Spring框架十一、Spring IOC源码概述

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一、Spring IOC Bean对象注入原理

Spring bean对象的注入，分为xml注入和注解注入，这两种方式都是利用反射来实现的。

1、xml方式注入

xml方式是通过反射找到类中的set方法，调用此方式实现注入的：

UserService.java

public class UserService {
}

UserController.java

public class UserController {private UserService userService;public void setUserService(UserService userService) {this.userService = userService;}public UserService getUserService() {return userService;}
}

测试类

public class MyTest {public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException, NoSuchMethodException, InvocationTargetException {UserController userController = new UserController();//获取class信息Class clazz = userController.getClass();//获取变量名Field userServiceField = clazz.getDeclaredField("userService");String name = userServiceField.getName();//获取set方法name = "set" + name.substring(0, 1).toUpperCase() + name.substring(1, name.length());Method method=clazz.getMethod(name,UserService.class);//调用set方法给userService赋值UserService userService=new UserService();method.invoke(userController,userService);System.out.println(userController.getUserService());}
}

运行输出：

com.bobo.UserService@610455d6

2、annotion方式注入

定义MyAutoWired注解

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface MyAutoWired {
}

UserService.java

public class UserService {
}

UserController.java

public class UserController {@MyAutoWiredprivate UserService userService;public UserService getUserService() {return userService;}
}

测试类

public class MyTest {public static void main(String[] args) throws IllegalAccessException, NoSuchMethodException, InvocationTargetException, InstantiationException {UserController userController = new UserController();Class clazz = userController.getClass();//遍历UserController成员变量for (Field field : clazz.getDeclaredFields()) {//筛选出使用MyAutoWired注解的变量MyAutoWired annotation = field.getAnnotation(MyAutoWired.class);if (annotation != null) {//获取变量类型，并创建变量对象Class<?> type = field.getType();Object o = type.getConstructor().newInstance();//给使用MyAutoWired注解的变量赋值field.setAccessible(true);field.set(userController, o);System.out.println(userController.getUserService());}}}
}