user-bean

spring 自定义标签测试工程 自定义标签的解析过程

1. 入口 BeanDefinitionParserDelegate

	public BeanDefinition parseCustomElement(Element ele) {
		return parseCustomElement(ele, null);
	}

	public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {
	    //获取对应的命名空间 http://www.byedbl.com/schema/user
		String namespaceUri = getNamespaceURI(ele);
		//根据命名空间找的对应的 UserNameSpaceHandler 
		// readercontext 为 XmlReaderContext
		//
		NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
		if (handler == null) {
			error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", ele);
			return null;
		}
		//调用自定义的 UserNameSpaceHandler 解析
		return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));
	}

1. 获取对应的命名空间

• 获取自定义标签处理器

	public NamespaceHandler resolve(String namespaceUri) {
	    //获取所有已经配置的handler
	    //map存储值为: "http://www.byedbl.com/schema/user" -> "com.byedbl.spring.custom.UserNameSpaceHandler"
		Map<String, Object> handlerMappings = getHandlerMappings();
		Object handlerOrClassName = handlerMappings.get(namespaceUri);
		if (handlerOrClassName == null) {
			return null;
		}
		else if (handlerOrClassName instanceof NamespaceHandler) {
			return (NamespaceHandler) handlerOrClassName;
		}
		else {
		    //第一次会走到这个分支,后面会走 else if 分支,以免每个bean都初始化一次
			String className = (String) handlerOrClassName;
			try {
				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 NamespaceHandler
				NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);
				// 这里调用 init方法指定 UserBeanDefinitionParser 转换器
				namespaceHandler.init();
				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);
			}
		}
	}

• 获取所有已经配置的 Handler 映射

	private Map<String, Object> getHandlerMappings() {
		if (this.handlerMappings == null) {
			synchronized (this) {
				if (this.handlerMappings == null) {
					try {
						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());
						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;
	}

• 标签解析 NamespaceHandlerSupport

	@Override
	public BeanDefinition parse(Element element, ParserContext parserContext) {
		return findParserForElement(element, parserContext).parse(element, parserContext);
	}

	private BeanDefinitionParser findParserForElement(Element element, ParserContext parserContext) {
	    // localName 为 user ; element 为 mu:user
		String localName = parserContext.getDelegate().getLocalName(element);
		//  parser 为我们自定义的 UserBeanDefinitionParser
		BeanDefinitionParser parser = this.parsers.get(localName);
		if (parser == null) {
			parserContext.getReaderContext().fatal(
					"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);
		}
		return parser;
	}

下面执行 findParserForElement(element, parserContext).parse(element, parserContext); parse方法 在 AbstractBeanDefinitionParser 中

	@Override
	public final BeanDefinition parse(Element element, ParserContext parserContext) {
		AbstractBeanDefinition definition = parseInternal(element, parserContext);
		if (definition != null && !parserContext.isNested()) {
			try {
			    //处理bean的ID属性值
				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 = null;
				if (shouldParseNameAsAliases()) {
				    //处理别名
					String name = element.getAttribute(NAME_ATTRIBUTE);
					if (StringUtils.hasLength(name)) {
						aliases = StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(name));
					}
				}
				//将 AbstractBeanDefinition 转换成 BeanDefinitionHolder 准备注册
				BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);
				registerBeanDefinition(holder, parserContext.getRegistry());
				if (shouldFireEvents()) {
				    //通知监听器处理
					BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);
					postProcessComponentDefinition(componentDefinition);
					parserContext.registerComponent(componentDefinition);
				}
			}
			catch (BeanDefinitionStoreException ex) {
				parserContext.getReaderContext().error(ex.getMessage(), element);
				return null;
			}
		}
		return definition;
	}

其中 parseInternal的方法如下 AbstractSingleBeanDefinitionParser

	@Override
	protected final AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
	
		BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
		String parentName = getParentName(element);
		if (parentName != null) {
			builder.getRawBeanDefinition().setParentName(parentName);
		}
		//此时会调用 UserBeanDefinitionParser 的 getBeanClass 方法
		Class<?> beanClass = getBeanClass(element);
		if (beanClass != null) {
			builder.getRawBeanDefinition().setBeanClass(beanClass);
		}
		else {
		    // 如果没有重写 getBeanClass 方法则尝试检查是否覆写了 getBeanClassName  方法
			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.
			builder.setScope(parserContext.getContainingBeanDefinition().getScope());
		}
		if (parserContext.isDefaultLazyInit()) {
			// Default-lazy-init applies to custom bean definitions as well.
			builder.setLazyInit(true);
		}
		//调用子类覆写的 doParse方法, 
		// 先调 AbstractSingleBeanDefinitionParser.doParse 再调 自定义的 UserBeanDefinitionParser
		doParse(element, parserContext, builder);
		return builder.getBeanDefinition();
	}