本文则将重点阐述context板块的自动配置类，观察其相关的特性并作相应的总结

自动配置类

直接查看cloudcontext板块下的spring.factories对应的EnableAutoConfiguration键值对

# AutoConfiguration
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration,\
org.springframework.cloud.autoconfigure.LifecycleMvcEndpointAutoConfiguration,\
org.springframework.cloud.autoconfigure.RefreshAutoConfiguration,\
org.springframework.cloud.autoconfigure.RefreshEndpointAutoConfiguration,\
org.springframework.cloud.autoconfigure.WritableEnvironmentEndpointAutoConfiguration

除了第一个自动配置类在前文有所提及，其余的四个可以分为步骤来进行一一的解析

MVC生命周期端点自动配置类

管理MVC的整个生命周期而暴露给外部的端点，LifecycleMvcEndpointAutoConfiguration的内部源码还是很简单的

// 排在MVC配置类之后
@Configuration
@AutoConfigureAfter(WebMvcAutoConfiguration.class)
public class LifecycleMvcEndpointAutoConfiguration {
    // 注册环境管理器EnvironmentManager
    @Bean
    @ConditionalOnMissingBean
    public EnvironmentManager environmentManager(ConfigurableEnvironment environment) {
        return new EnvironmentManager(environment);
    }
}

EnvironmentManager类内含上下文环境变量ConfigurableEnvironment和事件分发器publisher，同时内部也暴露了JMX接口供外部调用。
总的来说也就是通过该类变更上下文属性便会触发EnvironmentChangeEvent事件

刷新自动配置类

此处的刷新与前者的刷新属性不同，其针对的是bean。并通过相应的刷新操作触发RefreshScopeRefreshedEvent事件

@Configuration
@ConditionalOnClass(RefreshScope.class)
// 可通过更改spring.cloud.refresh.enabled值来确定是否让该配置生效。默认为true
@ConditionalOnProperty(name = RefreshAutoConfiguration.REFRESH_SCOPE_ENABLED, matchIfMissing = true)
@AutoConfigureBefore(HibernateJpaAutoConfiguration.class)
public class RefreshAutoConfiguration {
    // 主要bean类
    @Bean
    @ConditionalOnMissingBean(RefreshScope.class)
    public static RefreshScope refreshScope() {
        return new RefreshScope();
    }
}

其余的代码没贴出来，因为发现关键类就是此RefreshScope，其也暴露了JMX接口供外部调用来刷新bean

刷新端点自动配置类

此处的刷新针对的不是bean对象了，而是整个上下文context。

@Configuration
@ConditionalOnClass({EndpointAutoConfiguration.class, Health.class})
// 排在前者配置之后
@AutoConfigureAfter({ LifecycleMvcEndpointAutoConfiguration.class,
        RefreshAutoConfiguration.class})
// 导入类
@Import({ RestartEndpointWithIntegrationConfiguration.class,
        RestartEndpointWithoutIntegrationConfiguration.class,
        PauseResumeEndpointsConfiguration.class })
public class RefreshEndpointAutoConfiguration {
}

优先对导入类作简单的查看把

1.前两个类其实都是为了创建RestartEndpoint对象

    // 端点名为restart
    @Bean
    @ConditionalOnEnabledEndpoint
    @ConditionalOnMissingBean
    public RestartEndpoint restartEndpointWithoutIntegration() {
        return new RestartEndpoint();
    }

而RestartEndpoint端点也暴露了JMX接口供外界调用直接刷新context，但无事件触发，且其头上有一个注解

@Endpoint(id = "restart", enableByDefault = false)
public class RestartEndpoint implements ApplicationListener<ApplicationPreparedEvent> {
}

可通过配置management.endpoint.${id}.enabled属性来开关指定的端点，
也可以通过@Endpoint注解中的属性enableByDefault来指定(默认为true)；
全局的话也可通过环境属性management.endpoints.enabled-by-default来指定。
由此得知RestartEndPoint端点默认是不开启的

不过我发现此端点是ApplicationListener接口的实现类，但我的印象中，只有在spring.factories文件中定义才会被spring调用，那其又是怎么被调用，确保其内部的context是有值的呢？待商榷！

2.PauseEndpoint端点和ResumeEndpoint端点的使用，但彼此依赖RestartEndPoint端点

@Configuration
class PauseResumeEndpointsConfiguration {
    // 端点名为pause
    @Bean
    @ConditionalOnBean(RestartEndpoint.class)
    @ConditionalOnMissingBean
    @ConditionalOnEnabledEndpoint
    public RestartEndpoint.PauseEndpoint pauseEndpoint(RestartEndpoint restartEndpoint) {
        return restartEndpoint.getPauseEndpoint();
    }
    // 端点名为resume
    @Bean
    @ConditionalOnBean(RestartEndpoint.class)
    @ConditionalOnMissingBean
    @ConditionalOnEnabledEndpoint
    public RestartEndpoint.ResumeEndpoint resumeEndpoint(
            RestartEndpoint restartEndpoint) {
        return restartEndpoint.getResumeEndpoint();
    }
}

然后对内部的Bean作下简单的介绍

    // 健康检查类
    // 可通过management.health.${id}.enable属性来控制
    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnEnabledHealthIndicator("refresh")
    RefreshScopeHealthIndicator refreshScopeHealthIndicator(ObjectProvider<RefreshScope> scope,
                                                            ConfigurationPropertiesRebinder rebinder) {
        return new RefreshScopeHealthIndicator(scope, rebinder);
    }

可写环境端点自动配置类

对环境变量的属性可更改的端点则通过WritableEnvironmentEndpointAutoConfiguration来实现

@Configuration
@ConditionalOnClass({ EnvironmentEndpoint.class, EnvironmentEndpointProperties.class })
@ConditionalOnBean(EnvironmentManager.class)
@AutoConfigureBefore(EnvironmentEndpointAutoConfiguration.class)
@AutoConfigureAfter(LifecycleMvcEndpointAutoConfiguration.class)
@EnableConfigurationProperties({ EnvironmentEndpointProperties.class })
// 可通过management.endpoint.env.post.enabled属性开关，默认为true
@ConditionalOnProperty(value = "management.endpoint.env.post.enabled", matchIfMissing = true)
public class WritableEnvironmentEndpointAutoConfiguration {
}

内部的Bean对象也就是暴露属性的更改权限，有JMX方式也有MVC方式。

JMX方式

    // 端点名为env
    @Bean
    @ConditionalOnMissingBean
    @ConditionalOnEnabledEndpoint
    public WritableEnvironmentEndpoint environmentEndpoint(Environment environment) {
        WritableEnvironmentEndpoint endpoint = new WritableEnvironmentEndpoint(environment);
        String[] keysToSanitize = this.properties.getKeysToSanitize();
        if (keysToSanitize != null) {
            endpoint.setKeysToSanitize(keysToSanitize);
        }
        return endpoint;
    }

MVC方式则引用了上文提到的EnvironmentManager对象

    // 该端点以/env作为端点入口
    @Bean
    @ConditionalOnEnabledEndpoint
    public WritableEnvironmentEndpointWebExtension environmentEndpointWebExtension(
            WritableEnvironmentEndpoint endpoint, EnvironmentManager environment) {
        // 调用EnvironmentManager对象来操作上下文的环境变量
        return new WritableEnvironmentEndpointWebExtension(endpoint, environment);
    }

小结

cloudcontext板块暴露了针对环境变量、bean对象、上下文等方式的刷新操作，并暴露JMX方式以及MVC方式供外界调用。具体可查看前文