SpringBoot源码学习（更新中）

最近在项目中运用了Springboot，简单的学习了简单的使用，于是想去看看源码是如何实现的。

自己也是第一次尝试看源码，结合了网上的东西和自己的理解，在博客里写点东西，做做积累, 如果其中哪些地方解释有问题，

欢迎老司机指出

参考文章：

1.https://my.oschina.net/u/3081965/blog/916126

2.http://www.cfanz.cn/index.php?c=article&a=read&id=307782

首先不知道从哪里入手，于是我从项目的启动入口开始。

以下就是项目入口代码，很简单，由于是在慕课网上学习的，这里的报名就直接写imooc了（这个为对应springboot的学习地址：http://www.imooc.com/learn/767）

这边的spring-boot版本为1.4.7

package com.imooc;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class GirlApplication {

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

@SpringBootApplication 注解暂时不讲，先从下面这个方法开始讲起

SpringApplication.run(GirlApplication.class, args);

点击进去可以看到

	/**
	 * Static helper that can be used to run a {@link SpringApplication} from the
	 * specified source using default settings.
	 * @param source the source to load
	 * @param args the application arguments (usually passed from a Java main method)
	 * @return the running {@link ApplicationContext}
	 */
	public static ConfigurableApplicationContext run(Object source, String... args) {

		//第一次进入到达这里
		return run(new Object[] { source }, args);
	}

	/**
	 * Static helper that can be used to run a {@link SpringApplication} from the
	 * specified sources using default settings and user supplied arguments.
	 * @param sources the sources to load
	 * @param args the application arguments (usually passed from a Java main method)
	 * @return the running {@link ApplicationContext}
	 */
	public static ConfigurableApplicationContext run(Object[] sources, String[] args) {

		//上面方法后进入这里
		return new SpringApplication(sources).run(args);
	}

首先为第一步，第一步调用第二部的方法，这里主要看下第二步。

第二步这边分为两个步骤去看，第一个步骤为调用SpringApplication类的构造方法创建对象，第二步为调用创建对象的run方法，这里以这两个步骤进行解读。

构建对象：

	/**
	 * Create a new {@link SpringApplication} instance. The application context will load
	 * beans from the specified sources (see {@link SpringApplication class-level}
	 * documentation for details. The instance can be customized before calling
	 * {@link #run(String...)}.
	 * @param sources the bean sources
	 * @see #run(Object, String[])
	 * @see #SpringApplication(ResourceLoader, Object...)
	 */
	public SpringApplication(Object... sources) {

		//调用初始化方法
		initialize(sources);
	}

	@SuppressWarnings({ "unchecked", "rawtypes" })
	private void initialize(Object[] sources) {

		//将对象资源存放到sources这个linkedSet下，这里的sources就是上诉的com.imooc.GirlController对象
		if (sources != null && sources.length > 0) {
			this.sources.addAll(Arrays.asList(sources));
		}

		//这里暂时没有看懂，从字面上来看，是判断是否有web环境
		this.webEnvironment = deduceWebEnvironment();

		//实例化Initializer，initializers成员变量，是一个ApplicationContextInitializer类型对象的集合。 

		//顾名思义，ApplicationContextInitializer是一个可以用来初始化ApplicationContext的接口。

		//初始化ApplicationContext的Initializer程序
		//boot包下的META-INF/spring.factories
		0 = "org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer"
		1 = "org.springframework.boot.context.ContextIdApplicationContextInitializer"
		2 = "org.springframework.boot.context.config.DelegatingApplicationContextInitializer"
		3 = "org.springframework.boot.context.web.ServerPortInfoApplicationContextInitializer"
		//autoconfigure下的META-INF/spring.factories
		4 = "org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer"
		5 = "org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer"
		setInitializers((Collection) getSpringFactoriesInstances(
				ApplicationContextInitializer.class));

		//实例化监听器

		//初始化 ApplicationListener  boot下9个，autoconfigure一个

		//0 = "org.springframework.boot.ClearCachesApplicationListener"

		//1 = "org.springframework.boot.builder.ParentContextCloserApplicationListener"

//2 = "org.springframework.boot.context.FileEncodingApplicationListener"
//3 = "org.springframework.boot.context.config.AnsiOutputApplicationListener"
//4 = "org.springframework.boot.context.config.ConfigFileApplicationListener"
//5 = "org.springframework.boot.context.config.DelegatingApplicationListener"
//6 = "org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener"
//7 = "org.springframework.boot.logging.ClasspathLoggingApplicationListener"
//8 = "org.springframework.boot.logging.LoggingApplicationListener"
//9 = "org.springframework.boot.autoconfigure.BackgroundPreinitializer"setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));

		//找出main方法的全类名并返回其实例并设置到SpringApplication的this.mainApplicationClass完成初始化

		this.mainApplicationClass = deduceMainApplicationClass();
	}

这里附上deduceWebEnvironment()方法的实现，其中WEB_ENVIRONMENT_CLASSES的值为

	private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
			"org.springframework.web.context.ConfigurableWebApplicationContext" };

	private boolean deduceWebEnvironment() {
		for (String className : WEB_ENVIRONMENT_CLASSES) {
			if (!ClassUtils.isPresent(className, null)) {
				return false;
			}
		}
		return true;
	}

上面SpringApplication的初始化动作已经做完了，然后看下run方法里做了哪些操作。

public ConfigurableApplicationContext run(String... args) {

   
 //StopWatch是一个监视器，主要是用来记录程序的运行时间，这里是用来记录程序启动所需要的时间
   StopWatch stopWatch = new StopWatch();
   stopWatch.start();
   ConfigurableApplicationContext context = null;
   FailureAnalyzers analyzers = null;
   configureHeadlessProperty();
   SpringApplicationRunListeners listeners = getRunListeners(args);
   listeners.started();
   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);
   }
}