spring源码剖析（四）自定义标签解析流程

spring源码剖析（四）自定义标签解析流程

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目录(?)[+]

解析总流程

自定义标签解析入口

让我们先看BeanDefinitionParserDelegate类的parseCustomElement方法:

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public BeanDefinition parseCustomElement(Element ele) {

return parseCustomElement(ele, null);

}

//containingBd为父类bean,对顶层元素的解析应设置为null

public BeanDefinition parseCustomElement(Element ele, BeanDefinition containingBd) {

String namespaceUri = getNamespaceURI(ele);

//根据命名空间找到对应的NamespaceHandler进行解析

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NamespaceHandler进行解析

return handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));

}

提取自定义标签处理器

跟踪this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
进入DefaultNamespaceHandlerResolver中的resolve方法

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/**

* Locate the {@link NamespaceHandler} for the supplied namespace URI

* from the configured mappings.

* @param namespaceUri the relevant namespace URI

* @return the located {@link NamespaceHandler}, or {@code null} if none found

*/

public NamespaceHandler resolve(String namespaceUri) {

//获取所有已经配置的handler映射

Map<String, Object> handlerMappings = getHandlerMappings();

//根据命名空间找打对应信息

Object handlerOrClassName = handlerMappings.get(namespaceUri);

if (handlerOrClassName == null) {

return null;

}

else if (handlerOrClassName instanceof NamespaceHandler) {

//已做过解析的情况,直接从缓存读取

return (NamespaceHandler) handlerOrClassName;

}

else {

//没有做过解析,则返回的是类路径

String className = (String) handlerOrClassName;

try {

//使用反射将类路径转换成类

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");

}

//初始化类

NamespaceHandler namespaceHandler = (NamespaceHandler) BeanUtils.instantiateClass(handlerClass);

//调用自定义的NamespaceHandler的初始化方法

namespaceHandler.init();

//记录在缓存

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);

}

}

}

回忆上一篇的自定义标签使用中的MyNamespaceHandler便可以发现,其实上面的方法就是初始化了MyNamespaceHandler,然后调用了他的init()方法

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/**

*

* @author Administrator

*/

public class MyNamespaceHandler extends NamespaceHandlerSupport {

/* (non-Javadoc)

* @see org.springframework.beans.factory.xml.NamespaceHandler#init()

*/

@Override

public void init() {

registerBeanDefinitionParser("user", new UserBeanDefinitionParser());

}

}

让我们在看看spring是如何获取handler映射的,查看getHandlerMappings()方法

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/**

* Load the specified NamespaceHandler mappings lazily.

*/

private Map<String, Object> getHandlerMappings() {

//如果没有被缓存,则开始进入缓存

if (this.handlerMappings == null) {

synchronized (this) {

if (this.handlerMappings == null) {

try {

//this.handlerMappings在构造函数已被初始化为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());

//将properties文件合并到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;

}

标签解析

得到了解析器和分析的元素侯,Spring就可以将解析工作委托给自定义解析器去解析了

让我们回到BeanDefinitionParserDelegate的handler.parse(ele, new ParserContext(this.readerContext, this, containingBd));中

进入NamespaceHandlerSupport中的parse方法

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/**

* Parses the supplied {@link Element} by delegating to the {@link BeanDefinitionParser} that is

* registered for that {@link Element}.

*/

public BeanDefinition parse(Element element, ParserContext parserContext) {

//寻找解析器,并进行解析操作

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) {

//获取元素名称,也就是<myname:user 中的user,此时localname为user

String localName = parserContext.getDelegate().getLocalName(element);

//根据user找到对应的解析器也就是在

//registerBeanDefinitionParser("user", new UserBeanDefinitionParser());注册的解析器

BeanDefinitionParser parser = this.parsers.get(localName);

if (parser == null) {

parserContext.getReaderContext().fatal(

"Cannot locate BeanDefinitionParser for element [" + localName + "]", element);

}

return parser;

}

让我们再跟踪到AbstractBeanDefinitionParser 的parse()方法

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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));

}

//将AbstractBeanDefinition转换成BeanDefinitionHolder

BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);

registerBeanDefinition(holder, parserContext.getRegistry());

if (shouldFireEvents()) {

//需要通知监听器进行处理

BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);

postProcessComponentDefinition(componentDefinition);

parserContext.registerComponent(componentDefinition);

}

}

catch (BeanDefinitionStoreException ex) {

parserContext.getReaderContext().error(ex.getMessage(), element);

return null;

}

}

return definition;

}

虽然说是对自定义配置文件的解析,但是我们可以看到,在这个函数中大部分的大马士用来处理将解析后的AbstractBeanDefinition转换为BeanDefinitionHolder并注册的功能,而真正去做解析的事情委托了给parseInternal,真是这句代码调用了我们的自定义解析函数。在parseInternal中，并不是直接调用自定义的doParse函数，而是惊醒了一些列的数据准备，包括对beanClass，scope，lazyInit等属性的准备。

接下来，让我们看看parseInternal方法，先跟踪到AbstractSingleBeanDefinitionParser

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/**

* 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);

}

//获取自定义标签中的class,此时会调用自定义解析器,如UserBeanDefinitionParser中的getBeanClass方法

Class<?> beanClass = getBeanClass(element);

if (beanClass != null) {

builder.getRawBeanDefinition().setBeanClass(beanClass);

}

else {

//若子类没有重写getBeanClass方法则尝试检查子类是否重写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);

}

doParse(element, parserContext, builder);

return builder.getBeanDefinition();

}