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This article mainly introduces "the introduction of the startup process of Spring". In the daily operation, I believe that many people have doubts about the introduction of the startup process of Spring. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts of "introduction to the startup process of Spring". Next, please follow the editor to study!

  Spring has been used for a long time, but there is no systematic summary. I happened to be doing a Spring package project some time ago. I took the opportunity to review it and did a source code analysis based on Spring framework 4.3.22.

The examples of how   first came into contact with Spring are as follows:

  sets the configuration file path, initializes ApplicationContext, then gets Bean, and closes context after processing. This section starts with a look at the Spring startup process.

one。 Start

The construction method of the   trace ClassPathXmlApplicationContext can see the following:

  sets the path to the configuration file and calls the refresh method of the parent class AbstractApplicationContext, which initializes the Spring environment. As follows, this is the main process of the refresh method (to facilitate typesetting, the original comments and spaces are removed):

  below will introduce the content of each method step, but not too much in-depth, each in-depth details will be described in detail later, this section first introduces the general process.

1.1. Try

1.prepareRefresh

The content of   PrepareRefresh is as above, this method mainly prepares the environment, including the startup time and activity status of Context, and then sets the configuration data source in context, using the default StandardEnvironment object, which adds the System.env () attribute and System.properties () attribute. The initPropertySources method is used to initialize the property source of the environment in context. Null implementation in AbstractApplicationContext. The other subclasses are implemented as follows:

  has roughly the same implementation of GenericWebApplicationContext and AbstractRefreshableWebApplicationContext, both of which are:

  replaces the default StandardEnvironment with StandardServletEnvironment by overriding the createEnvironment method in the getEnvironment method. The diagram of Environment is as follows:

  therefore executes the initPropertySources method of this class, adding the configuration property source for ServletContext and ServletConfig for context. The loading of the configuration attribute source in the specific Environment will be described separately later.

2.obtainFreshBeanFactory

  the implementation of this method is as follows: reset the BeanFacotry held by AbstractApplicationContext through refreshBeanFacotry, then get the object through getBeanFacotry and return.

Both the refreshBeanFacoty method and the getBeanFactory method in   AbstractApplicationContext are abstract methods, which are implemented on AbstractRefreshableApplicationContext.

As mentioned above,   adds annotations to the method, focusing on the loadBeanDefinitions method. This abstract method is used to handle the loading of Bean definitions in different scenarios, such as Xml configuration, annotation configuration, Web environment, etc., on the concrete implementation subclass. The specific implementation will be expanded later.

At present,   has only finished loading the Bean definition, and there is no instantiation of Bean.

3.prepareBeanFactory

  sets the base properties for the BeanFactory returned in step 2. These include:

Set up ClassLoader

Set the expression language processor of beanFactory. EL expressions are used by default, and relevant attribute values can be called in the form of # {bean.xxx}.

Add a default attribute Editor

Add the post processor ApplicationContextAwareProcessor, and automatically execute the set methods of each Aware interface after Bean initialization, including ResourceLoaderAware, ApplicationEventPublisherAware, MessageSourceAware, ApplicationContextAware, EnvironmentAware

Add dependency injection types that need to be ignored, which are post-processed by BeanPostProcessor in ApplicationContextAwareProcessor, including those covered in point (4)

Pre-set interface objects for automatic dependency injection, including BeanFactory, ResourceLoader, ApplicationEventPublisher, ApplicationContext

If the Bean of loadTimeWeaver exists, add the corresponding post processor.

If the three default environment properties Bean of environment,systemProperties,systemEnvironment do not exist, register the corresponding singleton, and the three objects have been initialized in step 1

  can see the source code, this step is mainly to preset the common singleton Bean and add some common post-processing actions, mainly reflected in the BeanPostProcessor.

4.postProcessBeanFactory

  all Bean definitions have been loaded but not instantiated. This step can modify the bean definition or add a null implementation in the custom bean,AbstractApplicationContext.

  as above, take AbstractRefreshableWebApplicationContext as an example, which adds a ServletContextAwareProcessor post processor to handle the automatic injection of related objects in the ServletContextAware interface and the ServletConfigAware interface. At the same time, the application scope related to Web is added, including request,session,globalSession and application, and the default singleton object is added. Finally, the environment configuration Bean related to the Web environment is added, including servletContext,servletConfig,contextParameters and contextAttributes.

  the function of this step is similar to that of step 3, with the ability to add some post processors.

5.invokeBeanFactoryPostProcessors

  finds the Bean that implements the BeanFactoryPostProcessor interface in the Spring container and executes it. The Spring container delegates execution to the invokeBeanFactoryPostProcessors method of PostProcessorRegistrationDelegate, as follows:

  invokeBeanFactoryPostProcessors divides BeanFactoryPostProcessor into two categories for processing, BeanFactoryPostProcessor and BeanDefinitionRegistryPostProcessor, in which BeanDefinitionRegistryPostProcessor inherits from BeanFactoryPostProcessor. When executing, first find all BeanDefinitionRegistryPostProcessor execution and then find all BeanFactoryPostProcessor execution. Because BeanDefinitionRegistryPostProcessor inherits from BeanFactoryPostProcessor, executing the latter will filter out the contents of the former.

When executing BeanDefinitionRegistryPostProcessor,   will first execute postProcessBeanDefinitionRegistry methods according to the following priority, and then execute all postProcessBeanFactory methods uniformly. The rules are as follows:

The BeanDefinitionRegistryPostProcessor implementation of PriorityOrdered interface is filtered.

The BeanDefinitionRegistryPostProcessor implementation of the Ordered interface is filtered and executed.

Perform other BeanDefinitionRegistryPostProcessors

  also executes the BeanFactoryPostProcessor method in accordance with the above rules when executing BeanFactoryPostProcessor.

  will instantiate and initialize the class that implements the BeanFactoryPostProcessor interface and execute it. If there are dependencies, the Bean will also be initialized and instantiated. The specific process will be described in the Bean initialization process.

6.registerBeanPostProcessors

  finds the Bean of the BeanPostProcessor interface from the Spring container and adds it to the List attribute maintained internally by BeanFactory, so that this BeanPostProcessor can be called for callback processing when the Bean is instantiated later. This method is delegated to the registerBeanPostProcessors method execution of the PostProcessorRegistrationDelegate class. The execution process is similar to step 5 and is filtered by priority, in the following order:

Register the BeanPostProcessor list that implements the PriorityOrdered interface with ApplicationContext

Register the BeanPostProcessor list that implements the Ordered interface with ApplicationContext

Register the remaining BeanPostProcessor list with ApplicationContext

Register the BeanPostProcessor list that implements the MergedBeanDefinitionPostProcessor interface with ApplicationContext

  where the MergedBeanDefinitionPostProcessor interface inherits from the BeanPostProcessor interface, so the list of point (4) above intersects with the list of the first three points. However, when AbstraceApplicationContext adds BeanPostProcessor, it deletes the existing objects before adding new ones, as follows:

The order of execution of   is therefore: PriorityOrdered, Ordered, NotOrdered, MergedBeanDefinitionPostProcessor.

  instantiates and initializes the class that implements the BeanPostProcessor interface, but does not execute it, and the Bean that has dependencies will also be initialized and instantiated.

7.initMessageSource

  initializes some internationalization-related properties in the Spring container

8.initApplicationEventMulticaster

  initializes the event broadcaster object SimpleApplicationEventMulticaster in the Spring container and registers it with Context as a singleton applicationEventMulticaster. The broadcaster is used to broadcast the ApplicationListener interface Bean corresponding to ApplicationEvent events.

  PS: according to the above order, the Bean instantiated before will not be processed by BeanFactoryPostProcessor and BeanPostProcessor, including Bean instantiated because of dependency, and Bean registered through new in advance (only the bean obtained by calling the BeanFactory.getBean method directly will be called back). It should be noted that Context loads all the implementations of the two post processors in advance. Since the dependent Bean needs to be instantiated in advance before instantiation, the initialization action of the Bean that these two post processors depend on will not be monitored by it.

9.onRefresh

The   template method, which can be used for the extension of refresh actions, defaults to an empty implementation. In SpringBoot, it is mainly used to start the embedded web server.

10.registerListeners

  finds the ApplicationListener object in the system and registers it with the time broadcaster. If there is a need to broadcast in advance, the broadcast is performed.

11.finishBeanFactoryInitialization

  instantiates all instances in BeanFactory that have been registered but not instantiated (lazy loads do not need to be instantiated). The main operation is the preInstantiateSingletons method of BeanFacotry. The method is divided into two parts:

Iterate through all the beanDefinitionNames that has been parsed, instantiating and initializing if it is not an abstract class, a singleton, and no lazy loading is set.

Call the SmartInitializingSingleton callback API after all singleton objects (non-lazily loaded objects) managed by the spring container are initialized. Note that the callback will only occur in the startup phase. If the lazily loaded object is reinitialized later, there will be no callback.

FinishRefresh

Other actions after   refresh, including:

Initializes the lifecycle processor DefaultLifecycleProcessor, which manages all classes that implement the Lifecycle interface

Notify all Lifecycle.onRefresh that the method calls LifecycleProcessor.startBeans (false) internally. Here, only the SmartLifecycle interface is called and the instance of AutoStartup is set. The callback will be executed from low to high according to the set priority.

Publish ContextRefreshedEvent Notification event

Call the registerApplicationContext method of LiveBeansView

1.2. Catch

1.destroyBeans

  destroys all registered singletons. Classes that implement DisposableBean will be destroyed separately in order to execute callback methods, and then clean up the cache information of all singletons and the remaining singleton instances.

2.cancelRefresh

  identifies the current active status as false

1.3. Finally

ResetCommonCaches

  clears the cache

two。 Close

The close method of   AbstractApplicationContext is as follows:

  mainly calls the doClose method, then determines whether there is a shutdownHook, and if so, removes the hook to avoid repeated closures, because the default shutdownHook is also the called doClose method.

The   doClose method is as follows:

The   process is:

Remove the MBean of the current Context, if MBean is enabled

Send ContextClosedEvent notification event

Callback declares the onClose method of the cycle manager

Destroy the instantiated singleton, consistent with the above mentioned

Reset BeanFacotry id to empty

When the onClose method is called, the default implementation is empty. For SpringBoot applications, as mentioned earlier, the SpringBoot application overrides the onRefresh method to start the web server, and here, it is used to shut down the embedded web server. (PS: note that the web server is shut down after all Bean is destroyed, so web will also receive Http requests before shutting down the server, which may cause the request to fail to be processed. The official provides a solution, as detailed in [issue https://github.com/spring-projects/spring-boot/issues/4657](issue https://github.com/spring-projects/spring-boot/issues/4657)).

three。 Start Stop method

The two methods of   come from the Lifecycle interface, as follows, simply call the start and stop methods of DefaultLifecycleProcessor, and call back the implementation class of Lifecycle.

four。 Extended interface order

  We know that there are many preset interfaces in Spring for extension. Through the above analysis, the order of callback APIs obtained is as follows:

When   expands on other details later, you will see more extension interfaces, and then update the above figure.

At this point, the study of "introduction to the startup process of Spring" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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