Spring Ioc的原理解析之getBean流程分析

摘要：简单介绍模块和模块是框架的基础部分，提供控制反转和依赖注入特性。

Spring Framework简单介绍

Core Container模块:Core 和 Beans 模块是框架的基础部分，提供 IoC （控制反转）和 DI（依赖注入）特性。 Context构建于Core 和 Bean 之上，提供了一个BeanFactory来访问应用组件，添加了国际化（例如资源绑定）、事件传播、资源加载等。SpEL提供了强大的表达式语言。

Data Access/Integration模块：JDBC提供了一个JDBC抽象层，ORM对象关系映射如：JPA，XOM提供了一个ObjectXML映射关系，JMS提供了生产消息和消费消息的功能，Transactions：提供了编程和声明性的事务管理，这些事务类必须实现特定的接口。

Web模块：提供了面向Web的特性，比如Spring Mvc，使用servlet listeners初始化IoC容器以及一个面向Web的应用上下文，典型的父子容器关系。

Aop模块：Aspects模块提供了对AspectJ集成的支持。Instrumentation模块提供了class instrumentation支持和classloader实现，动态字节码插桩。

Test模块：Test模块支持使用Junit等对Spring组件进行测试

Ioc的核心思想以及常用注解和应用

Ioc的核心思想：资源组件不由使用方管理，而由不使用资源的第三方管理，这可以带来很多好处。第一，资源集中管理，实现资源的可配置和易管理。第二，降低了使用资源双方的依赖程度，也就是我们说的耦合度

常用的注解：

@Configuration 相对于配置文件中的
@Bean 相对于配置文件中的
@CompentScan 包扫描
@Scope 配置Bean的作用域
@Lazy 是否开启懒加载
@Conditional 条件注解 spring boot中经常用到
@Import 导入组件
......

应用：

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.beans.factory.annotation.Autowired;
    
   
    public class PrincipleAspect {
        @Autowired
        private PrincipleLog principleLog;
    
        /*public PrincipleLog getPrincipleLog() {
            return principleLog;
        }
    
        public void setPrincipleLog(PrincipleLog principleLog) {
            this.principleLog = principleLog;
        }*/
    }

    package com.toby.ioc.iocprinciple;
    
    public class PrincipleBean {
    }

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.beans.factory.annotation.Autowire;
    import org.springframework.context.annotation.*;
    
    @Configuration
    @ComponentScan(basePackages = {"com.toby.ioc.iocprinciple"})
    //@ImportResource("classpath:Beans.xml")
    @Import(PrincipleService.class)
    public class PrincipleConfig {
        @Bean
        public PrincipleBean principleBean(){
            return new PrincipleBean();
        }
    
        //@Bean(autowire = Autowire.BY_TYPE)
        @Bean
        public PrincipleAspect principleAspect(){
            return new PrincipleAspect();
        }
    
        @Bean
        @Primary
        public PrincipleLog principleLog(){
            return new PrincipleLog();
        }
    
        @Bean
        public PrincipleLog principleLog2(){
            return new PrincipleLog();
        }
    }

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.stereotype.Controller;
    
    @Controller
    public class PrincipleController {
    }

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.stereotype.Repository;
    
    @Repository
    public class PrincipleDao {
    }

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    /**
     * @desc: 循环依赖
     * @author: toby
     */
    @Component
    public class PrincipleInstanceA {
        @Autowired
        private PrincipleInstanceB instanceB;
    }

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    /**
     * @desc: 循环依赖
     * @author: toby
     */
    @Component
    public class PrincipleInstanceB {
        @Autowired
        private PrincipleInstanceA instanceA;
    }

    package com.toby.ioc.iocprinciple;
    
    /**
     * @desc:
     * @author: toby
     */
    public class PrincipleLog {
    }

    package com.toby.ioc.iocprinciple;
    
    /**
     * @desc:
     * @author: toby
     */
    public class PrincipleService {
    }

    package com.toby.ioc.iocprinciple;
    
    import org.springframework.context.annotation.AnnotationConfigApplicationContext;
    
    /**
     * @desc: ioc原理解析 启动
     * @author: toby
     */
    public class PrincipleMain {
        public static void main(String[] args) {
            AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(PrincipleConfig.class);
            /*for (String beanDefinitionName : context.getBeanDefinitionNames()) {
                System.out.println("bean定义名称:" + beanDefinitionName);
            }*/
            PrincipleAspect principleAspect = context.getBean(PrincipleAspect.class);
            context.close();
            System.out.println(principleAspect);
        }
    }

完整的代码请见：spring

getBean的源码解析

beanfactory的类继承图：

首先创建org.springframework.context.annotation.AnnotationConfigApplicationContext#AnnotationConfigApplicationContext(java.lang.Class...)

    public AnnotationConfigApplicationContext(Class... annotatedClasses) {
        //主要的作用往容器中注册系统级别的处理器，为处理我们自定义的配置类准备，以及初始化classpath下的bean定义扫描
        this();
        //注册我们自定义的配置类
        register(annotatedClasses);
        //Ioc容器刷新12大步
        refresh();
   }

org.springframework.context.support.AbstractApplicationContext#refresh 12大步

public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            //1:准备刷新上下文环境
            prepareRefresh();

            //2:获取初始化Bean工厂
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            //3:对bean工厂进行填充属性
            prepareBeanFactory(beanFactory);
            try {
                //4：Spring开放接口 留给子类去实现该接口
                postProcessBeanFactory(beanFactory);

                //:5：调用我们的bean工厂的后置处理器
                invokeBeanFactoryPostProcessors(beanFactory);

                // 6：注册我们bean后置处理器
                registerBeanPostProcessors(beanFactory);

                // 7：初始化国际化资源处理器
                initMessageSource();

                //8：初始化事件多播器
                initApplicationEventMulticaster();

                //9：// 这个方法同样也是留个子类实现的springboot也是从这个方法进行启动tomcat的.
                onRefresh();

                //10：把我们的事件监听器注册到多播器上
                registerListeners();

                //11：实例化所有的非懒加载的单实例bean
                finishBeanFactoryInitialization(beanFactory);

                //12：最后刷新容器 发布刷新事件(Spring cloud eureka也是从这里启动的)
                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();
            }
        }
    }

第11步：实例化所有的非懒加载的单实例bean
org.springframework.context.support.AbstractApplicationContext#finishBeanFactoryInitialization

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);

        //冻结所有的bean定义
        beanFactory.freezeConfiguration();
        
        //实例化剩余的非懒加载的单实例bean
        beanFactory.preInstantiateSingletons();
    }

实例化剩余的非懒加载的单实例bean：

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

        // 获取容器中所有beanName
        List beanNames = new ArrayList(this.beanDefinitionNames);

        //触发实例化所有的非懒加载的单实例bean
        for (String beanName : beanNames) {
            //合并bean定义
            RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
            //非抽象，单实例，非懒加载
            if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                //是否工厂bean，是要获取factorybean的getObject方法
                if (isFactoryBean(beanName)) {
                    //factorybean的bean那么前面加了一个FACTORY_BEAN_PREFIX就是&
                    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) {
                        //调用getBean流程
                        getBean(beanName);
                    }
                }
                else {//非工厂bean
                    //调用getBean流程
                    getBean(beanName);
                }
            }
        }

        //触发初始化之后的回调，到这里所有的bean都存放在了单例缓冲池中了
        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