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概述

模拟大致的底层原理，为学习Spring源码做铺垫。

实现的功能：扫描路径、依赖注入、aware回调、初始化前、初始化、初始化后、切面

未实现的功能：构造器推断、循环依赖

重点：BeanDefinition、BeanPostProcessor

学习Spring源码的重点：设计模式、编码规范、设计思想、扩展点

启动类：

public class Yeah
{public static void main(String[] args){GaxApplicationContext gaxApplicationContext = new GaxApplicationContext(AppConfig.class);UserInterface userService = (UserInterface) gaxApplicationContext.getBean("userService");userService.test();}
}

关键方法：

public class GaxApplicationContext
{private Class configClass;private static final String SINGLETON = "singleton";private Map<String, BeanDefinition> beanDefinitionMap = new HashMap<>();private Map<String, Object> singletonObjects = new HashMap<>();// Spring源码用的是LinkedListprivate List<BeanPostProcessor> beanPostProcessorList = new ArrayList<>();public GaxApplicationContext(Class configClass){this.configClass = configClass;// 扫描指定路径，找到所有@Component注解的类，封装成beanDefinition保存再Map中scan(configClass);// 思考个问题：beanDefinitionMap.keySet()和beanDefinitionMap.entrySet()两种遍历的区别？选用哪个好？for (Map.Entry<String, BeanDefinition> entry : beanDefinitionMap.entrySet()){String beanName = entry.getKey();BeanDefinition beanDefinition = entry.getValue();if (SINGLETON.equals(beanDefinition.getScope())){Object bean = createBean(beanName, beanDefinition);singletonObjects.put(beanName, bean);}}}private Object createBean(String beanName, BeanDefinition beanDefinition){Class clazz = beanDefinition.getType();Object instance = null;try{// 直接使用默认的无参构造器，多个构造器的场景未实现instance = clazz.getConstructor().newInstance();// 属性填充，依赖注入for (Field field : clazz.getDeclaredFields()){if (field.isAnnotationPresent(Autowired.class)){field.setAccessible(true);field.set(instance, getBean(field.getName()));}}// aware回调if (instance instanceof BeanNameAware){((BeanNameAware)instance).setBeanName(beanName);}// 初始化前for (BeanPostProcessor beanPostProcessor : beanPostProcessorList){instance = beanPostProcessor.postProcessBeforeInitialization(instance, beanName);}// 初始化if (instance instanceof InitializingBean){((InitializingBean)instance).afterPropertiesSet();}// 初始化后for (BeanPostProcessor beanPostProcessor : beanPostProcessorList){instance = beanPostProcessor.postProcessAfterInitialization(instance, beanName);}}catch (InstantiationException | NoSuchMethodException | IllegalAccessException | InvocationTargetException e){e.printStackTrace();}return instance;}public Object getBean(String beanName){if (!beanDefinitionMap.containsKey(beanName)){throw new NullPointerException();}BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);if (SINGLETON.equals(beanDefinition.getScope())){Object singletonBean = singletonObjects.get(beanName);if (null == singletonBean){singletonBean = createBean(beanName, beanDefinition);singletonObjects.put(beanName, singletonBean);}return singletonBean;}else{// 原型BeanObject prototypeBean = createBean(beanName, beanDefinition);return prototypeBean;}}private void scan(Class configClass){if (configClass.isAnnotationPresent(ComponentScan.class)){ComponentScan componentScanAnnotation = (ComponentScan)configClass.getAnnotation(ComponentScan.class);String path = componentScanAnnotation.value();// path = com/gax/servicepath = path.replace(".", "/");ClassLoader classLoader = GaxApplicationContext.class.getClassLoader();URL resource = classLoader.getResource(path);assert resource != null;File file = new File(resource.getFile());if (file.isDirectory()){for (File f : Objects.requireNonNull(file.listFiles())){String absolutePath = f.getAbsolutePath();absolutePath = absolutePath.substring(absolutePath.indexOf("com"), absolutePath.indexOf(".class"));// 类加载器入参需要的格式：com.gax.service.XXXabsolutePath = absolutePath.replace("\\", ".");try{Class<?> clazz = classLoader.loadClass(absolutePath);if (clazz.isAnnotationPresent(Component.class)){if (BeanPostProcessor.class.isAssignableFrom(clazz)){BeanPostProcessor instance = (BeanPostProcessor)clazz.getConstructor().newInstance();beanPostProcessorList.add(instance);}Component componentAnnotation = clazz.getAnnotation(Component.class);String beanName = componentAnnotation.value();if ("".equals(beanName)){// 默认beanNamebeanName = Introspector.decapitalize(clazz.getSimpleName());}BeanDefinition beanDefinition = new BeanDefinition();beanDefinition.setType(clazz);if (clazz.isAnnotationPresent(Scope.class)){Scope scopeAnnotation = clazz.getAnnotation(Scope.class);String value = scopeAnnotation.value();beanDefinition.setScope(value);}else{// 默认单例BeanbeanDefinition.setScope(SINGLETON);}beanDefinitionMap.put(beanName, beanDefinition);}}catch (ClassNotFoundException | NoSuchMethodException | InvocationTargetException| InstantiationException | IllegalAccessException e){e.printStackTrace();}}}}}
}

gitee地址：

git clone https://gitee.com/seek6174/spring-seek.git