今天我們編寫一個簡單的demo來分析一下spring中整個bean的生命週期
編寫Demo
1. 首先我們定義一個BeanFactoryProcessor的類,目的是爲了看出PostProcessBeanFactory接口被調用的時間點
package cn.sue.spring.test.lifecycle; import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanFactoryPostProcessor; import org.springframework.beans.factory.config.ConfigurableListableBeanFactory; import org.springframework.stereotype.Component; /** * <p> * * </p> * * @author Sue * @className MyBeanFactoryPostProcessor * @create 2023/4/25 **/ @Component public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor { public MyBeanFactoryPostProcessor() { super(); System.out.println("【BeanFactoryPostProcessor】實現類的構造函數"); } // 允許我們在工廠裏所有的bean被加載進來後但是還沒初始化前,對所有bean的屬性進行修改也可以add屬性值,該操作在對應bean的構造函數執行前 @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory arg0) throws BeansException { System.out.println("BeanFactoryPostProcessor.postProcessBeanFactory(),來自MyBeanFactoryPostProcessor"); //獲取到Spring中所有的beanName String[] beanStr = arg0.getBeanDefinitionNames(); //循環打印 for (String beanName : beanStr) { System.out.print("已加載的bean name:" + beanName + ";" + "\n"); } System.out.println(); } }
2. 接着再寫一個實現了BeanPostProcessor的類,目的是爲了看出bean初始化前後的時間點
package cn.sue.spring.test.lifecycle; import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanPostProcessor; import org.springframework.stereotype.Component; /** * <p> * * </p> * * @author Sue * @className MyBeanPostProcessor * @create 2023/4/25 **/ @Component public class MyBeanPostProcessor implements BeanPostProcessor { public MyBeanPostProcessor() { super(); System.out.println("BeanPostProcessor{}實現類的構造函數"); } // 實例化、依賴注入完畢,在調用顯示的初始化之前完成一些定製的業務 @Override public Object postProcessAfterInitialization(Object arg0, String arg1) throws BeansException { if (arg0.getClass() == TestBeanA.class || arg0.getClass() == TestBeanB.class) { System.out .println("BeanPostProcessor.postProcessAfterInitialization() 來自MyBeanPostProcessor,beanName:" + arg1); } return arg0; } // 實例化、依賴注入、初始化後完成一些定製的業務 @Override public Object postProcessBeforeInitialization(Object arg0, String arg1) throws BeansException { if (arg0.getClass() == TestBeanA.class || arg0.getClass() == TestBeanB.class) { System.out .println("BeanPostProcessor.postProcessBeforeInitialization() 來自MyBeanPostProcessor,beanName:" + arg1); } return arg0; } }
3. 再給出一個繼承了InstantiationAwareBeanPostProcessorAdapter的子類,目的是爲了看出postProcessBeforeInitialization、postProcessAfterInitialization、postProcessPropertyValues被調用的時間點
package cn.sue.spring.test.lifecycle; import org.springframework.beans.BeansException; import org.springframework.beans.PropertyValues; import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor; import org.springframework.stereotype.Component; import java.beans.PropertyDescriptor; /** * <p> * * </p> * * @author Sue * @className MyInstantiationAwareBeanPostProcessor * @create 2023/4/25 **/ @Component public class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor { public MyInstantiationAwareBeanPostProcessor() { super(); System.out .println("InstantiationAwareBeanPostProcessorAdapter{}實現類MyInstantiationAwareBeanPostProcessor{}的構造函數"); } // 接口方法、實例化Bean之前調用 @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { if (bean.getClass() == TestBeanA.class || bean.getClass() == TestBeanB.class) { System.out .println("InstantiationAwareBeanPostProcessorAdapter.postProcessBeforeInitialization() 來自MyInstantiationAwareBeanPostProcessor,beanName:" + beanName); } return bean; } // 接口方法、實例化Bean之後調用 @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { if (bean.getClass() == TestBeanA.class || bean.getClass() == TestBeanB.class) { System.out .println("InstantiationAwareBeanPostProcessorAdapter.postProcessAfterInitialization() 來自MyInstantiationAwareBeanPostProcessor,beanName:" + beanName); } return bean; } // 接口方法、設置某個屬性時調用 @Override public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException { if (bean.getClass() == TestBeanA.class || bean.getClass() == TestBeanB.class) { System.out .println("InstantiationAwareBeanPostProcessorAdapter.postProcessPropertyValues() 來自MyInstantiationAwareBeanPostProcessor,beanName:" + beanName); } return pvs; } }
4. 再定義一個Bean,它使用applicationContext.xml進行註冊並實現了BeanFactoryAware, BeanNameAware,InitializingBean,DisposableBean四個接口類,目的是爲了清晰的看出以下好幾個接口被調用的時間點
package cn.sue.spring.test.lifecycle; import org.springframework.beans.BeansException; import org.springframework.beans.factory.*; import javax.annotation.PostConstruct; public class TestBeanA implements BeanFactoryAware, BeanNameAware, InitializingBean, DisposableBean { private String name; private String address; private int phone; private BeanFactory beanFactory; private String beanName; @PostConstruct public void init() { System.out.println("TestBeanA{} @PostConstruct"); } public TestBeanA() { System.out.println("TestBeanA{} 默認構造函數"); } public TestBeanA(String name) { System.out.println("TestBeanA{} 有參構造函數"); } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public int getPhone() { return phone; } public void setPhone(int phone) { this.phone = phone; } @Override public String toString() { return "TestBeanA [address=" + address + ", name=" + name + ", phone=" + phone + "]"; } // 這是BeanFactoryAware接口方法 @Override public void setBeanFactory(BeanFactory arg0) throws BeansException { System.out .println("BeanFactoryAware.setBeanFactory() 來自TestBeanA"); this.beanFactory = arg0; } // 這是BeanNameAware接口方法 @Override public void setBeanName(String arg0) { System.out.println("BeanNameAware.setBeanName() 來自TestBeanA"); this.beanName = arg0; } // 這是InitializingBean接口方法 @Override public void afterPropertiesSet() throws Exception { System.out .println("InitializingBean.afterPropertiesSet() 來自TestBeanA"); } // 這是DiposibleBean接口方法 @Override public void destroy() throws Exception { System.out.println("DiposibleBean.destory() 來自TestBeanA"); } // 通過<bean>的init-method屬性指定的初始化方法 public void myInit() { System.out.println("TestBeanA.myInit()"); } // 通過<bean>的destroy-method屬性指定的初始化方法 public void myDestory() { System.out.println("TestBeanA.destroy-method()"); } }
5. 最後,再定義一個TestBeanB,它的作用比較簡單,爲了看出內部數據成員有其他容器Bean的時候Spring是如何加載bean的
package cn.sue.spring.test.lifecycle; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; @Component public class TestBeanB { @Autowired private TestBeanA testBeanA; public TestBeanB() { System.out.println("TestBeanB{} 默認構造器"); } }
6.applicationContext.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="cn.sue.spring.test.lifecycle" > </context:component-scan> <!-- <bean id="user" class="cn.sue.spring.test.core.UserService"></bean>--> <bean id="testBeanA" class="cn.sue.spring.test.lifecycle.TestBeanA" init-method="myInit" destroy-method="myDestory"> <property name="name" value="Sue.test"/> </bean> </beans>
7.加載容器進行測試
@Test public void testLifeCycle() { ClassPathXmlApplicationContext classPathXmlApplicationContext = new ClassPathXmlApplicationContext("spring.xml"); classPathXmlApplicationContext.destroy(); }
查看結果並分析
首先從
BeanFactoryPostProcessor{}實現類MyBeanFactoryPostProcessor{}的構造函數 BeanFactoryPostProcessor.postProcessBeanFactory(),來自MyBeanFactoryPostProcessor BeanPostProcessor{}實現類MyBeanPostProcessor{}的構造函數 InstantiationAwareBeanPostProcessorAdapter{}實現類MyInstantiationAwareBeanPostProcessor{}的構造函數
可以看出執行順序是:
- 調用postProcessBeanFactory實現類的構造函數
BeanFactoryPostProcessor是bean工廠的處理器
- 調用postProcessBeanFactory實現類的postProcessBeanFactory實現函數
postProcessBeanFactory函數允許我們在工廠裏所有的bean被加載進來後但是還沒初始化前,對所有bean的屬性進行修改也可以add屬性值
- 調用BeanPostProcessor實現類的構造函數
完成bean實例化、配置以及其他初始化方法前後要添加一些自己邏輯處理則要實現接口BeanPostProcessor
- 調用InstantiationAwareBeanPostProcessorAdapter實現類的構造函數
適配器類,基類是BeanPostProcessor的實現類
再從
TestBeanB{} 默認構造器 InstantiationAwareBeanPostProcessorAdapter.postProcessPropertyValues() 來自MyInstantiationAwareBeanPostProcessor,beanName:testBeanB
可以看到,此處spring容器先掃描到了TestBeanB,因此調用順序是
- TestBeanB的默認構造器【無參構造器】
- 調用InstantiationAwareBeanPostProcessorAdapter實現類的postProcessPropertyValues接口
postProcessPropertyValues在接口方法、設置某個屬性時調用,通過實驗看到實例化一個Bean的時候也會調用該接口方法
之後實例化TestBeanB的時候發現內部注入了TestBeanA,因此Spring轉而實例化TestBeanA。
接下來看到的是TestBeanA的實例化過程中調用的順序
TestBeanA{} 默認構造函數 InstantiationAwareBeanPostProcessorAdapter.postProcessPropertyValues() 來自MyInstantiationAwareBeanPostProcessor,beanName:testBeanA BeanNameAware.setBeanName() 來自TestBeanA BeanFactoryAware.setBeanFactory() 來自TestBeanA BeanPostProcessor.postProcessBeforeInitialization() 來自MyBeanPostProcessor,beanName:testBeanA InstantiationAwareBeanPostProcessorAdapter.postProcessBeforeInitialization() 來自MyInstantiationAwareBeanPostProcessor,beanName:testBeanA TestBeanA{} @PostConstruct InitializingBean.afterPropertiesSet() 來自TestBeanA TestBeanA.myInit() BeanPostProcessor.postProcessAfterInitialization() 來自MyBeanPostProcessor,beanName:testBeanA InstantiationAwareBeanPostProcessorAdapter.postProcessAfterInitialization() 來自MyInstantiationAwareBeanPostProcessor,beanName:testBeanA
- 調用了TestBeanA的默認構造器
- 調用InstantiationAwareBeanPostProcessorAdapter實現類的postProcessPropertyValues接口
- 調用BeanNameAware的setBeanName接口
可以從源碼看到TestBeanA實現了接口BeanNameAware
- 調用BeanFactoryAware的setBeanFactory接口
可以從源碼看到TestBeanA實現了接口BeanFactoryAware
- 調用BeanPostProcessor的postProcessBeforeInitialization接口
- 調用InstantiationAwareBeanPostProcessorAdapter的postProcessBeforeInitialization接口
- 調用TestBeanA中註解了@PostConstruct的函數
- 調用了InitializingBean的afterPropertiesSet接口
可以從源碼看到TestBeanA實現了接口InitializingBean
- 調用了TestBeanA的myInit接口
可以看到該init-method接口是在applicationContext中init-method配置上的
- 調用BeanPostProcessor實現類的postProcessAfterInitialization接口
- 調用InstantiationAwareBeanPostProcessorAdapter子類的postProcessAfterInitialization接口
等TestBeanA實例化結束後,則繼續TestBeanB的實例化路程
BeanPostProcessor.postProcessBeforeInitialization() 來自MyBeanPostProcessor,beanName:testBeanB InstantiationAwareBeanPostProcessorAdapter.postProcessBeforeInitialization() 來自MyInstantiationAwareBeanPostProcessor,beanName:testBeanB BeanPostProcessor.postProcessAfterInitialization() 來自MyBeanPostProcessor,beanName:testBeanB InstantiationAwareBeanPostProcessorAdapter.postProcessAfterInitialization() 來自MyInstantiationAwareBeanPostProcessor,beanName:testBeanB
- 調用BeanPostProcessor實現類的postProcessBeforeInitialization接口
- 調用InstantiationAwareBeanPostProcessorAdapter子類的postProcessBeforeInitialization接口
- 調用BeanPostProcessor實現類的postProcessAfterInitialization接口
- 調用InstantiationAwareBeanPostProcessorAdapter子類的postProcessAfterInitialization接口
最後
DiposibleBean.destory() 來自TestBeanA TestBeanA.destroy-method()
- 調用DiposibleBean實現類的destory接口
TestBeanA實現了DiposibleBean接口,實現了destroy接口
- 調用TestBeanA的myDestory函數
可以看到該myDestory接口是在applicationContext中destroy-method配置上的。
最終總結
【超重點,面試回答模板】
- 如果有bean實現了BeanFactoryPostProcessor接口類,則會實例化該bean,並且調用默認構造器,然後調用postProcessBeanFactory接口
- 如果有bean實現了BeanPostProcessor接口類,則會先實例化該bean,同樣調用默認構造器
- 如果有bean繼承了InstantiationAwareBeanPostProcessorAdapter類,則會先實例化該bean,同樣調用默認構造器
之後真正進入一個bean的生命週期過程
- 先調用bean的默認構造函數
- 如果有bean繼承了InstantiationAwareBeanPostProcessorAdapter類,此刻會調用postProcessPropertyValues函數
- 如果這個bean已經實現了BeanNameAware接口,會調用它實現的setBeanName方法,此處傳遞的就是applicationContext.xml配置文件中Bean的id值
- 如果這個bean已經實現了BeanFactoryAware接口,會調用它實現的setBeanFactory,傳遞的是Spring工廠自身
- 如果存在其他bean實現了BeanPostProcessor接口,將會調用postProcessBeforeInitialization(Object obj, String s)方法,BeanPostProcessor經常被用作是Bean內容的更改,並且由於這個是在Bean初始化結束時調用那個的方法,也可以被應用於內存或緩存技術;
- 如果存在其他bean繼承了InstantiationAwareBeanPostProcessorAdapter類,則會調用postProcessBeforeInitialization接口
- 如果這個bean中有函數加了@PostConstruct註解,則該函數會在此刻被調用
- 如果這個bean實現了InitializingBean接口重寫了afterPropertiesSet方法,該方法會在此刻被調用
- 如果這個bean在Spring配置文件中配置了init-method屬性,則會自動調用其配置的初始化方法。
- 如果存在其他bean實現了BeanPostProcessor接口,將會調用postProcessAfterInitialization(Object obj, String s)方法
- 如果存在其他bean繼承了InstantiationAwareBeanPostProcessorAdapter類,則會調用postProcessAfterInitialization接口
走到這一步以後就可以應用這個Bean了,而這個Bean是一個Singleton的,雖然在Spring配置文件中也可以配置非Singleton,這裏不做贅述。
走入銷燬階段
- 當bean不再需要時,會經過清理階段,如果這個bean實現了DisposableBean接口,會調用其實現的destroy()方法;
- 如果這個bean的applicationContext.xml配置中配置了destroy-method屬性,會自動調用其配置的銷燬方法。
本案例demo下載地址 suyang320/spring_study (github.com)