spring高级源码50讲-43-50(spring续)

其它

43) FactoryBean

演示 - FactoryBean

代码参考

package com.itheima.a43;import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;@ComponentScan
public class A43 {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A43.class);Bean1 bean1 = (Bean1) context.getBean("bean1");Bean1 bean2 = (Bean1) context.getBean("bean1");Bean1 bean3 = (Bean1) context.getBean("bean1");System.out.println(bean1);System.out.println(bean2);System.out.println(bean3);System.out.println(context.getBean(Bean1.class));System.out.println(context.getBean(Bean1FactoryBean.class));System.out.println(context.getBean("&bean1"));context.close();/*学到了什么: 一个在 Spring 发展阶段中重要, 但目前已经很鸡肋的接口 FactoryBean 的使用要点说它鸡肋有两点:1. 它的作用是用制造创建过程较为复杂的产品, 如 SqlSessionFactory, 但 @Bean 已具备等价功能2. 使用上较为古怪, 一不留神就会用错a. 被 FactoryBean 创建的产品- 会认为创建、依赖注入、Aware 接口回调、前初始化这些都是 FactoryBean 的职责, 这些流程都不会走- 唯有后初始化的流程会走, 也就是产品可以被代理增强- 单例的产品不会存储于 BeanFactory 的 singletonObjects 成员中, 而是另一个 factoryBeanObjectCache 成员中b. 按名字去获取时, 拿到的是产品对象, 名字前面加 & 获取的是工厂对象就说恶心不?但目前此接口的实现仍被大量使用, 想被全面废弃很难*/}}

package com.itheima.a43;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.annotation.Autowired;import javax.annotation.PostConstruct;public class Bean1 implements BeanFactoryAware {private static final Logger log = LoggerFactory.getLogger(Bean1.class);private Bean2 bean2;@Autowiredpublic void setBean2(Bean2 bean2) {log.debug("setBean2({})", bean2);this.bean2 = bean2;}public Bean2 getBean2() {return bean2;}@PostConstructpublic void init() {log.debug("init");}@Overridepublic void setBeanFactory(BeanFactory beanFactory) throws BeansException {log.debug("setBeanFactory({})", beanFactory);}
}

package com.itheima.a43;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;@Component("bean1")
public class Bean1FactoryBean implements FactoryBean<Bean1> {private static final Logger log = LoggerFactory.getLogger(Bean1FactoryBean.class);// 决定了根据【类型】获取或依赖注入能否成功@Overridepublic Class<?> getObjectType() {return Bean1.class;}// 决定了 getObject() 方法被调用一次还是多次@Overridepublic boolean isSingleton() {return true;}@Overridepublic Bean1 getObject() throws Exception {Bean1 bean1 = new Bean1();log.debug("create bean: {}", bean1);return bean1;}
}

收获💡

1. 它的作用是用制造创建过程较为复杂的产品, 如 SqlSessionFactory, 但 @Bean 已具备等价功能
2. 使用上较为古怪, 一不留神就会用错
   1. 被 FactoryBean 创建的产品
      • 会认为创建、依赖注入、Aware 接口回调、前初始化这些都是 FactoryBean 的职责, 这些流程都不会走
      • 唯有后初始化的流程会走, 也就是产品可以被代理增强
      • 单例的产品不会存储于 BeanFactory 的 singletonObjects 成员中, 而是另一个 factoryBeanObjectCache 成员中
   2. 按名字去获取时, 拿到的是产品对象, 名字前面加 & 获取的是工厂对象

44) @Indexed 原理

真实项目中，只需要加入以下依赖即可

<dependency><groupId>org.springframework</groupId><artifactId>spring-context-indexer</artifactId><optional>true</optional>
</dependency>

演示 - @Indexed

代码参考

package com.itheima.a44;import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.ClassPathBeanDefinitionScanner;import java.io.IOException;
import java.lang.reflect.InvocationTargetException;/*做这个试验前, 先在 target/classes 创建 META-INF/spring.components, 内容为com.itheima.a44.Bean1=org.springframework.stereotype.Componentcom.itheima.a44.Bean2=org.springframework.stereotype.Component做完实现建议删除, 避免影响其它组件扫描的结果真实项目中, 这个步骤可以自动完成, 加入以下依赖<dependency><groupId>org.springframework</groupId><artifactId>spring-context-indexer</artifactId><optional>true</optional></dependency>*/
public class A44 {public static void main(String[] args) throws IOException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();// 组件扫描的核心类ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(beanFactory);scanner.scan(A44.class.getPackageName());for (String name : beanFactory.getBeanDefinitionNames()) {System.out.println(name);}/*学到了什么a. @Indexed 的原理, 在编译时就根据 @Indexed 生成 META-INF/spring.components 文件扫描时1. 如果发现 META-INF/spring.components 存在, 以它为准加载 bean definition2. 否则, 会遍历包下所有 class 资源 (包括 jar 内的)*/}
}

收获💡

1. 在编译时就根据 @Indexed 生成 META-INF/spring.components 文件
2. 扫描时
   • 如果发现 META-INF/spring.components 存在, 以它为准加载 bean definition
   • 否则, 会遍历包下所有 class 资源 (包括 jar 内的)
3. 解决的问题，在编译期就找到 @Component 组件，节省运行期间扫描 @Component 的时间

45) 代理进一步理解

演示 - 代理

代码参考

package com.itheima.a45;import org.springframework.aop.framework.Advised;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;import java.lang.reflect.Method;@SpringBootApplication
public class A45 {public static void main(String[] args) throws Exception {ConfigurableApplicationContext context = SpringApplication.run(A45.class, args);Bean1 proxy = context.getBean(Bean1.class);/*1.演示 spring 代理的设计特点依赖注入和初始化影响的是原始对象代理与目标是两个对象，二者成员变量并不共用数据*/
//        showProxyAndTarget(proxy);
//
//        System.out.println(">>>>>>>>>>>>>>>>>>>");
//        System.out.println(proxy.getBean2());
//        System.out.println(proxy.isInitialized());/*2.演示 static 方法、final 方法、private 方法均无法增强*/proxy.m1();proxy.m2();proxy.m3();Method m4 = Bean1.class.getDeclaredMethod("m1");m4.setAccessible(true);m4.invoke(proxy);context.close();}public static void showProxyAndTarget(Bean1 proxy) throws Exception {System.out.println(">>>>> 代理中的成员变量");System.out.println("\tinitialized=" + proxy.initialized);System.out.println("\tbean2=" + proxy.bean2);if (proxy instanceof Advised advised) {System.out.println(">>>>> 目标中的成员变量");Bean1 target = (Bean1) advised.getTargetSource().getTarget();System.out.println("\tinitialized=" + target.initialized);System.out.println("\tbean2=" + target.bean2);}}}

收获💡

1. spring 代理的设计特点

   • 依赖注入和初始化影响的是原始对象

     • 因此 cglib 不能用 MethodProxy.invokeSuper()

   • 代理与目标是两个对象，二者成员变量并不共用数据

2. static 方法、final 方法、private 方法均无法增强

   • 进一步理解代理增强基于方法重写

46) @Value 装配底层

按类型装配的步骤

1. 查看需要的类型是否为 Optional，是，则进行封装（非延迟），否则向下走
2. 查看需要的类型是否为 ObjectFactory 或 ObjectProvider，是，则进行封装（延迟），否则向下走
3. 查看需要的类型（成员或参数）上是否用 @Lazy 修饰，是，则返回代理，否则向下走
4. 解析 @Value 的值
   1. 如果需要的值是字符串，先解析 ${ }，再解析 #{ }
   2. 不是字符串，需要用 TypeConverter 转换
5. 看需要的类型是否为 Stream、Array、Collection、Map，是，则按集合处理，否则向下走
6. 在 BeanFactory 的 resolvableDependencies 中找有没有类型合适的对象注入，没有向下走
7. 在 BeanFactory 及父工厂中找类型匹配的 bean 进行筛选，筛选时会考虑 @Qualifier 及泛型
8. 结果个数为 0 抛出 NoSuchBeanDefinitionException 异常
9. 如果结果 > 1，再根据 @Primary 进行筛选
10. 如果结果仍 > 1，再根据成员名或变量名进行筛选
11. 结果仍 > 1，抛出 NoUniqueBeanDefinitionException 异常

演示 - @Value 装配过程

代码参考

package com.itheima.a46;import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.config.BeanExpressionContext;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.stereotype.Component;import java.lang.reflect.Field;// 本章节作为第四讲的延续
@Configuration
@SuppressWarnings("all")
public class A46 {public static void main(String[] args) throws Exception {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A46.class);DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();resolver.setBeanFactory(beanFactory);//        test1(context, resolver, Bean1.class.getDeclaredField("home"));
//        test2(context, resolver, Bean1.class.getDeclaredField("age"));
//        test3(context, resolver, Bean2.class.getDeclaredField("bean3"));test3(context, resolver, Bean4.class.getDeclaredField("value"));}private static void test3(AnnotationConfigApplicationContext context, ContextAnnotationAutowireCandidateResolver resolver, Field field) {DependencyDescriptor dd1 = new DependencyDescriptor(field, false);// 获取 @Value 的内容String value = resolver.getSuggestedValue(dd1).toString();System.out.println(value);// 解析 ${}value = context.getEnvironment().resolvePlaceholders(value);System.out.println(value);System.out.println(value.getClass());// 解析 #{} @bean3Object bean3 = context.getBeanFactory().getBeanExpressionResolver().evaluate(value, new BeanExpressionContext(context.getBeanFactory(), null));// 类型转换Object result = context.getBeanFactory().getTypeConverter().convertIfNecessary(bean3, dd1.getDependencyType());System.out.println(result);}private static void test2(AnnotationConfigApplicationContext context, ContextAnnotationAutowireCandidateResolver resolver, Field field) {DependencyDescriptor dd1 = new DependencyDescriptor(field, false);// 获取 @Value 的内容String value = resolver.getSuggestedValue(dd1).toString();System.out.println(value);// 解析 ${}value = context.getEnvironment().resolvePlaceholders(value);System.out.println(value);System.out.println(value.getClass());Object age = context.getBeanFactory().getTypeConverter().convertIfNecessary(value, dd1.getDependencyType());System.out.println(age.getClass());}private static void test1(AnnotationConfigApplicationContext context, ContextAnnotationAutowireCandidateResolver resolver, Field field) {DependencyDescriptor dd1 = new DependencyDescriptor(field, false);// 获取 @Value 的内容String value = resolver.getSuggestedValue(dd1).toString();System.out.println(value);// 解析 ${}value = context.getEnvironment().resolvePlaceholders(value);System.out.println(value);}public class Bean1 {@Value("${JAVA_HOME}")private String home;@Value("18")private int age;}public class Bean2 {@Value("#{@bean3}") // SpringEL       #{SpEL}private Bean3 bean3;}@Component("bean3")public class Bean3 {}static class Bean4 {@Value("#{'hello, ' + '${JAVA_HOME}'}")private String value;}
}

收获💡

1. ContextAnnotationAutowireCandidateResolver 作用之一，获取 @Value 的值
2. 了解 ${ } 对应的解析器
3. 了解 #{ } 对应的解析器
4. TypeConvert 的一项体现

47) @Autowired 装配底层

演示 - @Autowired 装配过程

代码参考

package com.itheima.a47;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.ObjectFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.context.annotation.Lazy;
import org.springframework.core.MethodParameter;
import org.springframework.stereotype.Component;import java.lang.reflect.Method;
import java.util.Optional;@Configuration
public class A47_1 {public static void main(String[] args) throws NoSuchFieldException, NoSuchMethodException {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A47_1.class);DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");// 1. 根据成员变量的类型注入DependencyDescriptor dd1 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean2"), false);System.out.println(beanFactory.doResolveDependency(dd1, "bean1", null, null));System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");// 2. 根据参数的类型注入Method setBean2 = Bean1.class.getDeclaredMethod("setBean2", Bean2.class);DependencyDescriptor dd2 = new DependencyDescriptor(new MethodParameter(setBean2, 0), false);System.out.println(beanFactory.doResolveDependency(dd2, "bean1", null, null));System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");// 3. 结果包装为 Optional<Bean2>DependencyDescriptor dd3 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean3"), false);if (dd3.getDependencyType() == Optional.class) {dd3.increaseNestingLevel();Object result = beanFactory.doResolveDependency(dd3, "bean1", null, null);System.out.println(Optional.ofNullable(result));}System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");// 4. 结果包装为 ObjectProvider,ObjectFactoryDependencyDescriptor dd4 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean4"), false);if (dd4.getDependencyType() == ObjectFactory.class) {dd4.increaseNestingLevel();ObjectFactory objectFactory = new ObjectFactory() {@Overridepublic Object getObject() throws BeansException {return beanFactory.doResolveDependency(dd4, "bean1", null, null);}};System.out.println(objectFactory.getObject());}System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>");// 5. 对 @Lazy 的处理DependencyDescriptor dd5 = new DependencyDescriptor(Bean1.class.getDeclaredField("bean2"), false);ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();resolver.setBeanFactory(beanFactory);Object proxy = resolver.getLazyResolutionProxyIfNecessary(dd5, "bean1");System.out.println(proxy);System.out.println(proxy.getClass());/*学到了什么1. Optional 及 ObjectFactory 对于内嵌类型的处理, 源码参考 ResolvableType2. ObjectFactory 懒惰的思想3. @Lazy 懒惰的思想下一节, 继续学习 doResolveDependency 内部处理*/}static class Bean1 {@Autowired @Lazy private Bean2 bean2;@Autowired public void setBean2(Bean2 bean2) {this.bean2 = bean2;}@Autowired private Optional<Bean2> bean3;@Autowired private ObjectFactory<Bean2> bean4;}@Component("bean2")static class Bean2 {/*@Overridepublic String toString() {return super.toString();}*/}
}

package com.itheima.a47;import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.support.RootBeanDefinition;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.ContextAnnotationAutowireCandidateResolver;
import org.springframework.stereotype.Component;import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;@SuppressWarnings("all")
@Configuration
public class A47_2 {public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A47_2.class);DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 1. 数组类型");testArray(beanFactory);System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 2. List 类型");testList(beanFactory);System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 3. applicationContext");testApplicationContext(beanFactory);System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 4. 泛型");testGeneric(beanFactory);System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>>>>>> 5. @Qualifier");testQualifier(beanFactory);/*学到了什么1. 如何获取数组元素类型2. Spring 如何获取泛型中的类型3. 特殊对象的处理, 如 ApplicationContext, 并注意 Map 取值时的类型匹配问题 (另见  TestMap)4. 谁来进行泛型匹配 (另见 TestGeneric)5. 谁来处理 @Qualifier6. 刚开始都只是按名字处理, 等候选者确定了, 才会创建实例*/}private static void testQualifier(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {DependencyDescriptor dd5 = new DependencyDescriptor(Target.class.getDeclaredField("service"), true);Class<?> type = dd5.getDependencyType();ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();resolver.setBeanFactory(beanFactory);for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {BeanDefinition bd = beanFactory.getMergedBeanDefinition(name);//                                                             @Qualifier("service2")if (resolver.isAutowireCandidate(new BeanDefinitionHolder(bd,name), dd5)) {System.out.println(name);System.out.println(dd5.resolveCandidate(name, type, beanFactory));}}}private static void testGeneric(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {DependencyDescriptor dd4 = new DependencyDescriptor(Target.class.getDeclaredField("dao"), true);Class<?> type = dd4.getDependencyType();ContextAnnotationAutowireCandidateResolver resolver = new ContextAnnotationAutowireCandidateResolver();resolver.setBeanFactory(beanFactory);for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {BeanDefinition bd = beanFactory.getMergedBeanDefinition(name);// 对比 BeanDefinition 与 DependencyDescriptor 的泛型是否匹配if (resolver.isAutowireCandidate(new BeanDefinitionHolder(bd,name), dd4)) {System.out.println(name);System.out.println(dd4.resolveCandidate(name, type, beanFactory));}}}private static void testApplicationContext(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException, IllegalAccessException {DependencyDescriptor dd3 = new DependencyDescriptor(Target.class.getDeclaredField("applicationContext"), true);Field resolvableDependencies = DefaultListableBeanFactory.class.getDeclaredField("resolvableDependencies");resolvableDependencies.setAccessible(true);Map<Class<?>, Object> dependencies = (Map<Class<?>, Object>) resolvableDependencies.get(beanFactory);
//        dependencies.forEach((k, v) -> {
//            System.out.println("key:" + k + " value: " + v);
//        });for (Map.Entry<Class<?>, Object> entry : dependencies.entrySet()) {// 左边类型                      右边类型if (entry.getKey().isAssignableFrom(dd3.getDependencyType())) {System.out.println(entry.getValue());break;}}}private static void testList(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {DependencyDescriptor dd2 = new DependencyDescriptor(Target.class.getDeclaredField("serviceList"), true);if (dd2.getDependencyType() == List.class) {Class<?> resolve = dd2.getResolvableType().getGeneric().resolve();System.out.println(resolve);List<Object> list = new ArrayList<>();String[] names = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, resolve);for (String name : names) {Object bean = dd2.resolveCandidate(name, resolve, beanFactory);list.add(bean);}System.out.println(list);}}private static void testArray(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {DependencyDescriptor dd1 = new DependencyDescriptor(Target.class.getDeclaredField("serviceArray"), true);if (dd1.getDependencyType().isArray()) {Class<?> componentType = dd1.getDependencyType().getComponentType();System.out.println(componentType);String[] names = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, componentType);List<Object> beans = new ArrayList<>();for (String name : names) {System.out.println(name);Object bean = dd1.resolveCandidate(name, componentType, beanFactory);beans.add(bean);}Object array = beanFactory.getTypeConverter().convertIfNecessary(beans, dd1.getDependencyType());System.out.println(array);}}static class Target {@Autowired private Service[] serviceArray;@Autowired private List<Service> serviceList;@Autowired private ConfigurableApplicationContext applicationContext;@Autowired private Dao<Teacher> dao;@Autowired @Qualifier("service2") private Service service;}interface Dao<T> {}@Component("dao1") static class Dao1 implements Dao<Student> {}@Component("dao2") static class Dao2 implements Dao<Teacher> {}static class Student {}static class Teacher {}interface Service {}@Component("service1")static class Service1 implements Service {}@Component("service2")static class Service2 implements Service {}@Component("service3")static class Service3 implements Service {}
}

package com.itheima.a47;import org.springframework.beans.factory.BeanFactoryUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.beans.factory.support.BeanDefinitionBuilder;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;@Configuration
public class A47_3 {public static void main(String[] args) throws NoSuchFieldException {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A47_3.class);DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();testPrimary(beanFactory);testDefault(beanFactory);/*学到了什么1. @Primary 的处理, 其中 @Primary 会在 @Bean 解析或组件扫描时被解析 (另见 TestPrimary)2. 最后的防线, 通过属性或参数名匹配*/}private static void testDefault(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {DependencyDescriptor dd = new DependencyDescriptor(Target2.class.getDeclaredField("service3"), false);Class<?> type = dd.getDependencyType();for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {if(name.equals(dd.getDependencyName())) {System.out.println(name);}}}private static void testPrimary(DefaultListableBeanFactory beanFactory) throws NoSuchFieldException {DependencyDescriptor dd = new DependencyDescriptor(Target1.class.getDeclaredField("service"), false);Class<?> type = dd.getDependencyType();for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, type)) {if (beanFactory.getMergedBeanDefinition(name).isPrimary()) {System.out.println(name);}}}static class Target1 {@Autowired private Service service;}static class Target2 {@Autowired private Service service3;}interface Service {}@Component("service1") static class Service1 implements Service {}@Component("service2") static class Service2 implements Service {}@Component("service3") static class Service3 implements Service {}
}

收获💡

1. @Autowired 本质上是根据成员变量或方法参数的类型进行装配
2. 如果待装配类型是 Optional，需要根据 Optional 泛型找到 bean，再封装为 Optional 对象装配
3. 如果待装配的类型是 ObjectFactory，需要根据 ObjectFactory 泛型创建 ObjectFactory 对象装配
   • 此方法可以延迟 bean 的获取
4. 如果待装配的成员变量或方法参数上用 @Lazy 标注，会创建代理对象装配
   • 此方法可以延迟真实 bean 的获取
   • 被装配的代理不作为 bean
5. 如果待装配类型是数组，需要获取数组元素类型，根据此类型找到多个 bean 进行装配
6. 如果待装配类型是 Collection 或其子接口，需要获取 Collection 泛型，根据此类型找到多个 bean
7. 如果待装配类型是 ApplicationContext 等特殊类型
   • 会在 BeanFactory 的 resolvableDependencies 成员按类型查找装配
   • resolvableDependencies 是 map 集合，key 是特殊类型，value 是其对应对象
   • 不能直接根据 key 进行查找，而是用 isAssignableFrom 逐一尝试右边类型是否可以被赋值给左边的 key 类型
8. 如果待装配类型有泛型参数
   • 需要利用 ContextAnnotationAutowireCandidateResolver 按泛型参数类型筛选
9. 如果待装配类型有 @Qualifier
   • 需要利用 ContextAnnotationAutowireCandidateResolver 按注解提供的 bean 名称筛选
10. 有 @Primary 标注的 @Component 或 @Bean 的处理
11. 与成员变量名或方法参数名同名 bean 的处理

48) 事件监听器

演示 - 事件监听器

代码参考

package com.itheima.a48;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.stereotype.Component;// 事件解耦例子
@Configuration
public class A48_1 {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_1.class);context.getBean(MyService.class).doBusiness();context.close();}static class MyEvent extends ApplicationEvent {public MyEvent(Object source) {super(source);}}@Componentstatic class MyService {private static final Logger log = LoggerFactory.getLogger(MyService.class);@Autowiredprivate ApplicationEventPublisher publisher; // applicationContextpublic void doBusiness() {log.debug("主线业务");// 主线业务完成后需要做一些支线业务，下面是问题代码publisher.publishEvent(new MyEvent("MyService.doBusiness()"));}}//    @Componentstatic class SmsApplicationListener implements ApplicationListener<MyEvent> {private static final Logger log = LoggerFactory.getLogger(SmsApplicationListener.class);@Overridepublic void onApplicationEvent(MyEvent event) {log.debug("发送短信");}}@Componentstatic class EmailApplicationListener implements ApplicationListener<MyEvent> {private static final Logger log = LoggerFactory.getLogger(EmailApplicationListener.class);@Overridepublic void onApplicationEvent(MyEvent event) {log.debug("发送邮件");}}}

package com.itheima.a48;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.EventListener;
import org.springframework.context.event.SimpleApplicationEventMulticaster;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;import java.util.concurrent.ThreadPoolExecutor;@Configuration
public class A48_2 {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_2.class);context.getBean(MyService.class).doBusiness();context.close();}static class MyEvent extends ApplicationEvent {public MyEvent(Object source) {super(source);}}@Componentstatic class MyService {private static final Logger log = LoggerFactory.getLogger(MyService.class);@Autowiredprivate ApplicationEventPublisher publisher; // applicationContextpublic void doBusiness() {log.debug("主线业务");// 主线业务完成后需要做一些支线业务，下面是问题代码publisher.publishEvent(new MyEvent("MyService.doBusiness()"));}}@Componentstatic class SmsService {private static final Logger log = LoggerFactory.getLogger(SmsService.class);@EventListenerpublic void listener(MyEvent myEvent) {log.debug("发送短信");}}@Componentstatic class EmailService {private static final Logger log = LoggerFactory.getLogger(EmailService.class);@EventListenerpublic void listener(MyEvent myEvent) {log.debug("发送邮件");}}@Beanpublic ThreadPoolTaskExecutor executor() {ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();executor.setCorePoolSize(3);executor.setMaxPoolSize(10);executor.setQueueCapacity(100);return executor;}@Beanpublic SimpleApplicationEventMulticaster applicationEventMulticaster(ThreadPoolTaskExecutor executor) {SimpleApplicationEventMulticaster multicaster = new SimpleApplicationEventMulticaster();multicaster.setTaskExecutor(executor);return multicaster;}}

package com.itheima.a48;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.SmartInitializingSingleton;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.Method;@Configuration
public class A48_3 {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A48_3.class);context.getBean(MyService.class).doBusiness();context.close();}@Beanpublic SmartInitializingSingleton smartInitializingSingleton(ConfigurableApplicationContext context) {return () -> {for (String name : context.getBeanDefinitionNames()) {Object bean = context.getBean(name);for (Method method : bean.getClass().getMethods()) {if (method.isAnnotationPresent(MyListener.class)) {context.addApplicationListener((event) -> {System.out.println(event);Class<?> eventType = method.getParameterTypes()[0];// 监听器方法需要的事件类型if (eventType.isAssignableFrom(event.getClass())) {try {method.invoke(bean, event);} catch (Exception e) {e.printStackTrace();}}});}}}};}@Componentstatic class MyService {private static final Logger log = LoggerFactory.getLogger(MyService.class);@Autowiredprivate ApplicationEventPublisher publisher; // applicationContextpublic void doBusiness() {log.debug("主线业务");// 主线业务完成后需要做一些支线业务，下面是问题代码publisher.publishEvent(new MyEvent("MyService.doBusiness()"));}}@Componentstatic class SmsService {private static final Logger log = LoggerFactory.getLogger(SmsService.class);@MyListenerpublic void listener(MyEvent myEvent) {log.debug("发送短信");}}@Componentstatic class EmailService {private static final Logger log = LoggerFactory.getLogger(EmailService.class);@MyListenerpublic void listener(MyEvent myEvent) {log.debug("发送邮件");}}@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.METHOD)@interface MyListener {}static class MyEvent extends ApplicationEvent {public MyEvent(Object source) {super(source);}}
}

收获💡

事件监听器的两种方式

1. 实现 ApplicationListener 接口
   • 根据接口泛型确定事件类型
2. @EventListener 标注监听方法
   • 根据监听器方法参数确定事件类型
   • 解析时机：在 SmartInitializingSingleton（所有单例初始化完成后），解析每个单例 bean

49) 事件发布器

演示 - 事件发布器

代码参考

package com.itheima.a49;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationEventPublisher;
import org.springframework.context.ApplicationListener;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.GenericApplicationListener;
import org.springframework.core.ResolvableType;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.stereotype.Component;import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;@Configuration
public class A49 {public static void main(String[] args) {AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(A49.class);context.getBean(MyService.class).doBusiness();context.close();}static class MyEvent extends ApplicationEvent {public MyEvent(Object source) {super(source);}}@Componentstatic class MyService {private static final Logger log = LoggerFactory.getLogger(MyService.class);@Autowiredprivate ApplicationEventPublisher publisher; // applicationContextpublic void doBusiness() {log.debug("主线业务");// 主线业务完成后需要做一些支线业务，下面是问题代码publisher.publishEvent(new MyEvent("MyService.doBusiness()"));}}@Componentstatic class SmsApplicationListener implements ApplicationListener<MyEvent> {private static final Logger log = LoggerFactory.getLogger(SmsApplicationListener.class);@Overridepublic void onApplicationEvent(MyEvent event) {log.debug("发送短信");}}@Componentstatic class EmailApplicationListener implements ApplicationListener<MyEvent> {private static final Logger log = LoggerFactory.getLogger(EmailApplicationListener.class);@Overridepublic void onApplicationEvent(MyEvent event) {log.debug("发送邮件");}}@Beanpublic ThreadPoolTaskExecutor executor() {ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();executor.setCorePoolSize(3);executor.setMaxPoolSize(10);executor.setQueueCapacity(100);return executor;}@Beanpublic ApplicationEventMulticaster applicationEventMulticaster(ConfigurableApplicationContext context, ThreadPoolTaskExecutor executor) {return new AbstractApplicationEventMulticaster() {private List<GenericApplicationListener> listeners = new ArrayList<>();// 收集监听器public void addApplicationListenerBean(String name) {ApplicationListener listener = context.getBean(name, ApplicationListener.class);System.out.println(listener);// 获取该监听器支持的事件类型ResolvableType type = ResolvableType.forClass(listener.getClass()).getInterfaces()[0].getGeneric();System.out.println(type);// 将原始的 listener 封装为支持事件类型检查的 listenerGenericApplicationListener genericApplicationListener = new GenericApplicationListener() {// 是否支持某事件类型                真实的事件类型public boolean supportsEventType(ResolvableType eventType) {return type.isAssignableFrom(eventType);}public void onApplicationEvent(ApplicationEvent event) {executor.submit(() -> listener.onApplicationEvent(event));}};listeners.add(genericApplicationListener);}// 发布事件public void multicastEvent(ApplicationEvent event, ResolvableType eventType) {for (GenericApplicationListener listener : listeners) {if (listener.supportsEventType(ResolvableType.forClass(event.getClass()))) {listener.onApplicationEvent(event);}}}};}abstract static class AbstractApplicationEventMulticaster implements ApplicationEventMulticaster {@Overridepublic void addApplicationListener(ApplicationListener<?> listener) {}@Overridepublic void addApplicationListenerBean(String listenerBeanName) {}@Overridepublic void removeApplicationListener(ApplicationListener<?> listener) {}@Overridepublic void removeApplicationListenerBean(String listenerBeanName) {}@Overridepublic void removeApplicationListeners(Predicate<ApplicationListener<?>> predicate) {}@Overridepublic void removeApplicationListenerBeans(Predicate<String> predicate) {}@Overridepublic void removeAllListeners() {}@Overridepublic void multicastEvent(ApplicationEvent event) {}@Overridepublic void multicastEvent(ApplicationEvent event, ResolvableType eventType) {}}
}

package com.itheima.a49;import org.springframework.context.ApplicationEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.context.PayloadApplicationEvent;
import org.springframework.context.event.ApplicationEventMulticaster;
import org.springframework.context.event.GenericApplicationListener;
import org.springframework.context.support.GenericApplicationContext;
import org.springframework.core.ResolvableType;import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;// 演示事件发布器实现要点
public class TestEventPublisher {public static void main(String[] args) {GenericApplicationContext context = new GenericApplicationContext();context.registerBean("applicationEventMulticaster", MyApplicationEventMulticaster.class);context.refresh();context.publishEvent(new Object());context.publishEvent("aaaa");context.publishEvent(new Bean1());}interface Inter {}static class Bean1 implements Inter{}static class MyApplicationEventMulticaster implements ApplicationEventMulticaster {private List<ApplicationListener> listeners = new ArrayList<>();{listeners.add(new GenericApplicationListener() {@Overridepublic void onApplicationEvent(ApplicationEvent event) {if (event instanceof PayloadApplicationEvent payloadApplicationEvent) {System.out.println(payloadApplicationEvent.getPayload());}}@Overridepublic boolean supportsEventType(ResolvableType eventType) {System.out.println(eventType);// eventType --> PayloadApplicationEvent<Object>, PayloadApplicationEvent<String>return (Inter.class.isAssignableFrom(eventType.getGeneric().toClass()));}});}@Overridepublic void addApplicationListener(ApplicationListener<?> listener) {}@Overridepublic void addApplicationListenerBean(String listenerBeanName) {}@Overridepublic void removeApplicationListener(ApplicationListener<?> listener) {}@Overridepublic void removeApplicationListenerBean(String listenerBeanName) {}@Overridepublic void removeApplicationListeners(Predicate<ApplicationListener<?>> predicate) {}@Overridepublic void removeApplicationListenerBeans(Predicate<String> predicate) {}@Overridepublic void removeAllListeners() {}@Overridepublic void multicastEvent(ApplicationEvent event) {multicastEvent(event, null);}@SuppressWarnings("all")@Overridepublic void multicastEvent(ApplicationEvent event, ResolvableType eventType) {listeners.stream().filter(applicationListener -> {if (eventType == null) {return false;}if (applicationListener instanceof GenericApplicationListener genericApplicationListener) {return genericApplicationListener.supportsEventType(eventType);}return false;}).forEach(applicationListener -> {applicationListener.onApplicationEvent(event);});}}
}

收获💡

事件发布器模拟实现

1. addApplicationListenerBean 负责收集容器中的监听器
   • 监听器会统一转换为 GenericApplicationListener 对象，以支持判断事件类型
2. multicastEvent 遍历监听器集合，发布事件
   • 发布前先通过 GenericApplicationListener.supportsEventType 判断支持该事件类型才发事件
   • 可以利用线程池进行异步发事件优化
3. 如果发送的事件对象不是 ApplicationEvent 类型，Spring 会把它包装为 PayloadApplicationEvent 并用泛型技术解析事件对象的原始类型
   • 视频中未讲解