SpringBoot源码解析:创建SpringApplication对象实例

最新推荐文章于 2021-09-07 09:17:34 发布

原创最新推荐文章于 2021-09-07 09:17:34 发布 · 184 阅读

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本文深入剖析SpringBoot启动过程，从SpringApplication实例化开始，详细解读自动配置、环境判断及初始化器与监听器加载机制，适合希望深入了解SpringBoot内部工作原理的开发者。

上篇文章SpringBoot自动装配原理解析中，我们分析了SpringBoot的自动装配原理以及@SpringBootApplication注解的原理，本篇文章则继续基于上篇文章中的main方法来分析SpringApplication这个类

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

 

点击run方法一路跟踪下来，发现首先做的是实例化SpringApplication对象实例

  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);
	}
	public SpringApplication(Class<?>... primarySources) {
		this(null, primarySources);
	}
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
		this.resourceLoader = resourceLoader;
		Assert.notNull(primarySources, "PrimarySources must not be null");
		this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
		this.webApplicationType = deduceWebApplicationType();
		setInitializers((Collection) getSpringFactoriesInstances(
				ApplicationContextInitializer.class));
		setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
		this.mainApplicationClass = deduceMainApplicationClass();
	}

 

首先看一下deduceWebApplicationType方法

  private WebApplicationType deduceWebApplicationType() {
        if (ClassUtils.isPresent("org.springframework.web.reactive.DispatcherHandler", (ClassLoader)null) && !ClassUtils.isPresent("org.springframework.web.servlet.DispatcherServlet", (ClassLoader)null)) {
            return WebApplicationType.REACTIVE;
        } 
        for (String className : "javax.servlet.Servlet", org.springframework.web.context.ConfigurableWebApplicationContext") {
			if (!ClassUtils.isPresent(className, null)) {
				return WebApplicationType.NONE;
			}
	}
          return WebApplicationType.SERVLET;
        }
    }

 

大抵意思就是根据当前项目中是否存在上方的几个类来推断出当前的web环境，这里因为SpringBoot默认使用的web框架是SpringMVC，所以最后返回结果为WebApplicationType.SERVLET

加载所有的ApplicationContextInitializer和ApplicationListener的实现类

  private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
       ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
       Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
       List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
       AnnotationAwareOrderComparator.sort(instances);
       return instances;
   }

 