sping @Bean创建对象一 对象的实例化

一个简单的JavaBean==>Something.Java

package com.springl.bean;

import java.util.Date;

public class Something {

    private Integer id;

    private Date createTime;

    private Date updateTime;

    public Something() {
        System.out.println("==============>Something[Constructor]");
    }

    public Integer getId() {
        return id;
    }

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

    public Date getCreateTime() {
        return createTime;
    }

    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }

    public Date getUpdateTime() {
        return updateTime;
    }

    public void setUpdateTime(Date updateTime) {
        this.updateTime = updateTime;
    }


    @Override
    public String toString() {
        return "Something{" +
                "id=" + id +
                ", createTime=" + createTime +
                ", updateTime=" + updateTime +
                '}';
    }
}

一个配置类

package com.springl.bean;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.Date;

@Configuration
public class BeanCreateConfig {

    @Bean
    public Something something(){

        Date now = new Date();

        Something something  =  new Something();
        something.setId(1);
        something.setCreateTime(now);
        something.setUpdateTime(now);

        return something;
    }
}

一个测试类

package com.springl.test;


import com.springl.bean.BeanCreateConfig;
import com.springl.bean.Something;
import org.junit.Test;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class BeanCreateTest {

    @Test
    public void testBean(){
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanCreateConfig.class);
        Something something = (Something) applicationContext.getBean("something");
        System.out.println(something);
        applicationContext.close();
    }
}

最终测试结果：

==============>Something[Constructor]
Something{id=1, createTime=Fri Feb 07 22:18:47 EST 2020, updateTime=Fri Feb 07 22:18:47 EST 2020}

 

---

下边看下这个Bean到底是怎么创建出来的

---

在[Something.Java]构造函数上打上断点，总体看下执行的流程

 

1.在配置类中创建AnnotationConfigApplicationContext对象时，执行其构造函数

AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeanCreateConfig.class);

看下AnnotationConfigApplicationContext对象的构造函数

public AnnotationConfigApplicationContext(Class... annotatedClasses) {
	this();
	register(annotatedClasses);
        //创建AnnotationConfigApplicationContext对象的时候执行到这里
	refresh();
}

2.执行AnnotationConfigApplicationContext.refresh();------->AbstractApplicationContext.refresh();

@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.
            initMessageSource();

            // Initialize event multicaster for this context.
            initApplicationEventMulticaster();

            // Initialize other special beans in specific context subclasses.
            onRefresh();

            // Check for listener beans and register them.
            registerListeners();

            // Instantiate all remaining (non-lazy-init) singletons.
            //执行到这里，初始化所有剩下的非懒加载的单实例对象
            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();
        }
    }
}

3.继续执行AbstractApplicationContext.finishBeanFactoryInitialization(beanFactory);//初始化剩下的非懒加载的单例对象

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(new StringValueResolver() {
            @Override
            public String resolveStringValue(String strVal) {
                return 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.
    //执行到这里，初始化所有剩下的非懒加载的单实例对象
    beanFactory.preInstantiateSingletons();
}

4.继续执行beanFactory.preInstantiateSingletons();  在这里的beanFactory是DefaultListableBeanFactory的对象

@Override
public void preInstantiateSingletons() throws BeansException {
    if (this.logger.isDebugEnabled()) {
        this.logger.debug("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.
    List beanNames = new ArrayList(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    for (String beanName : beanNames) {
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        //不是抽象类，并且是单实例bean，并且不是懒加载
        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
            if (isFactoryBean(beanName)) {
                final FactoryBean factory = (FactoryBean) getBean(FACTORY_BEAN_PREFIX + beanName);
                boolean isEagerInit;
                if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                    isEagerInit = AccessController.doPrivileged(new PrivilegedAction() {
                        @Override
                        public Boolean run() {
                            return ((SmartFactoryBean) factory).isEagerInit();
                        }
                    }, getAccessControlContext());
                }
                else {
                    isEagerInit = (factory instanceof SmartFactoryBean &&
                            ((SmartFactoryBean) factory).isEagerInit());
                }
                if (isEagerInit) {
                    getBean(beanName);
                }
            }
            //执行到这里，不是工厂类
            else {
                getBean(beanName);
            }
        }
    }

    // Trigger post-initialization callback for all applicable beans...
    for (String beanName : beanNames) {
        Object singletonInstance = getSingleton(beanName);
        if (singletonInstance instanceof SmartInitializingSingleton) {
            final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
            if (System.getSecurityManager() != null) {
                AccessController.doPrivileged(new PrivilegedAction