Spring 初始化

痛定思痛。 2024-04-01 18:57 77阅读 0赞

**一、初始化常用方法**  
1、构造器Constructor  
2、ContextRefreshedEvent事件  
3、PostConstruct 注解（推荐）  
4、InitializingBean  
5、init-method方法（推荐）  
6、实现 SmartInitializingSingleton 接口  
7、重写 onRefresh()方法  
8、CommandLineRunner（仅限Spring Boot）（推荐）  
9、SpringApplicationRunListener（仅限Spring boot）（推荐）

**二、具体示例**  
1、ContextRefreshedEvent事件  
ContextRefreshedEvent：是Spring容器初始化完成后调用的事件。  
ContextRefreshedEvent的父类是ApplicationContextEvent，是一个事件。所以我们通过ApplicationListener来实现。

代码如下：

import com.example.springbootdemo.bean.Person;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.context.ApplicationListener;
    import org.springframework.context.event.ContextRefreshedEvent;
    import org.springframework.stereotype.Component;
    
    @Component
    public class PersonAfterListener implements ApplicationListener<ContextRefreshedEvent> {
        
        @Autowired
        private Person person;
    
        @Override
        public void onApplicationEvent(ContextRefreshedEvent event) {
        
            person.run("ContextRefreshedEvent");
        }
    }

输出结果：  
![在这里插入图片描述][e61633d695e9487c918ae82fec675764.png]

2、PostConstruct 注解  
PostConstruct注解修饰的方式，是在spring容器启动时运行的。优先级大于ContextRefreshedEvent事件。

代码如下：

import com.example.springbootdemo.bean.Person;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    import javax.annotation.PostConstruct;
    
    @Component
    public class PersonAfterPostConstruct {
        
        @Autowired
        private Person person;
    
        @PostConstruct
        public void postConstruct(){
        
            person.run("PostConstruct");
        }
    }

输出结果：  
![在这里插入图片描述][333ef288195943e0a736134176f5b9c6.png]

由此可见，PostConstruct优先级大于ContextRefreshedEvent事件。

3、InitializingBean  
InitializingBean是spring容器在启动并初始化好内部示例后调用的，用来最终为总体bean添加最后属性和操作。

官方原话：This method allows the bean instance to perform validation of its overall configuration and final initialization when all bean properties have been set.

代码如下：

import com.example.springbootdemo.bean.Person;
    import org.springframework.beans.factory.InitializingBean;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    @Component
    public class PersonAfterInitializingBean implements InitializingBean {
        
        @Autowired
        private Person person;
    
        @Override
        public void afterPropertiesSet() throws Exception {
        
            person.run("InitializingBean");
        }
    }

输出结果：  
![在这里插入图片描述][164e2dacce704d8db56d47a488cde91d.png]

4、init-method方法  
这种方法有一定的局限性，并且可能会覆盖曾经的init操作，需要慎用。

Bean在加载到Spring容器中时需要先将Bean的定义信息抽象为BeanDefinition，其中有一个属性init-method代表将来Bean初始化时要调用的方法。

我们通过BeanFactoryPostProcessor来注入init-method方法，并且该方法必须是没有参数的。

代码如下：

import org.springframework.beans.BeansException;
    import org.springframework.beans.factory.config.BeanDefinition;
    import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
    import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
    import org.springframework.stereotype.Component;
    
    @Component
    public class PersonAfterInit implements BeanFactoryPostProcessor {
        
    
        @Override
        public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        
            BeanDefinition person = beanFactory.getBeanDefinition("person");
            person.setInitMethodName("run");
        }
    }

输出结果：  
![在这里插入图片描述][73b3867be4f74b7fb1f4f87275ab8be8.png]

5 、实现 SmartInitializingSingleton 接口  
SmartInitializingSingleton是Bean容器在初始化所有非懒加载的单例Bean后调用的方法。

代码如下：

import com.example.springbootdemo.bean.Person;
    import org.springframework.beans.factory.SmartInitializingSingleton;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    
    @Component
    public class PersonAfterSmartInitializingSingleton implements SmartInitializingSingleton {
        
        @Autowired
        private Person person;
    
        @Override
        public void afterSingletonsInstantiated() {
        
            person.run("SmartInitializingSingleton");
        }
    }

输出结果：  
![在这里插入图片描述][835d178308924d398cc5c5cd3d614359.png]

6、重写 onRefresh()方法  
这个我实在是不会，但我不藏着掖着，告诉你也能实现。

7、CommandLineRunner（仅限Spring Boot）  
CommandLineRunner 是一个Spring boot 接口，在应用初始化后执行，且仅会执行一次。可以用来打印项目中配置文件的参数，方便排查问题。

代码如下：

import com.example.springbootdemo.bean.Person;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.boot.CommandLineRunner;
    import org.springframework.stereotype.Component;
    
    @Component
    public class PersonAfterCommandLineRunner implements CommandLineRunner {
        
        @Autowired
        private Person person;
    
        @Override
        public void run(String... args) throws Exception {
        
            person.run("CommandLineRunner");
        }
    }

输出结果：  
![在这里插入图片描述][d34630c8222745f383057061f3395cd1.png]

8、SpringApplicationRunListener（仅限Spring boot）  
SpringBoot的生命周期事件监听方法，需要搭配resource/META-INF/spring.factories 文件使用。

代码如下：  
JAVA代码：

import com.example.springbootdemo.bean.Person;
    import org.springframework.boot.ConfigurableBootstrapContext;
    import org.springframework.boot.SpringApplication;
    import org.springframework.boot.SpringApplicationRunListener;
    import org.springframework.context.ConfigurableApplicationContext;
    import org.springframework.core.env.ConfigurableEnvironment;
    
    import java.time.Duration;
    
    
    public class PersonAfterSpringApplicationRunListener implements SpringApplicationRunListener {
        
        private final SpringApplication application;
        private final String[] args;
    
        public PersonAfterSpringApplicationRunListener(SpringApplication application, String[] args) {
        
            this.application = application;
            this.args = args;
        }
    
        @Override
        public void starting(ConfigurableBootstrapContext bootstrapContext) {
        
            /*
             * Person has not been registered
             */
    //        Person person = bootstrapContext.get(Person.class);
    //        person.run("SpringApplicationRunListener:starting");
        }
    
        @Override
        public void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {
        
            /*
             * Person has not been registered
             */
    //        Person person = bootstrapContext.get(Person.class);
    //        person.run("SpringApplicationRunListener:environmentPrepared");
        }
    
        @Override
        public void contextPrepared(ConfigurableApplicationContext context) {
        
            /*
             * Person has not been registered
             */
    //        Person person = context.getBean(Person.class);
    //        person.run("SpringApplicationRunListener:contextPrepared");
        }
    
        @Override
        public void contextLoaded(ConfigurableApplicationContext context) {
        
            /*
             * Person has not been registered
             */
    //        Person person = context.getBean(Person.class);
    //        person.run("SpringApplicationRunListener:contextLoaded");
        }
    
        @Override
        public void started(ConfigurableApplicationContext context, Duration timeTaken) {
        
            Person person = context.getBean(Person.class);
            person.run("SpringApplicationRunListener:started");
        }
    
        @Override
        public void ready(ConfigurableApplicationContext context, Duration timeTaken) {
        
            Person person = context.getBean(Person.class);
            person.run("SpringApplicationRunListener:ready");
        }
    
        @Override
        public void failed(ConfigurableApplicationContext context, Throwable exception) {
        
            Person person = context.getBean(Person.class);
            person.run("SpringApplicationRunListener:failed");
        }
    }

spring.factories

org.springframework.boot.SpringApplicationRunListener=com.example.springbootdemo.impl.PersonAfterSpringApplicationRunListener

输出结果：  
![在这里插入图片描述][816f4f0fb64f4124a44f09c3980490d4.png]

总结：  
执行优先级：**Constructor** >> **init-Method** >> **InitializingBean** >> **PostConstruct** >> **SmartInitializingSingleton** >> **ContextRefreshedEvent** >> **SpringApplicationRunListener:started** >> **CommandLineRunner** >> **SpringApplicationRunListener:ready**

[e61633d695e9487c918ae82fec675764.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/d87b0f33f76a42a6b9a67f2d2c9ef17a.png
[333ef288195943e0a736134176f5b9c6.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/8959d8431cea454ba9b8485cfff5e4c4.png
[164e2dacce704d8db56d47a488cde91d.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/76dee513237e4d5e9e62382689246a89.png
[73b3867be4f74b7fb1f4f87275ab8be8.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/7b10c07dce2942649e8017116d252978.png
[835d178308924d398cc5c5cd3d614359.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/71f4efddebdf429b8ea81df44d2a5aeb.png
[d34630c8222745f383057061f3395cd1.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/778580510b104911985fbb077ac4cc3f.png
[816f4f0fb64f4124a44f09c3980490d4.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/01/c180c9f964e848bbab80b40053047d2f.png