This is the 17th day of my participation in Gwen Challenge

(^ U ^) Blue ~YO, today 4ye share this Springboot auto assembly with friends ~✌

website

Let’s see how the official website defines this autowiring ~

Spring Boot auto-configuration attempts to automatically configure your Spring application based on the jar dependencies that you have added

You can see here that when you introduce a JAR dependency, Springboot tries to automatically configure the Spring application based on that dependency.

You need to opt-in to auto-configuration by adding the @EnableAutoConfiguration or @SpringBootApplication annotations to one of your @Configuration classes.

It is also stated that you should select one of the @EnableAutoConfiguration and @SpringBootApplication annotations on a Configuration class @Configuration for the autoconfiguration to take effect.

So, after knowing these information, we began to look at the source link happily ~ blunt blunt! πŸ˜„

By the way, the Springboot version of Exploration is 2.4.5

@SpringBootApplication

If you go to the @SpringBootApplication annotation, you can see that it is a composite annotation. In addition to the first four basic meta-annotations, there are three @SpringBootConfiguration, @EnableAutoConfiguration, @ComponentScan

The source code is shown in figure

@SpringBootConfiguration

Let’s look at this first annotation, as shown here, and see that it’s actually an @Configuration annotation,

The @Configuration annotation is used as a Configuration class to configure the Spring context, equivalent to

in Spring’s XML Configuration file.

The source code is shown in figure

@ComponentScan

The purpose of this is to scan the components in the specified path and add them to the IOC container

in Spring’s XML configuration file

The source code is shown in figure

You can see that there is a @REPEATable (ComponentScan) annotation inside it, which indicates that the @ComponentScan annotation is Repeatable

Note that some classes are excluded in our own custom way by implementing the TypeFilter interface and overwriting the match method.

Small details

Here is another point to note ~πŸ˜„

AutoConfigurationExcludeFilter will check the configuration, if the configuration and the meta-inf/spring. The factories in the file EnableAutoConfiguration class is the same, the corresponding configuration will be rule out ~

@EnableAutoConfiguration

Finally, come to the focus of this article 🐷

You can see from its name that it is the protagonist of this autoconfiguration

The source code is shown in figure

You can see that it is a composite annotation

Let’s start with the annotation 1 @AutoConfigurationPackage

@AutoConfigurationPackage

As the name suggests, it is an annotation that automatically configures the package path

The source code is shown in figure

As you can see from this comment, when the basePackages or basePackageClasses are not configured, the class will automatically register the package in which the annotation is located as the base path

Then, we take a look at the contents of this box ~ @ Import 🐷 (AutoConfigurationPackages. The Registrar. The class)

@Import

Take a look at the function of this annotation πŸ˜‹

The source code is shown in figure

Can be found that its role is also very simple, it is an import component, such as common @ the Configuration class or ImportSelector and ImportBeanDefinitionRegistrar implementation class, Or some other generic Component like @Component, @Service, etc

Registrar

Continue to see this @ Import (AutoConfigurationPackages. The Registrar. The class), can be found that the annotation of Import is the Registrar class 🐷, then we continue to explore, take a look at what did it do ~ πŸ˜„

The source code is shown in figure

As can be seen from the annotation of the class, its role is through ImportBeanDefinitionRegistrar * * to save the basic package path * *

So, once we’ve done the first one, we’ve just seen that this @AutoConfigurationPackage is used to configure the base package, and then we can look at the second one, The @ Import annotations (AutoConfigurationImportSelector. Class).

We can find that it imports the AutoConfigurationImportSelector class.

AutoConfigurationImportSelector

From the name, you can get a sense that it is a component selector

Key Steps

process

This method is called when fetching the Import classes, as shown in the flowchart at the end ~

getAutoConfigurationEntry

Gets the auto-configuration entity class, which also contains the focus of this article

getCandidateConfigurations

It calls the SpringFactoriesLoader, which is the SPI mechanism for Springboot. !). What is different about the Java Spi mentioned in

Read on ~😝

Springboot SPI mechanisms

Old rules, see a note haha πŸ˜„ first

Spring. Factories file

For example, πŸ˜„

# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener
Copy the code

You can use the meta-INF /spring.factories file with the following differences:

  1. You can see a big difference in the name (one is a factories file, the other is named after the full name of the interface).

  2. Spring. factories act as an aggregation of interfaces and implementation classes in the spring.factories file as key = value.

  3. All the configuration items in the spring.factories are loaded into our cache as Map

    >, but not all are instantiated and loaded into the IOC container, In addition to the necessary class (EventPublishingRunListener, etc.), and to meet certain conditions of automatic configuration classes will be loaded into the IOC container
    ,list

☞ Satisfy certain criteria such as whether the dependency (starter in the POM) is used or not

Auto-configuration classes refer to those classes ending in AutoConfiguration

This on-demand implementation mechanism is much more flexible than Java’s one-size-fits-all implementation ~ πŸ˜„

Instance analysis

Here, for example, 130 auto-configuration classes are loaded from the Spring.factories file

But in actual use, after filtering, there are only 30

There is also some sorting by priority ~ 🐷

Automatic assembly flow chart

There are only a few key steps here, the specific process is too long, the SpringApplication source code refreshContext(context); Here is not introduced first, later have time to write to share this [[Springboot source boot process]]

The class name and method block in the same color correspond to ~

The processImports method in the lower left corner of the figure instantiates these auto-configuration classes, including @import, @bean, etc., into the Spring IOC container step by step.

conclusion

It is important to enable the @enableAutoConfiguration or @SpringBootApplication annotation on the configuration class for the automatic configuration to take effect.

2. At the heart of the automatic configuration is Springboot SPI mechanisms, as well as the component selector AutoConfigurationImportSelector, Concrete is through the getAutoConfigurationEntry method to get the automatic configuration of SPI classes and filtering, at last, by processImports will configure class loading to the IOC container, complete the automatic configuration

The last

Finally no more text ha ha ~ πŸ˜„

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Let’s start this unexpected meeting! ~

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I’m 4ye and I’ll see you soon next time!!