【框架源码】手写Spring框架IOC容器核心流程

    <!--JDOM 是一种使用 XML 的独特 Java 工具包，用于快速开发 XML 应用程序。JDOM 是一个开源项目，它基于树形结构，利用纯 Java 的技术对 XML 文档实现解析、生成、序列化及多种操作。-->
    <dependencies>
        <dependency>
            <groupId>org.jdom</groupId>
            <artifactId>jdom</artifactId>
            <version>2.0.2</version>
        </dependency>
    </dependencies>

public class OrderMapper {
    public void saveOrder(String orderNo){
        System.out.println("当前订单："+orderNo+" 已经落入数据库。");
    }
}

public interface OrderService {
    void saveOrder(String orderNo);
}

public class OrderServiceImpl implements OrderService {
    //注意这个OrderMapper 的 set、get方法一定要写，我们一会用反射的机制去设置属性。
    private OrderMapper orderMapper;
    public OrderMapper getOrderMapper() {
        return orderMapper;
    }
    public void setOrderMapper(OrderMapper orderMapper) {
        this.orderMapper = orderMapper;
    }
    @Override
    public void saveOrder(String orderNo) {
        orderMapper.saveOrder(orderNo);
    }
}

<?xml version="1.0" encoding="UTF-8" ?>
<beans>
    <bean id="orderMapper" class="com.lixiang.mapper.OrderMapper">
    </bean>
    <bean id="orderService" class="com.lixiang.service.impl.OrderServiceImpl">
        <property name="orderMapper" bean="orderMapper" />
    </bean>
</beans>

/**
 * @author lixiang
 * @date 2023/5/22 08:26
 */
public interface BeanFactory {
    /**
     * 根据名称获取bean
     * @param name
     * @return
     */
    Object getBean(String name);
    /**
     * 判断bean是否在容器里面
     * @param name
     * @return
     */
    boolean containsBean(String name);
    /**
     * 根据名称获取bean的类型
     * @param name
     * @return
     */
    Class<?> getType(String name) ;
}

/**
 * @author lixiang
 * @date 2023/5/22 08:29
 */
public class ClassPathXmlApplicationContext implements BeanFactory{
    /**
     * 定义map用于存放bean
     */
    private Map<String,Object> beans = new HashMap<>();
    public ClassPathXmlApplicationContext() throws Exception {
        //init 方法 做 解析和注入
        init();
    }
    /**
     * 初始化,核心就在这个
     */
    private void init() throws Exception {
        SAXBuilder saxBuilder = new SAXBuilder();
        //获取资源路径的xml文件
        InputStream resourceAsStream = this.getClass().getClassLoader().getResourceAsStream(fileName);
        //将xml文件构建成Document
        Document document = saxBuilder.build(resourceAsStream);
        //获取根结点的Element，对应的就是beans
        Element rootElement = document.getRootElement();
        //获取下面的bean节点
        List<Element> elements = rootElement.getChildren("bean");
        //遍历
        for (int i = 0; i < elements.size(); i++) {
            Element element = elements.get(i);
            //获取id属性
            String id = element.getAttributeValue("id");
            //获取class信息
            String clazz = element.getAttributeValue("class");
            //反射创建对象
            Object obj = Class.forName(clazz).getDeclaredConstructor().newInstance();
            //放到map中存储
            beans.put(id, obj);
            //判断属性中是否有需要注入的对象
            for(Element propertyElement: element.getChildren("property")){
                //获取名称
                String name = propertyElement.getAttributeValue("name");
                //获取bean的定义
                String bean = propertyElement.getAttributeValue("bean");
                //获取bean
                Object beanObject = beans.get(bean);
                //设置set方法
                String methodName = "set" + name.substring(0,1).toUpperCase() + name.substring(1);
                Class<?> aClass = beanObject.getClass();
                //反射将属性设置进去
                Method m = obj.getClass().getMethod(methodName,aClass);
                m.invoke(obj, beanObject);
            }
        }
    }
    @Override
    public Object getBean(String name) {
        return beans.get(name);
    }
    @Override
    public boolean containsBean(String name) {
        return beans.containsKey(name);
    }
    @Override
    public Class<?> getType(String name) {
        if(beans.containsKey(name)){
            return beans.get(name).getClass();
        }
        return null;
    }
}

/**
 * @author lixiang
 * @date 2023/5/22 08:11
 */
public class Main {
    public static void main(String[] args) throws Exception {
        String fileName= "beans.xml";
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext(fileName);
        OrderService orderService = (OrderService)applicationContext.getBean("orderService");
        orderService.saveOrder("202388474754758834");
        boolean containsBean = applicationContext.containsBean("orderService");
        System.out.println(containsBean);
        Class<?> type = applicationContext.getType("orderService");
        System.out.println(type.getName());
    }
}