Spring之对象解析及注册(一)

首先先看一下Spring是如何创建对象的

Spring创建对象

public interface IService {
    public String hello();
}
public class ServiceImpl implements IService {
    private String name;

    @Override
    public String hello() {
        return "hello";
    }
}

引入最小依赖POM&bean配置

 <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-beans</artifactId>
      <version>5.1.7.RELEASE</version>
 </dependency>
 <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.1.7.RELEASE</version>
 </dependency>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">
    <bean id="service" class="com.wyh.spring.core.ServiceImpl"
          init-method="hello">
    </bean>
</beans>

使用XmlBeanFactory创建对象

public class BeanFactoryDemo {
    public static void main(String[] args) {
        XmlBeanFactory xmlBeanFactory = new XmlBeanFactory(new ClassPathResource("beans.xml"));
        IService service = (IService) xmlBeanFactory.getBean("service");
        String hello = service.hello();
        System.out.println(hello);
    }
}

Bean解析及注册

首先看下new XmlBeanFactory(new ClassPathResource("beans.xml"))这行代码

1、构造ClassPathResource

获取到了Resource对象也就等于获取到了该资源文件，后面可以根据方法的定义对文件进行相关操作

public ClassPathResource(String path) {
        this(path, (ClassLoader)null);
    }

    public ClassPathResource(String path, @Nullable ClassLoader classLoader) {
        Assert.notNull(path, "Path must not be null");
        String pathToUse = StringUtils.cleanPath(path);
        if (pathToUse.startsWith("/")) {
            pathToUse = pathToUse.substring(1);
        }

        this.path = pathToUse;
        this.classLoader = classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader();
    }

ClassPathResource.png

2、初始化XmlBeanFactory

先放一张UML类图，对整体结构有个了解

XmlBeanFactory

构造方法

/**
     * Create a new XmlBeanFactory with the given resource,
     * which must be parsable using DOM.
     * @param resource the XML resource to load bean definitions from
     * @throws BeansException in case of loading or parsing errors
     */
    public XmlBeanFactory(Resource resource) throws BeansException {
        this(resource, null);
    }

    /**
     * Create a new XmlBeanFactory with the given input stream,
     * which must be parsable using DOM.
     * @param resource the XML resource to load bean definitions from
     * @param parentBeanFactory parent bean factory
     * @throws BeansException in case of loading or parsing errors
     */
    public XmlBeanFactory(Resource resource, BeanFactory parentBeanFactory) throws BeansException {
        super(parentBeanFactory);
        this.reader.loadBeanDefinitions(resource);
    }

super(parentBeanFactory);跟踪到父类AbstractAutowireCapableBeanFactory

/**
     * Create a new AbstractAutowireCapableBeanFactory.
     */
    public AbstractAutowireCapableBeanFactory() {
        super();
        ignoreDependencyInterface(BeanNameAware.class);
        ignoreDependencyInterface(BeanFactoryAware.class);
        ignoreDependencyInterface(BeanClassLoaderAware.class);
    }

ignoreDependencyInterface方法主要功能是忽略给定接口的自动装配功能。
例如：A有属性B，当Spring获取A对象时，B没有初始化，先初始化B。

下面重要的关键是loadBeanDefinitions方法，借了张时序图

image.png

1. 封装资源文件
2. 获取输入流
3. 通过构造InputSource和Resource继续执行doLoadBeanDefinitions()
   doLoadBeanDefinitions函数里主要做了三件事：

• 获取对XML文件的验证模式
• 加载XML文件，获取相应的Document
• 根据返回Document注册Bean信息

protected int doLoadBeanDefinitions(InputSource inputSource, Resource resource)
            throws BeanDefinitionStoreException {

        try {
            Document doc = doLoadDocument(inputSource, resource);
            int count = registerBeanDefinitions(doc, resource);
            if (logger.isDebugEnabled()) {
                logger.debug("Loaded " + count + " bean definitions from " + resource);
            }
            return count;
        }
        catch (BeanDefinitionStoreException ex) {
            throw ex;
        }
           ......
    }

流程图：

image.png