解析Spring源码（3）---XmlBeanDefinitionReader（1）

上节我们对XmlBeanFactory进行了初步了解

简化版源码：

    /**     * public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory        implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable        public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {        super(registry);        }        protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {        this.registry = registry;     */    //reader的registry得到初始化值为XmlBeanFactory对象，this指代的就是此时创建的XmlBeanFactory对象    private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);

首先分析一下上面这段代码（调用有参构造函数）；

    /**     * 在XmlBeanFactory进行了实例化操作，传递XmlBeanFactory对象参数     */    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {        super(registry);    }

    /**     *      */    protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {        //  private final BeanDefinitionRegistry registry;属性初始化XmlBeanFactory对象        this.registry = registry;            //private ResourceLoader resourceLoader;赋值            this.resourceLoader = new PathMatchingResourcePatternResolver();            this.environment = new StandardEnvironment();//初始化，创建StandardEnvironment对象    }

this.resourceLoader = new PathMatchingResourcePatternResolver();

private final ResourceLoader resourceLoader;    /**     * 默认构造函数，初始化     * Create a new PathMatchingResourcePatternResolver with a DefaultResourceLoader.     */    public PathMatchingResourcePatternResolver() {        this.resourceLoader = new DefaultResourceLoader();    }

    /**     * Create a new DefaultResourceLoader.     */    public DefaultResourceLoader() {        this.classLoader = ClassUtils.getDefaultClassLoader();    }

    /**     * 返回类加载器     * Return the default ClassLoader to use: typically the thread context     */    public static ClassLoader getDefaultClassLoader() {        ClassLoader cl = null;            //获得类加载器            cl = Thread.currentThread().getContextClassLoader();        return cl;    }

返回的是同一个类加载器；

通过以上操作：
我们得到了什么？

private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);//对象的属性this.registry = registry;this.resourceLoader = new PathMatchingResourcePatternResolver(); new PathMatchingResourcePatternResolver();对象的属性 this.resourceLoader = new DefaultResourceLoader();  new DefaultResourceLoader();对象的属性  this.classLoader = ClassUtils.getDefaultClassLoader();赋值与ClassPathResource同一个类加载器

综上所述：reader可以获取到XmlBeanFactory对象和类加载器！！！
原版代码：

    /**     * public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory        implements ConfigurableListableBeanFactory, BeanDefinitionRegistry, Serializable        public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {        super(registry);        }        protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {        Assert.notNull(registry, "BeanDefinitionRegistry must not be null");        this.registry = registry;     */    //reader的registry得到初始化值为XmlBeanFactory对象，this指代的就是此时创建的XmlBeanFactory对象    private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);

首先分析一下上面这段代码（调用有参构造函数）；

    /**     * 在XmlBeanFactory进行了实例化操作，传递XmlBeanFactory对象参数     * Create new XmlBeanDefinitionReader for the given bean factory.     * @param registry the BeanFactory to load bean definitions into,     * in the form of a BeanDefinitionRegistry     */    public XmlBeanDefinitionReader(BeanDefinitionRegistry registry) {        super(registry);    }

    /**     * Create a new AbstractBeanDefinitionReader for the given bean factory.     * <p>If the passed-in bean factory does not only implement the BeanDefinitionRegistry     * interface but also the ResourceLoader interface, it will be used as default     * ResourceLoader as well. This will usually be the case for     * {@link org.springframework.context.ApplicationContext} implementations.     * <p>If given a plain BeanDefinitionRegistry, the default ResourceLoader will be a     * {@link org.springframework.core.io.support.PathMatchingResourcePatternResolver}.     * <p>If the passed-in bean factory also implements {@link EnvironmentCapable} its     * environment will be used by this reader.  Otherwise, the reader will initialize and     * use a {@link StandardEnvironment}. All ApplicationContext implementations are     * EnvironmentCapable, while normal BeanFactory implementations are not.     * @param registry the BeanFactory to load bean definitions into,     * in the form of a BeanDefinitionRegistry     * @see #setResourceLoader     * @see #setEnvironment     */    protected AbstractBeanDefinitionReader(BeanDefinitionRegistry registry) {        Assert.notNull(registry, "BeanDefinitionRegistry must not be null");        //  private final BeanDefinitionRegistry registry;属性初始化XmlBeanFactory对象        this.registry = registry;        // Determine ResourceLoader to use.        //false        if (this.registry instanceof ResourceLoader) {            this.resourceLoader = (ResourceLoader) this.registry;        }        else {            //private ResourceLoader resourceLoader;赋值            this.resourceLoader = new PathMatchingResourcePatternResolver();        }        // Inherit Environment if possible        if (this.registry instanceof EnvironmentCapable) {            this.environment = ((EnvironmentCapable) this.registry).getEnvironment();        }        else {            this.environment = new StandardEnvironment();//初始化，创建StandardEnvironment对象        }    }

this.resourceLoader = new PathMatchingResourcePatternResolver();

private final ResourceLoader resourceLoader;    /**     * 默认构造函数，初始化     * Create a new PathMatchingResourcePatternResolver with a DefaultResourceLoader.     * <p>ClassLoader access will happen via the thread context class loader.     * @see org.springframework.core.io.DefaultResourceLoader     */    public PathMatchingResourcePatternResolver() {        this.resourceLoader = new DefaultResourceLoader();    }

    /**     * Create a new DefaultResourceLoader.     * <p>ClassLoader access will happen using the thread context class loader     * at the time of this ResourceLoader's initialization.     * @see java.lang.Thread#getContextClassLoader()     */    public DefaultResourceLoader() {        this.classLoader = ClassUtils.getDefaultClassLoader();    }

    /**     * 返回类加载器     * Return the default ClassLoader to use: typically the thread context     * ClassLoader, if available; the ClassLoader that loaded the ClassUtils     * class will be used as fallback.     * <p>Call this method if you intend to use the thread context ClassLoader     * in a scenario where you clearly prefer a non-null ClassLoader reference:     * for example, for class path resource loading (but not necessarily for     * {@code Class.forName}, which accepts a {@code null} ClassLoader     * reference as well).     * @return the default ClassLoader (only {@code null} if even the system     * ClassLoader isn't accessible)     * @see Thread#getContextClassLoader()     * @see ClassLoader#getSystemClassLoader()     */    public static ClassLoader getDefaultClassLoader() {        ClassLoader cl = null;        try {            //获得类加载器            cl = Thread.currentThread().getContextClassLoader();        }        catch (Throwable ex) {            // Cannot access thread context ClassLoader - falling back...        }        if (cl == null) {            // No thread context class loader -> use class loader of this class.            cl = ClassUtils.class.getClassLoader();            if (cl == null) {                // getClassLoader() returning null indicates the bootstrap ClassLoader                try {                    cl = ClassLoader.getSystemClassLoader();                }                catch (Throwable ex) {                    // Cannot access system ClassLoader - oh well, maybe the caller can live with null...                }            }        }        return cl;    }

返回的是同一个类加载器；

通过以上操作：
我们得到了什么？

private final XmlBeanDefinitionReader reader = new XmlBeanDefinitionReader(this);//对象的属性this.registry = registry;this.resourceLoader = new PathMatchingResourcePatternResolver(); new PathMatchingResourcePatternResolver();对象的属性 this.resourceLoader = new DefaultResourceLoader();  new DefaultResourceLoader();对象的属性  this.classLoader = ClassUtils.getDefaultClassLoader();赋值与ClassPathResource同一个类加载器

综上所述：reader可以获取到XmlBeanFactory对象和类加载器！！！