springboot应用启动过程分析(基于springboot 1.5.4)

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示例

springboot程序通过SpringBootApplication注解和Runner类中入口方法main执行SpringApplication.run()就可以执行起来，如下：

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@SpringBootApplication
public class DemoApplication {

	public static void main(String[] args) {
		SpringApplication.run(DemoApplication.class, args);
	}
}

内部代码分析

通过DemoApplication main方法进入之后，过掉各种中间多态或抽象的过程，主要包括两个方法: initializer和run

在启动过程中的各种Spring context和bean的配置，主要在spring-boot的 META-INF/spring.factories文件中

META-INF中这个文件也是开发springboot插件的一个方式

initializer方法

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@SuppressWarnings({ "unchecked", "rawtypes" })
private void initialize(Object[] sources) {
	if (sources != null && sources.length > 0) {
		this.sources.addAll(Arrays.asList(sources));
	}
	this.webEnvironment = deduceWebEnvironment();
	setInitializers((Collection) getSpringFactoriesInstances(
			ApplicationContextInitializer.class));
	setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
	this.mainApplicationClass = deduceMainApplicationClass();
}

主要包含如下几个过程：

  1. 判断是否为web环境
  2. 设置初始化类(initializers, springboot 封装的 spring-context中的ApplicationContext列表)
  3. 设置监听器(listeners, spring封装的spring-context中的ApplicationListener列表)

webEnvironment的过程

判断是否为web环境，主要是看有没有加载javax.servlet.Servlet 和 org.springframework.web.context.ConfigurableWebApplicationContext相关的类
另外，在DemoApplication的main方法中手动设置webEnvironment也会直接生效,如下：

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public static void main(String[] args) {
    SpringApplication application = new SpringApplication(DemoApplication.class);
    application.setWebEnvironment(false);
    application.run(args);
}

设置初始化类

设置初始化类是通过SpringApplication中的方法getSpringFactoriesInstances(),参数为 ApplicationContextInitializer.class

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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;
}

SpringFactoriesLoader.loadFactoryNames方法，获取了spring-boot包下的META-INF/spring.factories中的ApplicationListeners，主要包括:

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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.liquibase.LiquibaseServiceLocatorApplicationListener
org.springframework.boot.logging.ClasspathLoggingApplicationListener
org.springframework.boot.logging.LoggingApplicationListener

//TODO

run方法

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public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	FailureAnalyzers analyzers = null;
	configureHeadlessProperty();
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting();
	try {
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(
				args);
		ConfigurableEnvironment environment = prepareEnvironment(listeners,
				applicationArguments);
		Banner printedBanner = printBanner(environment);
		context = createApplicationContext();
		analyzers = new FailureAnalyzers(context);
		prepareContext(context, environment, listeners, applicationArguments,
				printedBanner);
		refreshContext(context);
		afterRefresh(context, applicationArguments);
		listeners.finished(context, null);
		stopWatch.stop();
		if (this.logStartupInfo) {
			new StartupInfoLogger(this.mainApplicationClass)
					.logStarted(getApplicationLog(), stopWatch);
		}
		return context;
	}
	catch (Throwable ex) {
		handleRunFailure(context, listeners, analyzers, ex);
		throw new IllegalStateException(ex);
	}
}

======== 未完待续 =========