Spring中Bean生命周期、实例化与初始化

系统管理员 2022-10-23 11:16 121阅读 0赞

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创建Bean的入口：org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory\#doCreateBean。

# 实例化 #

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory\#createBeanInstance

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) { 
    	// Make sure bean class is actually resolved at this point.
    	Class<?> beanClass = resolveBeanClass(mbd, beanName);
    
    	if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) { 
    		throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    				"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
    	}
    
    	Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
    	if (instanceSupplier != null) { 
    		return obtainFromSupplier(instanceSupplier, beanName);
    	}
    
    	// 如果factory-method属性不为空，则使用factory-method方式实例化
    	if (mbd.getFactoryMethodName() != null) { 
    		return instantiateUsingFactoryMethod(beanName, mbd, args);
    	}
    
    	// Shortcut when re-creating the same bean...
    	boolean resolved = false;
    	boolean autowireNecessary = false;
    	if (args == null) { 
    		synchronized (mbd.constructorArgumentLock) { 
    			if (mbd.resolvedConstructorOrFactoryMethod != null) { 
    				resolved = true;
    				autowireNecessary = mbd.constructorArgumentsResolved;
    			}
    		}
    	}
    	if (resolved) { 
    		if (autowireNecessary) { 
    			return autowireConstructor(beanName, mbd, null, null);
    		}
    		else { 
    			return instantiateBean(beanName, mbd);
    		}
    	}
    
    	// Candidate constructors for autowiring?
    	// 找到构造方法
    	Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
    	if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
    			mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) { 
    		return autowireConstructor(beanName, mbd, ctors, args);
    	}
    
    	// Preferred constructors for default construction?
    	ctors = mbd.getPreferredConstructors();
    	if (ctors != null) { 
    		// 构造器注入
    		return autowireConstructor(beanName, mbd, ctors, null);
    	}
    
    	// No special handling: simply use no-arg constructor.
    	// 使用默认的构造方法实例化
    	return instantiateBean(beanName, mbd);
    }

如果BeanDefinition的factory-method属性不为空，那么使用factory-method的实例化过程。

# 设置属性 #

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory\#populateBean

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) { 
    	... ...
    	if (hasInstAwareBpps) { 
    		if (pvs == null) { 
    			pvs = mbd.getPropertyValues();
    		}
    		for (BeanPostProcessor bp : getBeanPostProcessors()) { 
    			if (bp instanceof InstantiationAwareBeanPostProcessor) { 
    				InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
    				// 调用各个BeanPostProcessor.postProcessProperties对属性进行设置
    				/** * AutowiredAnnotationBeanPostProcessor处理@Autowired * CommonAnnotationBeanPostProcessor处理@Resource * * @see AutowiredAnnotationBeanPostProcessor#postProcessProperties(org.springframework.beans.PropertyValues, java.lang.Object, java.lang.String) * @see org.springframework.context.annotation.CommonAnnotationBeanPostProcessor#postProcessProperties(org.springframework.beans.PropertyValues, java.lang.Object, java.lang.String) */
    				PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
    				
    	... ...
    }

# 初始化 #

org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory\#initializeBean

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) { 
    	if (System.getSecurityManager() != null) { 
    		AccessController.doPrivileged((PrivilegedAction<Object>) () -> { 
    			invokeAwareMethods(beanName, bean);
    			return null;
    		}, getAccessControlContext());
    	}
    	else { 
    		// 调用aware方法
    		// BeanNameAware/BeanClassLoaderAware/BeanFactoryAware对应的setXxx方法
    		invokeAwareMethods(beanName, bean);
    	}
    
    	Object wrappedBean = bean;
    	if (mbd == null || !mbd.isSynthetic()) { 
    		// 处理EnvironmentAware/EmbeddedValueResolverAware/ResourceLoaderAware/
    		// ApplicationEventPublisherAware/MessageSourceAware/ApplicationContextAware
    		// 处理@PostConstruct
    		wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
    	}
    
    	try { 
    		// InitializingBean.afterPropertiesSet()
    		// 调用init-method
    		invokeInitMethods(beanName, wrappedBean, mbd);
    	}
    	catch (Throwable ex) { 
    		throw new BeanCreationException(
    				(mbd != null ? mbd.getResourceDescription() : null),
    				beanName, "Invocation of init method failed", ex);
    	}
    	if (mbd == null || !mbd.isSynthetic()) { 
    		wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    	}
    
    	return wrappedBean;
    }

# factory-method的实例化过程 #

spring中可以使用factory-method向容器中注入实例。

## 使用另一个类的实例方法注入 ##

package com.morris.spring.entity;
    
    import lombok.AllArgsConstructor;
    import lombok.Data;
    
    @Data
    public class Boy { 
    
    	private String name;
    	
    	public Boy(String name) { 
    		this.name = name;
    	}
    }

package com.morris.spring.service;
    
    import com.morris.spring.entity.Boy;
    
    public class BoyService { 
    
    	public Boy newInstance() { 
    		return new Boy("morris");
    	}
    
    }

## 使用本类的静态方法实例化 ##

package com.morris.spring.entity;
    
    import lombok.Data;
    
    @Data
    public class Boy { 
    
    	private String name;
    
    	public Boy(String name) { 
    		this.name = name;
    	}
    
    	public static Boy newInstance() { 
    		return new Boy("bob");
    	}
    
    }

## 源码分析 ##

org.springframework.beans.factory.support.ConstructorResolver\#instantiateUsingFactoryMethod

public BeanWrapper instantiateUsingFactoryMethod(
    		String beanName, RootBeanDefinition mbd, @Nullable Object[] explicitArgs) { 
    
    	BeanWrapperImpl bw = new BeanWrapperImpl();
    	this.beanFactory.initBeanWrapper(bw);
    
    	Object factoryBean;
    	Class<?> factoryClass;
    	boolean isStatic;
    
    	String factoryBeanName = mbd.getFactoryBeanName();
    	if (factoryBeanName != null) { 
    		// factoryBeanName不为空说明使用的是另一个类的实例方法来创建实例
    		if (factoryBeanName.equals(beanName)) { 
    			throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
    					"factory-bean reference points back to the same bean definition");
    		}
    		// 根据factoryBeanName获取另一个类的实例
    		factoryBean = this.beanFactory.getBean(factoryBeanName);
    		if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) { 
    			throw new ImplicitlyAppearedSingletonException();
    		}
    		this.beanFactory.registerDependentBean(factoryBeanName, beanName);
    		factoryClass = factoryBean.getClass();
    		isStatic = false; // 非静态
    	}
    	else { 
    		// factoryBeanName为空说明使用的是本类的静态方法来创建实例
    		// It's a static factory method on the bean class.
    		if (!mbd.hasBeanClass()) { 
    			throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
    					"bean definition declares neither a bean class nor a factory-bean reference");
    		}
    		factoryBean = null;
    		factoryClass = mbd.getBeanClass();
    		isStatic = true; // 静态
    	}
    
    	Method factoryMethodToUse = null;
    	ArgumentsHolder argsHolderToUse = null;
    	Object[] argsToUse = null;
    
    	if (explicitArgs != null) { 
    		argsToUse = explicitArgs;
    	}
    	else { 
    		Object[] argsToResolve = null;
    		synchronized (mbd.constructorArgumentLock) { 
    			factoryMethodToUse = (Method) mbd.resolvedConstructorOrFactoryMethod;
    			if (factoryMethodToUse != null && mbd.constructorArgumentsResolved) { 
    				// Found a cached factory method...
    				argsToUse = mbd.resolvedConstructorArguments;
    				if (argsToUse == null) { 
    					argsToResolve = mbd.preparedConstructorArguments;
    				}
    			}
    		}
    		if (argsToResolve != null) { 
    			argsToUse = resolvePreparedArguments(beanName, mbd, bw, factoryMethodToUse, argsToResolve);
    		}
    	}
    
    	if (factoryMethodToUse == null || argsToUse == null) { 
    		// Need to determine the factory method...
    		// Try all methods with this name to see if they match the given arguments.
    		factoryClass = ClassUtils.getUserClass(factoryClass);
    
    		List<Method> candidates = null;
    		if (mbd.isFactoryMethodUnique) { 
    			if (factoryMethodToUse == null) { 
    				factoryMethodToUse = mbd.getResolvedFactoryMethod();
    			}
    			if (factoryMethodToUse != null) { 
    				candidates = Collections.singletonList(factoryMethodToUse);
    			}
    		}
    		if (candidates == null) { 
    			candidates = new ArrayList<>();
    			Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
    			for (Method candidate : rawCandidates) { 
    				// 找到factory-method方法
    				if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) { 
    					candidates.add(candidate);
    				}
    			}
    		}
    
    		if (candidates.size() == 1 && explicitArgs == null && !mbd.hasConstructorArgumentValues()) { 
    			Method uniqueCandidate = candidates.get(0);
    			if (uniqueCandidate.getParameterCount() == 0) { 
    				mbd.factoryMethodToIntrospect = uniqueCandidate;
    				synchronized (mbd.constructorArgumentLock) { 
    					mbd.resolvedConstructorOrFactoryMethod = uniqueCandidate;
    					mbd.constructorArgumentsResolved = true;
    					mbd.resolvedConstructorArguments = EMPTY_ARGS;
    				}
    				// 调用factory-method方法进行实例化
    				bw.setBeanInstance(instantiate(beanName, mbd, factoryBean, uniqueCandidate, EMPTY_ARGS));
    				return bw;
    			}
    		}
    ... ...

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