How springboot improves the context loader

1. prepareContext

Source code:

```
 private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
    //注入环境属性
    context.setEnvironment(environment);
    //上下文后置处理
    this.postProcessApplicationContext(context);
    //完善初始化类的属性
    this.applyInitializers(context);
    //发送监听事件
    listeners.contextPrepared(context);
    //日志
    if (this.logStartupInfo) {
        this.logStartupInfo(context.getParent() == null);
        this.logStartupProfileInfo(context);
    }
    //注册传入的配置参数为bean，这里将传入的参数封装成applicationArguments，内部类似命令行
    ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
    beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
    //banner打印
    if (printedBanner != null) {
        beanFactory.registerSingleton("springBootBanner", printedBanner);
    }
    //这里默认情况下bean定义不允许重复
    if (beanFactory instanceof DefaultListableBeanFactory) {
        ((DefaultListableBeanFactory)beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
    }
    //默认不开启延迟加载
    if (this.lazyInitialization) {
        context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
    }
    //获取全部的资源
    //这里获取了启动类的资源和 当前SpringApplication中的source资源。
    //到目前来说实际上只有启动类资源
    Set<object> sources = this.getAllSources();
    Assert.notEmpty(sources, "Sources must not be empty");
    this.load(context, sources.toArray(new Object[0]));
    listeners.contextLoaded(context);
}
```</object>

Analyze one by one as usual. But this method is not complicated, and the overall configuration of the context and factory classes is improved.

1.1 postProcessApplicationContext method

Source code:

   protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
        //  是否自定义bean名称生成类
        if (this.beanNameGenerator != null) {
            context.getBeanFactory().registerSingleton("org.springframework.context.annotation.internalConfigurationBeanNameGenerator", this.beanNameGenerator);
        }
        //是否指定类加载器
        if (this.resourceLoader != null) {
            if (context instanceof GenericApplicationContext) {
                ((GenericApplicationContext)context).setResourceLoader(this.resourceLoader);
            }

            if (context instanceof DefaultResourceLoader) {
                ((DefaultResourceLoader)context).setClassLoader(this.resourceLoader.getClassLoader());
            }
        }
        
        //是否添加数据转换器 
        //在初始化环境对象的时候也有用到，这里可以直接通过 context.getEnvironment().getConversionService()获取到
        if (this.addConversionService) {
            context.getBeanFactory().setConversionService(ApplicationConversionService.getSharedInstance());
        }
    }

1.2 applyInitializers

Improve the object properties related to the ApplicationContextInitializer interface. These objects are in this.initializers and have been loaded as early as SpringApplication initialization. Improve related classes through the initialized context. Call the initialize method of the interface.

1.3 load

Source code:

	protected void load(ApplicationContext context, Object[] sources) {
		if (logger.isDebugEnabled()) {
			logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
		}
		//构建一个bean定义的加载器
		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);
		}
		//将资源加载成bean
		loader.load();
	}
	
	void load() {
		for (Object source : this.sources) {
			load(source);
		}
	}
    //按资源类型分别进行加载，
	private void load(Object source) {
		Assert.notNull(source, "Source must not be null");
		if (source instanceof Class>) {
			load((Class>) source);
			return;
		}
		if (source instanceof Resource) {
			load((Resource) source);
			return;
		}
		if (source instanceof Package) {
			load((Package) source);
			return;
		}
		if (source instanceof CharSequence) {
			load((CharSequence) source);
			return;
		}
		throw new IllegalArgumentException("Invalid source type " + source.getClass());
	}

Mainly loads the resources initialized in SpringApplication, including our startup class xxApplication, which will be registered as a bean.

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