在上一節XmlBeanFactory容器分析中,在parseDefaultElement
方法中是對默認的標籤進行解析的
/**
* 對四種不同的標籤進行處理
*
* @param ele
* @param delegate
*/
private void parseDefaultElement(Element ele, BeanDefinitionParserDelegate delegate) {
if (delegate.nodeNameEquals(ele, IMPORT_ELEMENT)) { // 對import標籤進行處理
importBeanDefinitionResource(ele);
}
else if (delegate.nodeNameEquals(ele, ALIAS_ELEMENT)) { // 對alias標籤進行處理
processAliasRegistration(ele);
}
else if (delegate.nodeNameEquals(ele, BEAN_ELEMENT)) { // 對bean標籤進行處理
processBeanDefinition(ele, delegate);
}
else if (delegate.nodeNameEquals(ele, NESTED_BEANS_ELEMENT)) { // 對beans標籤進行處理
doRegisterBeanDefinitions(ele);
}
}
在parseDefaultElement對四種不同的標籤進行處理
對bean標籤的解析最爲複雜也最爲重要,理解了bean標籤的解析,其他標籤解析就很輕鬆了
/**
* 調用decorateBeanDefinitionIfRequired方法解析bean標籤並調用registerBeanDefinition方法註冊bean
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele); // 對Element對象進行解析,返回BeanDefinitionHolder對象,BeanDefinitionHolder對象中已經包含了class、name、id、alias之類的屬性
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder); // 當存在默認標籤的子節點下還有自定義屬性時,再對其進行解析
try {
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry()); // 將解析後的bdHolder進行註冊
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder)); // 發出響應事件,通知相關的監聽器,這個bean已經加載完成了
}
}
下面主要看一下parseBeanDefinitionElement()
方法和registerBeanDefinition()
方法的源碼
/**
* 在BeanDefinitionParserDelegate類中
*/
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele) {
return parseBeanDefinitionElement(ele, null);
}
/**
* 解析bean元素標籤中各種屬性
*/
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
String id = ele.getAttribute(ID_ATTRIBUTE); // 解析id屬性
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE); // 解析name屬性
// 分割name屬性
List<String> 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); // bean的名稱默認是爲<bean>標籤的id,如果alias存在的話就是alias
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);
}
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean); // 解析BeanDefinition元素
if (beanDefinition != null) {
if (!StringUtils.hasText(beanName)) {
try {
if (containingBean != null) { // 如果beanName不存在,那麼按照Spring提供的命名規則爲當前bean生成對應的beanName
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 (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);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
/**
* 解析BeanDefinition元素
*/
@Nullable
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 {
// 創建用於保存bean屬性的AbstractBeanDefinition子類GenericBeanDefinition對象
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
// 硬編碼解析默認bean的各種屬性
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
// 提取description
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 解析元數據
parseMetaElements(ele, bd);
// 解析lookup-method屬性
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析replaced-method屬性
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;
}
parseBeanDefinitionElement()
方法主要是解析Bean標籤的屬性,然後封裝到BeanDefinition類中
/**
* 在BeanDefinitionReaderUtils類中
* 將bean的信息和bean的別名註冊到BeanDefinitionRegistry中
*/
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
String beanName = definitionHolder.getBeanName();
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition()); // 將bean的信息註冊到BeanDefinitionRegistry中
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias); // 將bean的別名註冊到BeanDefinitionRegistry中
}
}
}
registerBeanDefinition
主要是將封裝好的BeanDefinition對象進行註冊
/**
* 在DefaultListableBeanFactory類中
* 註冊bean到beanDefinitionMap中,beanDefinitionMap是Spring容器實際存儲bean的map集合
*/
@Override
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 ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Validation of bean definition failed", ex);
}
}
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName); // 先從beanDefinitionMap中根據beanName獲取value值
if (existingDefinition != null) { // 當beanDefinitionMap中已經存在該bean
if (!isAllowBeanDefinitionOverriding()) { // 不允許覆蓋bean時
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName, "Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName + "': There is already [" + existingDefinition + "] bound.");
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
if (logger.isWarnEnabled()) {
logger.warn("Overriding user-defined bean definition for bean '" + beanName + "' with a framework-generated bean definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(existingDefinition)) {
if (logger.isInfoEnabled()) {
logger.info("Overriding bean definition for bean '" + beanName + "' with a different definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]");
}
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName + "' with an equivalent definition: replacing [" + existingDefinition + "] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition); // 當允許覆蓋bean時覆蓋該bean
}
else { // 當beanDefinitionMap中已經不存在該bean
if (hasBeanCreationStarted()) {
synchronized (this.beanDefinitionMap) { // 保證線程安全
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
if (this.manualSingletonNames.contains(beanName)) {
Set<String> updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (existingDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
registerBeanDefinition
方法主要是具體實現將BeanDefinition註冊到beanDefinitionMap,beanDefinitionMap是BeanDefinitionRegistry中的屬性,beanDefinitionMap實現是一個ConcurrentHashMap,key爲beanName,value爲BeanDefinition對象,在Spring容器中,bean屬性都儲存在beanDefinitionMap中
總結
在默認標籤的解析過程中,有三個類或者變量很重要
- BeanDefinition
BeanDefinition是一個接口,是元素標籤在Spring容器的內部表現形式。在Spring中存在三種實現RootBeanDefinition、ChildBeanDefinition、GenericBeanDefinition,均繼承了AbstractBeanDefinition抽象類,在元素標籤中的class、scope、lazy-init等配置屬性,在BeanDefinition提供了相應了beanClass、scope、lazyInit屬性。BeanDefinition中的屬性是通過集成父類AbstractBeanDefinition中的和配置屬性保持一一對應。
private volatile Object beanClass; // 對應class屬性
private String scope = SCOPE_DEFAULT; // 對應scope屬性
private boolean lazyInit = false; // 對lazy-init屬性
......
- BeanDefinitionRegistry
Spring通過BeanDefinition將配置文件中的配置信息轉換爲容器的內部表示,並將這些BeanDefinition註冊到BeanDefinitionRegistry中,Spring容器的BeanDefinitionRegistry就像是Spring配置信息的內存數據庫,主要以map的形式保存,從Spring容器中獲取bean也是從BeanDefinitionRegistry中獲取bean的信息的,對外提供對BeanDefinition的增刪改查操作
XmlBeanFactory繼承了實現了BeanDefinitionRegistry接口的父類DefaultListableBeanFactory,在接口中定義了對BeanDefinition的增刪改查操作
void registerBeanDefinition(String beanName, BeanDefinition beanDefinition) throws BeanDefinitionStoreException; // 註冊BeanDefinition
void removeBeanDefinition(String beanName) throws NoSuchBeanDefinitionException; // 移除BeanDefinition
BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException; // 獲取BeanDefinition
boolean containsBeanDefinition(String beanName); // 判斷是否包含BeanDefinition
String[] getBeanDefinitionNames(); // 獲取beanName
int getBeanDefinitionCount(); // 獲取BeanDefinition總數
- beanDefinitionMap
beanDefinitionMap是BeanDefinitionRegistry中的屬性,beanDefinitionMap實現是一個ConcurrentHashMap,key爲beanName,value爲BeanDefinition對象,bean屬性都儲存在beanDefinitionMap中
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap<>(256);