SpringIoc源码（十八）BeanFactory（七）getBean（doCreateBeancreateBeanInstance实例创建）

目录

 1、Supplier方式创建对象

 2、工厂方法创建对象

 3、有参构造创建对象

 4、无参构造创建对象

    当创建Bean时&＃xff0c;肯定是先通过反射创建该对象。只是Spring除了直接用反射实例化对象外还允许传入Supplier、或者设置factory-mtehod等方式。不论哪种方式初始化完成对象的创建后&＃xff0c;会将该对象使用装饰器模式设置一些容器属性&＃xff08;丰富该对象&＃xff09;然后进行返回BeanWrapperImpl类型。

    1、先检查beanClass类型&＃xff1b;

    2、如果存在Supplier类型的instanceSupplier存在&＃xff0c;则调用其get方法初始化实例。

    3、然后判断是否存在FactoryMethodName&＃xff0c;是则调用instantiateUsingFactoryMethod获取&＃xff08;过程很复杂先不分析了&＃xff09;

    4、如果有设置resolvedConstructorOrFactoryMethod属性则可能直接就能决定初始化的有参或者无参构造&＃xff1b;否则就会遍历所有的SmartInstantiationAwareBeanPostProcessor&＃xff0c;也可以指定构造器。比如只有一个有参数构造函数时则通过AutowiredAnnotationBeanPostProcessor将在这里返回构造器。如下&＃xff1a;

&＃64;Component
public class AaaComponent {BbbComponent bbbComponent;public AaaComponent(BbbComponent bbbComponent) {this.bbbComponent &＃61; bbbComponent;}
}

    5、通过参数确定构造函数进行初始化调用autowireConstructor方法

    6、如果不存在工厂方法&＃xff0c;也不存在参数构造&＃xff0c;则调用默认无参构造函数初始化&＃xff08;instantiateBean方法&＃xff09;

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, &＃64;Nullable Object[] args) {// Make sure bean class is actually resolved at this point.Class beanClass &＃61; resolveBeanClass(mbd, beanName);if (beanClass !&＃61; null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {throw new BeanCreationException(mbd.getResourceDescription(), beanName,"Bean class isn&＃39;t public, and non-public access not allowed: " &＃43; beanClass.getName());}Supplier instanceSupplier &＃61; mbd.getInstanceSupplier();if (instanceSupplier !&＃61; null) {return obtainFromSupplier(instanceSupplier, beanName);}if (mbd.getFactoryMethodName() !&＃61; null) {return instantiateUsingFactoryMethod(beanName, mbd, args);}// Shortcut when re-creating the same bean...boolean resolved &＃61; false;boolean autowireNecessary &＃61; false;if (args &＃61;&＃61; null) {synchronized (mbd.constructorArgumentLock) {if (mbd.resolvedConstructorOrFactoryMethod !&＃61; null) {resolved &＃61; true;autowireNecessary &＃61; mbd.constructorArgumentsResolved;}}}if (resolved) {if (autowireNecessary) {return autowireConstructor(beanName, mbd, null, null);}else {return instantiateBean(beanName, mbd);}}// Candidate constructors for autowiring?Constructor[] ctors &＃61; determineConstructorsFromBeanPostProcessors(beanClass, beanName);if (ctors !&＃61; null || mbd.getResolvedAutowireMode() &＃61;&＃61; AUTOWIRE_CONSTRUCTOR ||mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {return autowireConstructor(beanName, mbd, ctors, args);}// Preferred constructors for default construction?ctors &＃61; mbd.getPreferredConstructors();if (ctors !&＃61; null) {return autowireConstructor(beanName, mbd, ctors, null);}// No special handling: simply use no-arg constructor.return instantiateBean(beanName, mbd);
}

 1、Supplier方式创建对象

protected BeanWrapper obtainFromSupplier(Supplier instanceSupplier, String beanName) {Object instance;String outerBean &＃61; this.currentlyCreatedBean.get();this.currentlyCreatedBean.set(beanName);// 省略try catchinstance &＃61; instanceSupplier.get();if (instance &＃61;&＃61; null) {instance &＃61; new NullBean();}BeanWrapper bw &＃61; new BeanWrapperImpl(instance);initBeanWrapper(bw);return bw;
}

     如果BeanDefinition发现设置了instanceSupplier属性&＃xff0c;则调用其get方法获取到的就认为是实例对象。

但是需要将其进行包装成BeanWrapperImpl返回。所以不论使用哪种方式创建对象都会调用initBeanWrapper方法。将容器级别的ConversionService和PropertyEditor列表&＃xff0c;都设置给所以的Bean。即这两个类型的配置即使容器级别的&＃xff0c;也是每个Bean都拥有的。

protected void initBeanWrapper(BeanWrapper bw) {bw.setConversionService(getConversionService());registerCustomEditors(bw);
}

 2、工厂方法创建对象

    如果在标签中设置了factory-bean属性&＃xff0c;或者在BeanDefinition中设置了factoryMethodName属性。那么可以直接从该指定方法中获取对象。

protected BeanWrapper instantiateUsingFactoryMethod(String beanName, RootBeanDefinition mbd, &＃64;Nullable Object[] explicitArgs) {return new ConstructorResolver(this).instantiateUsingFactoryMethod(beanName, mbd, explicitArgs);
}

    instantiateUsingFactoryMethod方法太长&＃xff0c;过程大致如下&＃xff1a;

1、处理initBeanWrapper&＃xff08;如上&＃xff09;

2、根据factoryBeanName名称字符串&＃xff0c;调用getBean(factoryBeanName)返回对象

3、根据对象的可用的方法&＃xff0c;已经传入的参数等&＃xff0c;排除其他最终决定调用方法和参数

4、调用下面的策略(CglibSubclassingInstantiationStrategy)方法实例化对象

beanFactory.getInstantiationStrategy().instantiate(mbd, beanName, this.beanFactory, factoryBean, factoryMethod, args)

核心代码为&＃xff1a;

Object result &＃61; factoryMethod.invoke(factoryBean, args)

 3、有参构造创建对象

protected BeanWrapper autowireConstructor(String beanName, RootBeanDefinition mbd, &＃64;Nullable Constructor[] ctors, &＃64;Nullable Object[] explicitArgs) {return new ConstructorResolver(this).autowireConstructor(beanName, mbd, ctors, explicitArgs);
}

     创建过程大致与上面的相同&＃xff0c;最终都会调用CglibSubclassingInstantiationStrategy的instantiate方法。

 4、无参构造创建对象

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {Object beanInstance;// 省略try catch代码final BeanFactory parent &＃61; this;beanInstance &＃61; getInstantiationStrategy().instantiate(mbd, beanName, parent);BeanWrapper bw &＃61; new BeanWrapperImpl(beanInstance);initBeanWrapper(bw);return bw;
}

    无参构造的过程&＃xff0c;上面的方法都会经历。