1. 创建两个自定义注解

1.1 Component注解

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

1.2 DI注解

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

2. ApplicationContext接口与实现类

2.1 ApplicationContext 接口

public interface ApplicationContext {// 获取beanObject getBean(String name);// 获取bean<T> T getBean(String name, Class<T> clazz);// 判断bean是否存在boolean exists(String name);boolean exists(String name, Class<?> clazz);
}

2.2 实现类：DefaultListableApplicationContext

// 实现类
public class DefaultListableApplicationContext implements ApplicationContext {/*** 存放bean对象容器*/private Map<String, Object> objectsMap = new ConcurrentHashMap<>(128);private Map<Class, Object> objectsTypeMap = new ConcurrentHashMap<>(128);private Logger log = LoggerFactory.getLogger(DefaultListableApplicationContext.class);// 扫描的基础路径private String basePath;public DefaultListableApplicationContext(String basePackage) {//public static void pathDemo1(String basePackageName){String packagePath = basePackage.replaceAll("\\.", "\\\\");try {URL url = Thread.currentThread().getContextClassLoader().getResource(packagePath);if (StringUtils.hasText(url.getPath())) {String filePath = URLDecoder.decode(url.getFile(), "UTF8");// 扫描的基础路径basePath = filePath.substring(0, filePath.length() - packagePath.length());//包扫描loadBeans(new File(filePath));// 依赖注入loadDI();}} catch (IOException e) {throw new RuntimeException(e);}}@Override@Nullablepublic Object getBean(String name) {return objectsMap.get(name);}@Override@Nullablepublic <T> T getBean(String name, Class<T> clazz) {Object obj = objectsMap.get(name);if (obj == null) {Object bean;if ((bean = objectsTypeMap.get(clazz)) == null) {for (Class<?> interfaceClazz : clazz.getInterfaces()) {if ((bean = objectsTypeMap.get(interfaceClazz)) != null)return (T) bean;getBean(name, interfaceClazz);}return null;}return (T) bean;}return clazz.isInstance(obj) ? clazz.cast(obj) : null;}@Overridepublic boolean exists(String name) {return objectsMap.get(name) == null ? false : true;}@Overridepublic boolean exists(String name, Class<?> clazz) {if (objectsMap.get(name) == null) {if (objectsTypeMap.get(clazz) == null) {for (Class<?> interfaceClazz : clazz.getInterfaces()) {if (objectsTypeMap.get(interfaceClazz) != null)return true;exists(name, interfaceClazz);}return false;}return true;}return true;}/*** 包扫描** @param file*/private void loadBeans(File file) {// 1 判断当前文件是否文件夹if (file.isDirectory()) {File[] childrenFiles = file.listFiles();// 2. 获取文件夹里面的所有内容// 3. 判断文件夹为空，直接返回if (childrenFiles == null || childrenFiles.length == 0) {return;}// 4. 如果文件夹不为空，遍历文件夹内容for (File childFile : childrenFiles) {// 4.1  遍历得到每个file对象，继续判断。如果是文件夹，递归if (childFile.isDirectory()) {loadBeans(childFile);} else {// 4.2 遍历得到的file不是文件夹，是文件// 4.3 得到包路径 + 类名称部分// C:/desktop/IdeaProjects/spring-mytest/src/main/java/com/ypy/contextString pathWithClass = childFile.getAbsolutePath().substring(basePath.length() - 1);// 4.4 判断当前文件类型是否为.classif (pathWithClass.endsWith(".class")) {// 4.5 如果是.class类型，把路径\替换成., 把.class去掉// com.ypy.context.beans.UserServiceImplString allName = pathWithClass.replaceAll("\\\\", ".").replace(".class", "");// 4.6 使用反射实例化try {Class<?> clazz = Class.forName(allName);if (!clazz.isInterface()) {// 4.6.1 判断是否有@Component注解,有if (clazz.getAnnotation(Component.class) != null) {Object instance = clazz.getConstructor().newInstance();// 优先使用用户自定义的bean名称if (StringUtils.hasText(clazz.getAnnotation(Component.class).value())) {String beanName = clazz.getAnnotation(Component.class).value();objectsMap.put(beanName, instance);log.warn(">>> objectsMap store bean(name,obj) ===> (" + beanName + "," + instance + ")");if (clazz.getInterfaces().length == 1) {objectsTypeMap.put(clazz.getInterfaces()[0], instance);log.warn(">>> objectsTypeMap store bean(class,obj) ===> (" + clazz.getInterfaces()[0].getSimpleName() + "," + instance + ")");} else if (clazz.getInterfaces().length == 0) {objectsTypeMap.put(clazz, instance);log.warn(">>> objectsTypeMap store bean(class,obj) ===> (" + clazz.getInterfaces()[0].getSimpleName() + "," + instance + ")");} else {throw new NotSupportMoreSuperInterface("Not support the bean that has more than two super interfaces.");}}// 其次使用父接口的类名作为bean名称else if (clazz.getInterfaces().length > 0) {String interfaceName = clazz.getInterfaces()[0].getSimpleName();String beanName = lowercaseFirstLetter(interfaceName);// 放入容器中objectsMap.put(beanName, instance);log.warn(">>> objectsMap store bean(name,obj) ===> (" + beanName + "," + instance + ")");// 可能出现bugobjectsTypeMap.put(clazz.getInterfaces()[0], instance);log.warn(">>> objectsTypeMap store bean(class,obj) ===> (" + clazz.getInterfaces()[0].getSimpleName() + "," + instance + ")");}// 如果说没有父接口,就使用类名作为bean名称else {String beanName = lowercaseFirstLetter(clazz.getSimpleName());// 放入容器中objectsMap.put(beanName, instance);log.warn(">>> objectsMap store bean(name,obj) ===> (" + beanName + "," + instance + ")");objectsTypeMap.put(clazz, instance);log.warn(">>> objectsTypeMap store bean(class,obj) ===> (" + clazz.getInterfaces()[0].getSimpleName() + "," + instance + ")");}}}} catch (Exception e) {throw new RuntimeException(e);}}}}}}private void loadDI() {for (Map.Entry<String, Object> entry : objectsMap.entrySet()) {Object obj = entry.getValue();Class<?> clazz = obj.getClass();Field[] fields = clazz.getDeclaredFields();for (Field field : fields) {try {field.setAccessible(true);if (field.getAnnotation(DI.class) != null) {Class<?>[] interfaces = field.getType().getInterfaces();String needWiredBeanName;Object autoWiredBean;// 优先使用注解DI的value注入if (StringUtils.hasText(needWiredBeanName = field.getAnnotation(DI.class).value())) {autoWiredBean = objectsMap.get(needWiredBeanName);if (autoWiredBean != null) {field.set(obj, autoWiredBean);log.warn("<<< DI: Class " + clazz.getSimpleName() + " of field named " + field.getName() + " is injected with value of " + autoWiredBean + " from " + "objectsMap, by value of annotation @DI");continue;} /*else {throw new NotExistsBean("Not exists the bean named <" + needWiredBeanName + "> to inject as property");}*/}// 没有父接口needWiredBeanName = lowercaseFirstLetter(field.getType().getSimpleName());if ((autoWiredBean = objectsMap.get(needWiredBeanName)) != null || (autoWiredBean = objectsTypeMap.get(field.getType())) != null) {field.set(obj, autoWiredBean);log.warn("<<< DI: Class " + clazz.getSimpleName() + " of field named " + field.getName() + " is injected with value of " + autoWiredBean + " , by value or type of property itself ");continue;}// 使用父接口的名字从bean容器中查找，注入if (interfaces.length > 0) {for (Class<?> interfaceClazz : interfaces) {String interfaceClazzName = interfaceClazz.getSimpleName();if (interfaceClazz.isAssignableFrom(field.getType())) {needWiredBeanName = lowercaseFirstLetter(interfaceClazzName);if ((autoWiredBean = objectsMap.get(needWiredBeanName)) != null || (autoWiredBean = objectsTypeMap.get(interfaceClazz)) != null) {field.set(obj, autoWiredBean);log.warn("<<< DI: Class " + clazz.getSimpleName() + " of field named " + field.getName() + " is injected with value of " + autoWiredBean + ", by value or type of super interface");}}}continue;}throw new InjectBeanException("There occurs an Exception while injecting property filed [" + field.getName() + "] of Class <" + clazz.getSimpleName() + "> , because bean factory doesn't exist the bean named " + needWiredBeanName);}} catch (IllegalAccessException e) {throw new RuntimeException(e);}}}}private String lowercaseFirstLetter(String name) {return name.substring(0, 1).toLowerCase() + name.substring(1);}}

3. 定义DAO层和Service层及其实现

// 3.1 dao层
public interface UserDao {void addUser(User user);
}/** 
*  userDao实现
*/
@Component("userDao")
public class UserDaoImpl implements UserDao {@Overridepublic void addUser(User user) {System.out.println();System.out.println("------------------>>>执行UserDaoImpl中的addUser方法开始<<<<------------------");System.out.println("\t\t\t\t\t\t名字\t\t\t\t年龄");System.out.println("\t\t\t\t\t\t"+user.getName()+"\t\t\t\t"+user.getAge());System.out.println("------------------>>>执行UserDaoImpl中的addUser方法完毕<<<<------------------");}
}// 3.2 service层public interface UserService {void add();
}// service实现
@Component("userService")
public class UserServiceImpl implements UserService {@DI("userDao")private UserDaoImpl userDao;@Overridepublic void add() {System.out.println("》》》 user service impl execute add method...");User user = new User("张三", 25);userDao.addUser(user);}
}

4. 定义异常信息类

4.1 InjectBeanException

public class InjectBeanException extends RuntimeException{public InjectBeanException() {super();}public InjectBeanException(String message) {super(message);}
}

4.2 NotExistsBean

public class NotExistsBean extends RuntimeException{public NotExistsBean() {}public NotExistsBean(String message) {super(message);}
}

4.3 NotSupportMoreSuperInterface

public class NotSupportMoreSuperInterface extends RuntimeException{public NotSupportMoreSuperInterface() {super();}public NotSupportMoreSuperInterface(String message) {super(message);}
}

5. 测试自定义bean容器(带依赖注入)

5.1 新建测试类TestUser

public class TestUser {public static void main(String[] args) {DefaultListableApplicationContext context = new DefaultListableApplicationContext("com.ypy.context");UserService userService = context.getBean("aaa", UserServiceImpl.class);UserDao userDao = context.getBean("userDaoImpl", UserDao.class);boolean existFlag = context.exists("aaa"/*, UserService.class*/);System.out.println("UserService exists ? " + existFlag);System.out.println("从Bean容器中获取aaa对象地址: " + userService);System.out.println("从Bean容器中获取userDao对象地址: " + userDao);userService.add();}
}

5.2 输出结果

一月 18, 2024 4:01:20 上午 com.sun.org.slf4j.internal.Logger warn
警告: >>> objectsMap store bean(name,obj) ===> (userDao,com.ypy.context.dao.impl.UserDaoImpl@2b193f2d)
一月 18, 2024 4:01:20 上午 com.sun.org.slf4j.internal.Logger warn
警告: >>> objectsTypeMap store bean(class,obj) ===> (UserDao,com.ypy.context.dao.impl.UserDaoImpl@2b193f2d)
一月 18, 2024 4:01:20 上午 com.sun.org.slf4j.internal.Logger warn
警告: >>> objectsMap store bean(name,obj) ===> (userService,com.ypy.context.service.impl.UserServiceImpl@7a81197d)
一月 18, 2024 4:01:20 上午 com.sun.org.slf4j.internal.Logger warn
警告: >>> objectsTypeMap store bean(class,obj) ===> (UserService,com.ypy.context.service.impl.UserServiceImpl@7a81197d)
一月 18, 2024 4:01:20 上午 com.sun.org.slf4j.internal.Logger warn
警告: <<< DI: Class UserServiceImpl of field named userDao is injected with value of com.ypy.context.dao.impl.UserDaoImpl@2b193f2d from objectsMap, by value of annotation @DI
UserService exists ? false
从Bean容器中获取aaa对象地址: com.ypy.context.service.impl.UserServiceImpl@7a81197d
从Bean容器中获取userDao对象地址: com.ypy.context.dao.impl.UserDaoImpl@2b193f2d
》》》 user service impl execute add method...------------------>>>执行UserDaoImpl中的addUser方法开始<<<<------------------名字				年龄张三				25
------------------>>>执行UserDaoImpl中的addUser方法完毕<<<<------------------Process finished with exit code 0