作者：襄垣
juejin.im/post/5c6f730ce51d457f14363a53
推荐阅读(点击即可跳转阅读)
2. 面试题内容聚合
3. 设计模式内容聚合
4. Mybatis内容聚合
5. 多线程内容聚合
程序入口
SpringApplication.run(BeautyApplication.class, args);
执行此方法来加载整个SpringBoot的环境。
1. 从哪儿开始？
SpringApplication.java
/**
* Run the Spring application, creating and refreshing a new
* {@link ApplicationContext}.
* @param args the application arguments (usually passed from a Java main method)
* @return a running {@link ApplicationContext}
*/
public ConfigurableApplicationContext run(String... args) {
//...
}
调用SpringApplication.java 中的 run 方法，目的是加载Spring Application，同时返回 ApplicationContext。
2. 执行了什么？
2.1 计时
记录整个Spring Application的加载时间！
StopWatch stopWatch = new StopWatch();
stopWatch.start();
// ...
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
2.2 声明
// 声明 ApplicationContext
ConfigurableApplicationContext context = null;
// 声明 一个异常报告集合
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
2.3 指定程序运行模式
指定 java.awt.headless，默认是true
一般是在程序开始激活headless模式，告诉程序，现在你要工作在Headless mode下，就不要指望硬件帮忙了，你得自力更生，依靠系统的计算能力模拟出这些特性来。
private void configureHeadlessProperty() {
System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, System.getProperty(
SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
}
2.4 配置监听并发布应用启动事件
SpringApplicationRunListener 负责加载 ApplicationListener事件。
SpringApplicationRunListeners listeners = getRunListeners(args);
// 开始
listeners.starting();
// 处理所有 property sources 配置和 profiles 配置，准备环境，分为标准 Servlet 环境和标准环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);
// 准备应用上下文
prepareContext(context, environment, listeners, applicationArguments,printedBanner);
// 完成
listeners.started(context);
// 异常
handleRunFailure(context, ex, exceptionReporters, listeners);
// 执行
listeners.running(context);
getRunListeners 中根据 type = SpringApplicationRunListener.class 去拿到了所有的 Listener 并根据优先级排序。
对应的就是 META-INF/spring.factories 文件中的 org.springframework.boot.SpringApplicationRunListener=org.springframework.boot.context.event.EventPublishingRunListener
private <T> Collection<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<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
在 ApplicationListener 中 , 可以针对任何一个阶段插入处理代码。
public interface SpringApplicationRunListener {
/**
* Called immediately when the run method has first started. Can be used for very
* early initialization.
*/
void starting();
/**
* Called once the environment has been prepared, but before the
* {@link ApplicationContext} has been created.
* @param environment the environment
*/
void environmentPrepared(ConfigurableEnvironment environment);
/**
* Called once the {@link ApplicationContext} has been created and prepared, but
* before sources have been loaded.
* @param context the application context
*/
void contextPrepared(ConfigurableApplicationContext context);
/**
* Called once the application context has been loaded but before it has been
* refreshed.
* @param context the application context
*/
void contextLoaded(ConfigurableApplicationContext context);
/**
* The context has been refreshed and the application has started but
* {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
* ApplicationRunners} have not been called.
* @param context the application context.
* @since 2.0.0
*/
void started(ConfigurableApplicationContext context);
/**
* Called immediately before the run method finishes, when the application context has
* been refreshed and all {@link CommandLineRunner CommandLineRunners} and
* {@link ApplicationRunner ApplicationRunners} have been called.
* @param context the application context.
* @since 2.0.0
*/
void running(ConfigurableApplicationContext context);
/**
* Called when a failure occurs when running the application.
* @param context the application context or {@code null} if a failure occurred before
* the context was created
* @param exception the failure
* @since 2.0.0
*/
void failed(ConfigurableApplicationContext context, Throwable exception);
}
3. 每个阶段执行的内容
3.1 listeners.starting();
在加载Spring Application之前执行，所有资源和环境未被加载。
3.2 prepareEnvironment(listeners, applicationArguments);
创建 ConfigurableEnvironment；
将配置的环境绑定到Spring Application中；
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (this.webApplicationType == WebApplicationType.NONE) {
environment = new EnvironmentConverter(getClassLoader())
.convertToStandardEnvironmentIfNecessary(environment);
}
ConfigurationPropertySources.attach(environment);
return environment;
}
3.3 prepareContext
配置忽略的Bean；
private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) {
if (System.getProperty(
CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) {
Boolean ignore = environment.getProperty("spring.beaninfo.ignore",
Boolean.class, Boolean.TRUE);
System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME,
ignore.toString());
}
}
打印日志-加载的资源
Banner printedBanner = printBanner(environment);
根据不同的WebApplicationType创建Context
context = createApplicationContext();
3.4 refreshContext
支持定制刷新
/**
* Register a shutdown hook with the JVM runtime, closing this context
* on JVM shutdown unless it has already been closed at that time.
* <p>This method can be called multiple times. Only one shutdown hook
* (at max) will be registered for each context instance.
* @see java.lang.Runtime#addShutdownHook
* @see #close()
*/
void registerShutdownHook();
3.5 afterRefresh
刷新后的实现方法暂未实现
/**
* Called after the context has been refreshed.
* @param context the application context
* @param args the application arguments
*/
protected void afterRefresh(ConfigurableApplicationContext context,
ApplicationArguments args) {
}
3.6 listeners.started(context);
到此为止， Spring Application的环境和资源都加载完毕了；
发布应用上下文启动完成事件；
执行所有 Runner 运行器 - 执行所有 ApplicationRunner 和 CommandLineRunner 这两种运行器
// 启动
callRunners(context, applicationArguments);
3.7 listeners.running(context);
触发所有 SpringApplicationRunListener 监听器的 running 事件方法