简易的通过xml实现自动实例化bean

一时失言乱红尘 2021-09-28 12:54 259阅读 0赞

*  bean.xml

<?xml version="1.0" encoding="UTF-8"?>
    <beans>
    	<bean id="obj" class="java.lang.Object" flag="true"></bean>
    	<bean id="user" class="com.qhf.pojo.User" flag="true"></bean>
    </beans>

*  Bean 类来封装bean.xml 的每个bean 节点

public class Bean {
    	private String id;
    	private String clazz;
    	private boolean flag;
    	public String getId() {
    		return id;
    	}
    	public void setId(String id) {
    		this.id = id;
    	}
    	public String getClazz() {
    		return clazz;
    	}
    	public void setClazz(String clazz) {
    		this.clazz = clazz;
    	}
    	public boolean isFlag() {
    		return flag;
    	}
    	public void setFlag(boolean flag) {
    		this.flag = flag;
    	}
    	@Override
    	public String toString() {
    		return "Bean [id=" + id + ", clazz=" + clazz + ", flag=" + flag + "]";
    	}	
    }

*  实现xml 读取数据并封装到 Bean 类中，使用流，java 的document 类

public abstract class XmlToBean {
    
    	protected Map<String, Bean> beanMap = new ConcurrentHashMap<String, Bean>();
    	
    	public XmlToBean(String xml) {
    		InputStream is = ClassLoader.getSystemResourceAsStream(xml);
    		handleSteam(is);
    	}
    
    	protected void handleSteam(InputStream is) {
    		try {
    			Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().parse(is);
    			handleDoc(doc);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	private void handleDoc(Document doc) {
    		NodeList beans = doc.getElementsByTagName("bean");
    		for(int i = 0; i < beans.getLength(); i++) {
    			Node bean = beans.item(i);
    			handlebean(bean);
    		}
    		
    	}
    
    	private void handlebean(Node bean) {
    		NamedNodeMap attributes = bean.getAttributes();
    		String id = attributes.getNamedItem("id").getNodeValue();
    		String clazz = attributes.getNamedItem("class").getNodeValue();
    		String flag = attributes.getNamedItem("flag").getNodeValue();
    		
    		Bean b = new Bean();
    		b.setId(id);
    		b.setClazz(clazz);
    		b.setFlag(new Boolean(flag));
    		
    		storeBean(b);
    	}
    
    	private void storeBean(Bean b) {
    		beanMap.put(b.getId(), b);
    	}
    }

*  BeanFactory 接口

public interface BeanFactory {
    	public <T>T getBean(String key, Class<T> cls);
    	public <T>T getBean(Class<T> cls);
    }

*  工厂类

public class ClassPathXmlApplicationContext extends XmlToBean implements BeanFactory{
    
    	private Map<String, Object> objMap = new ConcurrentHashMap<String, Object>();
    	
    	public ClassPathXmlApplicationContext(String xml) {
    		super(xml);
    	}	
    	
    	@Override
    	public <T>T getBean(String key, Class<T> cls) {
    		if(!beanMap.containsKey(key)) {
    			System.out.println("no such key");
    			return null;
    		}
    		
    		String name = beanMap.get(key).getClazz();
    		if(!name.equals(cls.getName())) {
    			System.out.println("no such bean");
    			return null;
    		}
    		
    		if(objMap.get(key) == null) {
    			Object obj = InstanceUtil.newInstance(cls);
    			objMap.put(key, obj);
    			return (T)obj;
    		}
    		return (T)objMap.get(key);
    	}
    
    	@Override
    	public <T> T getBean(Class<T> cls) {
    		
    		return null;
    	}
    }

*  反射实现new 新对象

public class InstanceUtil {
    	
    	public static Object newInstance(Class<?> cls) {
    		Object instance = null;
    		try {
    			Constructor<?> constructor = cls.getDeclaredConstructor();
    			if(!constructor.isAccessible())
    				constructor.setAccessible(true);
    			
    			instance = constructor.newInstance();
    			
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    		
    		return instance;
    	}
    }

*  测试类

public class TestXmlBeanFactory {
    	
    	public static void main(String[] args) {
    		ClassPathXmlApplicationContext xbf = new ClassPathXmlApplicationContext("bean.xml");
    				
    		Object obj1 = xbf.getBean("obj", Object.class);
    		Object obj2 = xbf.getBean("obj", Object.class);
    		System.out.println(obj1 == obj2);
    		
    		User user = xbf.getBean("user", User.class);
    		System.out.println(user);
    	}
    }