文章目录
spring中bean的创建流程
finishBeanFactoryInitialization(beanFactory)
在refresh方法中知道此方法就是初始化剩下的单实例
// Instantiate all remaining (non-lazy-init) singletons.
// 初始化剩下的单实例（非懒加载的）
finishBeanFactoryInitialization(beanFactory);
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
// Initialize conversion service for this context.
// 为上下文初始化类型转换器
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
}
// Register a default embedded value resolver if no bean post-processor
// (such as a PropertyPlaceholderConfigurer bean) registered any before:
// at this point, primarily for resolution in annotation attribute values.
// 如果beanFactory之前没有注册嵌入值解析器，则注册默认的嵌入值解析器，主要用于注解属性值的解析
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
}
// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
// 尽早初始化loadTimeWeaverAware bean,以便尽早注册它们的转换器
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
}
// Stop using the temporary ClassLoader for type matching.
// 禁止使用临时类加载器进行类型匹配
beanFactory.setTempClassLoader(null);
// Allow for caching all bean definition metadata, not expecting further changes.
// 冻结所有的bean定义，说明注册的bean定义将不被修改或任何进一步的处理
beanFactory.freezeConfiguration();
// Instantiate all remaining (non-lazy-init) singletons.
// 实例化剩下的单例对象
beanFactory.preInstantiateSingletons();
}
首先是初始化类型转换器，此转换器在spring mvc中较多，后续具体再看，这里的主要逻辑是获取名为conversionService类型为ConversionService.class的bean,使用此bean对对象做一个转换服务。
可以自定义实现这样的转换
public class Student {
private Integer id;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
}
import org.springframework.core.convert.converter.Converter;
public class StudentConverter implements Converter<String,Student> {
@Override
public Student convert(String source) {
System.out.println("-----");
Student s = new Student();
String[] splits = source.split("_");
s.setId(Integer.parseInt(splits[0]));
s.setName(splits[1]);
return s;
}
}
beanFactory.preInstantiateSingletons();
此方法是实例化剩下的单例对象
public void preInstantiateSingletons() throws BeansException {
if (logger.isTraceEnabled()) {
logger.trace("Pre-instantiating singletons in " + this);
}
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
// 将所有BeanDefinition的名字创建一个集合
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
// Trigger initialization of all non-lazy singleton beans...
// 触发所有非延迟加载单例bean的初始化，遍历集合的对象
for (String beanName : beanNames) {
// 合并父类BeanDefinition
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
// 条件判断，抽象，单例，非懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
// 判断是否实现了FactoryBean接口
if (isFactoryBean(beanName)) {
// 根据&+beanName来获取具体的对象
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
// 进行类型转换
if (bean instanceof FactoryBean) {
FactoryBean<?> factory = (FactoryBean<?>) bean;
// 判断这个FactoryBean是否希望立即初始化
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
// 如果希望急切的初始化，则通过beanName获取bean实例
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
// 如果beanName对应的bean不是FactoryBean，只是普通的bean，通过beanName获取bean实例
getBean(beanName);
}
}
}
// Trigger post-initialization callback for all applicable beans...
// 遍历beanNames，触发所有SmartInitializingSingleton的后初始化回调
for (String beanName : beanNames) {
// 获取beanName对应的bean实例
Object singletonInstance = getSingleton(beanName);
// 判断singletonInstance是否实现了SmartInitializingSingleton接口
if (singletonInstance instanceof SmartInitializingSingleton) {
// 类型转换
SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
// 触发SmartInitializingSingleton实现类的afterSingletonsInstantiated方法
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
}
else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}
getMergedLocalBeanDefinition(beanName);流程
此方法是合并父类BeanDefinition，这里面使用了递归处理
流程如下
实现FactoryBean接口,里面的对象实例化过程
if (isFactoryBean(beanName)) {
// 根据&+beanName来获取具体的对象
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
// 进行类型转换
if (bean instanceof FactoryBean) {
FactoryBean<?> factory = (FactoryBean<?>) bean;
// 判断这个FactoryBean是否希望立即初始化
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction<Boolean>) ((SmartFactoryBean<?>) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
// 如果希望急切的初始化，则通过beanName获取bean实例
if (isEagerInit) {
getBean(beanName);
}
}
}
何为FactoryBean？他与BeanFactory有什么区别
先看FactoryBean的类的结构，此接口里面仅有getObject()、getObjectType()、isSingleton()这三个方法，使用这个类将实例注入到bean工厂中，不需要严格遵循BeanFactory里面bean的构建流程（初始化、实例化、aware接口、前置处理、后置处理），可以在FactoryBean中直接调用getObject()直接生成bean对象，并放入到factoryBeanObjectCache集合中，此集合是个Map。没有放到三级缓存中。后续如果需要则从factoryBeanObjectCache这个集合中获取。
特别：非单例情况下，实例始终不会往factoryBeanObjectCache中放，即非单例不会有缓存
如何实现FactoryBean
public class MyFactoryBean implements FactoryBean<User> {
@Override
public User getObject() throws Exception {
return new User("zhangsan");
}
@Override
public Class<?> getObjectType() {
return User.class;
}
@Override
public boolean isSingleton() {
return false;
}
}
public class User {
private String username;
public User() {
}
public User(String username) {
this.username = username;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
@Override
public String toString() {
return "User{" +
"username='" + username + '\'' +
'}';
}
}
当上面的逻辑处理完成时（这里粗略的看就是refresh方法完成），这时FactoryBean中已经有实现了FactoryBean的bean了，但是里面的对现象还没有放入到缓存中，如果这个类实现了SmartFactoryBean这个接口，并重写了isEagerInit方法，将其返回为true。那么在实例化FactoryBean这个对象的时候，里面的对象也会实例化并放入到factoryBeanObjectCache缓存中（非单例情况下，实例始终不会往factoryBeanObjectCache中放，即非单例不会有缓存）。这里没有实现SmartFactoryBean，只是实现了FactoryBean，所以没有直接实例化，而是在调用的时候进行的实例化。
实现流程
