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Spring 源码解析(二十一)加载BeanFactory

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摘要: 本文结合《Spring源码深度解析》来分析Spring 5.0.6版本的源代码。若有描述错误之处,欢迎指正。

目录

一、定制化BeanFactory

二、加载BeanDefinition

obtainFreshBeanFactory方法从字面上理解是获取BeanFactory。之前有说过,ApplicationContext是对BeanFactory的功能上的扩展,不但包含了BeanFactory的全部功能更在其基础上添加了大量的扩展功能,那么obtainFreshBeanFactory正是实现BeanFactory的地方,也就是经过了这个函数后ApplicationContext就已经拥有了BeanFactory的全部功能。

/**
 * Tell the subclass to refresh the internal bean factory.
 * @return the fresh BeanFactory instance
 * @see #refreshBeanFactory()
 * @see #getBeanFactory()
 */
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
    // 初始化BeanFactory,并进行XML文件读取,并将得到的BeanFactory记录在当前实体的属性中
    refreshBeanFactory();
    // 返回当前实体的beanFactory属性
    return getBeanFactory();
}

方法中将核心实现委托给了refreshBeanFactory:

/**
 * This implementation performs an actual refresh of this context's underlying
 * bean factory, shutting down the previous bean factory (if any) and
 * initializing a fresh bean factory for the next phase of the context's lifecycle.
 */
@Override
protected final void refreshBeanFactory() throws BeansException {
    if (hasBeanFactory()) {
        destroyBeans();
        closeBeanFactory();
    }
    try {
        // 创建DefaultListableBeanFactory
        DefaultListableBeanFactory beanFactory = createBeanFactory();
        // 为了序列话指定id,如果需要的话,让这个BeanFactory从id反序列化到BeanFactory对象
        beanFactory.setSerializationId(getId());
        /**
         * 设置两个属性:
         * 1. 是否允许覆盖同名称的不同定义的对象
         * 2. 是否允许bean之间存在循环依赖
         */
        customizeBeanFactory(beanFactory);
        // 初始化DocumentReader,并进行XML文件读取和解析
        loadBeanDefinitions(beanFactory);
        synchronized (this.beanFactoryMonitor) {
            this.beanFactory = beanFactory;
        }
    }
    catch (IOException ex) {
        throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
    }
}

我们详细分析上面的每个步骤。

(1)创建DefaultListableBeanFactory。

在介绍BeanFactory的时候,不知道读者是否还有印象,声明方式为:BeanFactory factory = new XmlBeanFactory(“spring-test.xml”),其中的XmlBeanFactory继承自DefaultListableBeanFactory,并提供了XmlBeanDefinitionReader类型的reader属性也就是说DefaultListableBeanFactory是容器的基础。必须首先实例化,那么在这里就是实例化DefaultListableBeanFactory的步骤。

(2)指定序列化ID。

(3)定制BeanFactory。

(4)加载BeanDefinition。

(5)使用全局变量记录BeanFactory类实例。

因为DefaultListableBeanFactory类型的变量beanFactory是函数内的局部变量,所以要使用全局变量记录解析结果。

一、定制化BeanFactory

这里已经开始了对BeanFactory的扩展,在基本容器的基础上,增加了是否允许覆盖是否允许扩展的设置。

/**
 * Customize the internal bean factory used by this context.
 * Called for each {@link #refresh()} attempt.
 * <p>The default implementation applies this context's
 * {@linkplain #setAllowBeanDefinitionOverriding "allowBeanDefinitionOverriding"}
 * and {@linkplain #setAllowCircularReferences "allowCircularReferences"} settings,
 * if specified. Can be overridden in subclasses to customize any of
 * {@link DefaultListableBeanFactory}'s settings.
 * @param beanFactory the newly created bean factory for this context
 * @see DefaultListableBeanFactory#setAllowBeanDefinitionOverriding
 * @see DefaultListableBeanFactory#setAllowCircularReferences
 * @see DefaultListableBeanFactory#setAllowRawInjectionDespiteWrapping
 * @see DefaultListableBeanFactory#setAllowEagerClassLoading
 */
protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
    // 如果属性allowBeanDefinitionOverriding不为空,设置给beanFactory对象相应属性
    // 此属性的含义:是否允许覆盖同名称的不同定义的对象
    if (this.allowBeanDefinitionOverriding != null) {
        beanFactory.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
    }
    // 如果属性allowCircularReferences不为空,设置给beanFactory对象相应属性
    // 此属性的含义:是否允许bean之间存在循环依赖
    if (this.allowCircularReferences != null) {
        beanFactory.setAllowCircularReferences(this.allowCircularReferences);
    }
}

是否允许覆盖和允许依赖的设置这里这是判断了是否为空,如果不为空则进行设置,但是并没有看到在哪里进行设置,究竟这个设置是在哪里进行设置的呢?还是那句话,使用子类覆盖方法,例如:

public class MyClassPathXmlApplicationContext extends ClassPathXmlApplicationContext {

    ......

    @Override
    protected void customizeBeanFactory(DefaultListableBeanFactory beanFactory) {
        super.setAllowBeanDefinitionOverriding(false);
        super.setAllowCircularReferences(false);
        super.customizeBeanFactory(beanFactory);
    }
}

二、加载BeanDefinition

在第一步中提到了ClassPathXmlApplicationContext与XmlBeanFactory创建的对比,在实现配置文件的加载功能中除了我们在第一步中已经初始化的DefaultListableBeanFactory外,还需要XmlBeanDefinitionReader来读取XML,那么在这个步骤中首先要做的就是初始化XmlBeanDefinitionReader。

/**
 * Loads the bean definitions via an XmlBeanDefinitionReader.
 * @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
 * @see #initBeanDefinitionReader
 * @see #loadBeanDefinitions
 */
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
    // Create a new XmlBeanDefinitionReader for the given BeanFactory.
    // 为指定beanFactory创建XmlBeanDefinitionReader
    XmlBeanDefinitionReader beanDefinitionReader = new XmlBeanDefinitionReader(beanFactory);

    // Configure the bean definition reader with this context's
    // resource loading environment.
    // 对beanDefinitionReader进行环境变量的设置
    beanDefinitionReader.setEnvironment(this.getEnvironment());
    beanDefinitionReader.setResourceLoader(this);
    beanDefinitionReader.setEntityResolver(new ResourceEntityResolver(this));

    // Allow a subclass to provide custom initialization of the reader,
    // then proceed with actually loading the bean definitions.
    // 对beanDefinitionReader进行设置,可以覆盖
    initBeanDefinitionReader(beanDefinitionReader);
    loadBeanDefinitions(beanDefinitionReader);
}

在初始化了DefaultListableBeanFactory和XmlBeanDefinitionReader后就可以进行配置文件的读取了。

/**
 * Load the bean definitions with the given XmlBeanDefinitionReader.
 * <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}
 * method; hence this method is just supposed to load and/or register bean definitions.
 * @param reader the XmlBeanDefinitionReader to use
 * @throws BeansException in case of bean registration errors
 * @throws IOException if the required XML document isn't found
 * @see #refreshBeanFactory
 * @see #getConfigLocations
 * @see #getResources
 * @see #getResourcePatternResolver
 */
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
    Resource[] configResources = getConfigResources();
    if (configResources != null) {
        reader.loadBeanDefinitions(configResources);
    }
    String[] configLocations = getConfigLocations();
    if (configLocations != null) {
        reader.loadBeanDefinitions(configLocations);
    }
}

使用XmlBeanDefinitionReader的loadBeanDefinitions方法进行配置文件的加载注册相信大家已经不陌生,这完全就是开始BeanFactory的套路。因为在XmlBeanDefinitionReader中已经将之前初始化的DefaultListableBeanFactory注册进去了,所有XmlBeanDefinitionReader所读取的BeanDefinitionHolder都会注册到DefaultListableBeanFactory中,也就是经过此步骤,类型DefaultListableBeanFactory的变量beanFactory已经包含了所有解析好的配置。

文章永久链接:https://tech.souyunku.com/?p=15685


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