spring-beanFactory二

Posted 2020-10-02 holoyong

上一篇只是将xml解析为bean definitions，这一篇来看getBean通过bean definition得到实例。

 

1 //以XmlBeanFactory为例
2 BeanFactory factory = new XmlBeanFactory(new ClassPathResource("spring/spring-test.xml"));
3 MyBean bean = (MyBean) factory.getBean("myBean");
4 System.out.println(bean.getBeanName());//myBean

 

1 public class MyBean {
2     private String beanName = "myBean";
3     public String getBeanName() {
4         return beanName;
5     }
6     public void setBeanName(String beanName) {
7         this.beanName = beanName;
8     }
9 }

 

1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
5     <bean id="myBean" class="com.zyong.spring.beanfactory.MyBean"/>
6 </beans>

 

1 public Object getBean(String name) throws BeansException {
2     //name, requiredType, args, typeCheckOnly
3     return doGetBean(name, null, null, false);
4 }

 

 1 //doGetBean会真正的实例化对象，并回调beanFactory（BeanPostProcessor）、
 2 //bean（init，@PostConstruct和@PreDestroy通过CommonAnnotationBeanPostProcessor或开启<context:annotation-config />来支持）的相关方法
 3 protected <T> T doGetBean(
 4         final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
 5         throws BeansException {
 6         
 7     // Eagerly check singleton cache for manually registered singletons.
 8     //尝试从缓存中获取，首先会尝试从singletonObjects获取，再尝试从singletonFactories中获取获取beanFactory（beanName是beanFactory的名字），如果获取到则调用getObject获得bean
 9     Object sharedInstance = getSingleton(beanName);
10     if (sharedInstance != null && args == null) {
11         if (logger.isDebugEnabled()) {
12             if (isSingletonCurrentlyInCreation(beanName)) {
13                 logger.debug("Returning eagerly cached instance of singleton bean ‘" + beanName +
14                         "‘ that is not fully initialized yet - a consequence of a circular reference");
15             }
16             else {
17                 logger.debug("Returning cached instance of singleton bean ‘" + beanName + "‘");
18             }
19         }
20         //从bean实例中获取对象，可能是bean实例自身，如果bean实例是一个beanFactory，则返回beanFactroy创建的对象
21         bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
22     }else{
23         // Check if bean definition exists in this factory.
24         BeanFactory parentBeanFactory = getParentBeanFactory();
25         //如果本beanFactory不包含该beanName的bean definition，则从父级beanFactory获取bean
26         if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
27             // Not found -> check parent.
28             String nameToLookup = originalBeanName(name);
29             return (T) parentBeanFactory.getBean(nameToLookup, args);
30         }
31         
32         final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
33         checkMergedBeanDefinition(mbd, beanName, args);
34 
35         // Guarantee initialization of beans that the current bean depends on.
36         //这里只是为当前bean注册依赖，并没有注入，注册依赖是为了在销毁当前bean之前，先销毁依赖（为了实现该功能，需要2个注册表，一个是bean->dependences，另一个是dependence->beans）
37         String[] dependsOn = mbd.getDependsOn();
38         if (dependsOn != null) {
39             for (String dep : dependsOn) {
40                 if (isDependent(beanName, dep)) {
41                     throw new BeanCreationException(mbd.getResourceDescription(), beanName,
42                             "Circular depends-on relationship between ‘" + beanName + "‘ and ‘" + dep + "‘");
43                 }
44                 registerDependentBean(dep, beanName);
45                 //递归创建依赖bean
46                 getBean(dep);
47             }
48         }
49         
50         //从这里开始真正创建bean
51         // Create bean instance.
52         if (mbd.isSingleton()) {
53             sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {//策略模式，ObjectFactory不同，创建bean的策略也会有差异
54                 @Override
55                 public Object getObject() throws BeansException {
56                     try {
57                         //重要方法
58                         return createBean(beanName, mbd, args);
59                     }
60                     catch (BeansException ex) {
61                         // Explicitly remove instance from singleton cache: It might have been put there
62                         // eagerly by the creation process, to allow for circular reference resolution.
63                         // Also remove any beans that received a temporary reference to the bean.
64                         destroySingleton(beanName);
65                         throw ex;
66                     }
67                 }
68             });
69             //与之前从缓存获取bean实例类似
70             bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
71         }else if(mbd.isPrototype()){
72             ......
73         }else{
74             ......
75         }
76         
77     }//else
78 
79 }

 

 1 //createBean的主要逻辑，这里就真正开始创建bean的各种“花招”了
 2 protected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {
 3     // Make sure bean class is actually resolved at this point, and
 4     // clone the bean definition in case of a dynamically resolved Class
 5     // which cannot be stored in the shared merged bean definition.
 6     //加载bean的class，并存入bean definition
 7     Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
 8     if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
 9         mbdToUse = new RootBeanDefinition(mbd);
10         mbdToUse.setBeanClass(resolvedClass);
11     }
12     // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
13     //如果bean实现了InstantiationAwareBeanPostProcessor，
14     //这里就会调用InstantiationAwareBeanPostProcessor的Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName)接口来创建bean，
15     //如果返回非null，则继续调用boolean postProcessAfterInstantiation(Object bean, String beanName)接口
16     //PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)有机会在注入前执行
17     Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
18     //如果通过InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法得到一个实例，直接返回
19     if (bean != null) {
20         return bean;
21     }
22     //如果通过InstantiationAwareBeanPostProcessor的postProcessBeforeInstantiation方法无法得到一个实例，则进行常规实例化工作（实例化、注入、BeanPostProcessor等）
23     //重要方法
24     Object beanInstance = doCreateBean(beanName, mbdToUse, args);
25     return beanInstance;
26 }

 

 1 //doCreateBean的主要逻辑
 2 protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
 3     throws BeanCreationException {
 4     //使用工厂方法、构造器注入、简单实例化等策略实例化bean（不是策略模式，只是通过bean definition来决定使用哪种策略，类似switch）
 5     //BeanWrapper是bean的包装类，beanWrapper提供了便捷的方法去更新bean的字段、访问bean的方法，用于注入
 6     BeanWrapper instanceWrapper = createBeanInstance(beanName, mbd, args);//离我们很近
 7     final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
 8     //MergedBeanDefinitionPostProcessor的void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName)
 9     applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
10     // Initialize the bean instance.
11     //exposedObject即暴露的bean、原生的bean
12     Object exposedObject = bean;
13     //先执行InstantiationAwareBeanPostProcessor的postProcessAfterInstantiation，
14     //再执行InstantiationAwareBeanPostProcessor的postProcessPropertyValues，最后再进行xml注入
15     populateBean(beanName, mbd, instanceWrapper);
16     //什么情况下bean==null？
17     if (exposedObject != null) {
18         //初始化bean
19         //invokeAwareMethods（回调BeanNameAware、BeanClassLoaderAware、BeanFactoryAware的相关方法）、
20         //applyBeanPostProcessorsBeforeInitialization（回调BeanPostProcessor的postProcessBeforeInitialization方法）、
21         //invokeInitMethods（回调InitializingBean的afterPropertiesSet，以及init-method）、
22         //applyBeanPostProcessorsAfterInitialization（回调BeanPostProcessor的postProcessAfterInitialization方法）
23         exposedObject = initializeBean(beanName, exposedObject, mbd);//离我们很近
24     }
25     // Register bean as disposable.
26     registerDisposableBeanIfNecessary(beanName, bean, mbd);
27 }