ApplicationContext（九）初始化非延遲的 bean

ApplicationContext（九）初始化非延遲的 bean

此至，ApplicationContext 已經完成了所有的準備工做，開始初始化剩餘的 bean 了(第 11 步)。

public void refresh() throws BeansException, IllegalStateException {
    // 11. 初始化剩餘的 bean (部分在 invokeBeanFactoryPostProcessors 已經初始化)
    finishBeanFactoryInitialization(beanFactory);
}

finishBeanFactoryInitialization 主要是實例化非懶加載的 bean。

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // 1. 註冊 ConversionService，注意 beanName 必須爲 conversionService
    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));
    }

    // 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);

    // 2. 凍結全部的 bean 定義，說明註冊的 bean 定義將不被修改
    beanFactory.freezeConfiguration();

    // 3. 初始化剩下的 bean
    beanFactory.preInstantiateSingletons();
}

1、註冊 ConversionService

(1) String2DateConverter

public class String2DateConverter implements Converter<String, Date> {
    @Override
    public Date convert(String source) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        try {
            return sdf.parse(source);
        } catch (ParseException e) {
            ;
        }
        return null;
    }
}

(2) 註冊

注意：beanName 必須爲 conversionService

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <set>
            <bean class="com.github.binarylei.spring01.day0728.conversionservice.String2DateConverter"/>
        </set>
    </property>
</bean>

(3) 測試

@Test
public void test() {
    DefaultConversionService service = new DefaultConversionService();
    service.addConverter(new String2DateConverter());

    Date value = service.convert("2018-08-02", Date.class);
    System.out.println(value);
}

2、凍結配置

源代碼【DefaultListableBeanFactory】

public void freezeConfiguration() {
    this.configurationFrozen = true;
    this.frozenBeanDefinitionNames = StringUtils.toStringArray(this.beanDefinitionNames);
}

3、初始化非延遲加載

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

    // 1. 建立剩下的單實例 bean
    List<String> beanNames = new ArrayList<String>(this.beanDefinitionNames);

    // Trigger initialization of all non-lazy singleton beans...
    for (String beanName : beanNames) {
        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
        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<Boolean>() {
                        @Override
                        public Boolean run() {
                            return ((SmartFactoryBean<?>) factory).isEagerInit();
                        }
                    }, getAccessControlContext());
                }
                else {
                    isEagerInit = (factory instanceof SmartFactoryBean &&
                            ((SmartFactoryBean<?>) factory).isEagerInit());
                }
                if (isEagerInit) {
                    getBean(beanName);
                }
            }
            else {
                getBean(beanName);
            }
        }
    }

    // 2. 篩選出實現了 SmartInitializingSingleton 接口的 bean，回調 afterSingletonsInstantiated() 方法
    //    @EventListener 註解的方式註冊監聽器就是在這一步完成的
    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<Object>() {
                    @Override
                    public Object run() {
                        smartSingleton.afterSingletonsInstantiated();
                        return null;
                    }
                }, getAccessControlContext());
            }
            else {
                smartSingleton.afterSingletonsInstantiated();
            }
        }
    }
}

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