【死磕 Spring】----- IOC 之解析 bean 标签：constructor-arg、property 子元素

public class StudentService {    private String name;    private Integer age;    private BookService bookService;    StudentService(String name, Integer age, BookService bookService){        this.name = name;        this.age = age;        this.bookService = bookService;    }}    <bean id="bookService" class="org.springframework.core.service.BookService"/>    <bean id="studentService" class="org.springframework.core.service.StudentService">        <constructor-arg index="0" value="chenssy"/>        <constructor-arg name="age" value="100"/>        <constructor-arg name="bookService" ref="bookService"/>    </bean>

    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 (isCandidateElement(node) && nodeNameEquals(node, CONSTRUCTOR_ARG_ELEMENT)) {                parseConstructorArgElement((Element) node, bd);            }        }    }

    public void parseConstructorArgElement(Element ele, BeanDefinition bd) {        // 提取 index、type、name 属性值        String indexAttr = ele.getAttribute(INDEX_ATTRIBUTE);        String typeAttr = ele.getAttribute(TYPE_ATTRIBUTE);        String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);        // 如果有index        if (StringUtils.hasLength(indexAttr)) {            try {                int index = Integer.parseInt(indexAttr);                if (index < 0) {                    error("'index' cannot be lower than 0", ele);                }                else {                    try {                        // 构造一个 ConstructorArgumentEntry 并将其加入到 ParseState 中                        this.parseState.push(new ConstructorArgumentEntry(index));                        // 解析 ele 对应属性元素                        Object value = parsePropertyValue(ele, bd, null);                        // 根据解析的属性元素构造一个 valueHolder 对象                        ConstructorArgumentValues.ValueHolder valueHolder = new ConstructorArgumentValues.ValueHolder(value);                        if (StringUtils.hasLength(typeAttr)) {                            valueHolder.setType(typeAttr);                        }                        if (StringUtils.hasLength(nameAttr)) {                            valueHolder.setName(nameAttr);                        }                        //                        valueHolder.setSource(extractSource(ele));                        // 不允许重复指定相同参数                        if (bd.getConstructorArgumentValues().hasIndexedArgumentValue(index)) {                            error("Ambiguous constructor-arg entries for index " + index, ele);                        }                        else {                            // 加入到 indexedArgumentValues 中国                            bd.getConstructorArgumentValues().addIndexedArgumentValue(index, valueHolder);                        }                    }                    finally {                        this.parseState.pop();                    }                }            }            catch (NumberFormatException ex) {                error("Attribute 'index' of tag 'constructor-arg' must be an integer", ele);            }        }        else {            try {                this.parseState.push(new ConstructorArgumentEntry());                Object value = parsePropertyValue(ele, bd, null);                ConstructorArgumentValues.ValueHolder valueHolder = new ConstructorArgumentValues.ValueHolder(value);                if (StringUtils.hasLength(typeAttr)) {                    valueHolder.setType(typeAttr);                }                if (StringUtils.hasLength(nameAttr)) {                    valueHolder.setName(nameAttr);                }                valueHolder.setSource(extractSource(ele));                bd.getConstructorArgumentValues().addGenericArgumentValue(valueHolder);            }            finally {                this.parseState.pop();            }        }    }

    public Object parsePropertyValue(Element ele, BeanDefinition bd, @Nullable 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);            // meta 、description 不处理            if (node instanceof Element && !nodeNameEquals(node, DESCRIPTION_ELEMENT) &&                    !nodeNameEquals(node, META_ELEMENT)) {                // Child element is what we're looking for.                if (subElement != null) {                    error(elementName + " must not contain more than one sub-element", ele);                }                else {                    subElement = (Element) node;                }            }        }        // 解析 ref 元素        boolean hasRefAttribute = ele.hasAttribute(REF_ATTRIBUTE);        // 解析 value 元素        boolean hasValueAttribute = ele.hasAttribute(VALUE_ATTRIBUTE);        // constructor-arg 子元素有两种情况不存在        // 1. 即存在 ref 又存在 value        // 2. 存在 ref 或者 value，但是又有子元素        if ((hasRefAttribute && hasValueAttribute) ||                ((hasRefAttribute || hasValueAttribute) && subElement != null)) {            error(elementName +                    " is only allowed to contain either 'ref' attribute OR 'value' attribute OR sub-element", ele);        }        if (hasRefAttribute) {            // 获取 ref 属性值            String refName = ele.getAttribute(REF_ATTRIBUTE);            if (!StringUtils.hasText(refName)) {                error(elementName + " contains empty 'ref' attribute", ele);            }            // 将 ref 属性值构造为 RuntimeBeanReference 实例对象            RuntimeBeanReference ref = new RuntimeBeanReference(refName);            ref.setSource(extractSource(ele));            return ref;        }        else if (hasValueAttribute) {            // 解析 value 属性值，构造 TypedStringValue 实例对象            TypedStringValue valueHolder = new TypedStringValue(ele.getAttribute(VALUE_ATTRIBUTE));            valueHolder.setSource(extractSource(ele));            return valueHolder;        }        else if (subElement != null) {            // 解析子元素            return parsePropertySubElement(subElement, bd);        }        else {            // Neither child element nor "ref" or "value" attribute found.            error(elementName + " must specify a ref or value", ele);            return null;        }    }

    public Object parsePropertySubElement(Element ele, @Nullable BeanDefinition bd) {        return parsePropertySubElement(ele, bd, null);    }    public Object parsePropertySubElement(Element ele, @Nullable BeanDefinition bd, @Nullable String defaultValueType) {        if (!isDefaultNamespace(ele)) {            return parseNestedCustomElement(ele, bd);        }        else if (nodeNameEquals(ele, BEAN_ELEMENT)) {            BeanDefinitionHolder nestedBd = parseBeanDefinitionElement(ele, bd);            if (nestedBd != null) {                nestedBd = decorateBeanDefinitionIfRequired(ele, nestedBd, bd);            }            return nestedBd;        }        else if (nodeNameEquals(ele, REF_ELEMENT)) {            // A generic reference to any name of any bean.            String refName = ele.getAttribute(BEAN_REF_ATTRIBUTE);            boolean toParent = false;            if (!StringUtils.hasLength(refName)) {                // A reference to the id of another bean in a parent context.                refName = ele.getAttribute(PARENT_REF_ATTRIBUTE);                toParent = true;                if (!StringUtils.hasLength(refName)) {                    error("'bean' or 'parent' is required for <ref> element", ele);                    return null;                }            }            if (!StringUtils.hasText(refName)) {                error("<ref> element contains empty target attribute", ele);                return null;            }            RuntimeBeanReference ref = new RuntimeBeanReference(refName, toParent);            ref.setSource(extractSource(ele));            return ref;        }        else if (nodeNameEquals(ele, IDREF_ELEMENT)) {            return parseIdRefElement(ele);        }        else if (nodeNameEquals(ele, VALUE_ELEMENT)) {            return parseValueElement(ele, defaultValueType);        }        else if (nodeNameEquals(ele, NULL_ELEMENT)) {            // It's a distinguished null value. Let's wrap it in a TypedStringValue            // object in order to preserve the source location.            TypedStringValue nullHolder = new TypedStringValue(null);            nullHolder.setSource(extractSource(ele));            return nullHolder;        }        else if (nodeNameEquals(ele, ARRAY_ELEMENT)) {            return parseArrayElement(ele, bd);        }        else if (nodeNameEquals(ele, LIST_ELEMENT)) {            return parseListElement(ele, bd);        }        else if (nodeNameEquals(ele, SET_ELEMENT)) {            return parseSetElement(ele, bd);        }        else if (nodeNameEquals(ele, MAP_ELEMENT)) {            return parseMapElement(ele, bd);        }        else if (nodeNameEquals(ele, PROPS_ELEMENT)) {            return parsePropsElement(ele);        }        else {            error("Unknown property sub-element: [" + ele.getNodeName() + "]", ele);            return null;        }    }

    <bean id="studentService" class="org.springframework.core.service.StudentService">        <property name="name" value="chenssy"/>        <property name="age" value="18"/>    </bean>

    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 (isCandidateElement(node) && nodeNameEquals(node, PROPERTY_ELEMENT)) {                parsePropertyElement((Element) node, bd);            }        }    }

    public void parsePropertyElement(Element ele, BeanDefinition bd) {        // 获取 name 属性        String propertyName = ele.getAttribute(NAME_ATTRIBUTE);        if (!StringUtils.hasLength(propertyName)) {            error("Tag 'property' must have a 'name' attribute", ele);            return;        }        this.parseState.push(new PropertyEntry(propertyName));        try {            // 如果存在相同的 name            if (bd.getPropertyValues().contains(propertyName)) {                error("Multiple 'property' definitions for property '" + propertyName + "'", ele);                return;            }            // 解析属性值            Object val = parsePropertyValue(ele, bd, propertyName);            // 根据解析的属性值构造 PropertyValue 实例对象            PropertyValue pv = new PropertyValue(propertyName, val);            parseMetaElements(ele, pv);            pv.setSource(extractSource(ele));            // 添加到 MutablePropertyValues 中            bd.getPropertyValues().addPropertyValue(pv);        }        finally {            this.parseState.pop();        }    }