【Spring源码这样读】-细扒ApplicationContext之super(parent)

之前我们粗略的过了一遍IOC加载流程，现在我们开始细扒一下这个流程，不过我们不再去讲XmlBeanFactory，这里直接讲ApplicationContext，本文主要聊聊初始化的时候，super(parent)到底做了什么。

ClassPathXmlApplicationContext类图

深扒源码之前，一定要做好参考点，这里我们使用类图来做一个参考。

super涉及的代码

super这个方法对应的代码并不多，如果我们要去跟的话，只需要仔细一点，了解他的层级结构，基本问题不大。这里把所有源码都拿出来了

public ClassPathXmlApplicationContext(ApplicationContext parent) {
    super(parent);
}

public AbstractXmlApplicationContext(@Nullable ApplicationContext parent) {
    super(parent);
}

public AbstractRefreshableConfigApplicationContext(@Nullable ApplicationContext parent) {
    super(parent);
}

public AbstractRefreshableApplicationContext(@Nullable ApplicationContext parent) {
    super(parent);
}

public AbstractApplicationContext(@Nullable ApplicationContext parent) {
    this();
    this.setParent(parent);
}

public AbstractApplicationContext() {
	this.resourcePatternResolver = getResourcePatternResolver();
}

protected ResourcePatternResolver getResourcePatternResolver() {
    return new PathMatchingResourcePatternResolver(this);
}

public PathMatchingResourcePatternResolver(ResourceLoader resourceLoader) {
	Assert.notNull(resourceLoader, "ResourceLoader must not be null");
	this.resourceLoader = resourceLoader;
}

public void setParent(@Nullable ApplicationContext parent) {
	this.parent = parent;
	if (parent != null) {
		Environment parentEnvironment = parent.getEnvironment();
		if (parentEnvironment instanceof ConfigurableEnvironment) {
			getEnvironment().merge((ConfigurableEnvironment) parentEnvironment);
		}
	}
}

从我们的源码上来看，结合我们的类图，不难发现，其实super(parent)一直在调用父类的方法，直到AbstractApplicationContext，然后才有真正的操作代码。

AbstractApplicationContext中具体给super(parent)做了什么

先来看看this()，this()实际就是我们当前类里面的无参构造方法，最终其实也是给我们初始化了一个ClassPathXmlApplicationContext。这一点我们可以跟一下初始化的代码

public Resource getResource(String location) {
	return getResourceLoader().getResource(location);
}

public Resource getResource(String location) {
	Assert.notNull(location, "Location must not be null");

	for (ProtocolResolver protocolResolver : getProtocolResolvers()) {
		Resource resource = protocolResolver.resolve(location, this);
		if (resource != null) {
			return resource;
		}
	}

	if (location.startsWith("/")) {
		return getResourceByPath(location);
	}
	else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
		return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
	}
	else {
		try {
			// Try to parse the location as a URL...
			URL url = new URL(location);
			return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
		}
		catch (MalformedURLException ex) {
			// No URL -> resolve as resource path.
			return getResourceByPath(location);
		}
	}
}

最终是按照我们的路径的开头判断返回哪种resource

setParent(parent)到底做了些啥

setParent(parent);对应的代码并不多,也是比较简单明了的

public void setParent(@Nullable ApplicationContext parent) {
	this.parent = parent;
	if (parent != null) {
		Environment parentEnvironment = parent.getEnvironment();
		if (parentEnvironment instanceof ConfigurableEnvironment) {
			getEnvironment().merge((ConfigurableEnvironment) parentEnvironment);
		}
	}
}

这几部代码就做了一件事情：保存父容器，并将父容器的环境与当前容器环境合并。