從零開始造Spring00----從XML中讀取Bean并獲取實例

xml的配置

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

讀取XML

采用dom4j來讀取xml。在工廠類DefaultBeanFactory初始化時就加載xml。代碼如下：

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

//            獲取根節(jié)點
                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);
                }

獲取實例

我們將配置文件bean中的信息放在BeanDefinition中，然后將BeanDefinition放在一個全局的map中，key為id。
BeanDefinition 的實體如下：

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
}
獲取Bean的代碼如下：

    @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");
        }
    }

源碼地址：

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



作者：碼農(nóng)飛哥

微信公眾號：碼農(nóng)飛哥