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

水深无声 2023-01-14 12:00 185阅读 0赞

> 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。  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hsZWNobw_size_16_color_FFFFFF_t_70]

### 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。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hsZWNobw_size_16_color_FFFFFF_t_70]: /images/20221022/d8af2a97692f43369aeaee4a1c2486f2.png