先来一段经典的SpringBoot启动代码
@SpringBootApplication
public class SpringbootDemoApplication {
public static void main(String[] args) {
SpringApplication.run(SpringbootDemoApplication.class, args);
}
}SpringBoot应用程序的启动是调用SpringApplication的动态run办法开始的，咱们看一下其源代码
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}能够看到，启动程序是先将启动类，即示例代码中的SpringbootDemoApplication类作为参数，结构出一个SpringApplication实例，再调用这个SpringApplication实例的run办法进行启动
getSpringFactoriesInstances
这里咱们先理解一下SpringBoot中很常见的getSpringFactoriesInstances办法
// 从各个jar包中的spring.factories中获取到类型为type的类，并将其实例化
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
/**
* 从各个jar包中的spring.factories中获取到类型为type的类，并调用其结构函数参数类型为parameterTypes的函数进行初始化
* type: 从各个jar包中的spring.factories中获取到类型为type的类
* parameterTypes: 构造函数的参数类型列表
* args: 构造函数的参数列表
*/
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = getClassLoader();
// 调用SpringFactoriesLoader，找到其中类型为type的类，返回这些类的全限定名
Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
// 结构下面这些类的实例
List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
// 依照注解排个序，即@Order
AnnotationAwareOrderComparator.sort(instances);
// 返回这些实例
return instances;
}下面代码中，通过SpringFactoriesLoader加载类型为type的类。这里咱们不深入分析了，简略来说，SpringFactoriesLoader就是加载类门路下，所有的META-INF/spring.factories文件，这些文件中是一个properties文件，其中定义了各个类型（即type）及其实现子类，以下是一个文件实例
key就是type的全限定名，value就是咱们返回的类名的汇合
SpringApplication构造方法
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
/**
* resourceLoader 资源加载器，默认为空
* primarySources 咱们的启动类的class
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
// 资源加载器，默认为空
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
// 1. 检测Web应用程序类型
this.webApplicationType = WebApplicationType.deduceFromClasspath();
// 2. 加载疏导上下文的初始化器，疏导上下文也是一个容器，次要利用在SpringBoot启动阶段疏导应用程序上下文启动
this.bootstrapRegistryInitializers = new ArrayList<>(
getSpringFactoriesInstances(BootstrapRegistryInitializer.class));
// 3. 加载应用程序初始化器
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
// 4. 加载监听器
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
// 5. 设置主启动类
this.mainApplicationClass = deduceMainApplicationClass();
}咱们来挨个剖析其中的代码
检测Web应用程序类型
检测Web应用程序类型是由WebApplicationType实现的，以下是WebApplicationType的源代码
public enum WebApplicationType {
// 阐明不是Web应用程序，不应该启动Web服务器
NONE,
// 阐明应用程序是基于Servlet启动的，会启动内嵌的Web服务器
SERVLET,
// 阐明应用程序时基于响应式的web应用程序，会启动内嵌的响应式Web服务器
REACTIVE;
private static final String[] SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };
private static final String WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";
private static final String WEBFLUX_INDICATOR_CLASS = "org.springframework.web.reactive.DispatcherHandler";
private static final String JERSEY_INDICATOR_CLASS = "org.glassfish.jersey.servlet.ServletContainer";
static WebApplicationType deduceFromClasspath() {
// 如果类门路下有DispatcherHandler并且没有DispatcherServlet，也没有ServletContainer，阐明是响应式Web应用程序
if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
// 如果类门路下没有Setvlet相干类，则阐明不是Web应用程序
for (String className : SERVLET_INDICATOR_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
// 其余状况示意是一般的Servlet的Web应用程序
return WebApplicationType.SERVLET;
}
}加载疏导上下文的初始化器
接下来是加载疏导上下文的初始化器，即BootstrapRegistryInitializer的实例，咱们能够看一下BootstrapRegistryInitializer的源代码
// BootstrapRegistry的回调接口，在BootstrapRegistry应用之前对BootstrapRegistry进行解决
@FunctionalInterface
public interface BootstrapRegistryInitializer {
void initialize(BootstrapRegistry registry);
}在这里就不得不先提到疏导上下文BootstrapContext，它是一个小容器，专门在SpringBoot启动过程中疏导应用程序容器启动，而BootstrapContext目前只有惟一一个实现类DefaultBootstrapContext，而它同时实现了BootstrapRegistry。BootsstrapRegistryInitializer就是对这个DefaultBootstrapContext做解决的
而默认状况下，SpringBoot并没有定义任何的BootstrapRegistryInitializer
加载应用程序初始化器
应用程序初始化器，对应用程序上下文进行初始化解决的
/**
* ConfigurableApplicationContext的回调接口，会在refresh办法调用之前对ApplicationContext进行解决
* 个别用于对ApplicationContext进行一些初始化工作，比方注册一个属性源或者激活某个profile
*
* ApplicationContextInitializer会依照Ordered接口或者@Order注解定义的优先级进行排序
*/
@FunctionalInterface
public interface ApplicationContextInitializer<C extends ConfigurableApplicationContext> {
void initialize(C applicationContext);
}以下是SpringBoot默认提供的应用程序上下文的初始化器
加载监听器
// 应用程序监听器，监听ApplicationEvent接口。是基于观察者模式创立的接口
@FunctionalInterface
public interface ApplicationListener<E extends ApplicationEvent> extends EventListener {
void onApplicationEvent(E event);
/**
* 静态方法，为音讯类型T创立一个监听器
*/
static <T> ApplicationListener<PayloadApplicationEvent<T>> forPayload(Consumer<T> consumer) {
return event -> consumer.accept(event.getPayload());
}
}咱们再看看SpringBoot默认提供了哪些利用监听器
设置主启动类
private Class<?> deduceMainApplicationClass() {
try {
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
for (StackTraceElement stackTraceElement : stackTrace) {
if ("main".equals(stackTraceElement.getMethodName())) {
return Class.forName(stackTraceElement.getClassName());
}
}
}
catch (ClassNotFoundException ex) {
// Swallow and continue
}
return null;
}这个代码十分有意思，它是手动创立了一个异样，而后追踪异样堆栈信息，找到main办法所在的类，它就是启动类
run办法解析
看完了SpringApplication的构造方法逻辑，咱们接下来看看run办法的实现
// 创立应用程序的ApplicationContext，并进行刷新启动
public ConfigurableApplicationContext run(String... args) {
long startTime = System.nanoTime();
// 1. 创立疏导上下文
DefaultBootstrapContext bootstrapContext = createBootstrapContext();
ConfigurableApplicationContext context = null;
// 配置无头模式参数，不做剖析
configureHeadlessProperty();
// 2. 创立SpringBootRunListeners，即启动过程中的监听器。在启动过程中会触发这些监听器
SpringApplicationRunListeners listeners = getRunListeners(args);
// 触发应用程序开始启动的事件
listeners.starting(bootstrapContext, this.mainApplicationClass);
try {
// 解析命令行参数，封装到ApplicationArguments
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 3. 筹备好Environment
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
configureIgnoreBeanInfo(environment);
// 输入banner，不重要，疏忽
Banner printedBanner = printBanner(environment);
// 4. 创立应用程序上下文
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
// 5. 筹备好应用程序上下文
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
// 6. 刷新应用程序上下文
refreshContext(context);
// 刷新后的解决，默认没有实现，这个是交给子类实现的
afterRefresh(context, applicationArguments);
Duration timeTakenToStartup = Duration.ofNanos(System.nanoTime() - startTime);
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), timeTakenToStartup);
}
// 触发启动结束的事件
listeners.started(context, timeTakenToStartup);
// 7. 调用SpringRunner
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
// 解决启动失败
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
Duration timeTakenToReady = Duration.ofNanos(System.nanoTime() - startTime);
// 触发筹备结束的事件
listeners.ready(context, timeTakenToReady);
}
catch (Throwable ex) {
// 解决启动失败
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
}创立疏导上下文createBootstrapContext
SpringApplication会调用createBootstrapContext办法创立疏导上下文
private DefaultBootstrapContext createBootstrapContext() {
DefaultBootstrapContext bootstrapContext = new DefaultBootstrapContext();
this.bootstrapRegistryInitializers.forEach((initializer) -> initializer.initialize(bootstrapContext));
return bootstrapContext;
}这里就能够看到，在SpringApplication构造方法中的BootstrapRegistryInitializers就会利用到DefaultBootstrapContext中。这也是SpringBoot提供的扩大点之一
以后扩大点图谱
创立SpringApplicationRunListeners
private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger,
getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args),
this.applicationStartup);
}SpringApplicationRunListener
SpringApplicationRunListener监听run办法的各个阶段，在不同的阶段监听不同的事件
// 对run办法中的各个阶段进行监听触发，其实现类必须有一个公共结构参数，其承受的参数为
// SpringApplication和[]String，前者为SpringApplication的实例，后者为启动应用程序输出的参数
public interface SpringApplicationRunListener {
/**
* 在run办法开始启动时触发
* @param bootstrapContext 疏导上下文
*/
default void starting(ConfigurableBootstrapContext bootstrapContext) {
}
/**
* 当Environment筹备结束时触发，此时应用程序上下文ApplicationContext还没有被创立
* 触发办法为prepareEnvironment
* @param bootstrapContext 疏导上下文
* @param environment Environment实例
*/
default void environmentPrepared(ConfigurableBootstrapContext bootstrapContext,
ConfigurableEnvironment environment) {
}
/**
* 在应用程序上下文ApplicationContext创立并筹备实现时触发
* 触发办法为prepareContext
* @param context 应用程序上下文
*/
default void contextPrepared(ConfigurableApplicationContext context) {
}
/**
* 在应用程序上下文ApplicationContext载入初始化bean之后触发，此时还未触发上下文的refresh办法
* 触发办法文prepareContext
* @param context 应用程序上下文
*/
default void contextLoaded(ConfigurableApplicationContext context) {
}
/**
* 在应用程序上下文刷新并启动实现之后触发，此时CommandLineRunner和ApplicationRunner还未触发
* 在run办法内触发
* @param context 应用程序上下文
* @param timeTaken 从应用程序启动至触发started事件触发破费的工夫，可能为null
* @since 2.6.0
*/
default void started(ConfigurableApplicationContext context, Duration timeTaken) {
started(context);
}
/**
* 晚期的started办法，已弃用
*/
@Deprecated
default void started(ConfigurableApplicationContext context) {
}
/**
* 在应用程序启动并刷新实现，并且所有的CommandLineRunner和ApplicationRunner都运行实现之后触发
* 在run办法内触发
* @param context 应用程序上下文
* @param timeTaken 从应用程序启动至触发ready事件触发破费的事件，可能为null
* @since 2.6.0
*/
default void ready(ConfigurableApplicationContext context, Duration timeTaken) {
running(context);
}
/**
* 晚期的ready办法，已弃用
*/
@Deprecated
default void running(ConfigurableApplicationContext context) {
}
/**
* 当启动利用失败时触发
* @param context 应用程序上下文，可能为null
* @param exception 导致启动失败的异样
* @since 2.0.0
*/
default void failed(ConfigurableApplicationContext context, Throwable exception) {
}
}
接下来看看SpringBoot默认提供的SpringApplicationRunListener<br/>
SpringApplicationRunListeners
SpringApplicationRunListeners是一个封装类，其中封装了一个SpringApplicationRunListener的列表，当触发某个事件是，就挨个调用其中的SpringApplicationRunListener的对应办法
class SpringApplicationRunListeners {
private final Log log;
private final List<SpringApplicationRunListener> listeners;
private final ApplicationStartup applicationStartup;
SpringApplicationRunListeners(Log log, Collection<? extends SpringApplicationRunListener> listeners,
ApplicationStartup applicationStartup) {
this.log = log;
this.listeners = new ArrayList<>(listeners);
this.applicationStartup = applicationStartup;
}
void starting(ConfigurableBootstrapContext bootstrapContext, Class<?> mainApplicationClass) {
doWithListeners("spring.boot.application.starting", (listener) -> listener.starting(bootstrapContext),
(step) -> {
if (mainApplicationClass != null) {
step.tag("mainApplicationClass", mainApplicationClass.getName());
}
});
}
void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {
doWithListeners("spring.boot.application.environment-prepared",
(listener) -> listener.environmentPrepared(bootstrapContext, environment));
}
void contextPrepared(ConfigurableApplicationContext context) {
doWithListeners("spring.boot.application.context-prepared", (listener) -> listener.contextPrepared(context));
}
void contextLoaded(ConfigurableApplicationContext context) {
doWithListeners("spring.boot.application.context-loaded", (listener) -> listener.contextLoaded(context));
}
void started(ConfigurableApplicationContext context, Duration timeTaken) {
doWithListeners("spring.boot.application.started", (listener) -> listener.started(context, timeTaken));
}
void ready(ConfigurableApplicationContext context, Duration timeTaken) {
doWithListeners("spring.boot.application.ready", (listener) -> listener.ready(context, timeTaken));
}
void failed(ConfigurableApplicationContext context, Throwable exception) {
doWithListeners("spring.boot.application.failed",
(listener) -> callFailedListener(listener, context, exception), (step) -> {
step.tag("exception", exception.getClass().toString());
step.tag("message", exception.getMessage());
});
}
private void callFailedListener(SpringApplicationRunListener listener, ConfigurableApplicationContext context,
Throwable exception) {
try {
listener.failed(context, exception);
}
catch (Throwable ex) {
if (exception == null) {
ReflectionUtils.rethrowRuntimeException(ex);
}
if (this.log.isDebugEnabled()) {
this.log.error("Error handling failed", ex);
}
else {
String message = ex.getMessage();
message = (message != null) ? message : "no error message";
this.log.warn("Error handling failed (" + message + ")");
}
}
}
private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction) {
doWithListeners(stepName, listenerAction, null);
}
private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction,
Consumer<StartupStep> stepAction) {
StartupStep step = this.applicationStartup.start(stepName);
// 调用每个办法
this.listeners.forEach(listenerAction);
if (stepAction != null) {
stepAction.accept(step);
}
step.end();
}
}EventPublishingRunListener
SpringBoot默认应用EventPublishingRunListener作为run办法的监听者，咱们来看看其源代码
/**
* SpringApplicationRunListener 的实现类，它次要是依赖Spring的事件散发机制来触发事件
*/
public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
private final SpringApplication application;
private final String[] args;
private final SimpleApplicationEventMulticaster initialMulticaster;
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
@Override
public int getOrder() {
return 0;
}
@Override
public void starting(ConfigurableBootstrapContext bootstrapContext) {
this.initialMulticaster
.multicastEvent(new ApplicationStartingEvent(bootstrapContext, this.application, this.args));
}
@Override
public void environmentPrepared(ConfigurableBootstrapContext bootstrapContext,
ConfigurableEnvironment environment) {
this.initialMulticaster.multicastEvent(
new ApplicationEnvironmentPreparedEvent(bootstrapContext, this.application, this.args, environment));
}
@Override
public void contextPrepared(ConfigurableApplicationContext context) {
this.initialMulticaster
.multicastEvent(new ApplicationContextInitializedEvent(this.application, this.args, context));
}
@Override
public void contextLoaded(ConfigurableApplicationContext context) {
for (ApplicationListener<?> listener : this.application.getListeners()) {
if (listener instanceof ApplicationContextAware) {
((ApplicationContextAware) listener).setApplicationContext(context);
}
context.addApplicationListener(listener);
}
this.initialMulticaster.multicastEvent(new ApplicationPreparedEvent(this.application, this.args, context));
}
@Override
public void started(ConfigurableApplicationContext context, Duration timeTaken) {
context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context, timeTaken));
AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
}
@Override
public void ready(ConfigurableApplicationContext context, Duration timeTaken) {
context.publishEvent(new ApplicationReadyEvent(this.application, this.args, context, timeTaken));
AvailabilityChangeEvent.publish(context, ReadinessState.ACCEPTING_TRAFFIC);
}
@Override
public void failed(ConfigurableApplicationContext context, Throwable exception) {
ApplicationFailedEvent event = new ApplicationFailedEvent(this.application, this.args, context, exception);
if (context != null && context.isActive()) {
// Listeners have been registered to the application context so we should
// use it at this point if we can
context.publishEvent(event);
}
else {
// An inactive context may not have a multicaster so we use our multicaster to
// call all the context's listeners instead
if (context instanceof AbstractApplicationContext) {
for (ApplicationListener<?> listener : ((AbstractApplicationContext) context)
.getApplicationListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
this.initialMulticaster.setErrorHandler(new LoggingErrorHandler());
this.initialMulticaster.multicastEvent(event);
}
}
private static class LoggingErrorHandler implements ErrorHandler {
private static final Log logger = LogFactory.getLog(EventPublishingRunListener.class);
@Override
public void handleError(Throwable throwable) {
logger.warn("Error calling ApplicationEventListener", throwable);
}
}
}从代码中能够看到，EventPublishingRunListener会从SpringApplication中获取其Listener，即后面咱们在构造方法中看到的ApplicationListener实例，在触发事件时，就是利用Spring的事件机制公布事件，触发ApplicationListener进行触发
这里须要留神的是，ApplicationListener的起源是spring.factories，而不是咱们平时应用的@EventListener，也就是说，如果不写入到spring.factories，那么ApplicationListener就不会呈现在这里的EventPublishingRunListener中
以后扩大点图谱
筹备好Environment prepareEnvironment
先看源码
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {
// 1. 创立一个Environment实例
ConfigurableEnvironment environment = getOrCreateEnvironment();
// 2. 对Environment进行配置
configureEnvironment(environment, applicationArguments.getSourceArgs());
// 对environment减少configurationProperty的属性源
ConfigurationPropertySources.attach(environment);
// 3. 触发监听SpringApplicationRunListener的environmentPrepared事件
listeners.environmentPrepared(bootstrapContext, environment);
// 将名为defaultProperties的属性源挪动到最初
DefaultPropertiesPropertySource.moveToEnd(environment);
Assert.state(!environment.containsProperty("spring.main.environment-prefix"),
"Environment prefix cannot be set via properties.");
// 将environment的属性设置到SpringApplication中
bindToSpringApplication(environment);
// 依据状况对Environment进行一次转换
if (!this.isCustomEnvironment) {
EnvironmentConverter environmentConverter = new EnvironmentConverter(getClassLoader());
environment = environmentConverter.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}创立Environment实例，getOrCreateEnvironment
private ConfigurableEnvironment getOrCreateEnvironment() {
// 如果以后environment不为空，间接返回
if (this.environment != null) {
return this.environment;
}
// 依据利用类型创立Environment
ConfigurableEnvironment environment = this.applicationContextFactory.createEnvironment(this.webApplicationType);
// 如果用户本人通过编程形式定制了applicationContextFactory，且其自定义的applicationContextFactory没有胜利创立Environment
// 则采纳默认的形式创立一个environment
if (environment == null && this.applicationContextFactory != ApplicationContextFactory.DEFAULT) {
environment = ApplicationContextFactory.DEFAULT.createEnvironment(this.webApplicationType);
}
// 反正最初必定会返回一个不为空的Environment
return (environment != null) ? environment : new ApplicationEnvironment();
}
这里会应用成员属性applicationContextFactory创立Environment，其是一个ApplicationContextFactory接口类型。默认状况下SpringApplication中applicationContextFactory是DefaultApplicationContextFactory类型的
// SpringApplication中对applicationContextFactory的定义
private ApplicationContextFactory applicationContextFactory = ApplicationContextFactory.DEFAULT;
// ApplicationContextFactory 中对DEFAULT的定义
ApplicationContextFactory DEFAULT = new DefaultApplicationContextFactory();ApplicationContextFactory
咱们先来看看ApplicationContextFactory是做啥的
// 是提供给SpringApplication用来创立ConfigurableApplicationContext的策略接口
// 创立上下文时不应该扭转其初始的内容，而是交给SpringApplication负责进行配置和刷新
@FunctionalInterface
public interface ApplicationContextFactory {
// 定义了ApplicationContextFactory的默认实现DEFAULT
ApplicationContextFactory DEFAULT = new DefaultApplicationContextFactory();
/**
* 依据传入的利用类型WebApplicationType返回其冀望的Environment的类型
* 该办法次要用在转换已有的Environment
* @param webApplicationType 利用类型
* @since 2.6.14
*/
default Class<? extends ConfigurableEnvironment> getEnvironmentType(WebApplicationType webApplicationType) {
return null;
}
/**
* 依据利用类型WebApplicationType创立Environment，这个Environment随后会被设置到应用程序上下文中
* 请留神，这个办法的返回值必须和getEnvironmentType办法的保持一致
* @param webApplicationType 利用类型
* @since 2.6.14
*/
default ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
return null;
}
/**
* 创立应用程序上下文
* @param webApplicationType 利用类型
*/
ConfigurableApplicationContext create(WebApplicationType webApplicationType);
/**
* 传入一个应用程序上下文类型，创立一个会应用该类型创立上下文的ApplicationContextFactory
* @param contextClass 应用程序上下文类型
* @return the factory that will instantiate the context class
* @see BeanUtils#instantiateClass(Class)
*/
static ApplicationContextFactory ofContextClass(Class<? extends ConfigurableApplicationContext> contextClass) {
return of(() -> BeanUtils.instantiateClass(contextClass));
}
//工具办法，与ofContextClass配套应用
static ApplicationContextFactory of(Supplier<ConfigurableApplicationContext> supplier) {
return (webApplicationType) -> supplier.get();
}
}总的来说，ApplicationContextFactory正如其名，次要负责创立应用程序上下文，附带会创立所需的Environment
DefaultApplicationContextFactory
因而，接下来咱们看一下默认的DefaultApplicationContextFactory是如何创立Environment的
class DefaultApplicationContextFactory implements ApplicationContextFactory {
// 省略无关代码
@Override
public Class<? extends ConfigurableEnvironment> getEnvironmentType(WebApplicationType webApplicationType) {
return getFromSpringFactories(webApplicationType, ApplicationContextFactory::getEnvironmentType, null);
}
@Override
public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
return getFromSpringFactories(webApplicationType, ApplicationContextFactory::createEnvironment, null);
}
@Override
public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
try {
return getFromSpringFactories(webApplicationType, ApplicationContextFactory::create,
AnnotationConfigApplicationContext::new);
}
catch (Exception ex) {
throw new IllegalStateException("Unable create a default ApplicationContext instance, "
+ "you may need a custom ApplicationContextFactory", ex);
}
}
/**
* 从spring.factories中获取ApplicationContextFactory类型的实例，遍历这些实例创立Environment
* @param webApplicationType 利用类型，即后面提到的NONE，SERLVET，REACTIVE
* @param action 函数，定义对每个ApplicationContextFactory调用哪个办法进行解决
* @param defaultResult 定义默认值
*/
private <T> T getFromSpringFactories(WebApplicationType webApplicationType,
BiFunction<ApplicationContextFactory, WebApplicationType, T> action, Supplier<T> defaultResult) {
for (ApplicationContextFactory candidate : SpringFactoriesLoader.loadFactories(ApplicationContextFactory.class,
getClass().getClassLoader())) {
T result = action.apply(candidate, webApplicationType);
if (result != null) {
return result;
}
}
return (defaultResult != null) ? defaultResult.get() : null;
}
}DefaultApplicationContextFactory的设计采纳了组合模式，它自身没有太多逻辑，它的职责是通过SpringFactoriesLoader加载spring.factories中定义的ApplicationContextFactory，而后将相干逻辑交给这些spring.factories中的ApplicationContextFactory进行解决
其余ApplicationContextFactory
这里又看到了相熟的SpringFactoriesLoader，因而咱们持续看看默认状况下SpringBoot提供了哪些ApplicationContextFactory
简略看看SpringBoot默认提供的这些ApplicationContextFactory
// 对应响应式应用程序
public class AnnotationConfigReactiveWebServerApplicationContext extends ReactiveWebServerApplicationContext
implements AnnotationConfigRegistry {
// 省略无关代码
static class Factory implements ApplicationContextFactory {
@Override
public Class<? extends ConfigurableEnvironment> getEnvironmentType(WebApplicationType webApplicationType) {
return (webApplicationType != WebApplicationType.REACTIVE) ? null : ApplicationReactiveWebEnvironment.class;
}
@Override
public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
return (webApplicationType != WebApplicationType.REACTIVE) ? null : new ApplicationReactiveWebEnvironment();
}
@Override
public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
return (webApplicationType != WebApplicationType.REACTIVE) ? null
: new AnnotationConfigReactiveWebServerApplicationContext();
}
}
}
// 对应一般Web应用程序
public class AnnotationConfigServletWebServerApplicationContext extends ServletWebServerApplicationContext
implements AnnotationConfigRegistry {
// 省略无关代码
static class Factory implements ApplicationContextFactory {
@Override
public Class<? extends ConfigurableEnvironment> getEnvironmentType(WebApplicationType webApplicationType) {
return (webApplicationType != WebApplicationType.SERVLET) ? null : ApplicationServletEnvironment.class;
}
@Override
public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
return (webApplicationType != WebApplicationType.SERVLET) ? null : new ApplicationServletEnvironment();
}
@Override
public ConfigurableApplicationContext create(WebApplicationType webApplicationType) {
return (webApplicationType != WebApplicationType.SERVLET) ? null
: new AnnotationConfigServletWebServerApplicationContext();
}
}
}这里两个ApplicationContextFactory就别离对应SERVLET和REACTIVE两种利用类型。
咱们常常应用SpringBoot开发Web应用程序，基本上都是SERVLET类型的，所以，在创立Environment时就是ApplicationServletEnvironment。本文的重点不是Environment，因而不做深刻的解析了
对Environment进行配置，configureEnvironment
/**
* 模板办法，次要逻辑委托给configurePropertySources和configureProfiles进行解决
* 能够覆写本办法实现对environment的齐全管制
* 或者覆写configurePropertySources和configureProfiles实现部分的管制
* @param environment 应用程序的Environment
* @param args 传递给run办法的参数列表
*/
protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
// 1. 为environment设置上转换服务ConversionService
if (this.addConversionService) {
environment.setConversionService(new ApplicationConversionService());
}
// 2. 配置属性源
configurePropertySources(environment, args);
// 3. 配置profiles
configureProfiles(environment, args);
}设置转换服务ConversionService
这里咱们简略看一下ConversionService是做啥的
/**
* 用于类型转换的服务接口，ConversionService是Spring类型转换零碎的入口
* 调用convert(Object, class)能够进行一个线程平安的转换
* @since 3.0
*/
public interface ConversionService {
/**
* 判断类型sourceType是否能够转换为targetType类型
* 如果返回true，阐明能够通过convert(Object, Class)进行转换
*
* 对于汇合，数组，map这些容器类型须要特地留神：
* 对于这几个类型之间的互相转换，这个办法将总是返回true，即便其元素类型的转换会产生异样，也会返回true
* 这就须要调用者自行处理ConversionException异样了
* @param sourceType 源类型，如果source自身就是null，则传入null
* @param targetType 指标类型
* @throws 如果targetType为空，则会抛出非法参数异样
*/
boolean canConvert(@Nullable Class<?> sourceType, Class<?> targetType);
// 和前一个函数性能一样，只是参数不一样了
boolean canConvert(@Nullable TypeDescriptor sourceType, TypeDescriptor targetType);
/**
* 将指定的source转换为指标类型target
* @param source 数据源，可为null
* @param targetType 指标类型，不可为null
* @return 转换后果，targetType的实例
* @throws ConversionException 转换异样
* @throws IllegalArgumentException 如果targetType为null，抛出该异样
*/
@Nullable
<T> T convert(@Nullable Object source, Class<T> targetType);
// 和前一个函数性能一样，只是参数不一样了
@Nullable
Object convert(@Nullable Object source, @Nullable TypeDescriptor sourceType, TypeDescriptor targetType);
}简略来说，ConversionService负责转换类型，将某个source转成指标类型。因为Environment接口实现了PropertyResolver，其中有一个办法为
// 获取key的属性值，并依照targetType进行返回
@Nullable
<T> T getProperty(String key, Class<T> targetType);因而，Environment借助了ConversionService来实现将属性值转换成targetType的性能
配置属性源 configurePropertySources
/**
* 增加，删除或者重排序environment中的PropertySource的程序
* @param environment 应用程序的Environment实例
* @param args 传递给run办法的参数
*/
protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
MutablePropertySources sources = environment.getPropertySources();
if (!CollectionUtils.isEmpty(this.defaultProperties)) {
DefaultPropertiesPropertySource.addOrMerge(this.defaultProperties, sources);
}
// addConmandLineProperties: 是否要将命令行参数作为属性源增加到Environment中，默认为true
if (this.addCommandLineProperties && args.length > 0) {
// 将命令行参数作为属性源增加到Environment中
String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
if (sources.contains(name)) {
// 如果Environment中曾经蕴含了同名的属性源，则将这两个属性源合并后替换到原来的
PropertySource<?> source = sources.get(name);
CompositePropertySource composite = new CompositePropertySource(name);
composite.addPropertySource(
new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
composite.addPropertySource(source);
sources.replace(name, composite);
}
else {
// 将命令行参数放到第一优先级
sources.addFirst(new SimpleCommandLinePropertySource(args));
}
}
}
配置profiles configureProfiles
/**
* 能够在这里配置激活哪个profile，这和spring.profiles.active并不抵触。默认不激活任何profile
* @param environment Environment实例
* @param args 传递给run办法的参数
*/
protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
}
触发监听SpringApplicationRunListener的environmentPrepared事件
这里对environmentPrepared事件须要非凡介绍的起因是这外面还包含一个扩大点，咱们来剖析一下
后面剖析中提到，ApplicationListener也是SpringBoot提供的一个非凡扩大点，他是由默认的EventPublishingRunListener（SpringApplicationRunListener的实现）并联合事件机制实现的。而SpringBoot默认提供的ApplicationListener中有一个EnvironmentPostProcessorApplicationListener，咱们来剖析这个EnvironmentPostProcessorApplicationListener
EnvironmentPostProcessorApplicationListener
public class EnvironmentPostProcessorApplicationListener implements SmartApplicationListener, Ordered {
public static final int DEFAULT_ORDER = Ordered.HIGHEST_PRECEDENCE + 10;
private final DeferredLogs deferredLogs;
private int order = DEFAULT_ORDER;
private final Function<ClassLoader, EnvironmentPostProcessorsFactory> postProcessorsFactory;
// 能够回到后面的章节，在SpringApplication构造函数中创立ApplicationListener时，调用的是无参构造方法
public EnvironmentPostProcessorApplicationListener() {
this(EnvironmentPostProcessorsFactory::fromSpringFactories, new DeferredLogs());
}
public EnvironmentPostProcessorApplicationListener(EnvironmentPostProcessorsFactory postProcessorsFactory) {
this((classloader) -> postProcessorsFactory, new DeferredLogs());
}
EnvironmentPostProcessorApplicationListener(
Function<ClassLoader, EnvironmentPostProcessorsFactory> postProcessorsFactory, DeferredLogs deferredLogs) {
this.postProcessorsFactory = postProcessorsFactory;
this.deferredLogs = deferredLogs;
}
// 返回监听的事件类型，次要有三类事件
// 1. ApplicationEnvironmentPreparedEvent
// 2. ApplicationPreparedEvent
// 3. ApplicationFailedEvent
@Override
public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(eventType)
|| ApplicationPreparedEvent.class.isAssignableFrom(eventType)
|| ApplicationFailedEvent.class.isAssignableFrom(eventType);
}
// 监听入口，能够看到最初会调用onApplicationEnvironmentPreparedEvent进行解决
@Override
public void onApplicationEvent(ApplicationEvent event) {
if (event instanceof ApplicationEnvironmentPreparedEvent) {
onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
}
if (event instanceof ApplicationPreparedEvent) {
onApplicationPreparedEvent();
}
if (event instanceof ApplicationFailedEvent) {
onApplicationFailedEvent();
}
}
// 最初是遍历成员属性postProcessorsFactory获取到EnvironmentPostProcessor
private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
ConfigurableEnvironment environment = event.getEnvironment();
SpringApplication application = event.getSpringApplication();
for (EnvironmentPostProcessor postProcessor : getEnvironmentPostProcessors(application.getResourceLoader(),
event.getBootstrapContext())) {
postProcessor.postProcessEnvironment(environment, application);
}
}
private void onApplicationPreparedEvent() {
finish();
}
private void onApplicationFailedEvent() {
finish();
}
private void finish() {
this.deferredLogs.switchOverAll();
}
List<EnvironmentPostProcessor> getEnvironmentPostProcessors(ResourceLoader resourceLoader,
ConfigurableBootstrapContext bootstrapContext) {
ClassLoader classLoader = (resourceLoader != null) ? resourceLoader.getClassLoader() : null;
EnvironmentPostProcessorsFactory postProcessorsFactory = this.postProcessorsFactory.apply(classLoader);
return postProcessorsFactory.getEnvironmentPostProcessors(this.deferredLogs, bootstrapContext);
}
@Override
public int getOrder() {
return this.order;
}
public void setOrder(int order) {
this.order = order;
}
}这里能够看到EnvironmentPostProcessorApplicationListener的事件处理逻辑是调用外部的EnvironmentPostProcessor进行解决，而EnvironmentPostProcessor则是通过成员属性postProcessorsFactory获取到的。默认状况下，SpringBoot会调用EnvironmentPostProcessorApplicationListener的无参构造方法创立对应的监听请，而其无参构造方法中则是通过EnvironmentPostProcessorsFactory静态方法fromSpringFactories获取，对应源代码为：
static EnvironmentPostProcessorsFactory fromSpringFactories(ClassLoader classLoader) {
return new ReflectionEnvironmentPostProcessorsFactory(classLoader,
SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class, classLoader));
}该代码会返回一个ReflectionEnvironmentPostProcessorsFactory，同时这里也看到了相熟的SpringFactoriesLoader
咱们挨个来剖析
ReflectionEnvironmentPostProcessorsFactory
class ReflectionEnvironmentPostProcessorsFactory implements EnvironmentPostProcessorsFactory {
private final List<Class<?>> classes;
private ClassLoader classLoader;
private final List<String> classNames;
ReflectionEnvironmentPostProcessorsFactory(Class<?>... classes) {
this.classes = new ArrayList<>(Arrays.asList(classes));
this.classNames = null;
}
ReflectionEnvironmentPostProcessorsFactory(ClassLoader classLoader, String... classNames) {
this(classLoader, Arrays.asList(classNames));
}
// EnvironmentPostProcessorsFactory.fromSpringFactories调用的构造函数
ReflectionEnvironmentPostProcessorsFactory(ClassLoader classLoader, List<String> classNames) {
this.classes = null;
this.classLoader = classLoader;
this.classNames = classNames;
}
// 外围代码，EnvironmentPostProcessorApplicationListener 会调用这个办法来获取到
// EnvironmentPostProcessor
@Override
public List<EnvironmentPostProcessor> getEnvironmentPostProcessors(DeferredLogFactory logFactory,
ConfigurableBootstrapContext bootstrapContext) {
Instantiator<EnvironmentPostProcessor> instantiator = new Instantiator<>(EnvironmentPostProcessor.class,
(parameters) -> {
parameters.add(DeferredLogFactory.class, logFactory);
parameters.add(Log.class, logFactory::getLog);
parameters.add(ConfigurableBootstrapContext.class, bootstrapContext);
parameters.add(BootstrapContext.class, bootstrapContext);
parameters.add(BootstrapRegistry.class, bootstrapContext);
});
return (this.classes != null) ? instantiator.instantiateTypes(this.classes)
: instantiator.instantiate(this.classLoader, this.classNames);
}
}能够看到，ReflectionEnvironmentPostProcessorsFactory的性能就是接管spring.factories中指定的EnvironmentPostProcessor类型，并实例化后交给EnvironmentPostProcessorApplicationListener来触发
关系图
上面是整顿的关系图，能够帮忙理清相干关系
扩大点
创立应用程序上下文 createApplicationContext
protected ConfigurableApplicationContext createApplicationContext() {
return this.applicationContextFactory.create(this.webApplicationType);
}这里就是调用ApplicationContextFactory进行创立Context
依据前文的源码剖析咱们能够晓得，对于咱们罕用的Web应用程序来说，其ApplicationContextFactory是AnnotationConfigServletWebServerApplicationContext.Factory。其相干源码在前文能够查阅
筹备应用程序上下文 preparedContext
private void prepareContext(DefaultBootstrapContext bootstrapContext, ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
// 设置Environment
context.setEnvironment(environment);
// 1. 对context进行后置解决
postProcessApplicationContext(context);
// 2. 利用初始化器
applyInitializers(context);
// 触发ContextPreparedEvent事件
listeners.contextPrepared(context);
// 在疏导上下文中触发BootstrapContextClosedEvent事件
bootstrapContext.close(context);
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// 增加SpringBoot特有的一些单例bean到应用程序上下文中
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof AbstractAutowireCapableBeanFactory) {
((AbstractAutowireCapableBeanFactory) beanFactory).setAllowCircularReferences(this.allowCircularReferences);
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
}
// 增加懒加载相干的BeanFactoryPostProcessor
if (this.lazyInitialization) {
context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
}
context.addBeanFactoryPostProcessor(new PropertySourceOrderingBeanFactoryPostProcessor(context));
// 3. 对source进行解决，在这里咱们能够提前注册一些bean到应用程序上下文中
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}对context进行后置解决 postProcessApplicationContext
protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
// 注册单例的beanNameGenerator，它的性能是生成bean的名称
if (this.beanNameGenerator != null) {
context.getBeanFactory().registerSingleton(AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,
this.beanNameGenerator);
}
// 设置资源加载器
if (this.resourceLoader != null) {
if (context instanceof GenericApplicationContext) {
((GenericApplicationContext) context).setResourceLoader(this.resourceLoader);
}
if (context instanceof DefaultResourceLoader) {
((DefaultResourceLoader) context).setClassLoader(this.resourceLoader.getClassLoader());
}
}
// 设置转换服务
if (this.addConversionService) {
context.getBeanFactory().setConversionService(context.getEnvironment().getConversionService());
}
}这个后置解决就是减少一些bean，设置一些字段到context中
利用初始化器 applyInitializers
protected void applyInitializers(ConfigurableApplicationContext context) {
for (ApplicationContextInitializer initializer : getInitializers()) {
Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(initializer.getClass(),
ApplicationContextInitializer.class);
Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
initializer.initialize(context);
}
}
能够看到，这里是获取了SpringApplication外部的初始化器，对context进行初始化操作。而这里的initializers是在SpringApplication构造函数中实现加载的，能够回到后面看一下，它也是从spring.factories中获取的
对source进行解决
source是SpringBoot提供的一种注册bean的形式，souce能够是一个class，能够是一个包Package，能够是一个XML文件或者Groovy脚本的Resource，能够是上述三种的字符串形容
SpringApplication中用成员属性sources来保留这些资源
protected void load(ApplicationContext context, Object[] sources) {
if (logger.isDebugEnabled()) {
logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
}
// 结构一个BeanDefinitionLoader，用于从sources中加载BeanDefinition，将其注册到context中去
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);
}
// 进行加载
loader.load();
}这里就不进行深刻的源码解析了，总结一下source状况
- 如果source是一个Class类型，或者其是一个Class的全限定名字符串，则会将其对应的类注册到context中，非凡状况是Groovy脚本（这种状况没见到过，然而BeanDefinitionLoader的确会进行非凡解决）
- 如果source是一个Package类型，或者其是一个包名的字符串，则会进行扫描，相似于ComponentScan
-
如果source是一个Resource类型，或者是一个资源的字符串表白，则会尝试将其作为XML配置文件，或者Groovy脚本文件进行加载注册
扩大点
某种意义上，source也是一个扩大点，但思考到很少用，暂不退出
刷新应用程序上下文 refreshContext
private void refreshContext(ConfigurableApplicationContext context) { if (this.registerShutdownHook) { shutdownHook.registerApplicationContext(context); } refresh(context); } protected void refresh(ConfigurableApplicationContext applicationContext) { applicationContext.refresh(); }这里的代码比较简单，仅仅是调用applicationContext的刷新函数refresh即可。其外部是AbastactApplicationContext的刷新流程，本文暂不涉略其中
调用SpringRunner callRunners
private void callRunners(ApplicationContext context, ApplicationArguments args) { List<Object> runners = new ArrayList<>(); // 从应用程序上下文中获取所有ApplicationRunner的实例 runners.addAll(context.getBeansOfType(ApplicationRunner.class).values()); // 从应用程序上下文中获取所有CommandLineRunner的实例 runners.addAll(context.getBeansOfType(CommandLineRunner.class).values()); // 依照Ordered接口或者Order注解排序 AnnotationAwareOrderComparator.sort(runners); // 遍历，调用办法 for (Object runner : new LinkedHashSet<>(runners)) { if (runner instanceof ApplicationRunner) { callRunner((ApplicationRunner) runner, args); } if (runner instanceof CommandLineRunner) { callRunner((CommandLineRunner) runner, args); } } } private void callRunner(ApplicationRunner runner, ApplicationArguments args) { try { (runner).run(args); } catch (Exception ex) { throw new IllegalStateException("Failed to execute ApplicationRunner", ex); } } private void callRunner(CommandLineRunner runner, ApplicationArguments args) { try { (runner).run(args.getSourceArgs()); } catch (Exception ex) { throw new IllegalStateException("Failed to execute CommandLineRunner", ex); } }callRunners的办法比较简单，就是从容器中获取到ApplicationRunner和CommandLineRunner，调用其run办法
这也算一个扩大点扩大点
总结
SpringBoot的启动是一个非常复杂的流程，本文仅仅对SpringBoot的启动做了一些简要的梳理，同时总结了一些比拟常见的SpringBoot的扩大点
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