Spring5_容器与Bean_Bean的生命周期、Bean后处理器和BeanFactory后处理器

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1 Bean的生命周期

一个受 Spring 管理的 bean，生命周期主要阶段有

  • 创建：根据 bean 的构造方法或者工厂方法来创建 bean 实例对象
  • 依赖注入：根据 @Autowired，@Value 或其它一些手段，为 bean 的成员变量填充值、建立关系
  • 初始化：回调各种 Aware 接口，调用对象的各种初始化方法
  • 销毁：在容器关闭时，会销毁所有单例对象（即调用它们的销毁方法）
    • prototype 对象也能够销毁，不过需要容器这边主动调用
graph LR

创建 --> 依赖注入
依赖注入 --> 初始化
初始化 --> 可用
可用 --> 销毁

@Component
public class LifeCycleBean {
    private static final Logger log = LoggerFactory.getLogger(LifeCycleBean.class);

    public LifeCycleBean() {
        log.debug("构造");
    }

    @Autowired
    public void autowire(@Value("${JAVA_HOME}") String home) {
        log.debug("依赖注入: {}", home);
    }

    @PostConstruct
    public void init() {
        log.debug("初始化");
    }

    @PreDestroy
    public void destroy() {
        log.debug("销毁");
    }
}

打印结果

[DEBUG] 21:36:01.789 [main] com.itheima.a03.LifeCycleBean       - 构造 
[DEBUG] 21:36:01.791 [main] com.itheima.a03.LifeCycleBean       - 依赖注入: jdbc:mysql://localhost:3306/test 
[DEBUG] 21:36:01.792 [main] com.itheima.a03.LifeCycleBean       - 初始化 
[DEBUG] 21:36:03.579 [main] com.itheima.a03.LifeCycleBean       - 销毁

1.1 两个典型的bean 后处理器接口

除了以上4个阶段，各个阶段都会有一些功能增强（bean 后处理器提供的，如对@Autowired等注解进行解析等）

InstantiationAwareBeanPostProcessor、DestructionAwareBeanPostProcessor 都是 BeanPostProcessor 的子接口。

注意方法执行时机。

import org.springframework.beans.BeansException;
import org.springframework.beans.PropertyValues;
import org.springframework.beans.factory.config.DestructionAwareBeanPostProcessor;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
public class MyBeanPostProcessor implements InstantiationAwareBeanPostProcessor, DestructionAwareBeanPostProcessor {

    private static final Logger log = LoggerFactory.getLogger(MyBeanPostProcessor.class);

    @Override
    public void postProcessBeforeDestruction(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 销毁之前执行, 如 @PreDestroy");
    }

    @Override
    public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 实例化之前执行, 这里返回的对象会替换掉原本的 bean");
        return null;
    }

    @Override
    public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean")) {
            log.debug("<<<<<< 实例化之后执行, 这里如果返回 false 会跳过依赖注入阶段");
//            return false;
        }
        return true;
    }
    
    // 重点⭐️
    @Override
    public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 依赖注入阶段执行, 如 @Autowired、@Value、@Resource");
        return pvs;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 初始化之前执行, 这里返回的对象会替换掉原本的 bean, 如 @PostConstruct、@ConfigurationProperties");
        return bean;
    }

    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        if (beanName.equals("lifeCycleBean"))
            log.debug("<<<<<< 初始化之后执行, 这里返回的对象会替换掉原本的 bean, 如代理增强");
        return bean;
    }
}

创建前后的增强

  • postProcessBeforeInstantiation
    • 这里返回的对象若不为 null 会替换掉原本的 bean，并且仅会走postProcessAfterInitialization 流程
  • postProcessAfterInstantiation
    • 这里如果返回 false 会跳过依赖注入阶段

依赖注入前的增强

  • postProcessProperties
    • 如 @Autowired、@Value、@Resource

初始化前后的增强

  • postProcessBeforeInitialization
    • 这里返回的对象会替换掉原本的 bean
    • 如 @PostConstruct、@ConfigurationProperties
  • postProcessAfterInitialization
    • 这里返回的对象会替换掉原本的 bean
    • 如代理增强

销毁之前的增强

  • postProcessBeforeDestruction
    • 如 @PreDestroy

1.2 模板方法

模拟 Spring 写一个bean工厂

  • 静：固定不变的逻辑
  • 动：需要回调的接口
public class TestMethodTemplate {

    public static void main(String[] args) {
        MyBeanFactory beanFactory = new MyBeanFactory();
        beanFactory.addBeanPostProcessor(bean -> System.out.println("解析 @Autowired"));
        beanFactory.addBeanPostProcessor(bean -> System.out.println("解析 @Resource"));
        beanFactory.getBean();
    }

    // 模板方法  Template Method Pattern
    static class MyBeanFactory {
        public Object getBean() {
            Object bean = new Object();
            System.out.println("构造 " + bean);
            System.out.println("依赖注入 " + bean); // 后续扩展：添加@Autowired, @Resource的解析功能
            for (BeanPostProcessor processor : processors) {// 遍历所有后处理器
                processor.inject(bean);
            }
            System.out.println("初始化 " + bean);
            return bean;
        }

        // 集合存储后处理器
        private List<BeanPostProcessor> processors = new ArrayList<>();
        public void addBeanPostProcessor(BeanPostProcessor processor) {
            processors.add(processor);
        }
    }

    static interface BeanPostProcessor {
        // 变化的部分抽象成接口
        public void inject(Object bean); // 对依赖注入阶段的扩展
    }
}

2 Bean后处理器

Bean后处理器的作用：为bean生命周期各个阶段提供扩展

常见的后处理器

  • AutowiredAnnotationBeanPostProcessor
  • CommonAnnotationBeanPostProcessor
  • ConfigurationPropertiesBindingPostProcessor
public class A04 {
    public static void main(String[] args) {
        // ⬇️GenericApplicationContext 是一个【干净】的容器
        GenericApplicationContext context = new GenericApplicationContext();

        // ⬇️用原始方法注册三个 bean
        context.registerBean("bean1", Bean1.class);
        context.registerBean("bean2", Bean2.class);
        context.registerBean("bean3", Bean3.class);
        context.registerBean("bean4", Bean4.class);

        context.getDefaultListableBeanFactory().setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
        context.registerBean(AutowiredAnnotationBeanPostProcessor.class); // 解析@Autowired @Value 的bean后处理器

        context.registerBean(CommonAnnotationBeanPostProcessor.class); // @Resource @PostConstruct @PreDestroy

        ConfigurationPropertiesBindingPostProcessor.register(context.getDefaultListableBeanFactory());// 初始化前进行属性绑定

        // ⬇️初始化容器
        context.refresh(); // 执行beanFactory后处理器, 添加bean后处理器, 初始化所有单例

        System.out.println(context.getBean(Bean1.class));

        // ⬇️销毁容器
        context.close();

        /*
            学到了什么
                a. @Autowired 等注解的解析属于 bean 生命周期阶段(依赖注入, 初始化)的扩展功能
                b. 这些扩展功能由 bean 后处理器来完成
         */
    }
}

打印结果：

[DEBUG] 12:56:18.763 [main] com.itheima.a04.Bean1               - @Resource 生效: com.itheima.a04.Bean3@399c4be1 
[DEBUG] 12:56:18.781 [main] com.itheima.a04.Bean1               - @Autowired 生效: com.itheima.a04.Bean2@3c0be339 
[DEBUG] 12:56:18.796 [main] com.itheima.a04.Bean1               - @Value 生效: ${JAVA_HOME} 
[DEBUG] 12:56:18.796 [main] com.itheima.a04.Bean1               - @PostConstruct 生效 
Bean4{home='/Library/Java/JavaVirtualMachines/jdk-17.0.2.jdk/Contents/Home', version='17.0.2'}
[DEBUG] 12:56:18.898 [main] com.itheima.a04.Bean1               - @PreDestroy 生效

2.1 @Autowired bean 后处理器运行分析

  1. AutowiredAnnotationBeanPostProcessor.findAutowiringMetadata 用来获取某个 bean 上加了 @Value @Autowired 的成员变量，方法参数的信息，表示为 InjectionMetadata
  2. InjectionMetadata 可以完成依赖注入
  3. InjectionMetadata 内部根据成员变量，方法参数封装为 DependencyDescriptor 类型
  4. 有了 DependencyDescriptor，就可以利用 beanFactory.doResolveDependency 方法进行基于类型的查找
// AutowiredAnnotationBeanPostProcessor 运行分析
public class DigInAutowired {
    public static void main(String[] args) throws Throwable {
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        beanFactory.registerSingleton("bean2", new Bean2()); // 创建过程,依赖注入,初始化
        beanFactory.registerSingleton("bean3", new Bean3());
        beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver()); // @Value
        beanFactory.addEmbeddedValueResolver(new StandardEnvironment()::resolvePlaceholders); // ${} 的解析器

        // 1. 查找哪些属性、方法加了 @Autowired, 这称之为 InjectionMetadata
        AutowiredAnnotationBeanPostProcessor processor = new AutowiredAnnotationBeanPostProcessor();
        processor.setBeanFactory(beanFactory);

        Bean1 bean1 = new Bean1();
//        System.out.println(bean1);
//        processor.postProcessProperties(null, bean1, "bean1"); // 执行依赖注入 @Autowired @Value
//        System.out.println(bean1);

//        Method findAutowiringMetadata = AutowiredAnnotationBeanPostProcessor.class.getDeclaredMethod("findAutowiringMetadata", String.class, Class.class, PropertyValues.class);
//        findAutowiringMetadata.setAccessible(true);
//        InjectionMetadata metadata = (InjectionMetadata) findAutowiringMetadata.invoke(processor, "bean1", Bean1.class, null);// 获取 Bean1 上加了 @Value @Autowired 的成员变量，方法参数信息
//        System.out.println(metadata);

        // 2. 调用 InjectionMetadata 来进行依赖注入, 注入时按类型查找值
//        metadata.inject(bean1, "bean1", null);
//        System.out.println(bean1);

        // 3. 如何按类型查找值
        Field bean3 = Bean1.class.getDeclaredField("bean3");
        DependencyDescriptor dd1 = new DependencyDescriptor(bean3, false);
        Object o = beanFactory.doResolveDependency(dd1, null, null, null);
        System.out.println(o);

        Method setBean2 = Bean1.class.getDeclaredMethod("setBean2", Bean2.class);
        DependencyDescriptor dd2 =
                new DependencyDescriptor(new MethodParameter(setBean2, 0), true);
        Object o1 = beanFactory.doResolveDependency(dd2, null, null, null);
        System.out.println(o1);

        Method setHome = Bean1.class.getDeclaredMethod("setHome", String.class);
        DependencyDescriptor dd3 = new DependencyDescriptor(new MethodParameter(setHome, 0), true);
        Object o2 = beanFactory.doResolveDependency(dd3, null, null, null);
        System.out.println(o2);

    }
}

3 BeanFactory后处理器

  • BeanFactory 后处理器的作用：为 BeanFactory 提供扩展
  • 常见的 BeanFactory 后处理器

3.1 常见工厂后处理器

  • ConfigurationClassPostProcessor 可以解析
    • @ComponentScan
    • @Bean
    • @Import
    • @ImportResource
  • MapperScannerConfigurer 可以解析
    • Mapper 接口
/*
    BeanFactory 后处理器的作用
 */
public class A05 {
    private static final Logger log = LoggerFactory.getLogger(A05.class);

    public static void main(String[] args) throws IOException {

        // ⬇️GenericApplicationContext 是一个【干净】的容器
        GenericApplicationContext context = new GenericApplicationContext();
        context.registerBean("config", Config.class);
        context.registerBean(ConfigurationClassPostProcessor.class); // @ComponentScan @Bean @Import @ImportResource
        context.registerBean(MapperScannerConfigurer.class, bd -> { // @MapperScanner
            bd.getPropertyValues().add("basePackage", "com.itheima.a05.mapper");
        });

//        context.registerBean(ComponentScanPostProcessor.class); // 解析 @ComponentScan

        //context.registerBean(AtBeanPostProcessor.class); // 解析 @Bean
        //context.registerBean(MapperPostProcessor.class); // 解析 Mapper 接口

        // ⬇️初始化容器
        context.refresh();

        for (String name : context.getBeanDefinitionNames()) {
            System.out.println(name);
        }

        //Mapper1 mapper1 = context.getBean(Mapper1.class);
        //Mapper2 mapper2 = context.getBean(Mapper2.class);

        // ⬇️销毁容器
        context.close();

        /*
            学到了什么
                a. @ComponentScan, @Bean, @Mapper 等注解的解析属于核心容器(即 BeanFactory)的扩展功能
                b. 这些扩展功能由不同的 BeanFactory 后处理器来完成, 其实主要就是补充了一些 bean 定义
         */
    }
}

打印结果：

[DEBUG] 13:29:13.090 [main] com.itheima.a05.component.Bean2     - 我被 Spring 管理啦 
[DEBUG] 13:29:13.095 [main] com.itheima.a05.component.Bean3     - 我被 Spring 管理啦 
[DEBUG] 13:29:13.106 [main] com.itheima.a05.Bean1               - 我被 Spring 管理啦 
[INFO ] 13:29:13.271 [main] c.a.druid.pool.DruidDataSource      - {dataSource-1} inited 
config
org.springframework.context.annotation.ConfigurationClassPostProcessor
org.mybatis.spring.mapper.MapperScannerConfigurer
bean2
bean3
bean1
sqlSessionFactoryBean
dataSource
mapper1
mapper2

3.2 工厂后处理器模拟实现

组件扫描

public class ComponentScanPostProcessor implements BeanDefinitionRegistryPostProcessor {
    @Override // context.refresh
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {

    }

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanFactory) throws BeansException {
        try {
            ComponentScan componentScan = AnnotationUtils.findAnnotation(Config.class, ComponentScan.class);
            if (componentScan != null) {
                for (String p : componentScan.basePackages()) {
                    System.out.println(p);
                    // com.itheima.a05.component -> classpath*:com/itheima/a05/component/**/*.class
                    String path = "classpath*:" + p.replace(".", "/") + "/**/*.class";
                    System.out.println(path);
                    CachingMetadataReaderFactory factory = new CachingMetadataReaderFactory();
                    Resource[] resources = new PathMatchingResourcePatternResolver().getResources(path);
                    AnnotationBeanNameGenerator generator = new AnnotationBeanNameGenerator();
                    for (Resource resource : resources) {
                        // System.out.println(resource);
                        MetadataReader reader = factory.getMetadataReader(resource);
                        // System.out.println("类名:" + reader.getClassMetadata().getClassName());
                        AnnotationMetadata annotationMetadata = reader.getAnnotationMetadata();
                        // System.out.println("是否加了 @Component:" + annotationMetadata.hasAnnotation(Component.class.getName()));
                        // System.out.println("是否加了 @Component 派生:" + annotationMetadata.hasMetaAnnotation(Component.class.getName()));
                        
                        if (annotationMetadata.hasAnnotation(Component.class.getName())
                            || annotationMetadata.hasMetaAnnotation(Component.class.getName())) {
                            AbstractBeanDefinition bd = BeanDefinitionBuilder
                                    .genericBeanDefinition(reader.getClassMetadata().getClassName())
                                    .getBeanDefinition();
                            String name = generator.generateBeanName(bd, beanFactory);
                            beanFactory.registerBeanDefinition(name, bd);
                        }
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@Bean

public class AtBeanPostProcessor implements BeanDefinitionRegistryPostProcessor {
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory configurableListableBeanFactory) throws BeansException {

    }

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanFactory) throws BeansException {
        try {
            CachingMetadataReaderFactory factory = new CachingMetadataReaderFactory();
            MetadataReader reader = factory.getMetadataReader(new ClassPathResource("com/itheima/a05/Config.class"));
            Set<MethodMetadata> methods = reader.getAnnotationMetadata().getAnnotatedMethods(Bean.class.getName());
            for (MethodMetadata method : methods) {
                System.out.println(method);
                String initMethod = method.getAnnotationAttributes(Bean.class.getName()).get("initMethod").toString();
                BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
                builder.setFactoryMethodOnBean(method.getMethodName(), "config");
                builder.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);
                if (initMethod.length() > 0) {
                    builder.setInitMethodName(initMethod);
                }
                AbstractBeanDefinition bd = builder.getBeanDefinition();
                beanFactory.registerBeanDefinition(method.getMethodName(), bd);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Mapper 接口

// 生产mapper对象的工厂
@Bean
public MapperFactoryBean<Mapper1> mapper1(SqlSessionFactory sqlSessionFactory) {
    MapperFactoryBean<Mapper1> factory = new MapperFactoryBean<>(Mapper1.class);
    factory.setSqlSessionFactory(sqlSessionFactory);
    return factory;
}

@Bean
public MapperFactoryBean<Mapper2> mapper2(SqlSessionFactory sqlSessionFactory) {
    MapperFactoryBean<Mapper2> factory = new MapperFactoryBean<>(Mapper2.class);
    factory.setSqlSessionFactory(sqlSessionFactory);
    return factory;
}

如何批量添加？

public class MapperPostProcessor implements BeanDefinitionRegistryPostProcessor {

    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanFactory) throws BeansException {
        try {
            PathMatchingResourcePatternResolver resolver = new PathMatchingResourcePatternResolver();
            Resource[] resources = resolver.getResources("classpath:com/itheima/a05/mapper/**/*.class");
            AnnotationBeanNameGenerator generator = new AnnotationBeanNameGenerator();
            CachingMetadataReaderFactory factory = new CachingMetadataReaderFactory();
            for (Resource resource : resources) {
                MetadataReader reader = factory.getMetadataReader(resource);
                ClassMetadata classMetadata = reader.getClassMetadata();
                if (classMetadata.isInterface()) {
                    AbstractBeanDefinition bd = BeanDefinitionBuilder.genericBeanDefinition(MapperFactoryBean.class)
                            .addConstructorArgValue(classMetadata.getClassName())
                            .setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE)
                            .getBeanDefinition();
                    AbstractBeanDefinition bd2 = BeanDefinitionBuilder.genericBeanDefinition(classMetadata.getClassName()).getBeanDefinition();
                    String name = generator.generateBeanName(bd2, beanFactory);
                    beanFactory.registerBeanDefinition(name, bd);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

    }
}
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