spring源码阅读(二) Bean加载之默认标签加载

接着上文的内容，我们经历了xml资源文件的校验/解析/终于要进入到Bean的加载中了。

上文进行到：

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)) {
                        this.parseDefaultElement(ele, delegate);
                    } else {
                        delegate.parseCustomElement(ele);
                    }
                }
            }
        } else {
            delegate.parseCustomElement(root);
        }

    }

这里，加载代理类的一个判断是否是默认命名空间的标签，把过程分为两个步骤，我们先来看第一个分支，即默认标签的解析。

private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
        if (delegate.nodeNameEquals(ele, "import")) {
            this.importBeanDefinitionResource(ele);
        } else if (delegate.nodeNameEquals(ele, "alias")) {
            this.processAliasRegistration(ele);
        } else if (delegate.nodeNameEquals(ele, "bean")) {
            this.processBeanDefinition(ele, delegate);
        } else if (delegate.nodeNameEquals(ele, "beans")) {
            this.doRegisterBeanDefinitions(ele);
        }

    }

默认的这几个根标签的解析，我们就从最关注的"bean"标签解析开始吧。即：this.processBeanDefinition(ele, delegate)。

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);   //  1
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); // 2

            try {
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry()); // 3
            } catch (BeanDefinitionStoreException var5) {
                this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
            }

            this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder)); // 4
        }

    }

这里分为几个步骤：

1: 把ele元素解析为我们需要的 BeanDefinitionHolder 对象。

2: 判断子元素中，是否有自定义标签，如果有调用自定义标签的处理Handle进行处理，并获取返回的bdHolder

3: 将解析到的bdHolder注册到我们的配置读取上下文的注册表中

4: 触发Bean注册完成的事件通知

理完思路，那我们就从第一个步骤开始，即把ele xml节点翻译成我们的BeanDefinition对象。

public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, BeanDefinition containingBean) {
        String id = ele.getAttribute("id");
        String nameAttr = ele.getAttribute("name");
        List<String> aliases = new ArrayList();
        if (StringUtils.hasLength(nameAttr)) {
            String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, ",; ");
            aliases.addAll(Arrays.asList(nameArr));
        }

        String beanName = id;
        if (!StringUtils.hasText(id) && !aliases.isEmpty()) {
            beanName = (String)aliases.remove(0);
            if (this.logger.isDebugEnabled()) {
                this.logger.debug("No XML 'id' specified - using '" + beanName + "' as bean name and " + aliases + " as aliases");
            }
        }

        if (containingBean == null) {
            this.checkNameUniqueness(beanName, aliases, ele);
        }

        AbstractBeanDefinition beanDefinition = this.parseBeanDefinitionElement(ele, beanName, containingBean);
        if (beanDefinition != null) {
            if (!StringUtils.hasText(beanName)) {
                try {
                    if (containingBean != null) {
                        beanName = BeanDefinitionReaderUtils.generateBeanName(beanDefinition, this.readerContext.getRegistry(), true);
                    } else {
                        beanName = this.readerContext.generateBeanName(beanDefinition);
                        String beanClassName = beanDefinition.getBeanClassName();
                        if (beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) {
                            aliases.add(beanClassName);
                        }
                    }

                    if (this.logger.isDebugEnabled()) {
                        this.logger.debug("Neither XML 'id' nor 'name' specified - using generated bean name [" + beanName + "]");
                    }
                } catch (Exception var9) {
                    this.error(var9.getMessage(), ele);
                    return null;
                }
            }

            String[] aliasesArray = StringUtils.toStringArray(aliases);
            return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
        } else {
            return null;
        }
    }

这里首先获取AbstractBeanDefinition对象，然后组装成BeanDefinitionHolder。查看parseBeanDefinitionElement 的代码

public AbstractBeanDefinition parseBeanDefinitionElement(Element ele, String beanName, BeanDefinition containingBean) {
        this.parseState.push(new BeanEntry(beanName));
        String className = null;
        if (ele.hasAttribute("class")) {
            className = ele.getAttribute("class").trim();
        }

        try {
            String parent = null;
            if (ele.hasAttribute("parent")) {
                parent = ele.getAttribute("parent");
            }

            AbstractBeanDefinition bd = this.createBeanDefinition(className, parent);
            this.parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
            bd.setDescription(DomUtils.getChildElementValueByTagName(ele, "description"));
            this.parseMetaElements(ele, bd);
            this.parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
            this.parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
            this.parseConstructorArgElements(ele, bd);
            this.parsePropertyElements(ele, bd);
            this.parseQualifierElements(ele, bd);
            bd.setResource(this.readerContext.getResource());
            bd.setSource(this.extractSource(ele));
            AbstractBeanDefinition var7 = bd;
            return var7;
        } catch (ClassNotFoundException var13) {
            this.error("Bean class [" + className + "] not found", ele, var13);
        } catch (NoClassDefFoundError var14) {
            this.error("Class that bean class [" + className + "] depends on not found", ele, var14);
        } catch (Throwable var15) {
            this.error("Unexpected failure during bean definition parsing", ele, var15);
        } finally {
            this.parseState.pop();
        }

        return null;
    }

看这句createBeanDefinition(className, parent)，跟进代码到BeanDefinitionReaderUtils的createBeanDefinition方法

public static AbstractBeanDefinition createBeanDefinition(String parentName, String className, ClassLoader classLoader) throws ClassNotFoundException {
        GenericBeanDefinition bd = new GenericBeanDefinition();
        bd.setParentName(parentName);
        if (className != null) {
            if (classLoader != null) {
                bd.setBeanClass(ClassUtils.forName(className, classLoader));
            } else {
                bd.setBeanClassName(className);
            }
        }

        return bd;
    }

这里创建的是一个GenericBeanDefinition对象。AbstractBeanDefinition一共有三个子类

GenericBeanDefinition

ChildBeanDefinition

RootBeanDefinition

暂时没看到Root和Child的应用，我们这里就只关注下这个GenericBeanDefinition。className不为空，classLoader为空，那么只设置下BeanCassName属性。

继续解析：

public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName, BeanDefinition containingBean, AbstractBeanDefinition bd) {
        if (ele.hasAttribute("singleton")) {
            this.error("Old 1.x 'singleton' attribute in use - upgrade to 'scope' declaration", ele);
        } else if (ele.hasAttribute("scope")) {
            bd.setScope(ele.getAttribute("scope"));
        } else if (containingBean != null) {
            bd.setScope(containingBean.getScope());
        }

        if (ele.hasAttribute("abstract")) {
            bd.setAbstract("true".equals(ele.getAttribute("abstract")));
        }

        String lazyInit = ele.getAttribute("lazy-init");
        if ("default".equals(lazyInit)) {
            lazyInit = this.defaults.getLazyInit();
        }

        bd.setLazyInit("true".equals(lazyInit));
        String autowire = ele.getAttribute("autowire");
        bd.setAutowireMode(this.getAutowireMode(autowire));
        String dependencyCheck = ele.getAttribute("dependency-check");
        bd.setDependencyCheck(this.getDependencyCheck(dependencyCheck));
        String autowireCandidate;
        if (ele.hasAttribute("depends-on")) {
            autowireCandidate = ele.getAttribute("depends-on");
            bd.setDependsOn(StringUtils.tokenizeToStringArray(autowireCandidate, ",; "));
        }

        autowireCandidate = ele.getAttribute("autowire-candidate");
        String destroyMethodName;
        if (!"".equals(autowireCandidate) && !"default".equals(autowireCandidate)) {
            bd.setAutowireCandidate("true".equals(autowireCandidate));
        } else {
            destroyMethodName = this.defaults.getAutowireCandidates();
            if (destroyMethodName != null) {
                String[] patterns = StringUtils.commaDelimitedListToStringArray(destroyMethodName);
                bd.setAutowireCandidate(PatternMatchUtils.simpleMatch(patterns, beanName));
            }
        }

        if (ele.hasAttribute("primary")) {
            bd.setPrimary("true".equals(ele.getAttribute("primary")));
        }

        if (ele.hasAttribute("init-method")) {
            destroyMethodName = ele.getAttribute("init-method");
            if (!"".equals(destroyMethodName)) {
                bd.setInitMethodName(destroyMethodName);
            }
        } else if (this.defaults.getInitMethod() != null) {
            bd.setInitMethodName(this.defaults.getInitMethod());
            bd.setEnforceInitMethod(false);
        }

        if (ele.hasAttribute("destroy-method")) {
            destroyMethodName = ele.getAttribute("destroy-method");
            if (!"".equals(destroyMethodName)) {
                bd.setDestroyMethodName(destroyMethodName);
            }
        } else if (this.defaults.getDestroyMethod() != null) {
            bd.setDestroyMethodName(this.defaults.getDestroyMethod());
            bd.setEnforceDestroyMethod(false);
        }

        if (ele.hasAttribute("factory-method")) {
            bd.setFactoryMethodName(ele.getAttribute("factory-method"));
        }

        if (ele.hasAttribute("factory-bean")) {
            bd.setFactoryBeanName(ele.getAttribute("factory-bean"));
        }

        return bd;
    }

这里解析各种bd的属性，并设置到bd对象里。这些属性比如init-method / destroy-method / lazy-init 这些我们经常使用的，还有些不熟悉的，可以到时候用到的时候查看了解下。

下面解析META元素：

public void parseMetaElements(Element ele, BeanMetadataAttributeAccessor attributeAccessor) {
        NodeList nl = ele.getChildNodes();

        for(int i = 0; i < nl.getLength(); ++i) {
            Node node = nl.item(i);
            if (this.isCandidateElement(node) && this.nodeNameEquals(node, "meta")) {
                Element metaElement = (Element)node;
                String key = metaElement.getAttribute("key");
                String value = metaElement.getAttribute("value");
                BeanMetadataAttribute attribute = new BeanMetadataAttribute(key, value);
                attribute.setSource(this.extractSource(metaElement));
                attributeAccessor.addMetadataAttribute(attribute);
            }
        }

    }

遍历所有meta标签，创建BeanMetaAttribute属性，并添加到bd中，这里向上转型到了BeanMetadataAttributeAccessor类。这里还是很清晰的，接口该做什么事情，还是分开的很清楚的。这里是架构设计里 接口隔离原则的体现。不同接口里，做的事情是不一样的，并不混在一起，这样当一个部分需要改动的时候，不会影响另一个部分。我的理解。

继续：解析lookup-method元素

public void parseLookupOverrideSubElements(Element beanEle, MethodOverrides overrides) {
        NodeList nl = beanEle.getChildNodes();

        for(int i = 0; i < nl.getLength(); ++i) {
            Node node = nl.item(i);
            if (this.isCandidateElement(node) && this.nodeNameEquals(node, "lookup-method")) {
                Element ele = (Element)node;
                String methodName = ele.getAttribute("name");
                String beanRef = ele.getAttribute("bean");
                LookupOverride override = new LookupOverride(methodName, beanRef);
                override.setSource(this.extractSource(ele));
                overrides.addOverride(override);
            }
        }

    }

添加到db的overrides属性里了。

解析：replaced-method 根look-method标签类似不再赘述

解析：constructor-arg 标签，构造函数标签比较常见，这里也相对复杂些，至少从代码上看

public void parseConstructorArgElements(Element beanEle, BeanDefinition bd) {
        NodeList nl = beanEle.getChildNodes();

        for(int i = 0; i < nl.getLength(); ++i) {
            Node node = nl.item(i);
            if (this.isCandidateElement(node) && this.nodeNameEquals(node, "constructor-arg")) {
                this.parseConstructorArgElement((Element)node, bd);
            }
        }

    }

先遍历元素，然后具体的操作，由parseConstructorArgElement方法来负责

public void parseConstructorArgElement(Element ele, BeanDefinition bd) {
        String indexAttr = ele.getAttribute("index");
        String typeAttr = ele.getAttribute("type");
        String nameAttr = ele.getAttribute("name");
        if (StringUtils.hasLength(indexAttr)) {
            try {
                int index = Integer.parseInt(indexAttr);
                if (index < 0) {
                    this.error("'index' cannot be lower than 0", ele);
                } else {
                    try {
                        this.parseState.push(new ConstructorArgumentEntry(index));
                        Object value = this.parsePropertyValue(ele, bd, (String)null);
                        ValueHolder valueHolder = new ValueHolder(value);
                        if (StringUtils.hasLength(typeAttr)) {
                            valueHolder.setType(typeAttr);
                        }

                        if (StringUtils.hasLength(nameAttr)) {
                            valueHolder.setName(nameAttr);
                        }

                        valueHolder.setSource(this.extractSource(ele));
                        if (bd.getConstructorArgumentValues().hasIndexedArgumentValue(index)) {
                            this.error("Ambiguous constructor-arg entries for index " + index, ele);
                        } else {
                            bd.getConstructorArgumentValues().addIndexedArgumentValue(index, valueHolder);
                        }
                    } finally {
                        this.parseState.pop();
                    }
                }
            } catch (NumberFormatException var19) {
                this.error("Attribute 'index' of tag 'constructor-arg' must be an integer", ele);
            }
        } else {
            try {
                this.parseState.push(new ConstructorArgumentEntry());
                Object value = this.parsePropertyValue(ele, bd, (String)null);
                ValueHolder valueHolder = new ValueHolder(value);
                if (StringUtils.hasLength(typeAttr)) {
                    valueHolder.setType(typeAttr);
                }

                if (StringUtils.hasLength(nameAttr)) {
                    valueHolder.setName(nameAttr);
                }

                valueHolder.setSource(this.extractSource(ele));
                bd.getConstructorArgumentValues().addGenericArgumentValue(valueHolder);
            } finally {
                this.parseState.pop();
            }
        }

    }

先获取index/type/name属性，然后根据有没有index属性类分别处理

如果有index属性，那么获取value，并创建valueHolder最终添加到constructorArgumentValues 中。

来看具体的获取value的过程

public Object parsePropertyValue(Element ele, BeanDefinition bd, String propertyName) {
        String elementName = propertyName != null ? "<property> element for property '" + propertyName + "'" : "<constructor-arg> element";
        NodeList nl = ele.getChildNodes();
        Element subElement = null;

        for(int i = 0; i < nl.getLength(); ++i) {
            Node node = nl.item(i);
            if (node instanceof Element && !this.nodeNameEquals(node, "description") && !this.nodeNameEquals(node, "meta")) {
                if (subElement != null) {
                    this.error(elementName + " must not contain more than one sub-element", ele);
                } else {
                    subElement = (Element)node;
                }
            }
        }

        boolean hasRefAttribute = ele.hasAttribute("ref");
        boolean hasValueAttribute = ele.hasAttribute("value");
        if (hasRefAttribute && hasValueAttribute || (hasRefAttribute || hasValueAttribute) && subElement != null) {
            this.error(elementName + " is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);
        }

        if (hasRefAttribute) {
            String refName = ele.getAttribute("ref");
            if (!StringUtils.hasText(refName)) {
                this.error(elementName + " contains empty 'ref' attribute", ele);
            }

            RuntimeBeanReference ref = new RuntimeBeanReference(refName);
            ref.setSource(this.extractSource(ele));
            return ref;
        } else if (hasValueAttribute) {
            TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute("value"));
            valueHolder.setSource(this.extractSource(ele));
            return valueHolder;
        } else if (subElement != null) {
            return this.parsePropertySubElement(subElement, bd);
        } else {
            this.error(elementName + " must specify a ref or value", ele);
            return null;
        }
    }

获取value的过程分为几个主要部分，根据是ref类型，还是value类型不同，或者是子元素类型，操作不同

如果是ref类型，创建RuntimeBeanReference对象；如果是value类型，则封装为TypedStringVlue类型。如果是子元素类型，则继续由parsePropertySubElement处理

public Object parsePropertySubElement(Element ele, BeanDefinition bd) {
        return this.parsePropertySubElement(ele, bd, (String)null);
    }

    public Object parsePropertySubElement(Element ele, BeanDefinition bd, String defaultValueType) {
        if (!this.isDefaultNamespace((Node)ele)) {
            return this.parseNestedCustomElement(ele, bd);
        } else if (this.nodeNameEquals(ele, "bean")) {
            BeanDefinitionHolder nestedBd = this.parseBeanDefinitionElement(ele, bd);
            if (nestedBd != null) {
                nestedBd = this.decorateBeanDefinitionIfRequired(ele, nestedBd, bd);
            }

            return nestedBd;
        } else if (this.nodeNameEquals(ele, "ref")) {
            String refName = ele.getAttribute("bean");
            boolean toParent = false;
            if (!StringUtils.hasLength(refName)) {
                refName = ele.getAttribute("local");
                if (!StringUtils.hasLength(refName)) {
                    refName = ele.getAttribute("parent");
                    toParent = true;
                    if (!StringUtils.hasLength(refName)) {
                        this.error("'bean', 'local' or 'parent' is required for <ref> element", ele);
                        return null;
                    }
                }
            }

            if (!StringUtils.hasText(refName)) {
                this.error("<ref> element contains empty target attribute", ele);
                return null;
            } else {
                RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);
                ref.setSource(this.extractSource(ele));
                return ref;
            }
        } else if (this.nodeNameEquals(ele, "idref")) {
            return this.parseIdRefElement(ele);
        } else if (this.nodeNameEquals(ele, "value")) {
            return this.parseValueElement(ele, defaultValueType);
        } else if (this.nodeNameEquals(ele, "null")) {
            TypedStringValue nullHolder = new TypedStringValue((String)null);
            nullHolder.setSource(this.extractSource(ele));
            return nullHolder;
        } else if (this.nodeNameEquals(ele, "array")) {
            return this.parseArrayElement(ele, bd);
        } else if (this.nodeNameEquals(ele, "list")) {
            return this.parseListElement(ele, bd);
        } else if (this.nodeNameEquals(ele, "set")) {
            return this.parseSetElement(ele, bd);
        } else if (this.nodeNameEquals(ele, "map")) {
            return this.parseMapElement(ele, bd);
        } else if (this.nodeNameEquals(ele, "props")) {
            return this.parsePropsElement(ele);
        } else {
            this.error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);
            return null;
        }
    }

这里可以看到，所有支持的子类的分类处理都有了，里边的具体内容，就感兴趣的进去看了。

2019-07-01 15:11继续:

构造函数元素的解析说完了，我们继续主线解析到db中的，property元素的解析

public void parsePropertyElements(Element beanEle, BeanDefinition bd) {
        NodeList nl = beanEle.getChildNodes();

        for(int i = 0; i < nl.getLength(); ++i) {
            Node node = nl.item(i);
            if (this.isCandidateElement(node) && this.nodeNameEquals(node, "property")) {
                this.parsePropertyElement((Element)node, bd);
            }
        }

    }

public void parsePropertyElement(Element ele, BeanDefinition bd) {
        String propertyName = ele.getAttribute("name");
        if (!StringUtils.hasLength(propertyName)) {
            this.error("Tag 'property' must have a 'name' attribute", ele);
        } else {
            this.parseState.push(new PropertyEntry(propertyName));

            try {
                if (!bd.getPropertyValues().contains(propertyName)) {
                    Object val = this.parsePropertyValue(ele, bd, propertyName);
                    PropertyValue pv = new PropertyValue(propertyName, val);
                    this.parseMetaElements(ele, pv);
                    pv.setSource(this.extractSource(ele));
                    bd.getPropertyValues().addPropertyValue(pv);
                    return;
                }

                this.error("Multiple 'property' definitions for property '" + propertyName + "'", ele);
            } finally {
                this.parseState.pop();
            }

        }
    }

这里，跟构造函数的property元素解析不同的是，这里是构造了PropertyValue对象，并添加到bd的propertyValues里了。

qualifier元素解析

public void parseQualifierElements(Element beanEle, AbstractBeanDefinition bd) {
        NodeList nl = beanEle.getChildNodes();

        for(int i = 0; i < nl.getLength(); ++i) {
            Node node = nl.item(i);
            if (this.isCandidateElement(node) && this.nodeNameEquals(node, "qualifier")) {
                this.parseQualifierElement((Element)node, bd);
            }
        }

    }

public void parseQualifierElement(Element ele, AbstractBeanDefinition bd) {
        String typeName = ele.getAttribute("type");
        if (!StringUtils.hasLength(typeName)) {
            this.error("Tag 'qualifier' must have a 'type' attribute", ele);
        } else {
            this.parseState.push(new QualifierEntry(typeName));

            try {
                AutowireCandidateQualifier qualifier = new AutowireCandidateQualifier(typeName);
                qualifier.setSource(this.extractSource(ele));
                String value = ele.getAttribute("value");
                if (StringUtils.hasLength(value)) {
                    qualifier.setAttribute(AutowireCandidateQualifier.VALUE_KEY, value);
                }

                NodeList nl = ele.getChildNodes();

                for(int i = 0; i < nl.getLength(); ++i) {
                    Node node = nl.item(i);
                    if (this.isCandidateElement(node) && this.nodeNameEquals(node, "attribute")) {
                        Element attributeEle = (Element)node;
                        String attributeName = attributeEle.getAttribute("key");
                        String attributeValue = attributeEle.getAttribute("value");
                        if (!StringUtils.hasLength(attributeName) || !StringUtils.hasLength(attributeValue)) {
                            this.error("Qualifier 'attribute' tag must have a 'name' and 'value'", attributeEle);
                            return;
                        }

                        BeanMetadataAttribute attribute = new BeanMetadataAttribute(attributeName, attributeValue);
                        attribute.setSource(this.extractSource(attributeEle));
                        qualifier.addMetadataAttribute(attribute);
                    }
                }

                bd.addQualifier(qualifier);
            } finally {
                this.parseState.pop();
            }
        }
    }

构造Qualifier对象，并添加到bd的qualifier属性中。

到这里，从ele文档元素到BeanDefinition对象的解析基本就完成了。

我们梳理下大致的思路，其实就是解析各种元素，针对不同元素或是生成bd的属性，或是添加到对应的属性列表中，总之ele要完全转换成我们后续需要使用的BeanDefinition中。

下面，做了这么多解析工作，我们来完整的看一下BeanDefinition的属性

public abstract class AbstractBeanDefinition extends BeanMetadataAttributeAccessor implements BeanDefinition, Cloneable {
    public static final String SCOPE_DEFAULT = "";
    // 省略部分静态变量及final常量
    
private String scope = SCOPE_DEFAULT; // bean的作用域范围，对应bean属性scope
    private boolean abstractFlag;   // 是否是抽象，对应bean属性abstract
    private boolean lazyInit;   // 是否延迟加载，对应bean属性lazy-init
    private int autowireMode;    // 自动注入模式 AUTOWIRE_NO AUTOWIRE_BY_NAME AUTOWIRE_BY_TYPE AUTOWIRE_CONSTRUCTOR
    private int dependencyCheck;  // 依赖检查，spring3.0后弃用
    private String[] dependsOn; // 表示一个bean的实例化依靠另一个bean先实例化，对应bean的属性depend-on
    private boolean autowireCandidate; // autowireCandiate属性设置为false，这样容器在查找自动装配对象时，将不考虑该bean，即它不会考虑作为其他bean自动装配的候选者，但是该bean本身可以使用自动化装配来注入其他bean
    private boolean primary;   // 自动装配时，如果出现多个bean候选者，将作为首选者，对应baen属性primary
    private final Map<String, AutowireCandidateQualifier> qualifiers; // 用于记录Qualifier，对应子元素qualifier
    private boolean nonPublicAccessAllowed; // 允许访问非公开的构造起和方法，程序设置
    private boolean lenientConstructorResolution; // 是否以宽松模式解析构造函数，默认为true
    private ConstructorArgumentValues constructorArgumentValues; // 记录构造函数注入属性，对应bean属性constructor-arg
    private MutablePropertyValues propertyValues;  // 普通属性集合
    private MethodOverrides methodOverrides; // 方法重写持有者，记录lookup-method/ replace-method元素
    private String factoryBeanName; // 用于bean属性factoryBean
    private String factoryMethodName; // 对应bean属性factory-method
    private String initMethodName; // 初始化方法，对应bean属性init-method
    private String destroyMethodName; // 销毁方法，对应bean属性destroy-method
    private boolean enforceInitMethod; // 是否执行init-method，程序设置
    private boolean enforceDestroyMethod; // 是否执行destroy-method，程序设置
    private boolean synthetic; // 是否是用户定义的而不是应用程序本身定义的，创建AOP时候为true，程序设置
    private int role; // 定义bean的应用，APPLICATION:用户/ INFRASTRUCTURE：完全内部使用，与用户无关/ SUPPORT某些复杂配置的一部分，程序设置
    private String description;  // bean描述信息
    private Resource resource;  // 这个bean定义的资源

以上有些元素其实没怎么使用过，不是太熟悉，这些内容主要参考了《spring源码深度解析》- 郝佳著

OK，我们回到之前bean解析的代码再来继续：

protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
        BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
        if (bdHolder != null) {
            bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);

            try {
                BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, this.getReaderContext().getRegistry());
            } catch (BeanDefinitionStoreException var5) {
                this.getReaderContext().error("Failed to register bean definition with name '" + bdHolder.getBeanName() + "'", ele, var5);
            }

            this.getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
        }

    }

我们之前重点都是在delegate.parseBeanDefinitionElement 的解析说明上，我们继续下边这句

bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder) ，根据方法的名称，其实大概可以判断意思，如果有必要装饰BeanDefinition对象

我们进入代码来看一下：

public BeanDefinitionHolder decorateBeanDefinitionIfRequired(Element ele, BeanDefinitionHolder definitionHolder) {
        return this.decorateBeanDefinitionIfRequired(ele, definitionHolder, (BeanDefinition)null);
    }

public BeanDefinitionHolder decorateBeanDefinitionIfRequired(Element ele, BeanDefinitionHolder definitionHolder, BeanDefinition containingBd) {
        BeanDefinitionHolder finalDefinition = definitionHolder;
        NamedNodeMap attributes = ele.getAttributes();

        for(int i = 0; i < attributes.getLength(); ++i) {
            Node node = attributes.item(i);
            finalDefinition = this.decorateIfRequired(node, finalDefinition, containingBd);
        }

        NodeList children = ele.getChildNodes();

        for(int i = 0; i < children.getLength(); ++i) {
            Node node = children.item(i);
            if (node.getNodeType() == 1) {
                finalDefinition = this.decorateIfRequired(node, finalDefinition, containingBd);
            }
        }

        return finalDefinition;
    }

    public BeanDefinitionHolder decorateIfRequired(Node node, BeanDefinitionHolder originalDef, BeanDefinition containingBd) {
        String namespaceUri = this.getNamespaceURI(node);
        if (!this.isDefaultNamespace(namespaceUri)) {
            NamespaceHandler handler = this.readerContext.getNamespaceHandlerResolver().resolve(namespaceUri);
            if (handler != null) {
                return handler.decorate(node, originalDef, new ParserContext(this.readerContext, this, containingBd));
            }

            if (namespaceUri != null && namespaceUri.startsWith("http://www.springframework.org/")) {
                this.error("Unable to locate Spring NamespaceHandler for XML schema namespace [" + namespaceUri + "]", node);
            } else if (this.logger.isDebugEnabled()) {
                this.logger.debug("No Spring NamespaceHandler found for XML schema namespace [" + namespaceUri + "]");
            }
        }

        return originalDef;
    }

 可以看到主要动作是，对属性及子元素进行处理，如果是默认元素，直接掠过，如果不是则根据命名空间，查找对应的处理handler进行解析处理，具体的解析过程暂时先放这里，后续再说。这里

只介绍下做了什么事情。

继续我们的核心步骤，该到注册步骤了，将我们的beanDefinition注册到注册表中。

public static void registerBeanDefinition(BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry) throws BeanDefinitionStoreException {
        String beanName = definitionHolder.getBeanName();
        registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
        String[] aliases = definitionHolder.getAliases();
        if (aliases != null) {
            String[] var4 = aliases;
            int var5 = aliases.length;

            for(int var6 = 0; var6 < var5; ++var6) {
                String alias = var4[var6];
                registry.registerAlias(beanName, alias);
            }
        }

    }

这里有两个部分，一个是根据beanName注册，一个是根据alias注册

我们看第一个根据beanName注册：

public void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException {
        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 var4) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", var4);
            }
        }

        BeanDefinition oldBeanDefinition = (BeanDefinition)this.beanDefinitionMap.get(beanName);
        if (oldBeanDefinition != null) {
            if (!this.allowBeanDefinitionOverriding) {
                throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + oldBeanDefinition + "] bound.");
            }

            if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Overriding user-defined bean definition for bean '" + beanName + " with a framework-generated bean definition ': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
                }
            } else if (this.logger.isInfoEnabled()) {
                this.logger.info("Overriding bean definition for bean '" + beanName + "': replacing [" + oldBeanDefinition + "] with [" + beanDefinition + "]");
            }
        } else {
            this.beanDefinitionNames.add(beanName);  // 记录beanName
            this.manualSingletonNames.remove(beanName);
            this.frozenBeanDefinitionNames = null;
        }

        this.beanDefinitionMap.put(beanName, beanDefinition);
        if (oldBeanDefinition != null || this.containsSingleton(beanName)) {
            this.resetBeanDefinition(beanName); // 重置所有beanName对应的缓存
        }

    }

这里还有一个校验，这里的校验主要校验的是methodOverrides，主要校验是否有这个类和这个类是否有相应的方法。

这里的操作：

1:校验，校验methodOverrides属性的正确性和有效性

2:查看是否已经有了该beanName，如果有然后查看是否配置可覆盖，如果不是，直接抛出异常；如果设置可以覆盖，那么在后续的操作中覆盖掉即可

3:加入map缓存

4:清除解析前留下的beanName缓存

继续：通过别名注册BeanDefinition

public void registerAlias(String name, String alias) {
        Assert.hasText(name, "'name' must not be empty");
        Assert.hasText(alias, "'alias' must not be empty");
        if (alias.equals(name)) {
            this.aliasMap.remove(alias);
        } else {
            if (!this.allowAliasOverriding()) {
                String registeredName = (String)this.aliasMap.get(alias);
                if (registeredName != null && !registeredName.equals(name)) {
                    throw new IllegalStateException("Cannot register alias '" + alias + "' for name '" + name + "': It is already registered for name '" + registeredName + "'.");
                }
            }

            this.checkForAliasCircle(name, alias);
            this.aliasMap.put(alias, name);
        }

    }

步骤如下：

1:如果alias名字与name相同，直接删除原有alias

2:查看是否允许alias覆盖配置，如果不允许，进行校验，如果已经注册的alias的beanName跟当前注册的beanName不相同，则抛出alias名称已被注册到其他beanName上的异常

3:检查是否有循环alias

4:注册alias

至此，默认标签的解析就梳理完了，后续我们进行自定义标签的解析。2019-07-01 17:32分 于图书馆