開篇
- 通過前一篇文章3.spring初級容器XmlBeanFactory初始化(二)，我們已經(jīng)知道了spring是如何解析xml標(biāo)簽，如:meta,lookup-method等，解析完成之后，將會(huì)把解析好的標(biāo)簽信息封裝到BeanDefinition中.
- 現(xiàn)在我們來看下，BeanDefinition是如何注冊到spring容器中的
BeanDefinition是從哪里開始注冊到spring容器中的
在前兩篇的文章中，我們重點(diǎn)看了spring如何解析bean標(biāo)簽和屬性的，在解析完bean標(biāo)簽和屬性之后，將解析的結(jié)果放到BeanDefinition中，最后返回一個(gè)GenericBeanDefinition類型的BeanDefinition
/**
* Parse the bean definition itself, without regard to name or aliases. May return
* {@code null} if problems occurred during the parsing of the bean definition.
*/
@Nullable
public AbstractBeanDefinition parseBeanDefinitionElement(
Element ele, String beanName, @Nullable BeanDefinition containingBean) {
this.parseState.push(new BeanEntry(beanName));
String className = null;
//1.如果標(biāo)簽中存在class屬性，那么就獲取class屬性值
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
//2.如果標(biāo)簽中存在parent標(biāo)簽，那么就獲取parent標(biāo)簽的屬性值
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
//3.通過屬性class和parent，初步創(chuàng)建AbstractBeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//4.解析bean標(biāo)簽中的各種屬性，并封裝到AbstractBeanDefinition中
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 5.解析標(biāo)簽中各種子標(biāo)簽元素，并將解析結(jié)果封裝到AbstractBeanDefinition中
// 解析bean標(biāo)簽中的meta
parseMetaElements(ele, bd);
// 解析bean標(biāo)簽中的lookup-method子標(biāo)簽元素
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析bean標(biāo)簽中replace-method子標(biāo)簽元素
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 解析bean的子標(biāo)簽constructor-arg
parseConstructorArgElements(ele, bd);
//解析bean的子標(biāo)簽property
parsePropertyElements(ele, bd);
//解析bean的子標(biāo)簽qualifier
parseQualifierElements(ele, bd);
bd.setResource(this.readerContext.getResource());
bd.setSource(extractSource(ele));
//6.返回bd
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;
}
返回之后，我們繼續(xù)看調(diào)用parseBeanDefinitionElement方法的地方
/**
* Parses the supplied {@code <bean>} element. May return {@code null}
* if there were errors during parse. Errors are reported to the
* {@link org.springframework.beans.factory.parsing.ProblemReporter}.
*/
@Nullable
public BeanDefinitionHolder parseBeanDefinitionElement(Element ele, @Nullable BeanDefinition containingBean) {
//1.解析bean標(biāo)簽中的id和name屬性
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//2.將屬性name通過","或";"分隔符進(jìn)行分割，并將數(shù)據(jù)添加到aliases中
List<String> aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
// 3.如果屬性id為空，那么就取aliases集合中的第一個(gè)value的值，作為bean的名稱
String beanName = id;
if (!StringUtils.hasText(beanName) && !aliases.isEmpty()) {
beanName = aliases.remove(0);
if (logger.isTraceEnabled()) {
logger.trace("No XML 'id' specified - using '" + beanName +
"' as bean name and " + aliases + " as aliases");
}
}
if (containingBean == null) {
checkNameUniqueness(beanName, aliases, ele);
}
// 4. 開始解析bean標(biāo)簽，并將解析結(jié)果封裝為AbstractBeanDefinition
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
// beanName不為空，直接跳過
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.isTraceEnabled()) {
logger.trace("Neither XML 'id' nor 'name' specified - " +
"using generated bean name [" + beanName + "]");
}
}
catch (Exception ex) {
error(ex.getMessage(), ele);
return null;
}
}
// 5. 將解析的beanDefinition,beanName和aliase，創(chuàng)建一個(gè)BeanDefinitionHolder
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
這里會(huì)將解析好的bean標(biāo)簽的BeanDefinition連同aliasesArray一起封裝成BeanDefinitionHolder，BeanDefinitionHolder也可以理解成BeanDefinition的一個(gè)對象。
- 當(dāng)我們繼續(xù)向上去找調(diào)用源頭的時(shí)候，就會(huì)發(fā)現(xiàn)了，這里在解析完bean的屬性和標(biāo)簽之后，將解析的屬性和標(biāo)簽以BeanDefinitionHolder類型返回，其實(shí)就是一個(gè)BeanDefinition對象
- 然后執(zhí)行delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);，這里可以忽略，因?yàn)辄c(diǎn)進(jìn)去看下，基本上就是一些自定義標(biāo)簽的校驗(yàn)
- 接著執(zhí)行的就是我們的核心，把bean注如到spring容器當(dāng)中BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
/**
* Process the given bean element, parsing the bean definition
* and registering it with the registry.
*/
protected void processBeanDefinition(Element ele, BeanDefinitionParserDelegate delegate) {
// 1.解析bean標(biāo)簽元素
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
// 將解析到的bean注冊到spring容器當(dāng)中
BeanDefinitionReaderUtils.registerBeanDefinition(bdHolder, getReaderContext().getRegistry());
}
catch (BeanDefinitionStoreException ex) {
getReaderContext().error("Failed to register bean definition with name '" +
bdHolder.getBeanName() + "'", ele, ex);
}
// Send registration event.
getReaderContext().fireComponentRegistered(new BeanComponentDefinition(bdHolder));
}
}
接下來，我們來看下，bean是如何注入到spring容器中的
/**
* Register the given bean definition with the given bean factory.
* @param definitionHolder the bean definition including name and aliases
* @param registry the bean factory to register with
* @throws BeanDefinitionStoreException if registration failed
*/
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
// Register bean definition under primary name.
//首先，拿到bean的名稱
String beanName = definitionHolder.getBeanName();
//注冊BeanDefinition到spring容器中
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
//如果bean有別名，那么就注冊bean的別名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
繼續(xù)看下registerBeanDefinition
@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");
//如果beanDefinition是AbstractBeanDefinition的實(shí)例
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
//校驗(yàn)beanDefinition中的methodOverrides屬性
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
//判斷beanDefinitionMap中是否已經(jīng)存在beanName對應(yīng)的BeanDefinition，這里的beanDefinitionMap
//就是spring容器
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
//如果配置BeanDefinition不能被覆蓋，那么就直接報(bào)錯(cuò)
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionOverrideException(beanName, beanDefinition, existingDefinition);
}
else if (existingDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (logger.isInfoEnabled()) {
logger.info("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.isDebugEnabled()) {
logger.debug("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + existingDefinition +
"] with [" + beanDefinition + "]");
}
}
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
if (hasBeanCreationStarted()) {
// Cannot modify startup-time collection elements anymore (for stable iteration)
synchronized (this.beanDefinitionMap) {
this.beanDefinitionMap.put(beanName, beanDefinition);
List<String> updatedDefinitions = new ArrayList<>(this.beanDefinitionNames.size() + 1);
updatedDefinitions.addAll(this.beanDefinitionNames);
updatedDefinitions.add(beanName);
this.beanDefinitionNames = updatedDefinitions;
removeManualSingletonName(beanName);
}
}
else {
// Still in startup registration phase
//直接將beanDefinition放入到beanDefinitionMap
this.beanDefinitionMap.put(beanName, beanDefinition);
//記錄beanName
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
//如果當(dāng)前需要注冊的bean的beanName，已經(jīng)在spring容器中存在beanDefinition
//或者已經(jīng)根據(jù)beanName創(chuàng)建出來對應(yīng)的bean的單例bean對象了
if (existingDefinition != null || containsSingleton(beanName)) {
//重新調(diào)整beanName對應(yīng)的緩存
resetBeanDefinition(beanName);
}
else if (isConfigurationFrozen()) {
clearByTypeCache();
}
}
1.首先要校驗(yàn)beanDefinition中的methodOverrides屬性，在方法validate中不允許methodOverrides屬性和factoryMethodName屬性同時(shí)設(shè)置
1.1 在解析lookup-method標(biāo)簽和replaced-method標(biāo)簽時(shí)，會(huì)將這兩個(gè)標(biāo)簽需要覆蓋的方法名設(shè)置到MethodOverrides中
1.2 一旦MethodOverrides不為空，這就意味著Spring創(chuàng)建出來bean還要重新覆寫這些方法
1.3 而factoryMethodName屬性也就是工廠方法的名稱，通過工廠方法也可以創(chuàng)建一個(gè)bean出來，但是這相比于Spring默認(rèn)的創(chuàng)建方式而言，算是一種不允許外界覆蓋bean中方法的創(chuàng)建方式了
1.4 也就是說要么我們通過工廠方法創(chuàng)建bean，要么就按Spring普通的方式來創(chuàng)建bean，兩者選其一
- 接下來，可以看到，spring容器就是一個(gè)Map,key為beanName，value為BeanDefinition,beanDefinitionMap是成員變量，難免會(huì)有并發(fā)安全問題，所以這里使用多線程安全的ConcurrentHashMap作為Spring的容器
看完beanDefinition是如何注冊到spring的容器之后，會(huì)繼續(xù)判斷是否有別名，如果有別名的話，就注冊別名
檢查bean是否有別名
@Override
public void registerAlias(String name, String alias) {
Assert.hasText(name, "'name' must not be empty");
Assert.hasText(alias, "'alias' must not be empty");
synchronized (this.aliasMap) {
//如果別名alias和bean的名稱相同
if (alias.equals(name)) {
//就不記錄該別名，并且從別名map中刪除
this.aliasMap.remove(alias);
if (logger.isDebugEnabled()) {
logger.debug("Alias definition '" + alias + "' ignored since it points to same name");
}
}
else {
String registeredName = this.aliasMap.get(alias);
if (registeredName != null) {
//如果最新的別名，和從別名map中獲取的相同，那么就直接空操作，避免重復(fù)操作
if (registeredName.equals(name)) {
// An existing alias - no need to re-register
return;
}
//如果不允許表名覆蓋，就報(bào)錯(cuò)
if (!allowAliasOverriding()) {
throw new IllegalStateException("Cannot define alias '" + alias + "' for name '" +
name + "': It is already registered for name '" + registeredName + "'.");
}
if (logger.isDebugEnabled()) {
logger.debug("Overriding alias '" + alias + "' definition for registered name '" +
registeredName + "' with new target name '" + name + "'");
}
}
//檢查別名是否存在循環(huán)
checkForAliasCircle(name, alias);
this.aliasMap.put(alias, name);
if (logger.isTraceEnabled()) {
logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");
}
}
}
}
總結(jié)
spring初級容器初始化
