目录
@SpringBootApplication
开启spring boot。
@SpringBootApplication = @Configuration + @EnableAutoConfaguration + @ComponentScan。
@EnableAutoConfaguration：表示会自动为依赖的jar包进行配置，比如项目添加了spring-boot-starter-web依赖包，则该注解会自动为项目提供tomcat和spring MVC的配置。
@ComponentScan：spring会自动对入口类同级及下级包所有的类进行bean管理。
看一下该注解做了什么
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration//入口
@ComponentScan(
excludeFilters = {@Filter(
type = FilterType.CUSTOM,
classes = {TypeExcludeFilter.class}
), @Filter(
type = FilterType.CUSTOM,
classes = {AutoConfigurationExcludeFilter.class}
)}
)
public @interface SpringBootApplication {
@AliasFor(
annotation = EnableAutoConfiguration.class,
attribute = "exclude"
)
Class<?>[] exclude() default {};
@AliasFor(
annotation = EnableAutoConfiguration.class,
attribute = "excludeName"
)
String[] excludeName() default {};
@AliasFor(
annotation = ComponentScan.class,
attribute = "basePackages"
)
String[] scanBasePackages() default {};
@AliasFor(
annotation = ComponentScan.class,
attribute = "basePackageClasses"
)
Class<?>[] scanBasePackageClasses() default {};
}
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage//入口
@Import({EnableAutoConfigurationImportSelector.class})//入口
public @interface EnableAutoConfiguration {
String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
Class<?>[] exclude() default {};
String[] excludeName() default {};
}
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import({Registrar.class})//入口
public @interface AutoConfigurationPackage {
}
@Order(Ordered.HIGHEST_PRECEDENCE)
static class Registrar implements ImportBeanDefinitionRegistrar, DeterminableImports {
@Override
public void registerBeanDefinitions(AnnotationMetadata metadata,
BeanDefinitionRegistry registry) {
//默认将会扫描@SpringBootApplication标注的主配置类所在的包及其子包下所有组件
register(registry, new PackageImport(metadata).getPackageName());
}
@Override
public Set<Object> determineImports(AnnotationMetadata metadata) {
return Collections.<Object>singleton(new PackageImport(metadata));
}
}
@Deprecated
public class EnableAutoConfigurationImportSelector extends AutoConfigurationImportSelector {//入口为其父类的selectImports方法
public EnableAutoConfigurationImportSelector() {
}
protected boolean isEnabled(AnnotationMetadata metadata) {
return this.getClass().equals(EnableAutoConfigurationImportSelector.class) ? (Boolean)this.getEnvironment().getProperty("spring.boot.enableautoconfiguration", Boolean.class, true) : true;
}
}
//AutoConfigurationImportSelector
public String[] selectImports(AnnotationMetadata annotationMetadata) {
if (!this.isEnabled(annotationMetadata)) {
return NO_IMPORTS;
} else {
try {
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader.loadMetadata(this.beanClassLoader);
AnnotationAttributes attributes = this.getAttributes(annotationMetadata);
//入口
List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);
configurations = this.removeDuplicates(configurations);
configurations = this.sort(configurations, autoConfigurationMetadata);
Set<String> exclusions = this.getExclusions(annotationMetadata, attributes);
this.checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
configurations = this.filter(configurations, autoConfigurationMetadata);
this.fireAutoConfigurationImportEvents(configurations, exclusions);
return (String[])configurations.toArray(new String[configurations.size()]);
} catch (IOException var6) {
throw new IllegalStateException(var6);
}
}
}
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
List<String> configurations =
SpringFactoriesLoader.loadFactoryNames(this.getSpringFactoriesLoaderFactoryClass(), this.getBeanClassLoader());//入口
return configurations;
}
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
ArrayList result = new ArrayList();
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
} catch (IOException var8) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + "META-INF/spring.factories" + "]", var8);
}
}
- 通过启动注解引入自动配置类
- 将主配置类(@SpringBootApplication)所在的包及其子包里面的所有组件扫描到Spring容器中
- SpringBoot启动的时候从类路径下的 META-INF/spring.factories中获取EnableAutoConfiguration指定的值，并将这些值作为自动配置类导入到容器中，自动配置类就会生效，最后完成自动配置工作。
- EnableAutoConfiguration默认在spring-boot-autoconfigure这个包中
启动方法
@SpringBootApplication
public class HelloWorldMainApplication {
public static void main(String[] args) {
SpringApplication.run(HelloWorldMainApplication.class, args);
}
}
// 调用静态类，参数对应的就是HelloWorldMainApplication.class以及main方法中的args
public static ConfigurableApplicationContext run(Class<?> primarySource,String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
return (new SpringApplication(sources)).run(args);
}
- 构造一个SpringApplication的实例，并把我们的启动类HelloWorldMainApplication.class作为参数传进去
- 然后运行它的run方法
接下来分别看一下SpringApplication的构造器和他的run方法
构造器
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
//把HelloWorldMainApplication.class设置为属性存储起来
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
//设置应用类型是Standard还是Web
this.webApplicationType = deduceWebApplicationType();
//设置初始化器(Initializer),最后会调用这些初始化器
setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class));
//设置监听器(Listener)
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
- 先将HelloWorldMainApplication.class存储到SpringApplication中
- 设置应用类型：非web应用(Standard)还是web应用，我们是web应用
- 设置初始化器(Initializer),后续会执行初始化器
- 设置监听器(Listener)
接下来分别详细看一下上面这几步
设置应用类型
private WebApplicationType deduceWebApplicationType() {
if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
&& !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
return WebApplicationType.SERVLET;
}
// 相关常量
private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework."
+ "web.reactive.DispatcherHandler";
private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework."
+ "web.servlet.DispatcherServlet";
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
public enum WebApplicationType {
NONE,
SERVLET,
REACTIVE;
private WebApplicationType() {
}
}
设置初始化器(Initializer)
//设置初始化器(Initializer),最后会调用这些初始化器
setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class));
我们先来看看getSpringFactoriesInstances( ApplicationContextInitializer.class)
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
// 这里的入参type就是ApplicationContextInitializer.class
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// 使用Set保存names来避免重复元素
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));//入口1
// 根据names来进行实例化
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);//入口2
// 对实例进行排序
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
// 入参就是ApplicationContextInitializer.class
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
//从类路径的META-INF/spring.factories中加载所有默认的自动配置类
Enumeration<URL> urls = classLoader != null?classLoader.getResources("META-INF/spring.factories"):ClassLoader.getSystemResources("META-INF/spring.factories");
ArrayList result = new ArrayList();
while(urls.hasMoreElements()) {
URL url = (URL)urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
//获取ApplicationContextInitializer.class的所有值
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
} catch (IOException var8) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + "META-INF/spring.factories" + "]", var8);
}
}
// parameterTypes: 上一步得到的names集合
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
Set<String> names) {
List<T> instances = new ArrayList<T>(names.size());
for (String name : names) {
try {
Class<?> instanceClass = ClassUtils.forName(name, classLoader);
//确认被加载类是ApplicationContextInitializer的子类
Assert.isAssignable(type, instanceClass);
Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
//反射实例化对象
T instance = (T) BeanUtils.instantiateClass(constructor, args);
//加入List集合中
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException(
"Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}
- 从类路径的META-INF/spring.factories中加载所有的初始化器
- 每个spring.factories会有好多<String,List>格式的配置，取出key为org.springframework.context.ApplicationContextInitializer的value集合
- 然后取出这些初始化器的className，存入到集合中
- 遍历上面的初始化器集合，通过反射挨个进行实例化，最后加入到list中
- 到此，spring boot的初始化器已经被实例化到内存中了，后续等spring容器进行初始化的时候会挨个执行这些初始化器的initialize方法进行初始化。
设置监听器(Listener)
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
// 这里的入参type是：org.springframework.context.ApplicationListener.class
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<String>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
- 可以发现，这个过程和设置初始化器是一样的，找的是ApplicationListener的实现类。
- 到此，实例化了一堆监听器，后续在整个项目的生命周期中，各种事件会被这些监听器监听到
run方法
public ConfigurableApplicationContext run(String... args) {
// 计时工具
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
// 第一步：获取并启动监听器
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 第二步：根据SpringApplicationRunListeners以及参数来准备环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
configureIgnoreBeanInfo(environment);
// 准备Banner打印器 - 就是启动Spring Boot的时候打印在console上的ASCII艺术字体
Banner printedBanner = printBanner(environment);
// 第三步：创建Spring容器
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
// 第四步：Spring容器前置处理
prepareContext(context, environment, listeners, applicationArguments,printedBanner);
// 第五步：刷新容器
refreshContext(context);
// 第六步：Spring容器后置处理
afterRefresh(context, applicationArguments);
// 第七步：发出结束执行的事件
listeners.started(context);
// 第八步：执行Runners
this.callRunners(context, applicationArguments);
stopWatch.stop();
// 返回容器
return context;
}
catch (Throwable ex) {
handleRunFailure(context, listeners, exceptionReporters, ex);
throw new IllegalStateException(ex);
}
}
- 第一步：获取并启动启动事件发布器SpringApplicationRunListener
- 第二步：根据SpringApplicationRunListeners以及参数来准备环境
- 第三步：创建Spring容器
- 第四步：Spring容器前置处理
- 第五步：刷新容器
- 第六步：Spring容器后置处理
- 第七步：发出结束执行的事件
- 第八步：执行Runners
第一步：获取并启动启动事件发布器SpringApplicationRunListener
获取启动事件发布器
跟进getRunListeners方法：
private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}
public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
private final SpringApplication application;
private final String[] args;
//广播器
private final SimpleApplicationEventMulticaster initialMulticaster;
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
Iterator var3 = application.getListeners().iterator();
while(var3.hasNext()) {
ApplicationListener<?> listener = (ApplicationListener)var3.next();
//将上面设置到SpringApplication的十一个监听器全部添加到SimpleApplicationEventMulticaster这个广播器中
this.initialMulticaster.addApplicationListener(listener);
}
}
//略...
}
public abstract class AbstractApplicationEventMulticaster implements ApplicationEventMulticaster, BeanClassLoaderAware, BeanFactoryAware {
//广播器的父类中存放保存监听器的内部内
private final AbstractApplicationEventMulticaster.ListenerRetriever defaultRetriever = new AbstractApplicationEventMulticaster.ListenerRetriever(false);
@Override
public void addApplicationListener(ApplicationListener<?> listener) {
synchronized (this.retrievalMutex) {
Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);
if (singletonTarget instanceof ApplicationListener) {
this.defaultRetriever.applicationListeners.remove(singletonTarget);
}
//内部类对象
this.defaultRetriever.applicationListeners.add(listener);
this.retrieverCache.clear();
}
}
private class ListenerRetriever {
//保存所有的监听器
public final Set<ApplicationListener<?>> applicationListeners = new LinkedHashSet();
public final Set<String> applicationListenerBeans = new LinkedHashSet();
private final boolean preFiltered;
public ListenerRetriever(boolean preFiltered) {
this.preFiltered = preFiltered;
}
public Collection<ApplicationListener<?>> getApplicationListeners() {
LinkedList<ApplicationListener<?>> allListeners = new LinkedList();
Iterator var2 = this.applicationListeners.iterator();
while(var2.hasNext()) {
ApplicationListener<?> listener = (ApplicationListener)var2.next();
allListeners.add(listener);
}
if (!this.applicationListenerBeans.isEmpty()) {
BeanFactory beanFactory = AbstractApplicationEventMulticaster.this.getBeanFactory();
Iterator var8 = this.applicationListenerBeans.iterator();
while(var8.hasNext()) {
String listenerBeanName = (String)var8.next();
try {
ApplicationListener<?> listenerx = (ApplicationListener)beanFactory.getBean(listenerBeanName, ApplicationListener.class);
if (this.preFiltered || !allListeners.contains(listenerx)) {
allListeners.add(listenerx);
}
} catch (NoSuchBeanDefinitionException var6) {
;
}
}
}
AnnotationAwareOrderComparator.sort(allListeners);
return allListeners;
}
}
//略...
}
- 还是通过上面的方法获取SpringApplicationRunListener，它叫启动事件发布器，也就是在启动后由它来发布启动事件
- 第一步通过反射实例化SpringApplicationRunListener的时候，会触发EventPublishingRunListener的构造器
- EventPublishingRunListener是SpringApplicationRunListener的子类
- 定义一个广播器SimpleApplicationEventMulticaster
- 将设置监听器阶段实例化的所有监听器都添加到这个广播器中
- 到此，我们有一个广播器存储了所有监听器了。这个广播器被启动事件发布器所持有。也就是在启动的时候，启动事件发布器通过它的广播器向所有监听器发布事件。
启动启动事件发布器
先来看一下启动事件发布器都定义哪些功能：
package org.springframework.boot;
public interface SpringApplicationRunListener {
// 在run()方法开始执行时，该方法就立即被调用，可用于在初始化最早期时做一些工作
void starting();
// 当environment构建完成，ApplicationContext创建之前，该方法被调用
void environmentPrepared(ConfigurableEnvironment environment);
// 当ApplicationContext构建完成时，该方法被调用
void contextPrepared(ConfigurableApplicationContext context);
// 在ApplicationContext完成加载，但没有被刷新前，该方法被调用
void contextLoaded(ConfigurableApplicationContext context);
// 在ApplicationContext刷新并启动后，CommandLineRunners和ApplicationRunner未被调用前，该方法被调用
void started(ConfigurableApplicationContext context);
// 在run()方法执行完成前该方法被调用
void running(ConfigurableApplicationContext context);
// 当应用运行出错时该方法被调用
void failed(ConfigurableApplicationContext context, Throwable exception);
}
- 在Spring Boot启动初始化的过程中各种状态时都定义了接口。我们也可以添加自己的监听器，在SpringBoot初始化时监听事件执行自定义逻辑
举例看一下启动方法
@Override
public void starting() {
//关键代码，先创建application启动事件`ApplicationStartingEvent`
this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
}
@Override
public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {
ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
//通过事件类型ApplicationStartingEvent获取对应的监听器
for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
//获取线程池，如果为空则同步处理。这里线程池为空，还未没初始化。
Executor executor = getTaskExecutor();
if (executor != null) {
//异步发送事件
executor.execute(() -> invokeListener(listener, event));
}
else {
//同步发送事件
invokeListener(listener, event);
}
}
}
@Override
public void onApplicationEvent(ApplicationEvent event) {
//在springboot启动的时候
if (event instanceof ApplicationStartedEvent) {
onApplicationStartedEvent((ApplicationStartedEvent) event);
}
//springboot的Environment环境准备完成的时候
else if (event instanceof ApplicationEnvironmentPreparedEvent) {
onApplicationEnvironmentPreparedEvent(
(ApplicationEnvironmentPreparedEvent) event);
}
//在springboot容器的环境设置完成以后
else if (event instanceof ApplicationPreparedEvent) {
onApplicationPreparedEvent((ApplicationPreparedEvent) event);
}
//容器关闭的时候
else if (event instanceof ContextClosedEvent && ((ContextClosedEvent) event)
.getApplicationContext().getParent() == null) {
onContextClosedEvent();
}
//容器启动失败的时候
else if (event instanceof ApplicationFailedEvent) {
onApplicationFailedEvent();
}
}
- 启动的时候，创建一个事件ApplicationEvent，将其交给启动事件发布器的广播器来处理
- 广播器根据事件类型匹配它持有的监听器，进行发布。事件类型有哪些种：
- ApplicationStartedEvent:在springboot启动的时候
- ApplicationEnvironmentPreparedEvent:springboot的Environment环境准备完成的时候
- ApplicationPreparedEvent:在springboot容器的环境设置完成以后
- ContextClosedEvent:容器关闭的时候
- ApplicationFailedEvent:容器启动失败的时候
第二步：根据启动事件发布器以及参数来准备环境
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
//获取对应的ConfigurableEnvironment
ConfigurableEnvironment environment = getOrCreateEnvironment();//入口1
//配置
configureEnvironment(environment, applicationArguments.getSourceArgs());
//发布环境已准备事件，这是第二次发布事件
listeners.environmentPrepared(environment);//入口2
bindToSpringApplication(environment);
ConfigurationPropertySources.attach(environment);
return environment;
}
private ConfigurableEnvironment getOrCreateEnvironment() {
if (this.environment != null) {
return this.environment;
}
if (this.webApplicationType == WebApplicationType.SERVLET) {
return new StandardServletEnvironment();
}
return new StandardEnvironment();
}
- 构建Environment
- 启动事件发布器再次发布状态变更事件
第三步：创建Spring容器
public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext";
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, "
+ "please specify an ApplicationContextClass",
ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
- 这一步是实例化spring容器的。根据webApplicationType进行判断，该类型为SERVLET类型，所以会通过反射实例化AnnotationConfigServletWebServerApplicationContext
第四步：Spring容器前置处理
//SpringApplication
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
//设置容器环境，包括各种变量
context.setEnvironment(environment);
//执行容器后置处理
postProcessApplicationContext(context);
//执行容器中的ApplicationContextInitializer（包括 spring.factories和自定义的实例）
applyInitializers(context);//入口1
//发送容器已经准备好的事件，通知各监听器
listeners.contextPrepared(context);
//注册启动参数bean，这里将容器指定的参数封装成bean，注入容器
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
//设置banner
if (printedBanner != null) {
context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
}
//获取我们的启动类指定的参数，可以是多个
Set<Object> sources = getAllSources();//入口2
Assert.notEmpty(sources, "Sources must not be empty");
//加载我们的启动类，将启动类注入容器
load(context, sources.toArray(new Object[0]));//入口3
//发布容器已加载事件。
listeners.contextLoaded(context);
}
protected void applyInitializers(ConfigurableApplicationContext context) {
// 1. 从SpringApplication类中的initializers集合获取所有的ApplicationContextInitializer
for (ApplicationContextInitializer initializer : getInitializers()) {
// 2. 循环调用ApplicationContextInitializer中的initialize方法
Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(
initializer.getClass(), ApplicationContextInitializer.class);
Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
initializer.initialize(context);//入口
}
}
public Set<Object> getAllSources() {
Set<Object> allSources = new LinkedHashSet();
if (!CollectionUtils.isEmpty(this.primarySources)) {
//获取primarySources属性，也就是之前存储的HelloWorldMainApplication.class
allSources.addAll(this.primarySources);
}
if (!CollectionUtils.isEmpty(this.sources)) {
allSources.addAll(this.sources);
}
return Collections.unmodifiableSet(allSources);
}
protected void load(ApplicationContext context, Object[] sources) {
BeanDefinitionLoader loader = createBeanDefinitionLoader(getBeanDefinitionRegistry(context), sources);
if (this.beanNameGenerator != null) {
loader.setBeanNameGenerator(this.beanNameGenerator);
}
if (this.resourceLoader != null) {
loader.setResourceLoader(this.resourceLoader);
}
if (this.environment != null) {
loader.setEnvironment(this.environment);
}
loader.load();
}
private int load(Class<?> source) {
if (isGroovyPresent()
&& GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
// Any GroovyLoaders added in beans{} DSL can contribute beans here
GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source,
GroovyBeanDefinitionSource.class);
load(loader);
}
if (isComponent(source)) {
//以注解的方式，将启动类bean信息存入beanDefinitionMap，也就是将HelloWorldMainApplication.class存入了beanDefinitionMap
this.annotatedReader.register(source);
return 1;
}
return 0;
}
//ConfigurationWarningsApplicationContextInitializer
public void initialize(ConfigurableApplicationContext context) {
context.addBeanFactoryPostProcessor(new ConfigurationWarningsApplicationContextInitializer.ConfigurationWarningsPostProcessor(this.getChecks()));
}
- 获取之前实例化到内存中的所有初始化器，挨个调用其initialize方法
- 我们也可以自定义初始化器，并实现initialize方法，然后放入META-INF/spring.factories配置文件中Key为：org.springframework.context.ApplicationContextInitializer的value中，这里我们自定义的初始化器就会被调用，是我们项目初始化的一种方式
- 将启动类HelloWorldMainApplication.class被加载到 beanDefinitionMap中。后续进行bean实例化的时候，会根据这个类的@SpringBootApplication注解完成spring boot的自动配置。
这一步才是核心功能自动配置的重要桥梁。
后续要spring容器refresh的时候，遇到HelloWorldMainApplication这个启动类bean，会根据其注解@SpringBootApplication一步一步的找到所有的自动配置类，然后完成自动配置。
第五步：刷新容器
执行到这里，springBoot相关的处理工作已经结束，接下的工作就交给了spring。我们来看看refreshContext(context);
其实就是spring ioc的refresh方法。
第六步：Spring容器后置处理
扩展接口，设计模式中的模板方法，默认为空实现。如果有自定义需求，可以重写该方法。比如打印一些启动结束log，或者一些其它后置处理。
第七步：发出结束执行的事件
public void started(ConfigurableApplicationContext context) {
//这里就是获取的EventPublishingRunListener
Iterator var2 = this.listeners.iterator();
while(var2.hasNext()) {
SpringApplicationRunListener listener = (SpringApplicationRunListener)var2.next();
//执行EventPublishingRunListener的started方法
listener.started(context);
}
}
public void started(ConfigurableApplicationContext context) {
//创建ApplicationStartedEvent事件，并且发布事件
//我们看到是执行的ConfigurableApplicationContext这个容器的publishEvent方法，和前面的starting是不同的
context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context));
}
- 创建一个ApplicationStartedEvent事件，获取启动事件发布器，并执行其started方法，并且将创建的Spring容器传进去了
- 这里是调用的spring容器进行发布的
第八步：执行Runners
我们再来看看最后一步callRunners(context, applicationArguments);
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList<Object>();
//获取容器中所有的ApplicationRunner的Bean实例
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());
//获取容器中所有的CommandLineRunner的Bean实例
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
AnnotationAwareOrderComparator.sort(runners);
for (Object runner : new LinkedHashSet<Object>(runners)) {
if (runner instanceof ApplicationRunner) {
//执行ApplicationRunner的run方法
callRunner((ApplicationRunner) runner, args);
}
if (runner instanceof CommandLineRunner) {
//执行CommandLineRunner的run方法
callRunner((CommandLineRunner) runner, args);
}
}
}
如果是ApplicationRunner的话,则执行如下代码:
private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
try {
runner.run(args);
} catch (Exception var4) {
throw new IllegalStateException("Failed to execute ApplicationRunner", var4);
}
}
如果是CommandLineRunner的话,则执行如下代码:
private void callRunner(CommandLineRunner runner, ApplicationArguments args) {
try {
runner.run(args.getSourceArgs());
} catch (Exception var4) {
throw new IllegalStateException("Failed to execute CommandLineRunner", var4);
}
}
- Runner运行器用于在服务启动时进行一些业务初始化操作，这些操作只在服务启动后执行一次。
Spring Boot提供了ApplicationRunner和CommandLineRunner两种服务接口CommandLineRunner、ApplicationRunner