Spring 依赖注入(DI) 源码解析

我不是女神ヾ 2022-10-22 10:57 152阅读 0赞

# 引言 #

**概述：** Spring Bean 创建源码分析系列

[【1】Spring Bean 的实例化过程源码解析][1_Spring Bean]  
[【2】Spring 依赖注入(DI) 源码解析][2_Spring _DI_]  
[【3】Spring 三级缓存解决循环依赖][3_Spring]

# 1 工程 #

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## 1.1 StudentController ##

@Controller
    public class StudentController { 
    
        @Autowired
        private StudentService studentService;
    
        public StudentController(){ 
            System.out.println("StudentController invoke NoArgsConstructor");
        }
    
    }

## 1.2 StudentService ##

@Service
    public class StudentService { 
    
    
    
    }

## 1.3 applicationContext.xml ##

## 1.4 RoshTest ##

public class RoshTest { 
    
        @Test
        public void mainTest(){ 
            ClassPathXmlApplicationContext applicationContext=new ClassPathXmlApplicationContext("applicationContext.xml");
            applicationContext.close();
    
        }
    
    }

# 2 核心方法 #

**类：AbstractAutowireCapableBeanFactory**

protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
    			throws BeanCreationException { 
    
    		// Instantiate the bean.
    		BeanWrapper instanceWrapper = null;
    		if (mbd.isSingleton()) { 
    			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
    		}
    		if (instanceWrapper == null) { 
    
    			/** * 【1】创建实例 */
    			instanceWrapper = createBeanInstance(beanName, mbd, args);
    		}
    		Object bean = instanceWrapper.getWrappedInstance();
    		Class<?> beanType = instanceWrapper.getWrappedClass();
    		if (beanType != NullBean.class) { 
    			mbd.resolvedTargetType = beanType;
    		}
    
    		// Allow post-processors to modify the merged bean definition.
    		synchronized (mbd.postProcessingLock) { 
    			if (!mbd.postProcessed) { 
    				try { 
    					/** *【2】 收集有注解的属性、方法。 * * 1 AutowiredAnnotationBeanPostProcessor 扫描 @Autowired、@Value注解 * 2 CommonAnnotationBeanPostProcessor 扫描 @PostConstruct、@Resource、@preDestroy */
    					applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
    				}
    				catch (Throwable ex) { 
    					throw new BeanCreationException(mbd.getResourceDescription(), beanName,
    							"Post-processing of merged bean definition failed", ex);
    				}
    				mbd.postProcessed = true;
    			}
    		}
    
    		// Eagerly cache singletons to be able to resolve circular references
    		// even when triggered by lifecycle interfaces like BeanFactoryAware.
    		boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
    				isSingletonCurrentlyInCreation(beanName));
    		if (earlySingletonExposure) { 
    			if (logger.isTraceEnabled()) { 
    				logger.trace("Eagerly caching bean '" + beanName +
    						"' to allow for resolving potential circular references");
    			}
    			/** * 【3】 添加三级缓存，解决循环依赖 */
    			addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
    		}
    
    		// Initialize the bean instance.
    		Object exposedObject = bean;
    		try { 
    
    			/** * 【4】 依赖注入 */
    			populateBean(beanName, mbd, instanceWrapper);
    
    			/** * 【5】 初始化bean */
    			exposedObject = initializeBean(beanName, exposedObject, mbd);
    		}
    		catch (Throwable ex) { 
    			if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) { 
    				throw (BeanCreationException) ex;
    			}
    			else { 
    				throw new BeanCreationException(
    						mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
    			}
    		}
    
    		if (earlySingletonExposure) { 
    			Object earlySingletonReference = getSingleton(beanName, false);
    			if (earlySingletonReference != null) { 
    				if (exposedObject == bean) { 
    					exposedObject = earlySingletonReference;
    				}
    				else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) { 
    					String[] dependentBeans = getDependentBeans(beanName);
    					Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
    					for (String dependentBean : dependentBeans) { 
    						if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) { 
    							actualDependentBeans.add(dependentBean);
    						}
    					}
    					if (!actualDependentBeans.isEmpty()) { 
    						throw new BeanCurrentlyInCreationException(beanName,
    								"Bean with name '" + beanName + "' has been injected into other beans [" +
    								StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
    								"] in its raw version as part of a circular reference, but has eventually been " +
    								"wrapped. This means that said other beans do not use the final version of the " +
    								"bean. This is often the result of over-eager type matching - consider using " +
    								"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
    					}
    				}
    			}
    		}
    
    		// Register bean as disposable.
    		try { 
    			registerDisposableBeanIfNecessary(beanName, bean, mbd);
    		}
    		catch (BeanDefinitionValidationException ex) { 
    			throw new BeanCreationException(
    					mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
    		}
    
    		return exposedObject;
    	}

# 3 创建实例 #

**详情请看：**  
[Spring Bean 的实例化过程源码解析][1_Spring Bean]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 1]

# 4 收集注解 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 2]  
**描述：** AutowiredAnnotationBeanPostProcessor完成注解的收集  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][2021031700282292.png]  
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# 5 反射完成依赖注入 #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 8]

**描述：** AutowiredAnnotationBeanPostProcessor完成依赖注入

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 9]  
**描述：** 从缓存中获取meta信息  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 10]  
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**描述：** 用反射完成 依赖注入  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 12]  
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# 6 Bean实例初始化 #

**描述：** 加强bean  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 17]  
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[1_Spring Bean]: https://blog.csdn.net/qq_34125999/article/details/114858004
[2_Spring _DI_]: https://blog.csdn.net/qq_34125999/article/details/114908974
[3_Spring]: https://blog.csdn.net/qq_34125999/article/details/114957031
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