简易的通过注解自动实例化bean 应用

系统管理员 2021-09-28 12:32 221阅读 0赞

*  两个注解

@Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface Service {
    	String value() default "";
    }
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface ComponentScan {
    	String value() default "";
    }

*  配置类，指定扫描哪个包

@ComponentScan("com.qhf")
    class AppConfig {
    	
    }

*  组件标注的类，在com.qhf.spring 包下，自动实例化此包下的类

package com.qhf;
    
    @Service("userService")
    class UserService {
    	
    }

*  productService

package com.qhf.service;
    
    import com.qhf.Service;
    
    @Service
    public class ProductService {
    
    }

*  工厂类

public class BeanFactory {
    	private Map<String, Object> objMap = new ConcurrentHashMap<>();
    	private Map<Class<?>, String> clsMap = new ConcurrentHashMap<Class<?>, String>();//记录所有Service 注解的字节码对象
    	
    	public BeanFactory() {
    		
    	}
    	
    	/**
    	 * 对含有ComponentScan 注解的包进行扫描，获取字节码对象存在Set集合中，暂不实例化对象，当使用时再实例化存在Map 中
    	 */
    	public BeanFactory(Class<?> configClass) throws Exception {
    		ComponentScan componentScan = configClass.getAnnotation(ComponentScan.class);
    		String pack = componentScan.value();
    		if ("".equals(pack)) {
    			pack = configClass.getPackage().getName();
    		}
    		
    		String packPath = pack.replace(".", "/");
    		URL url = ClassLoader.getSystemResource(packPath);
    		// 若有中文路径
    		String realPath = URLDecoder.decode(url.getPath(), "gbk");
    		
    		File dir = new File(realPath);
    		loopDir(dir, pack);
    		System.out.println(clsMap);
    	}
    	
    	private void loopDir(File dir, String pack) throws Exception {
    		File[] files = dir.listFiles();
    		for (File file : files) {
    			if (file.isFile()) {
    				if (!file.getName().endsWith(".class")) {
    					continue;
    				}
    				// 是class 文件并且有@Service 注解，则加入clsMap
    				String simpleName = file.getName().split("\\.")[0];
    				Class<?> clazz = Class.forName(pack + "." + simpleName);
    				if (clazz.isAnnotationPresent(Service.class)) {
    					clsMap.put(clazz, simpleName.substring(0,1).toLowerCase() + simpleName.substring(1));
    				}
    				
    			} else {
    				// 是目录, 递归
    				loopDir(file, pack + "." + file.getName());
    			}
    		}
    		
    	}
    
    	private Object newInstance(String beanName, Class<?> clazz) throws Exception {
    		if (!clsMap.containsKey(clazz))
    			return null;
    		if (beanName == null) {
    			String simpleName = clazz.getSimpleName().substring(0,1).toLowerCase() + clazz.getSimpleName().substring(1);
    			if (objMap.containsKey(simpleName)) {
    				return objMap.get(simpleName);
    			} else {
    				Object instance = clazz.newInstance();
    				objMap.put(simpleName, instance);
    				return instance;
    			}
    		} else {
    			if (objMap.containsKey(beanName)) {
    				return objMap.get(beanName);
    			} else {
    				return null;
    			}
    		}
    	}
    	
    	public <T>T getBean(Class<T> clazz) throws Exception {
    		return (T)newInstance(null, clazz);
    	}
    	
    	public <T>T getBean(String beanName, Class<T> clazz) throws Exception {
    		return (T)newInstance(beanName, clazz);
    	}
    	
    	public static void main(String[] args) throws Exception {
    		BeanFactory factory = new BeanFactory(AppConfig.class);
    		ProductService ps = factory.getBean(ProductService.class);
    		
    		UserService us1 = factory.getBean(UserService.class);
    		UserService us2 = factory.getBean("userService", UserService.class);
    		
    		System.out.println(ps);
    		System.out.println(us1);
    		System.out.println(us2);
    		System.out.println(us1 == us2);
    	}
    }

*  结果

\{class com.qhf.service.ProductService=productService, class com.qhf.UserService=userService\}  
com.qhf.service.ProductService@45ee12a7  
com.qhf.UserService@330bedb4  
com.qhf.UserService@330bedb4  
true