V2AS问路
Spring02---IOC-Debug查看Bean的实例化过程
阅读原文时间：2023年07月08日阅读：6

1 简介

　　springIOC它是对bean进行管理。

　　我们通常可以通过xml、properties、yml、注解等来配置bean的信息

　　spring读取这些配置信息，解析，生成BeanDefinition(用来存储Bean的定义信息)

　　根据beanDefinition来创建对象，设置属性….，最后把对象放入容器(BeanFactory)中，但我们需要使用bean时，从容器中那就可以了。

2 bean

　　在spring中，可以把bean分为两大类，普通对象和容器对象

3 BeanFactory和FactoryBean

　　它们两个都是用来创建对象的

　　当使用BeanFactory的时候，必须遵循完整的过程，这个过程是由spring管理控制的

　　当使用FactoryBean的时候，只需要调用getObject就可以返回对象，整个对象的创建过程是由用户自己定义的，更加灵活，它在getObject中自己去创建对象

package org.springframework.beans.factory;

import org.springframework.lang.Nullable;

public interface FactoryBean {

String OBJECT\_TYPE\_ATTRIBUTE = "factoryBeanObjectType";

@Nullable  
T getObject() throws Exception;

@Nullable  
Class<?> getObjectType();

default boolean isSingleton() {  
    return true;  
}

}

4 BeanDefinition

从配置中读取到bean的配置信息，通过BeanDefinitionReader解析，生成的存储bean定义信息的实例

5 spring的bean默认是单例

　　scope属性用来配置创建bean采用什么模式。

　　spring创建对象时是采用反射创建的，且默认采用的是单例。

　　spring Bean可以设置一个属性，叫做scope，可以设置四种变量。最常用的是前两种。singleton(单例-默认的)、prototype(每次获取都创建新的)

6 aware方法

　　它是用来获取当前对象的容器对象

　　比如说我们要获取到bean的AplicationContext对象

　　演示获取ApplicationContext容器对象

public class BeanTest implements ApplicationContextAware {

private Integer id;

private String name;

private ApplicationContext applicationContext;

private BeanFactory beanFactory;

public Integer getId() {  
    return id;  
}

public void setId(Integer id) {  
    this.id = id;  
}

public String getName() {  
    return name;  
}

public void setName(String name) {  
    this.name = name;  
}

public ApplicationContext getApplicationContext() {  
    return applicationContext;  
}

public void setApplicationContext(ApplicationContext applicationContext) {  
    this.applicationContext = applicationContext;  
}

public BeanFactory getBeanFactory() {  
    return beanFactory;  
}

public void setBeanFactory(BeanFactory beanFactory) {  
    this.beanFactory = beanFactory;  
}

}


http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">

<bean id="beantest" class="com.spring.test1.BeanTest">  
    <property name="name" value="张三"></property>  
    <property name="id" value="111"></property>  
</bean>

public class Test1 {

public static void main(String\[\] args) {  
    ApplicationContext context = new ClassPathXmlApplicationContext("Test.xml");  
    BeanTest bean = context.getBean(BeanTest.class);  
    System.out.println(bean.getName());  
    System.out.println(bean.getApplicationContext());  
}

}

执行结果：

张三
org.springframework.context.support.ClassPathXmlApplicationContext@7e6cbb7a, started on Sun Mar 13 16:11:15 CST 2022

我们获得了ApplicationContext对象。

ApplicationContextAware 源码

public interface ApplicationContextAware extends Aware {
void setApplicationContext(ApplicationContext applicationContext) throws BeansException;
}

执行aware方法，也就是执行setApplicationContext方法，会把容器对象ApplicationContext赋值给我们定义的applicationContext属性。

7 postProcesser

在实例化的过程中，怎么对beanfactory和bean的信息进行修改呢？

可以使用 BeanFactoryPostProcesser和BeanPostProcesser

演示

package com.spring.test1;

import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class BeanTest implements ApplicationContextAware {

private Integer id;

private String name;

private ApplicationContext applicationContext;

private BeanFactory beanFactory;

public Integer getId() {  
    return id;  
}

public void setId(Integer id) {  
    this.id = id;  
}

public String getName() {  
    return name;  
}

public void setName(String name) {  
    this.name = name;  
}

public ApplicationContext getApplicationContext() {  
    return applicationContext;  
}

public void setApplicationContext(ApplicationContext applicationContext) {  
    this.applicationContext = applicationContext;  
}

public BeanFactory getBeanFactory() {  
    return beanFactory;  
}

public void setBeanFactory(BeanFactory beanFactory) {  
    this.beanFactory = beanFactory;  
}

}

package com.spring.test1;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;

public class MyBeanFactoryPostProcesser implements BeanFactoryPostProcessor {
public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {
System.out.println("自定义的BeanFactoryPostProcessor执行");
}
}

package com.spring.test1;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;

import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.lang.Nullable;
import org.springframework.stereotype.Component;

public class MyBeanPostProcesser implements BeanPostProcessor {

 public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {  
     System.out.println("自定义的BeanPostProcessor的before");  
    return bean;  
}

 public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {  
     System.out.println("自定义的BeanPostProcessor的after");  
    return bean;  
}

}


http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">

<bean id="beantest" class="com.spring.test1.BeanTest">  
    <property name="name" value="张三"></property>  
    <property name="id" value="111"></property>  
</bean>

<bean id="myBeanFactoryPostProcesser" class="com.spring.test1.MyBeanFactoryPostProcesser">

</bean>

<bean id="myBeanPostProcesser" class="com.spring.test1.MyBeanPostProcesser">

</bean>

package com.spring.test1;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.context.support.FileSystemXmlApplicationContext;

public class Test1 {

public static void main(String\[\] args) {  
    ApplicationContext context = new ClassPathXmlApplicationContext("Test.xml");  
    BeanTest bean = context.getBean(BeanTest.class);  
    System.out.println(bean.getName());  
    System.out.println(bean.getApplicationContext());  
}

}

自定义的BeanFactoryPostProcessor执行
自定义的BeanPostProcessor的before
自定义的BeanPostProcessor的after
张三
org.springframework.context.support.ClassPathXmlApplicationContext@7e6cbb7a, started on Sun Mar 13 16:28:59 CST 2022

Process finished with exit code 0

8 init-method

示例

其它代码不变，在BeanTest定义一个方法

package com.spring.test1;

import com.sun.org.apache.xml.internal.security.Init;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class BeanTest implements ApplicationContextAware {

private Integer id;

private String name;

private ApplicationContext applicationContext;

private BeanFactory beanFactory;

public Integer getId() {  
    return id;  
}

public void setId(Integer id) {  
    this.id = id;  
}

public String getName() {  
    return name;  
}

public void setName(String name) {  
    this.name = name;  
}

public ApplicationContext getApplicationContext() {  
    return applicationContext;  
}

public void setApplicationContext(ApplicationContext applicationContext) {  
    this.applicationContext = applicationContext;  
}

public BeanFactory getBeanFactory() {  
    return beanFactory;  
}

public void setBeanFactory(BeanFactory beanFactory) {

    this.beanFactory = beanFactory;  
}

public void init(){  
    System.out.println("init-method执行");  
}

}

在配置文件中加上init-method属性

执行结果，看到init-method方法是在BeanPostProcessor的before和after之间执行的

自定义的BeanFactoryPostProcessor执行
自定义的BeanPostProcessor的before
init-method执行
自定义的BeanPostProcessor的after
张三

8 springIOC的bean的创建主要过程

　　1 创建beanFactory容器

　　2 加载配置文件，解析bean定义的信息，包装成BeanDefinition

　　3 执行BeanFactoryPostProcesser

　　4 准备工作，准备BeanPostProcessor，广播器，监听器

　　5 实例化操作

　　6 初始化操作

　　7 获取对象

9 下面通过debug来看整个过程，测试准备

public class BeanTest implements ApplicationContextAware {

private Integer id;

private String name;

private ApplicationContext applicationContext;

private BeanFactory beanFactory;

public Integer getId() {  
    return id;  
}

public void setId(Integer id) {  
    this.id = id;  
}

public String getName() {  
    return name;  
}

public void setName(String name) {  
    this.name = name;  
}

public ApplicationContext getApplicationContext() {  
    return applicationContext;  
}

public void setApplicationContext(ApplicationContext applicationContext) {  
    this.applicationContext = applicationContext;  
}

public BeanFactory getBeanFactory() {  
    return beanFactory;  
}

public void setBeanFactory(BeanFactory beanFactory) {  
    this.beanFactory = beanFactory;  
}

}

Test.xml


http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">

<bean id="beantest" class="com.ruoyi.weixin.user.Test.BeanTest">  
    <property name="name" value="张三"></property>  
    <property name="id" value="111"></property>  
</bean>

public class SpringBeanInitTest {

public static void main(String\[\] args) {  
    ApplicationContext context = new ClassPathXmlApplicationContext("Test.xml");  
    BeanTest bean = context.getBean(BeanTest.class);  
    System.out.println(bean.getName());  
    System.out.println(bean.getApplicationContext());  
}

}

下面是debug的过程

public ClassPathXmlApplicationContext(
String[] configLocations, boolean refresh, @Nullable ApplicationContext parent)
throws BeansException {
　　　　　　//调用父类构造函数
super(parent);
　　　　　　//设置BeanDefinition的配置信息路径
setConfigLocations(configLocations);
if (refresh) {
　　　　　　//容器初始化
refresh();
}
}

@Override  
public void refresh() throws BeansException, IllegalStateException {  
    synchronized (this.startupShutdownMonitor) {  
        //前戏，做日容器刷新前的准备工作

　　　　　　　　//1.设置容器的启动时间
　　　　　　　　//2.设置活跃状态为true
　　　　　　　　//3.设置关闭状态为false
　　　　　　　　//4.获取Envirenment对象，并加载当前系统属性值到Envirenment
　　　　　　　　//5.准备监听器和事件的集合对象，默认为空的集合
prepareRefresh();

        //创建容器对象ConfigurableListableBeanFactory

　　　　　　　　//加载xml配置文件到当前容器对象中，最重要是就是BeanDefinition
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.

　　　　　　　//BeanFactory准备工作，对各种属性进行填充
prepareBeanFactory(beanFactory);

        try {  
            // Allows post-processing of the bean factory in context subclasses.

　　　　　　　　　　//这是一个空方法，子类可以覆盖这个方法，在这个方法做额外的处理。此处我们自己一般不做额外的处理工作
postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.

　　　　　　　　　　//调用各种BeanFactory增强器
invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.

　　　　　　　　　　//注册bean处理器，这里只有注册功能，真正调用是getBean方法
registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.

　　　　　　　　　　//为上下文初始化message资源，即不同语言的消息体，国际化处理，简单来说就是为了支持不同语言(如中文、英文不同语言的展示)
initMessageSource();

            // Initialize event multicaster for this context.

　　　　　　　　　　//初始化事件监听多路广播器
initApplicationEventMulticaster();

            // Initialize other special beans in specific context subclasses.

　　　　　　　　　　//留给子类来初始化其它的bean
onRefresh();

            // Check for listener beans and register them.

　　　　　　　　　　//在所有注册的bean中查找监听器bean，注册到消息广播中，也就是注册监听器
registerListeners();

            // Instantiate all remaining (non-lazy-init) singletons.

　　　　　　　　　　//初始化剩下的单实例(非懒加载的)
finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.  
            finishRefresh();  
        }

        catch (BeansException ex) {  
            if (logger.isWarnEnabled()) {  
                logger.warn("Exception encountered during context initialization - " +  
                        "cancelling refresh attempt: " + ex);  
            }

            // Destroy already created singletons to avoid dangling resources.  
            destroyBeans();

            // Reset 'active' flag.  
            cancelRefresh(ex);

            // Propagate exception to caller.  
            throw ex;  
        }

        finally {  
            // Reset common introspection caches in Spring's core, since we  
            // might not ever need metadata for singleton beans anymore...  
            resetCommonCaches();  
        }  
    }  
}

//前戏，做日容器刷新前的准备工作(不用太在意)
//1.设置容器的启动时间
//2.设置活跃状态为true
//3.设置关闭状态为false
//4.获取Envirenment对象，并加载当前系统属性值到Envirenment
//5.准备监听器和事件的集合对象，默认为空的集合

protected void prepareRefresh() {
// 设置容器启动时间.
this.startupDate = System.currentTimeMillis();
　　　　//容器的关闭标志位
this.closed.set(false);
　　　　//容器活跃状态
this.active.set(true);
　　　　//记录日志
if (logger.isDebugEnabled()) {
if (logger.isTraceEnabled()) {
logger.trace("Refreshing " + this);
}
else {
logger.debug("Refreshing " + getDisplayName());
}
}

    //空的方法，留给子类实现，用来初始化属性资源(可以不管它)  
    initPropertySources();

    //创建并获取环境对象，验证需要的属性文件是否已放入环境对象中  
    getEnvironment().validateRequiredProperties();

    // 判断刷新前的应用程序的监听器集合是否为空，如果为空，将监听器添加到集合中  
    if (this.earlyApplicationListeners == null) {  
        this.earlyApplicationListeners = new LinkedHashSet<>(this.applicationListeners);  
    }  
    else {  
        // 如果不为空，清空集合  
        this.applicationListeners.clear();  
        this.applicationListeners.addAll(this.earlyApplicationListeners);  
    }

    // Allow for the collection of early ApplicationEvents,  
    // to be published once the multicaster is available...

　　　　 //创建刷新前监听事件集合
this.earlyApplicationEvents = new LinkedHashSet<>();
}

1）创建容器对象ConfigurableListableBeanFactory
2）加载xml配置文件到当前容器对象中，最重要是就是BeanDefinition
往里面进入到方法refreshBeanFactory() 

protected final void refreshBeanFactory() throws BeansException {

　　　　//如果存在BeanFactory，则销毁
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory();
}
try {
　　　　　　//创建DefaultListableBeanFactory对象
DefaultListableBeanFactory beanFactory = createBeanFactory();
　　　　　　//为了序列化设置id，可以从id反序列化到BeanFactory对象
beanFactory.setSerializationId(getId());
　　　　　　//定制BeanFactory，设置相关属性，包括是否允许覆盖同名称的不同定义的对象以及循环依赖
customizeBeanFactory(beanFactory);
　　　　　　//初始化docunmentReader，并进行xml文件读取和解析，默认命名空间的解析，自定义标签的解析
loadBeanDefinitions(beanFactory);
this.beanFactory = beanFactory;
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}

我们debug到loadBeanDefinitions(beanFactory)这里，此时查看beanFactory的两个属性，beanDefinitionMap和beanDefinitionMapNames，发现都是空的

执行完loadBeanDefinitions(beanFactory)之后，再查看，发现大小变为1了

打开beanDefinitionMap属性查看，发现名字为beantest的BeanDefinition，类型为BeanTest，正式我们在xml中定义的bean对象的信息

beanclass往下找到propertyValues属性，可以看到name和id两个属性的值

*这里就完成了第二步，BeanDefinition已经加载完成了*

　　这个方法先不深究，就是对当前beanFactory的一些属性来填充值

这是一个空方法，子类可以覆盖这个方法，在这个方法做额外的处理。此处我们自己一般不做额外的处理工作
不用管这个方法

protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
}

　　这里面爱怎么执行怎么执行，不去看了，太多了

　　注册bean处理器。注意这里只有注册功能，把BeanPostProcessors准备好，真正调用是getBean方法

　　为上下文初始化message资源，即不同语言的消息体，国际化处理，简单来说就是为了支持国际化(如中文、英文不同语言的展示)

　　就好像这个网站，右侧有english和pyccknn(俄语)两种选项，可以转换语言 。它就是为了支持这个东西

　　初始化事件监听多路广播器。

　　广播事件给监听器用。

　　这里也就是观察者模式。

protected void onRefresh() throws BeansException {  
    // For subclasses: do nothing by default.  
}

注册监听器。在所有注册的bean中查找监听器bean，注册到消息广播中

初始化剩下的单实例(非懒加载的)
更详细的创建过程：https://www.cnblogs.com/jthr/p/15919598.html 

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {  
    // Initialize conversion service for this context.  
    if (beanFactory.containsBean(CONVERSION\_SERVICE\_BEAN\_NAME) &&  
            beanFactory.isTypeMatch(CONVERSION\_SERVICE\_BEAN\_NAME, ConversionService.class)) {  
        beanFactory.setConversionService(  
                beanFactory.getBean(CONVERSION\_SERVICE\_BEAN\_NAME, ConversionService.class));  
    }

    // Register a default embedded value resolver if no bean post-processor  
    // (such as a PropertyPlaceholderConfigurer bean) registered any before:  
    // at this point, primarily for resolution in annotation attribute values.  
    if (!beanFactory.hasEmbeddedValueResolver()) {  
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));  
    }

    // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.  
    String\[\] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);  
    for (String weaverAwareName : weaverAwareNames) {  
        getBean(weaverAwareName);  
    }

    // Stop using the temporary ClassLoader for type matching.  
    beanFactory.setTempClassLoader(null);

    // Allow for caching all bean definition metadata, not expecting further changes.  
    beanFactory.freezeConfiguration();

    // Instantiate all remaining (non-lazy-init) singletons.

　　　　　　//实例化剩下的非懒加载单利对象
beanFactory.preInstantiateSingletons();
}

方法前面做了一些列的set、add操作，还是在为BeanFactory做属性赋值，也就是还在做准备工作

到beanFactory.preInstantiateSingletons()方法：实例化剩下的非懒加载单利对象

进入preInstantiateSingletons()方法

@Override  
public void preInstantiateSingletons() throws BeansException {  
    if (logger.isTraceEnabled()) {  
        logger.trace("Pre-instantiating singletons in " + this);  
    }

    // Iterate over a copy to allow for init methods which in turn register new bean definitions.  
    // While this may not be part of the regular factory bootstrap, it does otherwise work fine.

　　　　　//创建一个集合，将所有的BeanDefinition的名字放入集合
List beanNames = new ArrayList<>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...

　　　　//触发所有非懒加载的单利bean的实例化，遍历集合的对象
for (String beanName : beanNames) {
　　　　　　　　//合并父类BeanDefinition
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
　　　　　　　　//条件判断 非抽象、单利、非懒加载
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
　　　　　　　　　　//判断是否实现了FactoryBean接口
if (isFactoryBean(beanName)) {
　　　　　　　　　　　　//根据&+beanName来获取具体的对象
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
　　　　　　　　　　　　　　//进行类型转换
if (bean instanceof FactoryBean) {
FactoryBean factory = (FactoryBean) bean;
　　　　　　　　　　　　　　//判断这个Factory是否需要立即初始化
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = AccessController.doPrivileged(
(PrivilegedAction) ((SmartFactoryBean) factory)::isEagerInit,
getAccessControlContext());
}
else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
}
else {
getBean(beanName);
}
}
}

    // Trigger post-initialization callback for all applicable beans...  
    for (String beanName : beanNames) {  
        Object singletonInstance = getSingleton(beanName);  
        if (singletonInstance instanceof SmartInitializingSingleton) {  
            SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;  
            if (System.getSecurityManager() != null) {  
                AccessController.doPrivileged((PrivilegedAction<Object>) () -> {  
                    smartSingleton.afterSingletonsInstantiated();  
                    return null;  
                }, getAccessControlContext());  
            }  
            else {  
                smartSingleton.afterSingletonsInstantiated();  
            }  
        }  
    }  
}

这里，前面做了一些列的判断，做到了getBean方法，进入getBean方法

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

再进入doGetBean方法。注意，在spring中，以do开头的方法，是实际上干活的方法

protected <T> T doGetBean(  
        String name, @Nullable Class<T> requiredType, @Nullable Object\[\] args, boolean typeCheckOnly)  
        throws BeansException {

    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.isTraceEnabled()) {  
            if (isSingletonCurrentlyInCreation(beanName)) {  
                logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +  
                        "' that is not fully initialized yet - a consequence of a circular reference");  
            }  
            else {  
                logger.trace("Returning cached instance of singleton bean '" + beanName + "'");  
            }  
        }  
        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 (parentBeanFactory instanceof AbstractBeanFactory) {  
                return ((AbstractBeanFactory) parentBeanFactory).doGetBean(  
                        nameToLookup, requiredType, args, typeCheckOnly);  
            }  
            else if (args != null) {  
                // Delegation to parent with explicit args.  
                return (T) parentBeanFactory.getBean(nameToLookup, args);  
            }  
            else if (requiredType != null) {  
                // No args -> delegate to standard getBean method.  
                return parentBeanFactory.getBean(nameToLookup, requiredType);  
            }  
            else {  
                return (T) parentBeanFactory.getBean(nameToLookup);  
            }  
        }

        if (!typeCheckOnly) {  
            markBeanAsCreated(beanName);  
        }

        try {  
            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) {  
                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);  
                    }  
                }  
            }

            // Create bean instance.  
            if (mbd.isSingleton()) {  
                sharedInstance = getSingleton(beanName, () -> {  
                    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();  
                if (!StringUtils.hasLength(scopeName)) {  
                    throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");  
                }  
                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, () -> {  
                        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 && !requiredType.isInstance(bean)) {  
        try {  
            T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);  
            if (convertedBean == null) {  
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());  
            }  
            return convertedBean;  
        }  
        catch (TypeMismatchException ex) {  
            if (logger.isTraceEnabled()) {  
                logger.trace("Failed to convert bean '" + name + "' to required type '" +  
                        ClassUtils.getQualifiedName(requiredType) + "'", ex);  
            }  
            throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());  
        }  
    }  
    return (T) bean;  
}

这个方法进行一系列的处理之后，会调用方法createBean(beanName, mbd, args);

进入createBean方法

@Override  
protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object\[\] args)  
        throws BeanCreationException {

    if (logger.isTraceEnabled()) {  
        logger.trace("Creating instance of bean '" + beanName + "'");  
    }  
    RootBeanDefinition mbdToUse = mbd;

    // Make sure bean class is actually resolved at this point, and  
    // clone the bean definition in case of a dynamically resolved Class  
    // which cannot be stored in the shared merged bean definition.  
    Class<?> resolvedClass = resolveBeanClass(mbd, beanName);  
    if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {  
        mbdToUse = new RootBeanDefinition(mbd);  
        mbdToUse.setBeanClass(resolvedClass);  
    }

    // Prepare method overrides.  
    try {  
        mbdToUse.prepareMethodOverrides();  
    }  
    catch (BeanDefinitionValidationException ex) {  
        throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),  
                beanName, "Validation of method overrides failed", ex);  
    }

    try {  
        // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.  
        Object bean = resolveBeforeInstantiation(beanName, mbdToUse);  
        if (bean != null) {  
            return bean;  
        }  
    }  
    catch (Throwable ex) {  
        throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,  
                "BeanPostProcessor before instantiation of bean failed", ex);  
    }

    try {  
        Object beanInstance = doCreateBean(beanName, mbdToUse, args);  
        if (logger.isTraceEnabled()) {  
            logger.trace("Finished creating instance of bean '" + beanName + "'");  
        }  
        return beanInstance;  
    }  
    catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {  
        // A previously detected exception with proper bean creation context already,  
        // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.  
        throw ex;  
    }  
    catch (Throwable ex) {  
        throw new BeanCreationException(  
                mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);  
    }  
}

再进行了一些列的处理，调用doCreateBean(beanName, mbdToUse, args)方法，这个方法就是实际创建bean的方法
进入doCreateBean方法 

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) {  
        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 {  
                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");  
        }  
        addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));  
    }

    // Initialize the bean instance.  
    Object exposedObject = bean;  
    try {  
        populateBean(beanName, mbd, instanceWrapper);  
        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;  
}

里面又调用了方法 createBeanInstance(beanName, mbd, args);它是根据执行bean使用对应的策略创建新的实例。如工厂方法、构造方法、简单初始化

进入createBeanInstance方法

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
　　　　　　//确定需要创建的bean的实例的类可以实例化
Class beanClass = resolveBeanClass(mbd, beanName);

    if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {  
        throw new BeanCreationException(mbd.getResourceDescription(), beanName,  
                "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());  
    }

　　　　//判断当前Definition是否包含实例供应器。此处相当于一个回调方法，利用回调方法来创建bean
Supplier instanceSupplier = mbd.getInstanceSupplier();
if (instanceSupplier != null) {
return obtainFromSupplier(instanceSupplier, beanName);
}
　　　　//如果工厂方法不为空，使用工厂方法策略来初始化策略
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}

    // Shortcut when re-creating the same bean...  
    boolean resolved = false;  
    boolean autowireNecessary = false;  
    if (args == null) {  
        synchronized (mbd.constructorArgumentLock) {  
            if (mbd.resolvedConstructorOrFactoryMethod != null) {  
                resolved = true;  
                autowireNecessary = mbd.constructorArgumentsResolved;  
            }  
        }  
    }  
    if (resolved) {  
        if (autowireNecessary) {  
            return autowireConstructor(beanName, mbd, null, null);  
        }  
        else {  
            return instantiateBean(beanName, mbd);  
        }  
    }

    // Candidate constructors for autowiring?

　　　　//获取构造方法
Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
return autowireConstructor(beanName, mbd, ctors, args);
}

    // Preferred constructors for default construction?  
    ctors = mbd.getPreferredConstructors();  
    if (ctors != null) {  
        return autowireConstructor(beanName, mbd, ctors, null);  
    }

    // No special handling: simply use no-arg constructor.  
    return instantiateBean(beanName, mbd);  
}

前面做了一系列的处理，获取了class对象，获取构造器，最后调用instantiateBean(beanName, mbd)方法
进入instantiateBean方法

protected BeanWrapper instantiateBean(String beanName, RootBeanDefinition mbd) {
try {
Object beanInstance;
if (System.getSecurityManager() != null) {
beanInstance = AccessController.doPrivileged(
(PrivilegedAction) () -> getInstantiationStrategy().instantiate(mbd, beanName, this),
getAccessControlContext());
}
else {
　　　　　　　　　　//获取实例化策略并进行实例化操作
beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, this);
}
BeanWrapper bw = new BeanWrapperImpl(beanInstance);
initBeanWrapper(bw);
return bw;
}
catch (Throwable ex) {
throw new BeanCreationException(
mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
}
}

里面调用beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, this);

进入instantiate方法

@Override
public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
// Don't override the class with CGLIB if no overrides.
if (!bd.hasMethodOverrides()) {
Constructor constructorToUse;
synchronized (bd.constructorArgumentLock) {
constructorToUse = (Constructor) bd.resolvedConstructorOrFactoryMethod;
if (constructorToUse == null) {
final Class clazz = bd.getBeanClass();
if (clazz.isInterface()) {
throw new BeanInstantiationException(clazz, "Specified class is an interface");
}
try {
if (System.getSecurityManager() != null) {
constructorToUse = AccessController.doPrivileged(
(PrivilegedExceptionAction>) clazz::getDeclaredConstructor);
}
else {
　　　　　　　　　　　　　　//获取无参构造器
constructorToUse = clazz.getDeclaredConstructor();
}
bd.resolvedConstructorOrFactoryMethod = constructorToUse;
}
catch (Throwable ex) {
throw new BeanInstantiationException(clazz, "No default constructor found", ex);
}
}
}
return BeanUtils.instantiateClass(constructorToUse);
}
else {
// Must generate CGLIB subclass.
return instantiateWithMethodInjection(bd, beanName, owner);
}
}

里面又获取了无参构造，后面调用了BeanUtils.instantiateClass(constructorToUse);

进入instantiateClass方法

public static T instantiateClass(Constructor ctor, Object… args) throws BeanInstantiationException {
Assert.notNull(ctor, "Constructor must not be null");
try {
ReflectionUtils.makeAccessible(ctor);
if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
return KotlinDelegate.instantiateClass(ctor, args);
}
else {
Class[] parameterTypes = ctor.getParameterTypes();
Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters"); Object[] argsWithDefaultValues = new Object[args.length]; for (int i = 0 ; i < args.length; i++) { if (args[i] == null) { Class parameterType = parameterTypes[i];
argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null);
}
else {
argsWithDefaultValues[i] = args[i];
}
}
return ctor.newInstance(argsWithDefaultValues);
}
}
catch (InstantiationException ex) {
throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
}
catch (IllegalAccessException ex) {
throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
}
catch (IllegalArgumentException ex) {
throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
}
catch (InvocationTargetException ex) {
throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
}
}

看到里面调用了return ctor.newInstance(argsWithDefaultValues);通过构造器创建了实例。这么深，终于看到了创建实例操作

回到doCreateBean方法，执行完了createBeanInstance，往下看

populateBean(beanName, mbd, instanceWrapper);

接下来执行了populateBean方法，这个方法是给bean的属性赋值的。

在这里执行后，id和name就有值了。application和beanFactory两个属性还没有值

接下来又执行了方法exposedObject = initializeBean(beanName, exposedObject, mbd);方法

进入initializeBean

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {  
    if (System.getSecurityManager() != null) {  
        AccessController.doPrivileged((PrivilegedAction<Object>) () -> {  
            invokeAwareMethods(beanName, bean);  
            return null;  
        }, getAccessControlContext());  
    }  
    else {  
        invokeAwareMethods(beanName, bean);  
    }

    Object wrappedBean = bean;  
    if (mbd == null || !mbd.isSynthetic()) {  
        wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);  
    }

    try {  
        invokeInitMethods(beanName, wrappedBean, mbd);  
    }  
    catch (Throwable ex) {  
        throw new BeanCreationException(  
                (mbd != null ? mbd.getResourceDescription() : null),  
                beanName, "Invocation of init method failed", ex);  
    }  
    if (mbd == null || !mbd.isSynthetic()) {  
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);  
    }

    return wrappedBean;  
}

里面执行了invokeAwareMethods(beanName, bean);

也就是执行aware方法。

该方法执行完成后，beanFactory赋值了，而applicationContext属性还没有值

我们进入invokeAwareMethods方法，发现它只调用了setBeanName，setBeanClassLoader，setBeanFactory，所以只会给beanName，beanClassLoader、beanFactory赋值

private void invokeAwareMethods(String beanName, Object bean) {
if (bean instanceof Aware) {
if (bean instanceof BeanNameAware) {
((BeanNameAware) bean).setBeanName(beanName);
}
if (bean instanceof BeanClassLoaderAware) {
ClassLoader bcl = getBeanClassLoader();
if (bcl != null) {
((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
}
}
if (bean instanceof BeanFactoryAware) {
((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
}
}
}

invokeAwareMethods执行完成，我们继续看initializeBean方法，接下来执行了applyBeanPostProcessorsBeforeInitialization方法

wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);

执行了BeanPostProcessors里面的before，

这个方法会为applicationContext属性赋值

在下面又会执行invokeInitMethods(beanName, wrappedBean, mbd);方法

这里会执行bean的init方法

再下一步执行applyBeanPostProcessorsAfterInitialization

wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);

执行了BeanPostProcessors里面的after

这样子，就有了创建bean的完整脉络。

手机扫一扫

移动阅读更方便

阿里云服务器
腾讯云服务器
七牛云服务器

你可能感兴趣的文章

《系列二》-- 1、BeanFactory.getBean 总览
Spring源码核心剖析
解析BeanDefinitionRegistry与BeanDefinition合并

4

SpringBoot 启动流程追踪(第二篇)

5

Spring面试攻略：如何展现你对Spring的深入理解

6

Spring源码学习之容器的基本实现(一)

7

Spring，IOC源码分析

8

Spring的IOC源码分析

9

【spring 注解驱动开发】spring对象的生命周期

10

进阶：spring-bean生命周期流程