[Java知识库] 【Spring篇】基于xml的自动装配

①场景模拟

创建类 UserController

public class UserController {

    private UserService userService;
    public void setUserService(UserService userService) {
        this.userService = userService;
    }
    public void saveUser(){
        userService.saveUser();
    }
}

创建接口 UserService

public interface UserService {
    void saveUser();
}

创建类 UserServiceImpl 实现接口 UserService

public class UserServiceImpl implements UserService {
    private UserDao userDao;

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    @Override
    public void saveUser(){
        userDao.saveUser();
    }

}

创建接口 UserDao

public interface UserDao {
    void saveUser();
}

创建类 UserDaoImpl 实现接口 UserDao

public class UserDaoImpl implements UserDao {
    @Override
    public void saveUser() {
        System.out.println("保存成功");
    }
}

②配置 bean

    <bean id="userController" class="com.atguigu.spring.Controller.UserController">
        <property name="userService" ref="userService"></property>
    </bean>
    <bean id="userService"  class="com.atguigu.spring.Service.impl.UserServiceImpl">
        <property name="userDao" ref="userDao"></property>
    </bean>
    <bean id="userDao" class="com.atguigu.spring.Dao.impl.UserDaoImpl"></bean>

③测试

    @Test
    public void test2(){
        ConfigurableApplicationContext ioc = new ClassPathXmlApplicationContext("spring-autowire-xml.xml");
        UserController userController = ioc.getBean("userController", UserController.class);
        userController.saveUser();
    }

④使用bean标签的autowire属性设置自动装配效果

自动装配方式：byType

byType ：根据类型匹配 IOC 容器中的某个兼容类型的 bean ，为属性自动赋值

若在IOC中，没有任何一个兼容类型的bean能够为属性赋值，则该属性不装配，即值为默认值 null
若在IOC中，有多个兼容类型的bean能够为属性赋值，则抛出异常 NoUniqueBeanDefinitionException

    <bean id="userController" class="com.atguigu.spring.Controller.UserController" autowire="byType">
<!--        <property name="userService" ref="userService"></property>-->
    </bean>
    <bean id="userService"  class="com.atguigu.spring.Service.impl.UserServiceImpl" autowire="byType">
<!--        <property name="userDao" ref="userDao"></property>-->
    </bean>
    <bean id="userDao" class="com.atguigu.spring.Dao.impl.UserDaoImpl"></bean>

⑤测试

自动装配方式：byName

byName ：将自动装配的属性的属性名，作为 bean 的 id 在 IOC 容器中匹配相对应的 bean 进行赋值

    <bean id="userController" class="com.atguigu.spring.Controller.UserController" autowire="byName">
<!--        <property name="userService" ref="userService"></property>-->
    </bean>
    <bean id="userService"  class="com.atguigu.spring.Service.impl.UserServiceImpl" autowire="byName">
<!--        <property name="userDao" ref="userDao"></property>-->
    </bean>
    <bean id="userDao" class="com.atguigu.spring.Dao.impl.UserDaoImpl"></bean>

[Java知识库]【Spring篇】基于xml的自动装配