Spring源码学习（二）

深碍√TFBOYSˉ_ 2022-05-25 06:20 193阅读 0赞

装配完Bean的配置信息，如何实例化bean呢？

Spring获取bean的显式方法举个例子

DefaultListableBeanFactory f = new XmlBeanFactory(new ClassPathResource("test.xml"));
    System.out.println(f.getBeanDefinitionCount());
    TestBean bean = (TestBean) f.getBean("testStr");

关键就是getBean（"xxx"）；

@Override
    public Object getBean(String name) throws BeansException {
    	return doGetBean(name, null, null, false);
    }

进入具体的处理逻辑

protected <T> T doGetBean(final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly) throws BeansException {
    		// 获取Bean的Name，这个地方的name不会重复相当于bean 的id
    		final String beanName = transformedBeanName(name);
    		Object bean;
    		// Eagerly check singleton cache for manually registered singletons.
    		Object sharedInstance = getSingleton(beanName);
    		if (sharedInstance != null && args == null) {
    			if (logger.isDebugEnabled()) {
    				if (isSingletonCurrentlyInCreation(beanName)) {
    					logger.debug("Returning eagerly cached instance of singleton bean '" + beanName
    							+ "' that is not fully initialized yet - a consequence of a circular reference");
    				} else {
    					logger.debug("Returning cached instance of singleton bean '" + beanName + "'");
    				}
    			}
    			// 已存在单例子的bean的时候直接返回了
    			bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    		} else {
    			// Fail if we're already creating this bean instance:
    			// We're assumably within a circular reference.
    			if (isPrototypeCurrentlyInCreation(beanName)) {
    				throw new BeanCurrentlyInCreationException(beanName);
    			}
    			// Check if bean definition exists in this factory.
    			BeanFactory parentBeanFactory = getParentBeanFactory();
    			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
    				// Not found -> check parent.
    				String nameToLookup = originalBeanName(name);
    				if (args != null) {
    					// Delegation to parent with explicit args.
    					return (T) parentBeanFactory.getBean(nameToLookup, args);
    				} else {
    					// No args -> delegate to standard getBean method.
    					return parentBeanFactory.getBean(nameToLookup, requiredType);
    				}
    			}
    
    			if (!typeCheckOnly) {
    				markBeanAsCreated(beanName);
    			}
    			try {
    				// 如果有指定beanName的实例是子bean的话，会合并父类的属性
    				final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
    				checkMergedBeanDefinition(mbd, beanName, args);
    
    				// Guarantee initialization of beans that the current bean depends on.
    				String[] dependsOn = mbd.getDependsOn();
    				if (dependsOn != null) {
    					// 依赖的bean的初始化
    					for (String dep : dependsOn) {
    						if (isDependent(beanName, dep)) {
    							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
    						}
    						registerDependentBean(dep, beanName);
    						try {
    							getBean(dep);
    						} catch (NoSuchBeanDefinitionException ex) {
    							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
    						}
    					}
    				}
    				// 依赖bean的实例化完成后会开始自身的实例化
    				// Create bean instance.
    				if (mbd.isSingleton()) {
    					sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
    						@Override
    						public Object getObject() throws BeansException {
    							try {
    								return createBean(beanName, mbd, args);
    							} catch (BeansException ex) {
    								// Explicitly remove instance from singleton cache: It might have been put there
    								// eagerly by the creation process, to allow for circular reference resolution.
    								// Also remove any beans that received a temporary reference to the bean.
    								destroySingleton(beanName);
    								throw ex;
    							}
    						}
    					});
    					bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
    				}else if (mbd.isPrototype()) {
    					// It's a prototype -> create a new instance.
    					Object prototypeInstance = null;
    					try {
    						beforePrototypeCreation(beanName);
    						prototypeInstance = createBean(beanName, mbd, args);
    					} finally {
    						afterPrototypeCreation(beanName);
    					}
    					bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
    				}else {
    					String scopeName = mbd.getScope();
    					final Scope scope = this.scopes.get(scopeName);
    					if (scope == null) {
    						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
    					}
    					try {
    						Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
    							@Override
    							public Object getObject() throws BeansException {
    								beforePrototypeCreation(beanName);
    								try {
    									return createBean(beanName, mbd, args);
    								} finally {
    									afterPrototypeCreation(beanName);
    								}
    							}
    						});
    						bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
    					} catch (IllegalStateException ex) {
    						throw new BeanCreationException(beanName, "Scope '" + scopeName
    								+ "' is not active for the current thread; consider "
    								+ "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
    								ex);
    					}
    				}
    			} catch (BeansException ex) {
    				cleanupAfterBeanCreationFailure(beanName);
    				throw ex;
    			}
    		}
    
    		// Check if required type matches the type of the actual bean instance.
    		if (requiredType != null && bean != null && !requiredType.isInstance(bean)) {
    			try {
    				return getTypeConverter().convertIfNecessary(bean, requiredType);
    			} catch (TypeMismatchException ex) {
    				if (logger.isDebugEnabled()) {
    					logger.debug("Failed to convert bean '" + name + "' to required type '"
    							+ ClassUtils.getQualifiedName(requiredType) + "'", ex);
    				}
    				throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
    			}
    		}
    		return (T) bean;
    	}