Spring干预Bean的生命周期的方法详解

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

@Service
public class DataProcessor {

    @Autowired
    private DataSource dataSource; // 依赖会被先注入

    private Connection connection;

    public DataProcessor() {
        System.out.println("1. 调用构造函数: dataSource is null? " + (dataSource == null));
    }

    @PostConstruct
    public void openConnection() {
        System.out.println("3. 执行 @PostConstruct: dataSource is null? " + (dataSource == null));
        System.out.println("正在打开数据库连接...");
        // 此时 dataSource 已经被注入，可以安全使用
        // this.connection = dataSource.getConnection(); 
    }

    public void process() {
        System.out.println("正在处理数据...");
    }

    @PreDestroy
    public void closeConnection() {
        System.out.println("执行 @PreDestroy: 正在关闭数据库连接...");
        // if (this.connection != null) this.connection.close();
    }
}

import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.DisposableBean;

@Component
public class LegacyService implements InitializingBean, DisposableBean {

    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("执行 InitializingBean.afterPropertiesSet()");
    }

    @Override
    public void destroy() throws Exception {
        System.out.println("执行 DisposableBean.destroy()");
    }
}

<bean id="myService" class="com.example.MyService" 
      init-method="customInit" 
      destroy-method="customCleanup"/>

@Configuration
public class AppConfig {
    @Bean(initMethod = "customInit", destroyMethod = "customCleanup")
    public MyService myService() {
        return new MyService();
    }
}

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("质检员[Before]: 正在检查 " + beanName);
        return bean; // 必须返回 bean，否则后续流程拿不到对象
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("质检员[After]: " + beanName + " 已完成初始化。");
        // 这里可以返回原始 bean，也可以返回一个包装后的代理 bean
        return bean;
    }
}

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class AwareService implements ApplicationContextAware {

    private ApplicationContext context;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("AwareService 感知到了 ApplicationContext");
        this.context = applicationContext;
    }
    
    public void doSomething() {
        // 可以通过 context 手动获取其他 bean
        DataProcessor processor = context.getBean(DataProcessor.class);
        processor.process();
    }
}