从零开始造Spring00----从XML中读取Bean并获取实例

xml的配置

<bean id="petStoreService" class="com.jay.spring.PetStoreService"></bean>

读取XML

采用dom4j来读取xml。在工厂类DefaultBeanFactory初始化时就加载xml。代码如下：

  SAXReader saxReader = new SAXReader();
                Document document = saxReader.read(inputStream);

//            获取根节点
                Element rootElement = document.getRootElement();
                Iterator<Element> iterator = rootElement.elementIterator();
                while (iterator.hasNext()) {
                    Element element = iterator.next();
                    String id = element.attributeValue(ID_ATTRIBUTE);
                    String className = element.attributeValue(CLASS_ATTRIBUTE);
                    BeanDefinition beanDefinition = new BeanDefinition(id, className);
                    beanDefinitionMap.put(id, beanDefinition);
                }

获取实例

我们将配置文件bean中的信息放在BeanDefinition中，然后将BeanDefinition放在一个全局的map中，key为id。
BeanDefinition 的实体如下：

public class BeanDefinition {
    private String id;
    private String beanClassName;

    public BeanDefinition(String id, String beanClassName) {
        this.id = id;
        this.beanClassName = beanClassName;
    }
    set和get方法省略
}
获取Bean的代码如下：

    @Override
    public Object getBean(String id) {
        BeanDefinition bd = getDefinition(id);
        if (bd == null) {
            throw  new BeanException("BeanDefinition is not exist");
        }
        try {
            return Class.forName(bd.getBeanClassName()).newInstance();
        } catch (Exception e) {
            throw new BeanException("bean create exception");
        }
    }

源码地址：

https://github.com/XWxiaowei/spring-learn/tree/master/liu-spring-demo

作者：码农飞哥

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