参考源
《Spring源码深度解析(第2版)》
版本
本文章基于 Spring 5.3.15
项目地址
模拟 Spring
注解
自动装配
Autowired
@Target(ElementType.FIELD)@Retention(RetentionPolicy.RUNTIME)public @interface Autowired {} 组件
Component
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)public @interface Component { String value() default ""; } 组件扫描
ComponentScan
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)public @interface ComponentScan { String value() default ""; } 范围
Scope
@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)public @interface Scope { String value() default "";} Bean 定义信息
BeanDefinition
public class BeanDefinition { /** * 类型 */ private Class type; /** * 范围 */ private String scope; public Class getType() { return type; } public void setType(Class type) { this.type = type; } public String getScope() { return scope; } public void setScope(String scope) { this.scope = scope; }} Bean 名称感知
BeanNameAware
public interface BeanNameAware { /** * 设置 Bean 名称 * @param beanName Bean名称 */ void setBeanName(String beanName);} Bean 后置处理器
BeanPostProcessor
public interface BeanPostProcessor { /** * 初始化前 * @param beanName Bean名称 * @param bean Bean对象 * @return */ Object postProcessBeforeInitialization(String beanName, Object bean); /** * 初始化后 * @param beanName Bean名称 * @param bean Bean对象 * @return */ Object postProcessAfterInitialization(String beanName, Object bean);} 初始化 Bean
InitializationBean
public interface InitializationBean { /** * 属性设置后 */ void afterPropertiesSet(); } 注解配置应用上下文
AnnotationConfigApplicationContext
public class AnnotationConfigApplicationContext { /** * 配置的类 */ private Class configClass; /** * Bean 后置处理器列表 */ private List beanPostProcessorList = new ArrayList<>(); /** * Bean 定义信息池 */ private ConcurrentHashMap beanDefinitionMap = new ConcurrentHashMap<>(); /** * 单例池 */ private ConcurrentHashMap singletonObjects = new ConcurrentHashMap<>(); public AnnotationConfigApplicationContext(Class configClass) { this.configClass = configClass; /* 扫描 -> BeanDefinition -> beanDefinitionMap */ // 是否有 @ComponentScan 注解 if (configClass.isAnnotationPresent(ComponentScan.class)) { ComponentScan componentScan = (ComponentScan) configClass.getAnnotation(ComponentScan.class); // 注解中的路径 String path = componentScan.value(); // 处理路径 path = path.replace(".", "/"); // 类加载器 ClassLoader classLoader = AnnotationConfigApplicationContext.class.getClassLoader(); // 资源 URL resource = classLoader.getResource(path); // 文件 File file = new File(resource.getFile()); // 如果为目录 if (file.isDirectory()) { // 文件列表 File[] files = file.listFiles(); for (File f : files) { // 绝对路径 String fileName = f.getAbsolutePath(); // 是否为 class 文件 if (fileName.endsWith(".class")) { // 类名 cn\sail\test\文件名 String className = fileName.substring(fileName.indexOf("cn"), fileName.indexOf(".class")); // 处理路径 className = className.replace("\\", "."); try { Class clazz = classLoader.loadClass(className); // 是否有 @Component 注解 if (clazz.isAnnotationPresent(Component.class)) { // 接口和类是否相同或者是否为其超类或超接口 if (BeanPostProcessor.class.isAssignableFrom(clazz)) { BeanPostProcessor instance = (BeanPostProcessor) clazz.newInstance(); beanPostProcessorList.add(instance); } Component component = clazz.getAnnotation(Component.class); String beanName = component.value(); if ("".equals(beanName)) { beanName = Introspector.decapitalize(clazz.getSimpleName()); } BeanDefinition beanDefinition = new BeanDefinition(); beanDefinition.setType(clazz); // 是否有 @Scope 注解 if (clazz.isAnnotationPresent(Scope.class)) { // 如果有，以传入的模式为准 Scope scope = clazz.getAnnotation(Scope.class); beanDefinition.setScope(scope.value()); } else { // 如果没有，默认为单例模式 beanDefinition.setScope("singleton"); } beanDefinitionMap.put(beanName, beanDefinition); } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (InstantiationException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } } } } } // 实例化单例 Bean for (String beanName : beanDefinitionMap.keySet()) { BeanDefinition beanDefinition = beanDefinitionMap.get(beanName); // 如果为单例模式，将 BeanDefinition 放入单例池中，下次直接从池中取，以保证单例 if ("singleton".equals(beanDefinition.getScope())) { Object bean = createBean(beanName, beanDefinition); singletonObjects.put(beanName, bean); } } } /** * 创建 Bean * @param beanName Bean 名称 * @param beanDefinition Bean 定义信息 * @return Bean 对象 */ private Object createBean(String beanName, BeanDefinition beanDefinition) { Class clazz = beanDefinition.getType(); try { Object instance = clazz.getConstructor().newInstance(); // 依赖注入 for (Field f : clazz.getDeclaredFields()) { // 是否有 @Autowired 注解 if (f.isAnnotationPresent(Autowired.class)) { // 忽略访问修饰符限制 f.setAccessible(true); // 注入 f.set(instance, getBean(f.getName())); } } // Aware if (instance instanceof BeanNameAware) { ((BeanNameAware) instance).setBeanName(beanName); } // 初始化前 for (BeanPostProcessor beanPostProcessor : beanPostProcessorList) { instance = beanPostProcessor.postProcessBeforeInitialization(beanName, instance); } // 初始化 if (instance instanceof InitializationBean) { ((InitializationBean) instance).afterPropertiesSet(); } // 初始化后 for (BeanPostProcessor beanPostProcessor : beanPostProcessorList) { instance = beanPostProcessor.postProcessAfterInitialization(beanName, instance); } return instance; } catch (InstantiationException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } catch (NoSuchMethodException e) { e.printStackTrace(); } return null; } public Object getBean(String beanName) { BeanDefinition beanDefinition = beanDefinitionMap.get(beanName); if (beanDefinition == null) { throw new NullPointerException(); } else { String scope = beanDefinition.getScope(); if ("singleton".equals(scope)) { Object bean = singletonObjects.get(beanName); // 如果单例池中没有对应 Bean，创建 Bean 后再放入池中 if (bean == null) { bean = createBean(beanName, beanDefinition); singletonObjects.put(beanName, bean); } return bean; } else { // 如果不是单例模式，直接创建 Bean return createBean(beanName, beanDefinition); } } } } 使用 Spring
应用配置
AppConfig
@ComponentScan("cn.sail.test")public class AppConfig {} 用户服务
UserInterface
public interface UserInterface { /** * 测试 */ void test();} 用户服务实现类
UserService
@Componentpublic class UserService implements UserInterface{ @Autowired private OrderService orderService; @Override public void test() { System.out.println(orderService); }} 排序服务
OrderService
@Componentpublic class OrderService {} Bean 后置处理器
MyBeanPostProcessor
@Componentpublic class MyBeanPostProcessor implements BeanPostProcessor { /** * 初始化前 * * @param beanName * @param bean * @return */ @Override public Object postProcessBeforeInitialization(String beanName, Object bean) { if ("userService".equals(beanName)) { System.out.println("1111"); } return bean; } /** * 初始化后 * * @param beanName * @param bean * @return */ @Override public Object postProcessAfterInitialization(String beanName, Object bean) { if ("userService".equals(beanName)) { Object proxyInstance = Proxy.newProxyInstance(MyBeanPostProcessor.class.getClassLoader(), bean.getClass().getInterfaces(), new InvocationHandler() { @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { System.out.println("切面逻辑"); return method.invoke(bean, args); } }); return proxyInstance; } return bean; }} 测试
Test
public class Test { public static void main(String[] args) { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(AppConfig.class); UserInterface userService = (UserInterface) applicationContext.getBean("userService"); userService.test(); }}