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Editor to share with you how the Nacos client is integrated and implemented in SpringCloud, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Automatic registration of Spring Boot

The story starts with the automatic injection of Spring Boot from the beginning. Many friends have probably learned about the auto-configuration feature of Spring Boot, and Spring Cloud is based on the Spring Boot framework.

Therefore, before we learn about the Nacos registration business, let's review the automatic configuration principle of Spring Boot, which is also the entry point for learning.

SpringBoot loads all eligible @ Configuration configurations into the IoC container currently created and used by SpringBoot through the @ EnableAutoConfiguration annotation.

The above process is to import the configuration function through @ Import (AutoConfigurationImportSelector.class), the method getCandidateConfigurations in AutoConfigurationImportSelector to get the collection of class names of the class to be configured, that is, all the xxxAutoConfiguration classes that need to be configured automatically, which are placed in the META-INF/spring.factories file.

Finally, according to the comments on these fully qualified name classes, such as: OnClassCondition, OnBeanCondition, OnWebApplicationCondition conditional decision whether to automatically configure.

Now that we understand the basic configuration of Spring Boot, let's take a look at where the automatic configuration for Nacos is.

Automatic configuration of Nacos in Spring Cloud

To view the project dependency of Spring Cloud, I introduce the corresponding jar package of dependency as spring-cloud-starter-alibaba-nacos-discovery-2021.1.jar

The corresponding pom dependencies are:

Com.alibaba.cloud spring-cloud-starter-alibaba-nacos-discovery

View the contents of the META-INF/spring.factories file in the jar package:

Org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ com.alibaba.cloud.nacos.discovery.NacosDiscoveryAutoConfiguration,\ com.alibaba.cloud.nacos.endpoint.NacosDiscoveryEndpointAutoConfiguration,\ com.alibaba.cloud.nacos.registry.NacosServiceRegistryAutoConfiguration,\ com.alibaba.cloud.nacos.discovery.NacosDiscoveryClientConfiguration,\ com.alibaba.cloud.nacos.discovery.reactive.NacosReactiveDiscoveryClientConfiguration,\ com.alibaba.cloud.nacos.discovery.configclient.NacosConfigServerAutoConfiguration,\ com.alibaba.cloud.nacos.NacosServiceAutoConfiguration org.springframework.cloud.bootstrap.BootstrapConfiguration=\ com.alibaba.cloud.nacos.discovery.configclient.NacosDiscoveryClientConfigServiceBootstrapConfiguration

You can see that the EnableAutoConfiguration class corresponds to a series of Nacos autoconfiguration classes.

NacosServiceRegistryAutoConfiguration is used to encapsulate the components needed to instantiate the Nacos registration process, loading three objects NacosServiceRegistry, NacosRegistration, and NacosAutoServiceRegistration, all of which are used for Nacos service registration as a whole.

@ Configuration (proxyBeanMethods = false) @ EnableConfigurationProperties @ ConditionalOnNacosDiscoveryEnabled @ ConditionalOnProperty (value = "spring.cloud.service-registry.auto-registration.enabled", matchIfMissing = true) @ AutoConfigureAfter ({AutoServiceRegistrationConfiguration.class, AutoServiceRegistrationAutoConfiguration.class, NacosDiscoveryAutoConfiguration.class}) public class NacosServiceRegistryAutoConfiguration {@ Bean public NacosServiceRegistry nacosServiceRegistry (NacosDiscoveryProperties nacosDiscoveryProperties) {return new NacosServiceRegistry (nacosDiscoveryProperties) } @ Bean @ ConditionalOnBean (AutoServiceRegistrationProperties.class) public NacosRegistration nacosRegistration (ObjectProvider registrationCustomizers, NacosDiscoveryProperties nacosDiscoveryProperties, ApplicationContext context) {return new NacosRegistration (registrationCustomizers.getIfAvailable (), nacosDiscoveryProperties, context) @ Bean @ ConditionalOnBean (AutoServiceRegistrationProperties.class) public NacosAutoServiceRegistration nacosAutoServiceRegistration (NacosServiceRegistry registry, AutoServiceRegistrationProperties autoServiceRegistrationProperties, NacosRegistration registration) {return new NacosAutoServiceRegistration (registry, autoServiceRegistrationProperties, registration);}}

NacosServiceRegistry encapsulates the registration process, which inherits from ServiceRegistry:

Public class NacosServiceRegistry implements ServiceRegistry {...}

Looking at the source code of this class, you can see that five functions of service registration, logout, shutdown, setting status and getting status have been realized in this class.

The service registration function that we want to track is implemented through the register method it provides.

At this point, we can comb through the process that the Nacos client integrates and instantiates in Spring Cloud.

ServiceRegistry interface of Spring Cloud

It is mentioned above that NacosServiceRegistry is integrated from ServiceRegistry, so what is ServiceRegistry?

ServiceRegistry interface is a class of Spring Cloud. Let's take a look at the definition of ServiceRegistry interface:

Public interface ServiceRegistry {void register (R registration); void deregister (R registration); void close (); void setStatus (R registration, String status); T getStatus (R registration);}

You can see that there are five interfaces defined in the ServiceRegistry interface: service registration, logout, shutdown, setting status, and getting status.

If you look at other service discovery frameworks that integrate Spring Cloud, you basically implement this interface. In other words, ServiceRegistry is an integrated specification of a service discovery framework provided by Spring Cloud. The corresponding framework installation specification implements the corresponding functions and can be integrated.

We can see that Eureka, Zookeeper, Consul integration in Spring Cloud also implements this interface, at the same time, if you need to customize the service discovery function, you can also achieve the goal by implementing this interface.

NacosServiceRegistry service registration implementation

Without paying attention to other auxiliary classes, let's look directly at the NacosServiceRegistry#register method, which provides the core business logic implementation of service registration.

Let's remove the auxiliary judgment of this class and directly show the core code as follows:

@ Override public void register (Registration registration) {/ / get NamingService NamingService namingService = namingService (); String serviceId = registration.getServiceId (); String group = nacosDiscoveryProperties.getGroup (); / / construct an instance. The encapsulation information comes from the configuration attribute Instance instance = getNacosInstanceFromRegistration (registration); / / registers the instance with namingService.registerInstance (serviceId, group, instance);}

NamingService in the above code is already part of the API support provided by the Nacos Client project.

For viewing the API process of Nacos Client, you can directly view the source code corresponding to Nacos. The flow chart corresponding to NamingService#registerInstance method is sorted out as follows:

The above flow chart can continue to be refined, which we will explain specifically in the following chapters, here we know the general call process.

Spring Cloud Service Registration Link

Let's sort out how Spring Cloud carries out service registration, in which almost all the service registration frameworks in the first 2/3 parts of the process are the same process, and only the last part will call the specific framework to implement when the instance registration is carried out.

Look directly at the link diagram of the entire call:

The different colors in the figure represent the different frameworks, gray represents the business code, light green represents the SpringBoot framework, dark green represents the Spring framework, light orange represents the SpringCloud framework, this part also contains the dependent Nacos components, and finally light purple represents the package of Nacos Client.

The core process consists of the following steps:

In the first step, SpringBoot calls refresh, the core method of Spring, when it starts the main method

The second step is to instantiate the WebServerStartStopLifecycle object in Spring.

Focus on the WebServerStartStopLifecycle object, whose start method is called to issue a ServletWebServerInitializedEvent event class that inherits from WebServerInitializedEvent. The class AbstractAutoServiceRegistration that is later used to handle service registration is also a listener dedicated to listening for WebServerInitializedEvent events.

Third, the startBeans method of DefaultLifecycleProcessor is called indirectly in the finishRefresh of AbstractApplicationContext, which in turn invokes the start method of WebServerStartStopLifecycle. As mentioned above, the release of the ServletWebServerInitializedEvent event is triggered.

In the fourth step, AbstractAutoServiceRegistration listens for the corresponding event and registers the service based on the ServiceRegistry interface defined by Spring Cloud.

The above description omits some details, but the whole process is basically that SpringBoot publishes an event at startup, and Spring Cloud listens for the corresponding event, and then registers the service.

These are all the contents of the article "how Nacos clients are integrated and implemented in SpringCloud". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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