Spring IoC注入过程原理模拟

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/u013967628/article/details/81043016

Spring Ioc就是对java反射及读取xml文件的使用的封装

public interface BeanFactory {
	public Object getBean(String id);
}

public class ClassPathXmlApplicationContext implements BeanFactory {

	// 存储解析xml后各个实例的键值对
	private Map<String, Object> beans = new HashMap<String, Object>();

	public ClassPathXmlApplicationContext() throws Exception {
		SAXBuilder sb = new SAXBuilder();// 读取XML文件
		Document doc = sb.build(this.getClass().getClassLoader().getResourceAsStream("beans.xml"));
		Element root = doc.getRootElement();
		List list = root.getChildren("bean");
		for (int i = 0; i < list.size(); i++) {
			Element element = (Element) list.get(i);
			String id = element.getAttributeValue("id");
			String clazz = element.getAttributeValue("class");
			// 利用反射生成类对象保存到beans
			Object o = Class.forName(clazz).newInstance();
			beans.put(id, o);
			// 对bena下的property元素遍历
			for (Element propertyElement : (List<Element>) element.getChildren("property")) {
				String name = propertyElement.getAttributeValue("name");
				String beanInstance = propertyElement.getAttributeValue("bean");
				// 取得注入的实例
				Object beanObject = beans.get(beanInstance);
				// 获取属性set方法
				String methodName = "set" + name.substring(0, 1).toUpperCase() + name.substring(1);
				Method m = o.getClass().getMethod(methodName, beanObject.getClass());
				m.invoke(o, beanObject);
			}
		}
	}

	@Override
	public Object getBean(String id) {
		return beans.get(id);
	}

}

测试类

public class Test {

	public static void main(String[] args) throws Exception {
		ClassPathXmlApplicationContext app = new ClassPathXmlApplicationContext();
		Whr whr = (Whr) app.getBean("whr");
		whr.print();
	}
}

实体类

public class BMWCar {
	public void print() {
		System.out.println("hhh");
	}
}
public class Whr {
	public BMWCar bmWCar;

	public void setBmWCar(BMWCar bmWCar) {
		this.bmWCar = bmWCar;
	}

	public void print() {
		bmWCar.print();
	}

}