint(id = "health")
public class HealthEndpoint extends HealthEndpointSupport<HealthContributor, HealthComponent>{
public HealthEndpoint(HealthContributorRegistry registry, HealthEndpointGroups groups) {
super(registry, groups);
}
@ReadOperation
public HealthComponent health() {
HealthComponent health = health(ApiVersion.V3, EMPTY_PATH);
return (health != null) ? health : DEFAULT_HEALTH;
}
」
3.2 自动配置部分
1、实例化HealthEndpoint
2、将所有实现了HealthContributor 接口部分的类注册到HealthContributorRegistry中。
@Configuration(proxyBeanMethods = false)
class HealthEndpointConfiguration {
@Bean
@ConditionalOnMissingBean
HealthContributorRegistry healthContributorRegistry(ApplicationContext applicationContext,
HealthEndpointGroups groups) {
Map<String, HealthContributor> healthContributors = new LinkedHashMap<>(
applicationContext.getBeansOfType(HealthContributor.class));
if (ClassUtils.isPresent("reactor.core.publisher.Flux", applicationContext.getClassLoader())) {
healthContributors.putAll(new AdaptedReactiveHealthContributors(applicationContext).get());
}
return new AutoConfiguredHealthContributorRegistry(healthContributors, groups.getNames());
}
@Bean
@ConditionalOnMissingBean
HealthEndpoint healthEndpoint(HealthContributorRegistry registry, HealthEndpointGroups groups) {
return new HealthEndpoint(registry, groups);
}
}
3.3 自定义 HealthContributor 举例
NacosConfigHealthIndicator 继承AbstractHealthIndicator
public class NacosConfigHealthIndicator extends AbstractHealthIndicator {
private final ConfigService configService;
public NacosConfigHealthIndicator(ConfigService configService) {
this.configService = configService;
}
@Override
protected void doHealthCheck(Health.Builder builder) throws Exception {
// Just return "UP" or "DOWN"
String status = configService.getServerStatus();
// Set the status to Builder
builder.status(status);
switch (status) {
case "UP":
builder.up();
break;
case "DOWN":
builder.down();
break;
default:
builder.unknown();
break;
}
}
}
添加bean 定义
@Bean
@ConditionalOnMissingBean
@ConditionalOnEnabledHealthIndicator("nacos-config")
public NacosConfigHealthIndicator nacosConfigHealthIndicator() {
return new NacosConfigHealthIndicator(nacosConfigManager.getConfigService());
}
访问health 接口将返回Nacos 配置状态。
小结：
对线上环境的监控非常重要，Spring Boot Actuator 为我们提供一些常用的监控和管理功能。我们在需要监控xx 的时候，可以先看下有没有现成的实现，它已经实现的大部分常用功能。我们在使用Spring Boot Actuator同时 ，还需要注意接口的安全性。避免非法调用，跨权限使用。
