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Spring IOC 特性有哪些,不会读不懂源码!

作者:互联网


作者:小傅哥
博客:https://bugstack.cn

沉淀、分享、成长,让自己和他人都能有所收获!????

一、前言

多线程、锁、JVM调优,都背出花啦,怎么一写代码还是乱糟糟?

为什么这些无论从书本、课堂、面试都显得非常重要的知识,但是在实际的编程中没有提升你的编码能力呢?

首先这些这些知识在实际的互联网业务开发中,几乎是不常用的,几乎有锁和多线程的场景,为了性能的提升也基本都是采用分布式设计和实现了。而这些看上去很有技术含量的知识多数都被包装在非业务逻辑功能的组件中,而程序员在做业务开发时候几乎是关心不到。所以会了这些也几乎不太可能就把你的编码能提升起来,多数提升的是你在查复杂bug时候有一臂之力。

就像会汉字就能写出诗词歌赋吗?懂RGB就能绘出山河大川吗?能蹦跳就可以舞出摇曳生姿吗?那都是不可能的,不要想着屁股围噶补就说会武术!

如果真的想把代码写好,就要一点点从积累数据结构和算法逻辑(不只是机械式的刷几道题就算了。你不理解为什么,刷再多也只是徒劳),接下来要做的是对设计模式和架构设计的理解,最终是不断的运用和总结。在这个过程你会接触到业务、产品、运营,编码只是最后的具体实现,并不是全流程中最重要的一部分,与编码相比更重要的是逻辑设计。

二、面试题

谢飞机,小记!,这次放假一遍撸串一遍被Spring,嘿嘿,检验成果面试去!

面试官:飞机,今天准备咋样,上次问你的都学会了吗?

谢飞机:@Resource 是 JDK javax.annotation.Resource 提供的注解,哈哈哈哈哈,另外也学习了Bean的注入。

面试官:挺好记住了一些,那你在做 Bean 注入学习的时候,有注意到 Spring IOC 的特性吗,你都用到了什么?

谢飞机:嗯,用到 Bean 的配置、BeanDefinitionRegistryPostProcessor 对 Bean 的定义、还有 FactoryBean

面试官:好,那今天再和你聊聊,alias、autowire、depends-on、factory-method、lookup-method等,实践验证下看看它们是怎么应用的。

三、SpringIOC 特性

IOC(Inversion of Control),控制反转的核心思想在于,资源的使用不由使用各自管理,而是交给不使用资源的第三方进行管理。这样的好处是资源是集中管理的,可配置、易维护,同时也降低了双方的依赖度做到了低耦合。

早在1988年,Ralph E. Johnson & Brian Foote在论文《Designing Reusable Classes》

One important characteristic of a framework is that the methods defined by the user to tailor the framework will often be called from within the framework itself, rather than from the user’s application code.
The framework often plays the role of the main program in coordinating and sequencing application activity.
This inversion of control gives frameworks the power to serve as extensible skeletons. The methods supplied by the user tailor the generic algorithms defined in the framework for a particular application.

接下来就给大家介绍一下 IOC 的一些核心特性,因为这些内容不仅是面试考点,也是在开发中间件或者小组件时需要用到的功能类,概括如下:

1. xml 配置

1.1 alias

测试类

public class UserService {

    private UserDao userDao;

    public UserService() {
        System.out.println("我被初始化了,UserService");
    }

    // ...get/set

}

xml配置

<bean id="userService" class="org.itstack.interview.UserService"/>
<!-- 起个别名 -->
<alias name="userService" alias="userService-alias01"/>
<!-- 别名的别名 -->
<alias name="userService-alias01" alias="userService-alias02"/>

单元测试

@Test
public void test_alias() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-alias.xml");
    logger.info("获取 Bean:{}", beanFactory.getBean("userService"));
    logger.info("获取 Bean 通过别名:{}", beanFactory.getBean("userService-alias01"));
    logger.info("获取 Bean 通过别名的别名:{}", beanFactory.getBean("userService-alias02"));
}

测试结果

23:01:29.872 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserService@2a40cd94
23:01:29.872 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'userService'
23:01:29.872 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean 通过别名:org.itstack.interview.UserService@2a40cd94
23:01:29.872 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'userService'
23:01:29.872 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean 通过别名的别名:org.itstack.interview.UserService@2a40cd94

1.2 autowire

测试类

public class UserDao {
    public UserDao() {
        System.out.println("我被初始化了,UserDao");
    }
}

xml配置

<bean id="userDao" class="org.itstack.interview.UserDao"/>

<!-- 手动配置依赖 -->
<bean id="userService-by-property" class="org.itstack.interview.UserService">
    <property name="userDao" ref="userDao"/>
</bean>

<!-- 自动配置依赖 -->
<bean id="userService-by-autowire" class="org.itstack.interview.UserService" autowire="byName"/>

单元测试

@Test
public void test_autowire() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-autowire.xml");
    logger.info("获取 Bean by 手动配置依赖:{}", beanFactory.getBean("userService-by-property"));
    logger.info("获取 Bean by 自动配置依赖:{}", beanFactory.getBean("userService-by-autowire"));
}

测试结果

23:05:55.501 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean by 手动配置依赖:org.itstack.interview.UserService@679b62af
23:05:55.501 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'userService-by-autowire'
23:05:55.501 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean by 自动配置依赖:org.itstack.interview.UserService@5cdd8682

1.3 factory-method

测试类

public class StaticFactoryBean {

    static public UserDao getUserDaoByStatic(){
        return new UserDao();
    }

}

xml配置

<bean id="staticFactory-method" class="org.itstack.interview.StaticFactoryBean" factory-method="getUserDaoByStatic"/>

单元测试

@Test
public void test_factory_method() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-factory-method.xml");
    logger.info("获取 Bean:{}", beanFactory.getBean("staticFactory-method"));
}

测试结果

23:15:28.950 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserDao@588df31b
23:15:28.950 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Returning cached instance of singleton bean 'staticFactory-bean'

1.4 factory-bean

测试类

public class StaticFactoryBean {
    public UserDao getUserDao(){
        return new UserDao();
    }
}

xml配置

<bean id="staticFactory" class="org.itstack.interview.StaticFactoryBean"/>
<bean id="staticFactory-bean" factory-bean="staticFactory" factory-method="getUserDao"/>

单元测试

@Test
public void test_factory_bean_method() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-factory-method.xml");
    logger.info("获取 Bean:{}", beanFactory.getBean("staticFactory-bean"));
}

测试结果

23:15:28.950 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserDao@33b37288

1.5 depends-on

xml配置

<bean id="userService" class="org.itstack.interview.UserService" depends-on="userDao"/>
<bean id="userDao" class="org.itstack.interview.UserDao"/>

单元测试

@Test
public void test_depends_on() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-depends-on.xml");
    logger.info("获取 Bean:{}", beanFactory.getBean(UserService.class, "userService").getUserDao());
}

测试结果

我被初始化了,UserDao
我被初始化了,UserService
23:24:14.678 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserDao@45afc369

1.6 lookup-method & ApplicationContextAware

测试类

public class UserDaoProvider implements ApplicationContextAware {

    private ApplicationContext applicationContext;

    public UserDao getUserDao() {
        return applicationContext.getBean("userDao", UserDao.class);
    }

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }

}

xml配置

<bean id="userDao" class="org.itstack.interview.UserDao" scope="prototype"/>
<bean id="provider" class="org.itstack.interview.UserDaoProvider"/>

单元测试

@Test
public void test_lookup_method() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-lookup-method.xml");
    logger.info("获取 Bean:{}", beanFactory.getBean(UserDaoProvider.class, "provider").getUserDao());
    logger.info("获取 Bean:{}", beanFactory.getBean(UserDaoProvider.class, "provider").getUserDao());
}

测试结果

我被初始化了,UserDao
16:29:25.813 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Finished creating instance of bean 'userDao'
16:29:25.813 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserDao@1188e820
16:29:25.813 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Creating instance of bean 'userDao'
我被初始化了,UserDao
16:29:25.814 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Finished creating instance of bean 'userDao'
16:29:25.814 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserDao@2f490758

2. 接口类

2.1 FactoryBean

测试类

public class MyFactoryBean implements FactoryBean<UserDao> {

    @Override
    public UserDao getObject() throws Exception {
        return new UserDao();
    }

    @Override
    public Class<?> getObjectType() {
        return UserDao.class;
    }

    @Override
    public boolean isSingleton() {
        return true;
    }
    
}

xml配置

<bean id="userDao" class="org.itstack.interview.MyFactoryBean"/>

单元测试

@Test
public void test_factory_bean() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-factory-bean.xml");
    logger.info("获取 Bean:{}", beanFactory.getBean("userDao"));
}

测试结果

23:36:19.339 [main] INFO  org.itstack.interview.test.ApiTest - 获取 Bean:org.itstack.interview.UserDao@3bd94634

2.2 BeanPostProcessor

测试类

public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("初始化前:" + beanName);
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("初始化后:" + beanName);
        return bean;
    }
    
}

xml配置

<bean id="beanPostProcessor" class="org.itstack.interview.MyBeanPostProcessor"/>
<bean id="userDao" class="org.itstack.interview.UserDao"/>

单元测试

@Test
public void test_bean_post_processor() {
    BeanFactory beanFactory = new ClassPathXmlApplicationContext("spring-config-bean-post-processor.xml");
}

测试结果

初始化前:userDao
初始化后:userDao
16:38:32.686 [main] DEBUG o.s.b.f.s.DefaultListableBeanFactory - Finished creating instance of bean 'userDao'

2.3 BeanFactoryAware

测试类

public class MyBeanFactoryAware implements BeanFactoryAware {
    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        
    }
}

四、总结

五、系列推荐

标签:Spring,itstack,Bean,bean,源码,interview,org,IOC,public
来源: https://blog.51cto.com/u_14943622/2844494