开篇
- 通过前一篇文章3.spring初级容器XmlBeanFactory初始化(二)，我们已经知道了spring是如何解析xml标签，如:meta,lookup-method等，解析完成之后，将会把解析好的标签信息封装到BeanDefinition中.
- 现在我们来看下，BeanDefinition是如何注册到spring容器中的
BeanDefinition是从哪里开始注册到spring容器中的
在前两篇的文章中，我们重点看了spring如何解析bean标签和属性的，在解析完bean标签和属性之后，将解析的结果放到BeanDefinition中，最后返回一个GenericBeanDefinition类型的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.如果标签中存在class属性，那么就获取class属性值
if (ele.hasAttribute(CLASS_ATTRIBUTE)) {
className = ele.getAttribute(CLASS_ATTRIBUTE).trim();
}
String parent = null;
//2.如果标签中存在parent标签，那么就获取parent标签的属性值
if (ele.hasAttribute(PARENT_ATTRIBUTE)) {
parent = ele.getAttribute(PARENT_ATTRIBUTE);
}
try {
//3.通过属性class和parent，初步创建AbstractBeanDefinition
AbstractBeanDefinition bd = createBeanDefinition(className, parent);
//4.解析bean标签中的各种属性，并封装到AbstractBeanDefinition中
parseBeanDefinitionAttributes(ele, beanName, containingBean, bd);
bd.setDescription(DomUtils.getChildElementValueByTagName(ele, DESCRIPTION_ELEMENT));
// 5.解析标签中各种子标签元素，并将解析结果封装到AbstractBeanDefinition中
// 解析bean标签中的meta
parseMetaElements(ele, bd);
// 解析bean标签中的lookup-method子标签元素
parseLookupOverrideSubElements(ele, bd.getMethodOverrides());
// 解析bean标签中replace-method子标签元素
parseReplacedMethodSubElements(ele, bd.getMethodOverrides());
// 解析bean的子标签constructor-arg
parseConstructorArgElements(ele, bd);
//解析bean的子标签property
parsePropertyElements(ele, bd);
//解析bean的子标签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，我们继续看调用parseBeanDefinitionElement方法的地方
/**
* Parses the supplied {@code } 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标签中的id和name属性
String id = ele.getAttribute(ID_ATTRIBUTE);
String nameAttr = ele.getAttribute(NAME_ATTRIBUTE);
//2.将属性name通过","或";"分隔符进行分割，并将数据添加到aliases中
List aliases = new ArrayList<>();
if (StringUtils.hasLength(nameAttr)) {
String[] nameArr = StringUtils.tokenizeToStringArray(nameAttr, MULTI_VALUE_ATTRIBUTE_DELIMITERS);
aliases.addAll(Arrays.asList(nameArr));
}
// 3.如果属性id为空，那么就取aliases集合中的第一个value的值，作为bean的名称
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. 开始解析bean标签，并将解析结果封装为AbstractBeanDefinition
AbstractBeanDefinition beanDefinition = parseBeanDefinitionElement(ele, beanName, containingBean);
if (beanDefinition != null) {
// beanName不为空，直接跳过
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. 将解析的beanDefinition,beanName和aliase，创建一个BeanDefinitionHolder
String[] aliasesArray = StringUtils.toStringArray(aliases);
return new BeanDefinitionHolder(beanDefinition, beanName, aliasesArray);
}
return null;
}
这里会将解析好的bean标签的BeanDefinition连同aliasesArray一起封装成BeanDefinitionHolder，BeanDefinitionHolder也可以理解成BeanDefinition的一个对象。
- 当我们继续向上去找调用源头的时候，就会发现了，这里在解析完bean的属性和标签之后，将解析的属性和标签以BeanDefinitionHolder类型返回，其实就是一个BeanDefinition对象
- 然后执行delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);，这里可以忽略，因为点进去看下，基本上就是一些自定义标签的校验
- 接着执行的就是我们的核心，把bean注如到spring容器当中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标签元素
BeanDefinitionHolder bdHolder = delegate.parseBeanDefinitionElement(ele);
if (bdHolder != null) {
bdHolder = delegate.decorateBeanDefinitionIfRequired(ele, bdHolder);
try {
// Register the final decorated instance.
// 将解析到的bean注册到spring容器当中
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));
}
}
接下来，我们来看下，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的名称
String beanName = definitionHolder.getBeanName();
//注册BeanDefinition到spring容器中
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
//如果bean有别名，那么就注册bean的别名
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
registry.registerAlias(beanName, alias);
}
}
}
继续看下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的实例
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
//校验beanDefinition中的methodOverrides属性
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
//判断beanDefinitionMap中是否已经存在beanName对应的BeanDefinition，这里的beanDefinitionMap
//就是spring容器
BeanDefinition existingDefinition = this.beanDefinitionMap.get(beanName);
if (existingDefinition != null) {
//如果配置BeanDefinition不能被覆盖，那么就直接报错
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 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
//直接将beanDefinition放入到beanDefinitionMap
this.beanDefinitionMap.put(beanName, beanDefinition);
//记录beanName
this.beanDefinitionNames.add(beanName);
removeManualSingletonName(beanName);
}
this.frozenBeanDefinitionNames = null;
}
//如果当前需要注册的bean的beanName，已经在spring容器中存在beanDefinition
//或者已经根据beanName创建出来对应的bean的单例bean对象了
if (existingDefinition != null || containsSingleton(beanName)) {
//重新调整beanName对应的缓存
resetBeanDefinition(beanName);
}
else if (isConfigurationFrozen()) {
clearByTypeCache();
}
}
1.首先要校验beanDefinition中的methodOverrides属性，在方法validate中不允许methodOverrides属性和factoryMethodName属性同时设置
1.1 在解析lookup-method标签和replaced-method标签时，会将这两个标签需要覆盖的方法名设置到MethodOverrides中
1.2 一旦MethodOverrides不为空，这就意味着Spring创建出来bean还要重新覆写这些方法
1.3 而factoryMethodName属性也就是工厂方法的名称，通过工厂方法也可以创建一个bean出来，但是这相比于Spring默认的创建方式而言，算是一种不允许外界覆盖bean中方法的创建方式了
1.4 也就是说要么我们通过工厂方法创建bean，要么就按Spring普通的方式来创建bean，两者选其一
- 接下来，可以看到，spring容器就是一个Map,key为beanName，value为BeanDefinition,beanDefinitionMap是成员变量，难免会有并发安全问题，所以这里使用多线程安全的ConcurrentHashMap作为Spring的容器
看完beanDefinition是如何注册到spring的容器之后，会继续判断是否有别名，如果有别名的话，就注册别名
检查bean是否有别名
@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) {
//如果别名alias和bean的名称相同
if (alias.equals(name)) {
//就不记录该别名，并且从别名map中删除
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) {
//如果最新的别名，和从别名map中获取的相同，那么就直接空操作，避免重复操作
if (registeredName.equals(name)) {
// An existing alias - no need to re-register
return;
}
//如果不允许表名覆盖，就报错
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 + "'");
}
}
//检查别名是否存在循环
checkForAliasCircle(name, alias);
this.aliasMap.put(alias, name);
if (logger.isTraceEnabled()) {
logger.trace("Alias definition '" + alias + "' registered for name '" + name + "'");
}
}
}
}
总结
spring初级容器初始化