Spring-IoC注入过程

缺乏、安全感 2022-04-25 06:40 222阅读 0赞

###### 本文基于spring5.1.6 ######

### 一、大体流程 ###

1.  使用ResourceLoader加载资源
2.  创建Bean工厂
3.  获得BeanDefinition
4.  装载资源  
    资源定位、装载、注册  
    装载。装载就是 BeanDefinition 的载入

//加载资源
    ClassPathResource resource = new ClassPathResource("bean.xml");
    //创建bean工厂
    DefaultListableBeanFactory factory = new DefaultListableBeanFactory();
    //xml解析器
    XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(factory);
    //装载资源
    reader.loadBeanDefinitions(resource);

不理解资源解析的请参考[Spring-Resource源码解析][Spring-Resource]

### 1.1 new XmlBeanDefinitionReader(factory)其实是调用的父类的构造方法 ###

> ## 关系 ##
> 
> public abstract class AbstractBeanDefinitionReader implements BeanDefinitionReader,EnvironmentCapable  
> public class XmlBeanDefinitionReader extends AbstractBeanDefinitionReader

![关系图][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0VsbGVuX1Rhbmd4aWFuZw_size_16_color_FFFFFF_t_70]

### 1.2AbstractBeanDefinitionReader ###

1.  创建对象就是初始化资源加载器和环境的过程

protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) { 
    	Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
    	this.registry = registry;
    
    	// 确定加载器如果BeanDefinitionRegistry是一个资源加载器，那么就使用它作为加载器，否则使用路径匹配加载器
    	if (this.registry instanceof ResourceLoader) { 
    		this.resourceLoader = (ResourceLoader) this.registry;
    	}
    	else { 
    		this.resourceLoader = new PathMatchingResourcePatternResolver();
    	}
    
    	//EnvironmentCapable：Spring中所有的应用上下文类都实现了此接口。这个接口的主要作用是用于类型检查的
    	if (this.registry instanceof EnvironmentCapable) { 
    		this.environment = ((EnvironmentCapable) this.registry).getEnvironment();
    	}
    	else { 
    		this.environment = new StandardEnvironment();
    	}
    }

环境类Environment

/** * 环境的一些参数 */
    public interface Environment extends PropertyResolver { 
    	//获取激活的配置
    	String[] getActiveProfiles();
    	//默认的配置
    	String[] getDefaultProfiles();
    	//废弃的方法通过字符串的配置判断是否可以使用该配置
    	@Deprecated
    	boolean acceptsProfiles(String... profiles);
    	//通过Profiles对象判断是否可以使用该配置
    	boolean acceptsProfiles(Profiles profiles);
    
    }
    
    public interface PropertyResolver { 
    
    	boolean containsProperty(String key);
    	//获取参数
    	@Nullable
    	String getProperty(String key);
    	//获取参数，如果为空，返回默认值
    	String getProperty(String key, String defaultValue);
    	//返回指定的对象的字节码对象
    	@Nullable
    	<T> T getProperty(String key, Class<T> targetType);
    	//返回指定的对象的字节码类，如果为空返回默认值
    	<T> T getProperty(String key, Class<T> targetType, T defaultValue);
    	//获取要求的参数
    	String getRequiredProperty(String key) throws IllegalStateException;
    	//获取要求的参数的对象的字节码对象
    	<T> T getRequiredProperty(String key, Class<T> targetType) throws IllegalStateException;
    	//解析占位符
    	String resolvePlaceholders(String text);
    	//解析要求的占位符
    	String resolveRequiredPlaceholders(String text) throws IllegalArgumentException;
    
    }

### 1.3加载过程 ###

loadBeanDefinitions会将资源进行编码，然后执行的是下面的代码

> 将encodedResource放入Set，去重  
> 将encodedResource转成流并且将Resource对象传入doLoadBeanDefinitions，详见1.4源码

public int loadBeanDefinitions(EncodedResource encodedResource) throws BeanDefinitionStoreException { 
    	Assert.notNull(encodedResource, "EncodedResource must not be null");
    	if (logger.isTraceEnabled()) { 
    		logger.trace("Loading XML bean definitions from " + encodedResource);
    	}
    	//resourcesCurrentlyBeingLoaded是一个ThreadLocal对象
    	Set<EncodedResource> currentResources = this.resourcesCurrentlyBeingLoaded.get();
    	//如果是空的，那么就初始化一个set
    	if (currentResources == null) { 
    		currentResources = new HashSet<>(4);
    		this.resourcesCurrentlyBeingLoaded.set(currentResources);
    	}
    	//如果set集合添加不进去，那么抛出异常,说明已经加载过了，防止重复加载
    	if (!currentResources.add(encodedResource)) { 
    		throw new BeanDefinitionStoreException(
    				"Detected cyclic loading of " + encodedResource + " - check your import definitions!");
    	}
    	try { 
    		//转换成流
    		InputStream inputStream = encodedResource.getResource().getInputStream();
    		try { 
    			InputSource inputSource = new InputSource(inputStream);
    			if (encodedResource.getEncoding() != null) { 
    				//设置编码
    				inputSource.setEncoding(encodedResource.getEncoding());
    			}
    			//见下方源码1.4
    			return doLoadBeanDefinitions(inputSource, encodedResource.getResource());
    		}
    		finally { 
    			inputStream.close();
    		}
    	}
    	catch (IOException ex) { 
    		throw new BeanDefinitionStoreException(
    				"IOException parsing XML document from " + encodedResource.getResource(), ex);
    	}
    	finally { 
    		currentResources.remove(encodedResource);
    		if (currentResources.isEmpty()) { 
    			//ThreadLocal必须要remove掉，防止线程池下的线程复用
    			this.resourcesCurrentlyBeingLoaded.remove();
    		}
    	}
    }

1.4doLoadBeanDefinitions方法

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
    			throws BeanDefinitionStoreException { 
    
    	try { 
    		//获取Document 实例
    		Document doc = doLoadDocument(inputSource, resource);
    		//注册到ioc容器中详见1.5
    		int count = registerBeanDefinitions(doc, resource);
    		if (logger.isDebugEnabled()) { 
    			logger.debug("Loaded " + count + " bean definitions from " + resource);
    		}
    		return count;
    	}
    	catch (BeanDefinitionStoreException ex) { 
    		throw ex;
    	}
    	catch (SAXParseException ex) { 
    		throw new XmlBeanDefinitionStoreException(resource.getDescription(),
    				"Line " + ex.getLineNumber() + " in XML document from " + resource + " is invalid", ex);
    	}
    	catch (SAXException ex) { 
    		throw new XmlBeanDefinitionStoreException(resource.getDescription(),
    				"XML document from " + resource + " is invalid", ex);
    	}
    	catch (ParserConfigurationException ex) { 
    		throw new BeanDefinitionStoreException(resource.getDescription(),
    				"Parser configuration exception parsing XML from " + resource, ex);
    	}
    	catch (IOException ex) { 
    		throw new BeanDefinitionStoreException(resource.getDescription(),
    				"IOException parsing XML document from " + resource, ex);
    	}
    	catch (Throwable ex) { 
    		throw new BeanDefinitionStoreException(resource.getDescription(),
    				"Unexpected exception parsing XML document from " + resource, ex);
    	}
    }

1.5 registerBeanDefinitions

public int registerBeanDefinitions(Document doc, Resource resource) throws BeanDefinitionStoreException { 
    	//利用反射创建对象详见1。6
    	BeanDefinitionDocumentReader documentReader = createBeanDefinitionDocumentReader();
    	//registry是不是有点眼熟XmlBeanDefinitionReader extends AbstractBeanDefinitionReader
    	//在创建XmlBeanDefinitionReader的时候初始化了registry和environment
    	//也就是DefaultListableBeanFactory 
    	//获取容器总数量
    	int countBefore = getRegistry().getBeanDefinitionCount();
    	//将Resource包装成XmlReaderContext详见1.7
    	documentReader.registerBeanDefinitions(doc, createReaderContext(resource));
    	//返回成功的个数beanDefinitionMap新增的数量
    	return getRegistry().getBeanDefinitionCount() - countBefore;
    }

1.6 instantiateClass

public static <T> T instantiateClass(Class<T> clazz) throws BeanInstantiationException { 
    	Assert.notNull(clazz, "Class must not be null");
    	//如果是接口，抛出异常
    	if (clazz.isInterface()) { 
    		throw new BeanInstantiationException(clazz, "Specified class is an interface");
    	}
    	try { 
    		//如果不是接口，根据反射实例化对象
    		return instantiateClass(clazz.getDeclaredConstructor());
    	}
    	catch (NoSuchMethodException ex) { 
    		Constructor<T> ctor = findPrimaryConstructor(clazz);
    		if (ctor != null) { 
    			return instantiateClass(ctor);
    		}
    		throw new BeanInstantiationException(clazz, "No default constructor found", ex);
    	}
    	catch (LinkageError err) { 
    		throw new BeanInstantiationException(clazz, "Unresolvable class definition", err);
    	}
    }

1.7registerBeanDefinitions

@Override
    public void registerBeanDefinitions(Document doc, XmlReaderContext readerContext) { 
    	this.readerContext = readerContext;
    	//详见1.8
    	doRegisterBeanDefinitions(doc.getDocumentElement());
    }

1.8doRegisterBeanDefinitions

@SuppressWarnings("deprecation")  // for Environment.acceptsProfiles(String...)
    protected void doRegisterBeanDefinitions(Element root) { 
    	//解析器
    	BeanDefinitionParserDelegate parent = this.delegate;
    	//this.delegate重新指向新的delegate
    	this.delegate = createDelegate(getReaderContext(), root, parent);
    	//根节点是否为默认的命名空间，node.getNamespaceURI()为空
    	//或者为BeanDefinitionParserDelegate.BEANS_NAMESPACE_URI
    	//"http://www.springframework.org/schema/beans"
    	if (this.delegate.isDefaultNamespace(root)) { 
    		String profileSpec = root.getAttribute(PROFILE_ATTRIBUTE);
    		if (StringUtils.hasText(profileSpec)) { 
    			String[] specifiedProfiles = StringUtils.tokenizeToStringArray(profileSpec, BeanDefinitionParserDelegate.MULTI_VALUE_ATTRIBUTE_DELIMITERS);
    			// 如果这个配置不合法
    			if (!getReaderContext().getEnvironment().acceptsProfiles(specifiedProfiles)) { 
    				if (logger.isDebugEnabled()) { 
    					logger.debug("Skipped XML bean definition file due to specified profiles [" + profileSpec +
    							"] not matching: " + getReaderContext().getResource());
    				}
    				return;
    			}
    		}
    	}
    	//什么都没做，需要子类来实现
    	preProcessXml(root);
    	//解析BeanDefinitions，详见1.9parseBeanDefinitions
    	parseBeanDefinitions(root, this.delegate);
    	//什么都没做，需要子类来实现
    	postProcessXml(root);
    
    	this.delegate = parent;
    }

1.9parseBeanDefinitions

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) { 
    	//检测根节点是否使用默认的命名空间
    	if (delegate.isDefaultNamespace(root)) { 
    		NodeList nl = root.getChildNodes();
    		//遍历节点
    		for (int i = 0; i < nl.getLength(); i++) { 
    			Node node = nl.item(i);
    			if (node instanceof Element) { 
    				Element ele = (Element) node;
    				if (delegate.isDefaultNamespace(ele)) { 
    					//处理默认的元素
    					parseDefaultElement(ele, delegate);
    				}
    				else { 
    					//处理自定义的元素
    					delegate.parseCustomElement(ele);
    				}
    			}
    		}
    	}
    	else { 
    		//处理自定义的元素
    		delegate.parseCustomElement(root);
    	}
    }

2.0 parseDefaultElement处理默认的元素

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) { 
    	//import标签
    	if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) { 
    		importBeanDefinitionResource(ele);
    	}
    	//alias标签
    	else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) { 
    		processAliasRegistration(ele);
    	}
    	//bean标签
    	else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) { 
    		//2.2processBeanDefinition
    		processBeanDefinition(ele, delegate);
    	}
    	//beans标签
    	else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) { 
    		//调用1.9的方法继续往下解析即解析bean
    		doRegisterBeanDefinitions(ele);
    	}
    }

2.1parseCustomElement处理客户自定义的元素

@Nullable
    public BeanDefinition parseCustomElement(Element ele, @Nullable BeanDefinition containingBd) { 
    	String namespaceUri = getNamespaceURI(ele);
    	if (namespaceUri == null) { 
    		return null;
    	}
    	NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
    	if (handler == null) { 
    		error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
    		return null;
    	}
    	return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
    }

2.2 processBeanDefinition

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) { 
    	//解析ele并且将bean封装到BeanDefinitionHolder
    	BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
    	//如果不为空
    	if (bdHolder != null) { 
    		//获取属性
    		bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
    		try { 
    			// 注册到IOC容器
    			BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
    		}
    		catch (BeanDefinitionStoreException ex) { 
    			getReaderContext().error("Failed to register bean definition with name '" +
    					bdHolder.getBeanName() + "'", ele, ex);
    		}
    		// Send registration event.
    		getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
    	}
    }

2.3parseBeanDefinitionElement 从xml中解析bean

@Nullable
    public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) { 
    	//获取id熟悉
    	String id = ele.getAttribute(ID_ATTRIBUTE);
    	//获取name熟悉
    	String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
    	
    	List<String> aliases = new ArrayList<>();
    	if (StringUtils.hasLength(nameAttr)) { 
    		//将name属性值进行分割放入aliases中
    		String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
    		aliases.addAll(Arrays.asList(nameArr));
    	}
    	//将id作为beanName，也就是说，id优先级最高
    	String beanName = id;
    	//id不存在的时候
    	if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) { 
    		//是否真的有值，把aliases的第一个元素放进来，那么把name作为beanname
    		beanName = aliases.remove(0);
    		if (logger.isTraceEnabled()) { 
    			logger.trace("No XML 'id' specified - using '" + beanName +
    					"' as bean name and " + aliases + " as aliases");
    		}
    	}
    
    	if (containingBean == null) { 
    		//检查是否唯一如果存在抛出异常，如果不存在那么缓存起来
    		checkNameUniqueness(beanName, aliases, ele);
    	}
    	//获取beanDefinition
    	AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
    	if (beanDefinition != null) { 
    		//如果别名和id都为空的情况
    		if (!StringUtils.hasText(beanName)) { 
    			try { 
    				//如果不为空的情况下获取beanName
    				if (containingBean != null) { 
    					beanName = BeanDefinitionReaderUtils.generateBeanName(
    							beanDefinition, this.readerContext.getRegistry(), true);
    				}
    				else { 
    					//根据上下文生成beanName
    					beanName = this.readerContext.generateBeanName(beanDefinition);
    					// 获取真正的java类名
    					String beanClassName = beanDefinition.getBeanClassName();
    					if (beanClassName != null &&
    							beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() &&
    							!this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) { 
    						aliases.add(beanClassName);
    					}
    				}
    				if (logger.isTraceEnabled()) { 
    					logger.trace("Neither XML 'id' nor 'name' specified - " +
    							"using generated bean name [" + beanName + "]");
    				}
    			}
    			catch (Exception ex) { 
    				error(ex.getMessage(), ele);
    				return null;
    			}
    		}
    		String[] aliasesArray = StringUtils.toStringArray(aliases);
    		return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
    	}
    
    	return null;
    }

2.4registerBeanDefinition

public static void registerBeanDefinition(
    			BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
    			throws BeanDefinitionStoreException { 
    
    	// 获取bean名称
    	String beanName = definitionHolder.getBeanName();
    	//注册到IOC容器中
    	registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
    	//注册别名
    	String[] aliases = definitionHolder.getAliases();
    	if (aliases != null) { 
    		for (String alias : aliases) { 
    			registry.registerAlias(beanName, alias);
    		}
    	}
    }

2.5 registerBeanDefinition

@Override
    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)
    		throws BeanDefinitionStoreException { 
    	//校验
    	Assert.hasText(beanName, "Bean name must not be empty");
    	Assert.notNull(beanDefinition, "BeanDefinition must not be null");
    
    	if (beanDefinition instanceof AbstractBeanDefinition) { 
    		try { 
    			((AbstractBeanDefinition) beanDefinition).validate();
    		}
    		catch (BeanDefinitionValidationException ex) { 
    			throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
    					"Validation of bean definition failed", ex);
    		}
    	}
    	//通过Map查询是否存在BeanDefinition
    	BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
    	//如果存在
    	if (existingDefinition != null) { 
    		if (!isAllowBeanDefinitionOverriding()) { 
    			throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
    		}
    		else if (existingDefinition.getRole() < beanDefinition.getRole()) { 
    			// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
    			if (logger.isInfoEnabled()) { 
    				logger.info("Overriding user-defined bean definition for bean '" + beanName +
    						"' with a framework-generated bean definition: replacing [" +
    						existingDefinition + "] with [" + beanDefinition + "]");
    			}
    		}
    		else if (!beanDefinition.equals(existingDefinition)) { 
    			if (logger.isDebugEnabled()) { 
    				logger.debug("Overriding bean definition for bean '" + beanName +
    						"' with a different definition: replacing [" + existingDefinition +
    						"] with [" + beanDefinition + "]");
    			}
    		}
    		//如果不存在BeanDefinition
    		else { 
    			if (logger.isTraceEnabled()) { 
    				logger.trace("Overriding bean definition for bean '" + beanName +
    						"' with an equivalent definition: replacing [" + existingDefinition +
    						"] with [" + beanDefinition + "]");
    			}
    		}
    		//注册进去IOC容器
    		this.beanDefinitionMap.put(beanName, beanDefinition);
    	}
    	else { 
    		if (hasBeanCreationStarted()) { 
    			// Cannot modify startup-time collection elements anymore (for stable iteration)
    			synchronized (this.beanDefinitionMap) { 
    				this.beanDefinitionMap.put(beanName, beanDefinition);
    				List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
    				updatedDefinitions.addAll(this.beanDefinitionNames);
    				updatedDefinitions.add(beanName);
    				this.beanDefinitionNames = updatedDefinitions;
    				if (this.manualSingletonNames.contains(beanName)) { 
    					Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
    					updatedSingletons.remove(beanName);
    					this.manualSingletonNames = updatedSingletons;
    				}
    			}
    		}
    		else { 
    			// Still in startup registration phase
    			this.beanDefinitionMap.put(beanName, beanDefinition);
    			this.beanDefinitionNames.add(beanName);
    			this.manualSingletonNames.remove(beanName);
    		}
    		this.frozenBeanDefinitionNames = null;
    	}
    
    	if (existingDefinition != null || containsSingleton(beanName)) { 
    		resetBeanDefinition(beanName);
    	}
    }

# 小结 #

> ###### 1. 将Resource转成EncodedResource设置编码 ######
> 
> ###### 2. 通过Resource和Resource的流获取Document ######
> 
> ###### 3. 通过命名空间（BEANS\_NAMESPACE\_URI = “[http://www.springframework.org/schema/beans][http_www.springframework.org_schema_beans]”;）判断是否是用户自定义的xml，然后解析不同的xml（我们这里只分析默认的） ######
> 
> ###### 4. 根据标签解析xml，spring解析import、alias、bean、beans ######
> 
> ###### 5. 解析bean标签、将Element对象封装成BeanDefinitionHolder ######
> 
> ###### 6. 将beanName作为key，BeanDefinition作为value保存到beanDefinitionMap中 ######

[Spring-Resource]: https://blog.csdn.net/Ellen_Tangxiang/article/details/90637329
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0VsbGVuX1Rhbmd4aWFuZw_size_16_color_FFFFFF_t_70]: /images/20220126/5c3ed4efa9734161abf6021d5cff9be1.png
[http_www.springframework.org_schema_beans]: http://www.springframework.org/schema/beans