Spring之BeanDefinitionParserDelegate原始碼解讀
阿新 • • 發佈：2018-12-11
BeanDefinitionParserDelegate從字面意思上來看就是一個委託類，用來輔助解析bean的，這也確實是他的作用:
public static final String TRUE_VALUE = "true"; public static final String FALSE_VALUE = "false"; public static final String DEFAULT_VALUE = "default"; public static final String DESCRIPTION_ELEMENT = "description"; public static final String AUTOWIRE_NO_VALUE = "no"; public static final String AUTOWIRE_BY_NAME_VALUE = "byName"; public static final String AUTOWIRE_BY_TYPE_VALUE = "byType"; public static final String AUTOWIRE_CONSTRUCTOR_VALUE = "constructor"; public static final String AUTOWIRE_AUTODETECT_VALUE = "autodetect"; public static final String NAME_ATTRIBUTE = "name"; public static final String BEAN_ELEMENT = "bean"; public static final String META_ELEMENT = "meta"; public static final String ID_ATTRIBUTE = "id"; public static final String PARENT_ATTRIBUTE = "parent"; public static final String CLASS_ATTRIBUTE = "class"; public static final String ABSTRACT_ATTRIBUTE = "abstract"; public static final String SCOPE_ATTRIBUTE = "scope"; private static final String SINGLETON_ATTRIBUTE = "singleton"; public static final String LAZY_INIT_ATTRIBUTE = "lazy-init"; public static final String AUTOWIRE_ATTRIBUTE = "autowire"; public static final String AUTOWIRE_CANDIDATE_ATTRIBUTE = "autowire-candidate"; public static final String PRIMARY_ATTRIBUTE = "primary"; public static final String DEPENDS_ON_ATTRIBUTE = "depends-on"; public static final String INIT_METHOD_ATTRIBUTE = "init-method"; public static final String DESTROY_METHOD_ATTRIBUTE = "destroy-method"; public static final String FACTORY_METHOD_ATTRIBUTE = "factory-method"; public static final String FACTORY_BEAN_ATTRIBUTE = "factory-bean"; public static final String CONSTRUCTOR_ARG_ELEMENT = "constructor-arg"; public static final String INDEX_ATTRIBUTE = "index"; public static final String TYPE_ATTRIBUTE = "type"; public static final String VALUE_TYPE_ATTRIBUTE = "value-type"; public static final String KEY_TYPE_ATTRIBUTE = "key-type"; public static final String PROPERTY_ELEMENT = "property"; public static final String REF_ATTRIBUTE = "ref"; public static final String VALUE_ATTRIBUTE = "value"; public static final String LOOKUP_METHOD_ELEMENT = "lookup-method"; public static final String REPLACED_METHOD_ELEMENT = "replaced-method"; public static final String REPLACER_ATTRIBUTE = "replacer"; public static final String ARG_TYPE_ELEMENT = "arg-type"; public static final String ARG_TYPE_MATCH_ATTRIBUTE = "match"; public static final String REF_ELEMENT = "ref"; public static final String IDREF_ELEMENT = "idref"; public static final String BEAN_REF_ATTRIBUTE = "bean"; public static final String PARENT_REF_ATTRIBUTE = "parent"; public static final String VALUE_ELEMENT = "value"; public static final String NULL_ELEMENT = "null"; public static final String ARRAY_ELEMENT = "array"; public static final String LIST_ELEMENT = "list"; public static final String SET_ELEMENT = "set"; public static final String MAP_ELEMENT = "map"; public static final String ENTRY_ELEMENT = "entry"; public static final String KEY_ELEMENT = "key"; public static final String KEY_ATTRIBUTE = "key"; public static final String KEY_REF_ATTRIBUTE = "key-ref"; public static final String VALUE_REF_ATTRIBUTE = "value-ref"; public static final String PROPS_ELEMENT = "props"; public static final String PROP_ELEMENT = "prop"; public static final String MERGE_ATTRIBUTE = "merge"; public static final String QUALIFIER_ELEMENT = "qualifier"; public static final String QUALIFIER_ATTRIBUTE_ELEMENT = "attribute"; public static final String DEFAULT_LAZY_INIT_ATTRIBUTE = "default-lazy-init"; public static final String DEFAULT_MERGE_ATTRIBUTE = "default-merge"; public static final String DEFAULT_AUTOWIRE_ATTRIBUTE = "default-autowire"; public static final String DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE = "default-autowire-candidates"; public static final String DEFAULT_INIT_METHOD_ATTRIBUTE = "default-init-method"; public static final String DEFAULT_DESTROY_METHOD_ATTRIBUTE = "default-destroy-method";
一開始就聲明瞭各種常量字串，都是在Spring的配置檔案中常見的屬性值。
private final DocumentDefaultsDefinition defaults = new DocumentDefaultsDefinition();
接著，又是一個類，裡面存了一個bean必須有的屬性，沒有就採用預設值。
protected void populateDefaults(DocumentDefaultsDefinition defaults, @Nullable DocumentDefaultsDefinition parentDefaults, Element root) { String lazyInit = root.getAttribute(DEFAULT_LAZY_INIT_ATTRIBUTE); if (DEFAULT_VALUE.equals(lazyInit)) { // Potentially inherited from outer <beans> sections, otherwise falling back to false. lazyInit = (parentDefaults != null ? parentDefaults.getLazyInit() : FALSE_VALUE); } defaults.setLazyInit(lazyInit); String merge = root.getAttribute(DEFAULT_MERGE_ATTRIBUTE); if (DEFAULT_VALUE.equals(merge)) { // Potentially inherited from outer <beans> sections, otherwise falling back to false. merge = (parentDefaults != null ? parentDefaults.getMerge() : FALSE_VALUE); } defaults.setMerge(merge); String autowire = root.getAttribute(DEFAULT_AUTOWIRE_ATTRIBUTE); if (DEFAULT_VALUE.equals(autowire)) { // Potentially inherited from outer <beans> sections, otherwise falling back to 'no'. autowire = (parentDefaults != null ? parentDefaults.getAutowire() : AUTOWIRE_NO_VALUE); } defaults.setAutowire(autowire); if (root.hasAttribute(DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE)) { defaults.setAutowireCandidates(root.getAttribute(DEFAULT_AUTOWIRE_CANDIDATES_ATTRIBUTE)); } else if (parentDefaults != null) { defaults.setAutowireCandidates(parentDefaults.getAutowireCandidates()); } if (root.hasAttribute(DEFAULT_INIT_METHOD_ATTRIBUTE)) { defaults.setInitMethod(root.getAttribute(DEFAULT_INIT_METHOD_ATTRIBUTE)); } else if (parentDefaults != null) { defaults.setInitMethod(parentDefaults.getInitMethod()); } if (root.hasAttribute(DEFAULT_DESTROY_METHOD_ATTRIBUTE)) { defaults.setDestroyMethod(root.getAttribute(DEFAULT_DESTROY_METHOD_ATTRIBUTE)); } else if (parentDefaults != null) { defaults.setDestroyMethod(parentDefaults.getDestroyMethod()); } defaults.setSource(this.readerContext.extractSource(root)); }
填充各種預設的屬性。
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) { //獲取當前節點的id和name屬性 String id = ele.getAttribute(ID_ATTRIBUTE); String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); //獲取別名列表 List<String> aliases = new ArrayList<>(); if (StringUtils.hasLength(nameAttr)) { String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS); aliases.addAll(Arrays.asList(nameArr)); } //如果id為空，且存在別名，那麼把第一個別名當作beanName，並將他從別名列表中移除 String beanName = id; if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) { beanName = aliases.remove(0); if (logger.isDebugEnabled()) { logger.debug("No XML 'id' specified - using '" + beanName + "' as bean name and " + aliases + " as aliases"); } } if (containingBean == null) { checkNameUniqueness(beanName, aliases, ele); } //解析bean標籤並封裝成物件 AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); if (beanDefinition != null) { //如果beanName為空，那麼麼就根據指定的規則來建立一個beanName if (!StringUtils.hasText(beanName)) { try { if (containingBean != null) { beanName = BeanDefinitionReaderUtils.generateBeanName( beanDefinition, this.readerContext.getRegistry(), true); } else { beanName = this.readerContext.generateBeanName(beanDefinition); // Register an alias for the plain bean class name, if still possible, // if the generator returned the class name plus a suffix. // This is expected for Spring 1.2/2.0 backwards compatibility. String beanClassName = beanDefinition.getBeanClassName(); if (beanClassName != null && beanName.startsWith(beanClassName) && beanName.length() > beanClassName.length() && !this.readerContext.getRegistry().isBeanNameInUse(beanClassName)) { aliases.add(beanClassName); } } if (logger.isDebugEnabled()) { logger.debug("Neither XML 'id' nor 'name' specified - " + "using generated bean name [" + beanName + "]"); } } catch (Exception ex) { error(ex.getMessage(), ele); return null; } } String[] aliasesArray = StringUtils.toStringArray(aliases); //返回一個封裝了beanDefinition、beanName、aliasesArray的物件 return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray); } return null; }
這個方法主要是處理了beanName和別名，具體解析屬性在下面這個方法裡面
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
//解析class屬性
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
//解析parent屬性
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//設定描述符
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//解析其他屬性
parseMetaElements(ele, bd);
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
parseConstructorArgElements(ele, bd);
parsePropertyElements(ele, bd);
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
return bd;
}
catch (ClassNotFoundException ex) {
error("Bean class [" + className + "] not found", ele, ex);
}
catch (NoClassDefFoundError err) {
error("Class that bean class [" + className + "] depends on not found", ele, err);
}
catch (Throwable ex) {
error("Unexpected failure during bean definition parsing", ele, ex);
}
finally {
this.parseState.pop();
}
return null;
}
這個方法就是對各種屬性的解析
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
@Nullable BeanDefinition containingBean, AbstractBeanDefinition bd)
這個方法用來解析預設的屬性 其餘的方法都是對不同的標籤提供的不同的方法，就不細加註釋了。 BeanDefinitionParserDelegate類提供瞭解析spring配置檔案功能,對於預設空間下的元素()在該類內部實現,對於其它名稱空間下的元素可以通過繫結NamespaceHandler的方式來實現,針對每個名稱空間下的元素提供不同BeanDefinitionParser來實現.