review
The previous article talked about the general startup process of springboot:
[1] Get listener
[2] Prepare the environment
[3] Console print Banner
[4] Create containers, and create different containers according to different types
[5] Instantiate an exception reporting period instance to record errors during startup.
[6] Prepare the container and do some initialization for the container just created
[7] This step is crucial to refresh the container. Analyze later
[8] Some operations after refreshing the container. Here is an empty method
Here's a detailed analysis.
Instantiation of spring application
In the process of calling the run method, a SpringApplication object will be instantiated. There are several steps, which are described in detail here.
[1] Set the startup environment: non web environment, web environment and reactive environment
[2] Load spring Factories file, get container initializer ApplicationContextInitializer
[3] Load spring Factories file, get listener
[4] Get the class where the main method is currently executed from the current stack
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
// Determine whether the startup class is null
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
// [1] Set the startup environment: non web environment, web environment and reactive environment
this.webApplicationType = WebApplicationType.deduceFromClasspath();
// [2] The startup process loads spring for the first time Factories file, get container initializer ApplicationContextInitializer
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
// [3] Load spring Factories file, get listener
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
// [4] Get the class where the main method is currently executed from the current stack
this.mainApplicationClass = deduceMainApplicationClass();
}
Set the startup environment webapplicationtype deduceFromClasspath()
It determines the current environment according to the existence of relevant bytecode files
// Judge the project startup environment and set
static WebApplicationType deduceFromClasspath() {
// If the DispatcherHandler bytecode file does not exist, and the dispatcherservlet and servletcontainer bytecode files exist, it is a REACTIVE environment
if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
// If the Servlet and ConfigurableWebApplicationContext do not exist in the class file, set the environment to NONE
for (String className : SERVLET_INDICATOR_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
// Set the environment to SERVLET
return WebApplicationType.SERVLET;
}
Get ApplicationContextInitializer and listener
Read spring.inf in META-INF directory Configuration information in the factories file: ApplicationContextInitializer and listener. This is the first and second reading. The whole spring boot process reads spring Factories use the following three methods
// From spring General method of obtaining value in factories
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
// From spring General method of obtaining value in factories
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = getClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
// From spring A general method for obtaining values in factories to instantiate various objects
@SuppressWarnings("unchecked")
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
Set<String> names) {
List<T> instances = new ArrayList<>(names.size());
for (String name : names) {
try {
Class<?> instanceClass = ClassUtils.forName(name, classLoader);
Assert.isAssignable(type, instanceClass);
Constructor<?> constructor = instanceClass
.getDeclaredConstructor(parameterTypes);
T instance = (T) BeanUtils.instantiateClass(constructor, args);
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException(
"Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}
Read spring There are 4 Initializers in factories, plus 2 automatically configured ones, a total of 6
spring.factories
# Application Context Initializers org.springframework.context.ApplicationContextInitializer=\ org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ org.springframework.boot.context.ContextIdApplicationContextInitializer,\ org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\ org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer
Plus 2:
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
Read spring There are 9 listeners in factories, plus 1 automatically configured listener, a total of 10
spring.factories:
# Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.ClearCachesApplicationListener,\ org.springframework.boot.builder.ParentContextCloserApplicationListener,\ org.springframework.boot.context.FileEncodingApplicationListener,\ org.springframework.boot.context.config.AnsiOutputApplicationListener,\ org.springframework.boot.context.config.ConfigFileApplicationListener,\ org.springframework.boot.context.config.DelegatingApplicationListener,\ org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\ org.springframework.boot.context.logging.LoggingApplicationListener,\ org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
There's another one: org springframework. boot. autoconfigure. BackgroundPreinitializer
Get listener getRunListeners(args) from the core run method
Get spring Listener EventPublishingRunListener corresponding to SpringApplicationRunListener in factories
// Get the current listener from the core run method
private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
SpringApplicationRunListener.class, types, this, args));
}