BeanDefinitionParserDelegate从字面意思上来看就是一个委托类，用来辅助解析bean的，这也确实是他的作用:
下面我们就看一下这个类里面到底有什么东西
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";
一开始就声明了各种常量字符串，都是在Spring的配置文件中常见的属性值。
private final DocumentDefaultsDefinition defaults = new DocumentDefaultsDefinition();
接着，又是一个类，里面存了一个bean必须有的属性，没有就采用默认值。
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));
}
填充各种默认的属性。
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//获取当前节点的id和name属性
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//获取别名列表
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为空，且存在别名，那么把第一个别名当作beanName，并将他从别名列表中移除
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标签并封装成对象
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
//如果beanName为空，那么么就根据指定的规则来创建一个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);
//返回一个封装了beanDefinition、beanName、aliasesArray的对象
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
这个方法主要是处理了beanName和别名，具体解析属性在下面这个方法里面
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
//解析class属性
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
//解析parent属性
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
//设置描述符
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
//解析其他属性
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;
}
这个方法就是对各种属性的解析
public AbstractBeanDefinition parseBeanDefinitionAttributes(Element ele, String beanName,
@Nullable BeanDefinition containingBean, AbstractBeanDefinition bd)
这个方法用来解析默认的属性
其余的方法都是对不同的标签提供的不同的方法，就不细加注释了。
BeanDefinitionParserDelegate类提供了解析spring配置文件功能,对于默认空间下的元素()在该类内部实现,对于其它命名空间下的元素可以通过绑定NamespaceHandler的方式来实现,针对每个命名空间下的元素提供不同BeanDefinitionParser来实现.