Spring如何实现默认标签解析

这篇文章的内容主要围绕Spring如何实现默认标签解析进行讲述，文章内容清晰易懂，条理清晰，非常适合新手学习，值得大家去阅读。感兴趣的朋友可以跟随小编一起阅读吧。希望大家通过这篇文章有所收获！

进入parseBeanDefinitions（）方法

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)) {                        //默认标签解析，此次着重分析这个方法                        parseDefaultElement(ele, delegate);                    }                    else {                        //自定义标签解析                        delegate.parseCustomElement(ele);                    }                }            }        }        else {            delegate.parseCustomElement(root);        }    }

-进入parseDefaultElement（）方法,此方法在parseBeanDefinitions的下方

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {        //import标签解析 ，可看可不看        if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) {            importBeanDefinitionResource(ele);        }        //alias标签解析 别名标签 可看可不看        else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) {            processAliasRegistration(ele);        }        //bean标签，重要（看这个方法）        else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) {            processBeanDefinition(ele, delegate);        }        //beans标签，不重要        else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) {            // recurse            doRegisterBeanDefinitions(ele);        }    }

-进入到bean标签解析方法

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {        //重点看这个方法 ，解析document，封装成BeanDefinition        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);        if (bdHolder != null) {            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);            try {                //完成document到BeanDefinition对象转换后，对BeanDefinition对象进行缓存注册                // Register the final decorated instance.                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));        }    }

进入

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {        //思考一下这个的第二个参数为啥要传入null（BeanDefinition类型），进入方法        return parseBeanDefinitionElement(ele, null);    }

打开parseBeanDefinitionElement方法

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {        //获取id        String id = ele.getAttribute(ID_ATTRIBUTE);        //获取别名        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);        //将别名添加到aliases内        List aliases = new ArrayList<>();        if (StringUtils.hasLength(nameAttr)) {            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);            aliases.addAll(Arrays.asList(nameArr));        }        String beanName = id;        if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {            beanName = aliases.remove(0);            if (logger.isTraceEnabled()) {                logger.trace("No XML 'id' specified - using '" + beanName +                        "' as bean name and " + aliases + " as aliases");            }        }        //检查beanName是否重复        if (containingBean == null) {            checkNameUniqueness(beanName, aliases, ele);        }        //标签解析的核心方法        AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);        if (beanDefinition != null) {            ......不重要的就不要看了，浪费时间        }        return null;    }

看核心方法parseBeanDefinitionElement

public AbstractBeanDefinition parseBeanDefinitionElement(            Element ele, String beanName, @Nullable BeanDefinition containingBean) {        this.parseState.push(new BeanEntry(beanName));        String className = null;        if (ele.hasAttribute(CLASS_ATTRIBUTE)) {            className = ele.getAttribute(CLASS_ATTRIBUTE).trim();        }        String parent = null;        if (ele.hasAttribute(PARENT_ATTRIBUTE)) {            parent = ele.getAttribute(PARENT_ATTRIBUTE);        }        try {            //创建GenericBeanDefinition对象            AbstractBeanDefinition bd = createBeanDefinition(className, parent);            //解析bean标签的属性，并把解析出来的属性设置到BeanDefinition对象中            parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));            //解析bean中的meta标签            parseMetaElements(ele, bd);            //解析bean中的lookup-method标签  ，可看可不看            parseLookupOverrideSubElements(ele, bd.getMethodOverrides());            //解析bean中的replaced-method标签  ，可看可不看            parseReplacedMethodSubElements(ele, bd.getMethodOverrides());            //解析bean中的constructor-arg标签 ，可看可不看            parseConstructorArgElements(ele, bd);            //解析bean中的property标签 可看可不看            parsePropertyElements(ele, bd);            //可以不看，用不到            parseQualifierElements(ele, bd);            bd.setResource(this.readerContext.getResource());            bd.setSource(extractSource(ele));            return bd;        }            ......有兴趣自己看        return null;    }

打开这个方法parseBeanDefinitionAttributes（），对BeanDefinition属性进行默认的封装，然后返回BeanDefinition对象

public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,            @Nullable BeanDefinition containingBean, AbstractBeanDefinition bd) {        //        if (ele.hasAttribute(SINGLETON_ATTRIBUTE)) {            error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);        }        else if (ele.hasAttribute(SCOPE_ATTRIBUTE)) {            bd.setScope(ele.getAttribute(SCOPE_ATTRIBUTE));        }        else if (containingBean != null) {            // Take default from containing bean in case of an inner bean definition.            bd.setScope(containingBean.getScope());        }        if (ele.hasAttribute(ABSTRACT_ATTRIBUTE)) {            bd.setAbstract(TRUE_VALUE.equals(ele.getAttribute(ABSTRACT_ATTRIBUTE)));        }        String lazyInit = ele.getAttribute(LAZY_INIT_ATTRIBUTE);        if (isDefaultValue(lazyInit)) {            lazyInit = this.defaults.getLazyInit();        }        bd.setLazyInit(TRUE_VALUE.equals(lazyInit));        String autowire = ele.getAttribute(AUTOWIRE_ATTRIBUTE);        bd.setAutowireMode(getAutowireMode(autowire));        if (ele.hasAttribute(DEPENDS_ON_ATTRIBUTE)) {            String dependsOn = ele.getAttribute(DEPENDS_ON_ATTRIBUTE);            bd.setDependsOn(StringUtils.tokenizeToStringArray(dependsOn, MULTI_VALUE_ATTRIBUTE_DELIMITERS));        }        String autowireCandidate = ele.getAttribute(AUTOWIRE_CANDIDATE_ATTRIBUTE);        if (isDefaultValue(autowireCandidate)) {            String candidatePattern = this.defaults.getAutowireCandidates();            if (candidatePattern != null) {                String[] patterns = StringUtils.commaDelimitedListToStringArray(candidatePattern);                bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));            }        }        else {            bd.setAutowireCandidate(TRUE_VALUE.equals(autowireCandidate));        }        if (ele.hasAttribute(PRIMARY_ATTRIBUTE)) {            bd.setPrimary(TRUE_VALUE.equals(ele.getAttribute(PRIMARY_ATTRIBUTE)));        }        if (ele.hasAttribute(INIT_METHOD_ATTRIBUTE)) {            String initMethodName = ele.getAttribute(INIT_METHOD_ATTRIBUTE);            bd.setInitMethodName(initMethodName);        }        else if (this.defaults.getInitMethod() != null) {            bd.setInitMethodName(this.defaults.getInitMethod());            bd.setEnforceInitMethod(false);        }        if (ele.hasAttribute(DESTROY_METHOD_ATTRIBUTE)) {            String destroyMethodName = ele.getAttribute(DESTROY_METHOD_ATTRIBUTE);            bd.setDestroyMethodName(destroyMethodName);        }        else if (this.defaults.getDestroyMethod() != null) {            bd.setDestroyMethodName(this.defaults.getDestroyMethod());            bd.setEnforceDestroyMethod(false);        }        if (ele.hasAttribute(FACTORY_METHOD_ATTRIBUTE)) {            bd.setFactoryMethodName(ele.getAttribute(FACTORY_METHOD_ATTRIBUTE));        }        if (ele.hasAttribute(FACTORY_BEAN_ATTRIBUTE)) {            bd.setFactoryBeanName(ele.getAttribute(FACTORY_BEAN_ATTRIBUTE));        }        return bd;    }

然后回到processBeanDefinition方法，将BeanDefinition注册到缓存中，此时看

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {        //重点看这个方法，重要程度 5 ，解析document，封装成BeanDefinition        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);        if (bdHolder != null) {            //该方法功能不重要，设计模式重点看一下，装饰者设计模式，加上SPI设计思想            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);            try {                //完成document到BeanDefinition对象转换后，对BeanDefinition对象进行缓存注册                // Register the final decorated instance.                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));        }    }

打开registerBeanDefinition方法

public static void registerBeanDefinition(            BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)            throws BeanDefinitionStoreException {        // Register bean definition under primary name.        String beanName = definitionHolder.getBeanName();        //完成BeanDefinition的注册，重点看        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());        //建立别名和 id的映射，这样就可以根据别名获取到id        // Register aliases for bean name, if any.        String[] aliases = definitionHolder.getAliases();        if (aliases != null) {            for (String alias : aliases) {                registry.registerAlias(beanName, alias);            }        }    }

打开registerBeanDefinition方法，将创建好的beanDefinition存入map。默认标签解析就此完毕

@Override    public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition)            throws BeanDefinitionStoreException {        Assert.hasText(beanName, "'beanName' must not be empty");        Assert.notNull(beanDefinition, "BeanDefinition must not be null");        this.beanDefinitionMap.put(beanName, beanDefinition);    }

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