以AnnotationConfigApplicationContext来学习ioc容器的初始化过程
AnnotationConfigApplicationContext的构造函数
public AnnotationConfigApplicationContext(Class... annotatedClasses) {
this();
register(annotatedClasses);
refresh();
}
this()函数调用默认构造函数
public AnnotationConfigApplicationContext() {
// 给容器添加注解型bean配置信息的阅读器
this.reader = new AnnotatedBeanDefinitionReader(this);
// 添加类路径下的bean配置类的扫描器
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
- register()方法
public void register(Class... annotatedClasses) {
Assert.notEmpty(annotatedClasses, "At least one annotated class must be specified");
//调用AnnotatedBeanDefinitionReader的register方法
this.reader.register(annotatedClasses);
}
- 进入到AnnotatedBeanDefinitionReader的register方法里面
public void register(Class... annotatedClasses) {
for (Class annotatedClass : annotatedClasses) {
// 该循环就是先将配置的config类信息优先加载进去
registerBean(annotatedClass);
}
}
例如：
public static void main(String [] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(MainConfig.class, SecondConfig.class);
Person person = (Person) context.getBean(Person.class);
Cat cat = (Cat) context.getBean(Cat.class);
log.info(person.toString());
log.info(cat.toString());
}
当显式创建一个容器，传递容器的配置类则会优先将MainConfig.class和SecondConfig.class这两个类的BeanDefinition优先加载到容器的一个Map里
registerBean方法真实调用doRegisterBean方法()
void doRegisterBean(Class annotatedClass, @Nullable Supplier instanceSupplier, @Nullable String name,
@Nullable Class[] qualifiers, BeanDefinitionCustomizer... definitionCustomizers) {
// 将配置类包装成AnnotatedGenericBeanDefinition的类型
AnnotatedGenericBeanDefinition abd = new AnnotatedGenericBeanDefinition(annotatedClass);
// 是否跳过， @Condition注解（解析改注解类是否需要被注册在容器里）
if (this.conditionEvaluator.shouldSkip(abd.getMetadata())) {
return;
}
abd.setInstanceSupplier(instanceSupplier);
// 解析bean的范围，如request_session、singleton等
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(abd);
abd.setScope(scopeMetadata.getScopeName());
// 决定系统内的BeanName ，如在@Bean注解上用@value或@name等注解，则beanName就是该值,否则返回方法名作为beanName
String beanName = (name != null ? name : this.beanNameGenerator.generateBeanName(abd, this.registry));
// 处理bean的通用注解信息，比如bean是否是懒加载，是否被@Primary标注，dependsOn是什么，解析出来
AnnotationConfigUtils.processCommonDefinitionAnnotations(abd);
if (qualifiers != null) {
for (Class qualifier : qualifiers) {
if (Primary.class == qualifier) {
abd.setPrimary(true);
}
else if (Lazy.class == qualifier) {
abd.setLazyInit(true);
}
else {
abd.addQualifier(new AutowireCandidateQualifier(qualifier));
}
}
}
// 定制beanDefinition的属性，比如是否改为lazy-init 是否为primary等
for (BeanDefinitionCustomizer customizer : definitionCustomizers) {
customizer.customize(abd);
}
// 装在BeanDefinition的类
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(abd, beanName);
definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
// 真正去注册beanDefinition的地方
BeanDefinitionReaderUtils.registerBeanDefinition(definitionHolder, this.registry);
}
进入registerBeanDefinition（）方法里
public static void registerBeanDefinition(
BeanDefinitionHolder definitionHolder, BeanDefinitionRegistry registry)
throws BeanDefinitionStoreException {
String beanName = definitionHolder.getBeanName();
// BeanDefinitionRegistry类是一个接口，里面定义了一些通用的方法，比如registerBeanDefinition，
// removeBeanDefinition等方法，就是对一个beanDefinition的增删改查
registry.registerBeanDefinition(beanName, definitionHolder.getBeanDefinition());
// Register aliases for bean name, if any.
String[] aliases = definitionHolder.getAliases();
if (aliases != null) {
for (String alias : aliases) {
// 注册该bean的别名
registry.registerAlias(beanName, alias);
}
}
}
最后的registerBeanDefinition的最终实现是在DefaultListableBeanFactory里面实现的
@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");
// 注册前验证bean是否合法
if (beanDefinition instanceof AbstractBeanDefinition) {
try {
((AbstractBeanDefinition) beanDefinition).validate();
}
catch (BeanDefinitionValidationException ex) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Validation of bean definition failed", ex);
}
}
BeanDefinition oldBeanDefinition;
// 现在装在beanDefinition的map里面查看是否有旧的definition信息
oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!isAllowBeanDefinitionOverriding()) {
throw new BeanDefinitionStoreException(beanDefinition.getResourceDescription(), beanName,
"Cannot register bean definition [" + beanDefinition + "] for bean '" + beanName +
"': There is already [" + oldBeanDefinition + "] bound.");
}
else if (oldBeanDefinition.getRole() < beanDefinition.getRole()) {
// e.g. was ROLE_APPLICATION, now overriding with ROLE_SUPPORT or ROLE_INFRASTRUCTURE
if (this.logger.isWarnEnabled()) {
this.logger.warn("Overriding user-defined bean definition for bean '" + beanName +
"' with a framework-generated bean definition: replacing [" +
oldBeanDefinition + "] with [" + beanDefinition + "]");
}
}
else if (!beanDefinition.equals(oldBeanDefinition)) {
if (this.logger.isInfoEnabled()) {
this.logger.info("Overriding bean definition for bean '" + beanName +
"' with a different definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
else {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Overriding bean definition for bean '" + beanName +
"' with an equivalent definition: replacing [" + oldBeanDefinition +
"] with [" + beanDefinition + "]");
}
}
// 覆盖之前的BeanDefinition信息
this.beanDefinitionMap.put(beanName, beanDefinition);
}
else {
// beanDefinitionMap里面没有当前要注册的definition信息，所以开始将这个信息put进去
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;
if (this.manualSingletonNames.contains(beanName)) {
Set updatedSingletons = new LinkedHashSet<>(this.manualSingletonNames);
updatedSingletons.remove(beanName);
this.manualSingletonNames = updatedSingletons;
}
}
}
else {
// Still in startup registration phase
this.beanDefinitionMap.put(beanName, beanDefinition);
this.beanDefinitionNames.add(beanName);
this.manualSingletonNames.remove(beanName);
}
this.frozenBeanDefinitionNames = null;
}
if (oldBeanDefinition != null || containsSingleton(beanName)) {
resetBeanDefinition(beanName);
}
}
最终将beanDefinition装在容器维护的一个beanDefinitionMap里面