Spring - 手写模拟Spring底层原理

手写Spring

定义配置类AppConfig

@ComponentScan("com.spring.zsj")
public class AppConfig {@Beanpublic ApplicationListener applicationListener() {return new ApplicationListener() {@Overridepublic void onApplicationEvent(ApplicationEvent event) {System.out.println("接收到了一个事件"+event );}};}}

定义容器ZSJApplicationContext

public class ZSJApplicationContext {private Class configClass;private Map<String,BeanDefinition> beanDefinitionMap =new HashMap<>();//bean定义private Map<String,Object> singleObjects = new HashMap<>(); //单例池private List<BeanPostProcessor> beanPostProcessorList =new ArrayList<>(); //后置处理public ZSJApplicationContext(Class configClass)  {this.configClass = configClass;scanComponent(configClass);//找出单例beanfor (Map.Entry<String,BeanDefinition> entry: beanDefinitionMap.entrySet()) {String beanName = entry.getKey();BeanDefinition beanDefinition = entry.getValue();if(beanDefinition.equals("singleton")){Object bean = createBean(beanName, beanDefinition);singleObjects.put(beanName,bean);}}}private Object createBean(String beanName,BeanDefinition beanDefinition){Class clazz = beanDefinition.getType();Object newInstance = null;try {newInstance =  clazz.getConstructor().newInstance();//依赖注入for (Field field : clazz.getDeclaredFields()) {if (clazz.isAnnotationPresent(Autowired.class)) {field.setAccessible(true);field.set(newInstance, getBean(field.getName()));}}//执行回调方法if (newInstance instanceof  BeanNameAware){((BeanNameAware) newInstance).setBeanName(beanName);}//执行初始化前的方法for (BeanPostProcessor beanPostProcessor: beanPostProcessorList) {newInstance = beanPostProcessor.postProcessBeforeInitialization(newInstance, beanName);}//当前对象是否实例化了if(newInstance instanceof  InitializingBean){((InitializingBean) newInstance).afterPropertiesSet();}//执行初始化后的方法（例如Aop）for (BeanPostProcessor beanPostProcessor: beanPostProcessorList) {newInstance = beanPostProcessor.postProcessAfterInitialization(newInstance, beanName);}} catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();} catch (NoSuchMethodException e) {e.printStackTrace();}return newInstance;}private void scanComponent(Class configClass) {if(configClass.isAnnotationPresent(ComponentScan.class)){ComponentScan annotation =(ComponentScan) configClass.getAnnotation(ComponentScan.class);String path = annotation.value();path = path.replace(".", "/");ClassLoader classLoader = ZSJApplicationContext.class.getClassLoader();URL resource = classLoader.getResource(path);File file = new File(resource.getFile());if(file.isDirectory()){//若是文件夹，则取出对应的文件for (File f: file.listFiles()) {String absolutePath = f.getAbsolutePath();//System.out.println(absolutePath);String com = absolutePath.substring(absolutePath.indexOf("com"), absolutePath.indexOf(".class"));String replace = com.replace("\\", ".");// System.out.println(replace);try {Class<?> clazz = classLoader.loadClass(replace);if(clazz.isAnnotationPresent(Component.class)){//clazz 是否实现了BeanPostProcessor接口if(BeanPostProcessor.class.isAssignableFrom(clazz)){BeanPostProcessor instance = (BeanPostProcessor)clazz.getConstructor().newInstance();beanPostProcessorList.add(instance);}//获取bean 的名字Component annotation1 = clazz.getAnnotation(Component.class);String beanName = annotation1.value();if("".equals(beanName)){String name = Introspector.decapitalize(clazz.getSimpleName());}BeanDefinition beanDefinition = new BeanDefinition();beanDefinition.setType(clazz);if(clazz.isAnnotationPresent(Scope.class)){//圆型的Scope scope = clazz.getAnnotation(Scope.class);String value = scope.value();beanDefinition.setScope(value);}else {//单例的beanDefinition.setScope("singleton");}beanDefinitionMap.put(beanName,beanDefinition);//   System.out.println(clazz);}} catch (ClassNotFoundException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();} catch (InstantiationException e) {e.printStackTrace();} catch (NoSuchMethodException e) {e.printStackTrace();} catch (InvocationTargetException e) {e.printStackTrace();}}}//   System.out.println(path);}}//通过bean名称获取bean对象public Object getBean(String beanName){if(!beanDefinitionMap.containsKey(beanName)){throw new NullPointerException();}BeanDefinition beanDefinition = beanDefinitionMap.get(beanName);if(beanDefinition.getScope().equals("singleton")){Object singletonBean = singleObjects.get(beanName);if(singletonBean== null){singletonBean = createBean(beanName, beanDefinition);singleObjects.put(beanName,singletonBean);}return singletonBean;}else {//原型的Object prototypeBean = createBean(beanName, beanDefinition);return prototypeBean;}}
}

定义注解@Autowired @Component @Scope @ComponentScan

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Autowired {String value() default "";
}@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Component {String value() default "";
}@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface ComponentScan {String value() default "";
}@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
public @interface Scope {String value() default "";
}

定义后置处理器BeanPostProcessor，用于初始化

public interface BeanPostProcessor {default Object postProcessBeforeInitialization(Object bean, String beanName)  {return bean;}default Object postProcessAfterInitialization(Object bean, String beanName) {return bean;}
}

定义ZSJBeanPostProcessor实现BeanPostProcesso

@Component
public class ZSJBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessAfterInitialization(Object bean, String beanName) {if(beanName.equals("userService")){Object proxyInstance = Proxy.newProxyInstance(ZSJBeanPostProcessor.class.getClassLoader(), bean.getClass().getInterfaces(), new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {//切面System.out.println("切面逻辑");return method.invoke(bean,args);}});return proxyInstance;}return bean;}
}

定义初始化接口InitializingBean

public interface InitializingBean {void afterPropertiesSet();
}

定义普通的类（可实例化成单例bean）

@Component("userService")
@Scope("singleton")
//public class UserService implements InitializingBean {
public class UserService implements UserInterface {@Autowiredprivate OrderService orderService;@ZSanValue("zhangsan")private String user;//圆型bean 表示多例beanpublic void test(){System.out.println(orderService);}//    @Override
//    public void afterPropertiesSet() {
//        System.out.println("初始化");
//    }
}

定义普通的类（可实例化成原型bean）

@Component("orderService")
@Scope("prototype")
public class OrderService {//圆型bean 表示多例beanpublic void test(){System.out.println("hello");}
}

定义启动类main


public class Test {public static void main(String[] args) {//非懒加载的单例bean
//        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
//        UserService userService = (UserService)context.getBean("userService");
//
//        userService.test();ZSJApplicationContext context = new ZSJApplicationContext(AppConfig.class);UserInterface userService = (UserInterface)context.getBean("userService");userService.test();//      System.out.println(context.getBean("userService"));
//        System.out.println(context.getBean("userService"));
//        System.out.println(context.getBean("userService"));
//        System.out.println(context.getBean("orderService"));
//        System.out.println(context.getBean("orderService"));
//        System.out.println(context.getBean("orderService"));//        AnnotatedBeanDefinitionReader reader = new AnnotatedBeanDefinitionReader(context);
//        reader.register(User.class);
//        System.out.println(context.getBean("user"));StringToUserPropertyEditor propertyEditor = new StringToUserPropertyEditor();propertyEditor.setAsText("1");User value =new User();System.out.println(value);}
}

BeanPostProcesso扩展使用方法

自定义注解@ZSanValue

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface ZSanValue {String value() default "";
}

使用注解时，将注解的值赋给属性：如

@ZSanValue("zhangsan")
private String user;

实现后置处理器，并执行初始化前的操作，将自定义的注解值进行属性赋值

@Component
public class ZSanValueBeanPostProcessor implements BeanPostProcessor {@Overridepublic Object postProcessBeforeInitialization(Object bean, String beanName) {for (Field field : bean.getClass().getDeclaredFields()) {if(field.isAnnotationPresent(ZSanValue.class)){field.setAccessible(true);try {field.set(bean,field.getAnnotation(ZSanValue.class).value());} catch (IllegalAccessException e) {e.printStackTrace();}}}return bean;}
}

回调方法使用BeanNameAware

定义回调接口

public interface BeanNameAware {void setBeanName(String name);
}

则实现类需要实现BeanNameAware接口

@Component("userService")
@Scope("singleton")
//public class UserService implements InitializingBean {
public class UserService implements UserInterface,BeanNameAware {@Autowiredprivate OrderService orderService;@ZSanValue("zhangsan")private String user;private String beanName;//圆型bean 表示多例beanpublic void test(){System.out.println(orderService);}@Overridepublic void setBeanName(String name) {this.beanName=name;}//    @Override
//    public void afterPropertiesSet() {
//        System.out.println("初始化");
//    }
}