1 通过 ClassLoader 进行加载
将 beanName 对应 RootBeanDefinition 通过 ClassLoader 方式解析成 Class<?>。
2 Class 加载阶段（源码分析）
Class 加载阶段方法入口：AbstractBeanFactory#resolveBeanClass
...
/**
* Resolve the bean class for the specified bean definition,
* resolving a bean class name into a Class reference (if necessary)
* and storing the resolved Class in the bean definition for further use.
* @param mbd the merged bean definition to determine the class for
* @param beanName the name of the bean (for error handling purposes)
* @param typesToMatch the types to match in case of internal type matching purposes
* (also signals that the returned {@code Class} will never be exposed to application code)
* @return the resolved bean class (or {@code null} if none)
* @throws CannotLoadBeanClassException if we failed to load the class
*/
@Nullable
protected Class<?> resolveBeanClass(final RootBeanDefinition mbd, String beanName, final Class<?>... typesToMatch)
throws CannotLoadBeanClassException {
try {
if (mbd.hasBeanClass()) {
return mbd.getBeanClass();
}
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged((PrivilegedExceptionAction<Class<?>>) () ->
doResolveBeanClass(mbd, typesToMatch), getAccessControlContext());
}
else {
return doResolveBeanClass(mbd, typesToMatch);
}
}
catch (PrivilegedActionException pae) {
ClassNotFoundException ex = (ClassNotFoundException) pae.getException();
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (ClassNotFoundException ex) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (LinkageError err) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), err);
}
}
...
3 总结
通过获取当前的 ClassLoader ，通过 Class<?> resolvedClass = ClassUtils.forName(className, classLoader); 方式获取到 Class，从而为后续的实例化对象提供依据。
