使用传统的三层架构出现的问题.引入Spring底层实现原理来解决(工厂模式+反射+XML配置文件/注解)

以前写的代码

mapper层

public interface PersonMapper {
    void selectPersonList();
}

public class PersonMapperImpl implements PersonMapper {
    @Override
    public void selectPersonList() {
        System.out.println("PersonMapperImpl selectPersonList");
    }
}

service层

public interface PersonService {
    void selectPersonList();
}

public class PersonServiceImpl implements PersonService {

    private PersonMapper personMapper = new PersonMapperImpl;

    @Override
    public void selectPersonList() {
        personMapper.selectPersonList();
    }
}

controller层

private PersonService personService = new PersonServiceImpl();

    public void selectPersonList(){
        personService.selectPersonList();
    }

可以发现的是代码耦合度非常的高,当我们修改PersonService的实现类需要修改多出代码,如何解决呢?

首先使用工厂模式创建对象

public class MyBeanFactory {
	public static Object getBean(String beanName) {
		if ("personService".equals(beanName)) {
			return new PersonServiceImpl();
		} else if ("personController".equals(beanName)) {
			return new PersonController();
		} else {
			return new PersonMapperImpl();
		}
	}
}

mapper层

public interface PersonMapper {
    void selectPersonList();
}

public class PersonMapperImpl implements PersonMapper {
    @Override
    public void selectPersonList() {
        System.out.println("PersonMapperImpl selectPersonList");
    }
}

service层

public interface PersonService {
    void selectPersonList();
}

public class PersonServiceImpl implements PersonService {

    private PersonMapper personMapper =(PersonMapper) MyBeanFactory.getBean("personMapper");

    @Override
    public void selectPersonList() {
        personMapper.selectPersonList();
    }
}

controller层

private PersonService personService = (PersonService) MyBeanFactory.getBean("personService");

    public void selectPersonList(){
        personService.selectPersonList();
    }

测试一下是可以达到效果的,但是还是存在代码耦合度高的问题

继续优化,我们把MyBeanFactory的创建bean方法修改一下

public static Object getBean(String clazzName) {
	if (clazzName != null) {
		Object obj = null;
		try {
			obj = Class.forName(clazzName).newInstance();
			return obj;
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	return null;
}

mapper层

public interface PersonMapper {
    void selectPersonList();
}

public class PersonMapperImpl implements PersonMapper {
    @Override
    public void selectPersonList() {
        System.out.println("PersonMapperImpl selectPersonList");
    }
}

service层

public interface PersonService {
    void selectPersonList();
}

public class PersonServiceImpl implements PersonService {

    private PersonMapper personMapper =(PersonMapper) MyBeanFactory.getBean("com.qbb.spring.mapper.impl.PersonMapperImpl");

    @Override
    public void selectPersonList() {
        personMapper.selectPersonList();
    }
}

controller层

private PersonService personService = (PersonService) MyBeanFactory.getBean("com.qbb.spring.service.impl.PersonServiceImpl");

    public void selectPersonList(){
        personService.selectPersonList();
    }

此时我们传递的是权限定类名,降低了一些代码耦合度,但是又带来了字符串硬编码问题

继续优化,修改MyBeanFactory

    // 创建对象时就加载
    public MyBeanFactory() {
        parseXML();
    }

    // 定义一个Map<String,Object>存储bean对象
    private static Map<String, Object> map = new HashMap<>();

	// 解决字符串硬编码
    public void parseXML() {
        // 创建解析XML对象
        SAXReader saxReader = new SAXReader();
        InputStream is = MyBeanFactory.class.getClassLoader().getResourceAsStream("MyBean.xml");
        try {
            // 读取配置文件
            Document docment = saxReader.read(is);
            // 获取跟标签
            Element rootElement = docment.getRootElement();
            // 获取字标签
            List<Element> elements = rootElement.elements();
            for (Element element : elements) {
                String id = element.attributeValue("id");
                String clazz = element.attributeValue("class");
                Object newInstance = Class.forName(clazz).newInstance();
                map.put(id, newInstance);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
	// 获取bean
    public static Object getBean(String id) {
        return map.get(id);
    }