1. 程式人生 > >Spring原始碼解析之三(自定義標籤的解析)

Spring原始碼解析之三(自定義標籤的解析)

自定義標籤的解析

1、概述:通過前面的文章我們分析了預設標籤的解析,我們先回顧下自定義標籤解析所使用的方法

/**
	 * Parse the elements at the root level in the document:
	 * "import", "alias", "bean".
	 * @param root the DOM root element of the document
	 */
	protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
		if (delegate.isDefaultNamespace(root)) {
			NodeList nl = root.getChildNodes();
			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)) {
						parseDefaultElement(ele, delegate);
					}
					else {
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
			delegate.parseCustomElement(root);
		}
	}

其中delegate.parseCustomElement(root);就是自定義標籤解析的方法,本篇文章主要圍繞此篇文章展開。

2、自定義標籤的解析

public BeanDefinition parseCustomElement(Element ele) {
		return parseCustomElement(ele, null);
	}
//containingBd為父類的bean,對頂層元素的解析應該設定為null
	public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
//獲取相應的名稱空間
		String namespaceUri = getNamespaceURI(ele);
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
//呼叫自定義的NamespaceHandler進行解析
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

主要思路就是根據對應的bean獲取對應的名稱空間,根據名稱空間解析對應的處理器,然後根據使用者自定義的處理器進行解析。

3、獲取標籤的名稱空間、String namespaceUri = getNamespaceURI(ele);

4、提取自定義標籤處理器、NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);

public final NamespaceHandlerResolver getNamespaceHandlerResolver() {
        return this.namespaceHandlerResolver;
    }
實際是public class DefaultNamespaceHandlerResolver implements NamespaceHandlerResolver 中的resolve的方法

@Override
	public NamespaceHandler resolve(String namespaceUri) {
//獲取所有已經配置的handler對映
		Map<String, Object> handlerMappings = getHandlerMappings();
//根據名稱空間找到相對應的資訊
		Object handlerOrClassName = handlerMappings.get(namespaceUri);
		if (handlerOrClassName == null) {
			return null;
		}
		else if (handlerOrClassName instanceof NamespaceHandler) {
//已經解析過的,直接從快取讀取
			return (NamespaceHandler) handlerOrClassName;
		}
		else {
			String className = (String) handlerOrClassName;
			try {
//使用反射將類路徑轉化為類
				Class<?> handlerClass = ClassUtils.forName(className, this.classLoader);
				if (!NamespaceHandler.class.isAssignableFrom(handlerClass)) {
					throw new FatalBeanException("Class [" + className + "] for namespace [" + namespaceUri +
							"] does not implement the [" + NamespaceHandler.class.getName() + "] interface");
				}
//初始化類
				NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
//呼叫自己的namespaceHandler的初始化方法
				namespaceHandler.init();
//記錄在快取
				handlerMappings.put(namespaceUri, namespaceHandler);
				return namespaceHandler;
			}
			catch (ClassNotFoundException ex) {
				throw new FatalBeanException("NamespaceHandler class [" + className + "] for namespace [" +
						namespaceUri + "] not found", ex);
			}
			catch (LinkageError err) {
				throw new FatalBeanException("Invalid NamespaceHandler class [" + className + "] for namespace [" +
						namespaceUri + "]: problem with handler class file or dependent class", err);
			}
		}
	}

程式碼中的流程已經很清楚,這裡面的程式碼namespaceHandler.init()其實就是用到我們自定義的handler的init方法。我們具體看下getHandlerMappings()方法,Map<String, Object> handlerMappings = getHandlerMappings(); 進入到函式體:

/**
	 * Load the specified NamespaceHandler mappings lazily.
	 */
	private Map<String, Object> getHandlerMappings() {
//如果沒有被快取,則開始被快取
		if (this.handlerMappings == null) {
			synchronized (this) {
				if (this.handlerMappings == null) {
					try {
//this.handlerMappingsLocation在建構函式中已經被初始化為:META-INF/Spring.handlers
						Properties mappings =
								PropertiesLoaderUtils.loadAllProperties(this.handlerMappingsLocation, this.classLoader);
						if (logger.isDebugEnabled()) {
							logger.debug("Loaded NamespaceHandler mappings: " + mappings);
						}
						Map<String, Object> handlerMappings = new ConcurrentHashMap<String, Object>(mappings.size());
//將properties格式檔案合併到Map格式的handlerMappings中
						CollectionUtils.mergePropertiesIntoMap(mappings, handlerMappings);
						this.handlerMappings = handlerMappings;
					}
					catch (IOException ex) {
						throw new IllegalStateException(
								"Unable to load NamespaceHandler mappings from location [" + this.handlerMappingsLocation + "]", ex);
					}
				}
			}
		}
		return this.handlerMappings;
	}

5、標籤的解析、return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));

委託給自定義的解析器去解析。此時的handler已經被例項化為我們自定義的了。

 * Parses the supplied {@link Element} by delegating to the {@link BeanDefinitionParser} that is
	 * registered for that {@link Element}.
	 */
	@Override
	public BeanDefinition parse(Element element, ParserContext parserContext) {
//尋找解析器並進行解析操作
		return findParserForElement(element, parserContext).parse(element, parserContext);
	}

	/**
	 * Locates the {@link BeanDefinitionParser} from the register implementations using
	 * the local name of the supplied {@link Element}.
	 */
	private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
//獲取元素名稱
		String localName = parserContext.getDelegate().getLocalName(element);
//註冊解析器		
BeanDefinitionParser parser = this.parsers.get(localName);
		if (parser == null) {
			parserContext.getReaderContext().fatal(
					"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
		}
		return parser;
	}

 

@Override
	public final BeanDefinition parse(Element element, ParserContext parserContext) {
		AbstractBeanDefinition definition = parseInternal(element, parserContext);
		if (definition != null && !parserContext.isNested()) {
			try {
				String id = resolveId(element, definition, parserContext);
				if (!StringUtils.hasText(id)) {
					parserContext.getReaderContext().error(
							"Id is required for element '" + parserContext.getDelegate().getLocalName(element)
									+ "' when used as a top-level tag", element);
				}
				String[] aliases = new String[0];
				String name = element.getAttribute(NAME_ATTRIBUTE);
				if (StringUtils.hasLength(name)) {
					aliases = StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(name));
				}
//將AbstractBeanDefinition轉化為BeanDefinitionHolder,並進行註冊
				BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);
				registerBeanDefinition(holder, parserContext.getRegistry());
				if (shouldFireEvents()) {
//需要通知監聽器則進行處理
					BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);
					postProcessComponentDefinition(componentDefinition);
					parserContext.registerComponent(componentDefinition);
				}
			}
			catch (BeanDefinitionStoreException ex) {
				parserContext.getReaderContext().error(ex.getMessage(), element);
				return null;
			}
		}
		return definition;
	}

從程式碼中可以看出真正進行解析的事情委託給了函式AbstractBeanDefinition definition = parseInternal(element, parserContext);

public abstract class AbstractSingleBeanDefinitionParser extends AbstractBeanDefinitionParser {

	/**
	 * Creates a {@link BeanDefinitionBuilder} instance for the
	 * {@link #getBeanClass bean Class} and passes it to the
	 * {@link #doParse} strategy method.
	 * @param element the element that is to be parsed into a single BeanDefinition
	 * @param parserContext the object encapsulating the current state of the parsing process
	 * @return the BeanDefinition resulting from the parsing of the supplied {@link Element}
	 * @throws IllegalStateException if the bean {@link Class} returned from
	 * {@link #getBeanClass(org.w3c.dom.Element)} is {@code null}
	 * @see #doParse
	 */
	@Override
	protected final AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
		BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
		String parentName = getParentName(element);
		if (parentName != null) {
			builder.getRawBeanDefinition().setParentName(parentName);
		}
//獲取自定義標籤中的class
		Class<?> beanClass = getBeanClass(element);
		if (beanClass != null) {
			builder.getRawBeanDefinition().setBeanClass(beanClass);
		}
		else {
			String beanClassName = getBeanClassName(element);
			if (beanClassName != null) {
				builder.getRawBeanDefinition().setBeanClassName(beanClassName);
			}
		}
		builder.getRawBeanDefinition().setSource(parserContext.extractSource(element));
		if (parserContext.isNested()) {
			// Inner bean definition must receive same scope as containing bean.
//若存在父類則使用父類的scope屬性
		builder.setScope(parserContext.getContainingBeanDefinition().getScope());
		}
		if (parserContext.isDefaultLazyInit()) {
			// Default-lazy-init applies to custom bean definitions as well.
//配置延遲載入		
	builder.setLazyInit(true);
		}
//呼叫子類重寫的方法
		doParse(element, parserContext, builder);
		return builder.getBeanDefinition();
	}
/**
	 * Parse the supplied {@link Element} and populate the supplied
	 * {@link BeanDefinitionBuilder} as required.
	 * <p>The default implementation delegates to the {@code doParse}
	 * version without ParserContext argument.
	 * @param element the XML element being parsed
	 * @param parserContext the object encapsulating the current state of the parsing process
	 * @param builder used to define the {@code BeanDefinition}
	 * @see #doParse(Element, BeanDefinitionBuilder)
	 */
	protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
		doParse(element, builder);
	}

在parseInternal中並不是直接呼叫子定義的doParse函式,而是進行了一些列的資料準備,包括,beanClass、scope、lazyInit等屬性的準備。

/**
 * Abstract parser for &lt;context:property-.../&gt; elements.
 *
 * @author Juergen Hoeller
 * @author Arjen Poutsma
 * @author Dave Syer
 * @since 2.5.2
 */
abstract class AbstractPropertyLoadingBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {

	@Override
	protected boolean shouldGenerateId() {
		return true;
	}

	@Override
	protected void doParse(Element element, BeanDefinitionBuilder builder) {
		String location = element.getAttribute("location");
		if (StringUtils.hasLength(location)) {
			String[] locations = StringUtils.commaDelimitedListToStringArray(location);
			builder.addPropertyValue("locations", locations);
		}

		String propertiesRef = element.getAttribute("properties-ref");
		if (StringUtils.hasLength(propertiesRef)) {
			builder.addPropertyReference("properties", propertiesRef);
		}

		String fileEncoding = element.getAttribute("file-encoding");
		if (StringUtils.hasLength(fileEncoding)) {
			builder.addPropertyValue("fileEncoding", fileEncoding);
		}

		String order = element.getAttribute("order");
		if (StringUtils.hasLength(order)) {
			builder.addPropertyValue("order", Integer.valueOf(order));
		}

		builder.addPropertyValue("ignoreResourceNotFound",
				Boolean.valueOf(element.getAttribute("ignore-resource-not-found")));

		builder.addPropertyValue("localOverride",
				Boolean.valueOf(element.getAttribute("local-override")));

		builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	}

}

我們已經瞭解spring將bean從配置檔案解析到記憶體的全部過程,接下來我們就要詳細介紹spring中bean的載入過程了。