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Spring之【Bean的实例化方式】

news 2025/8/5 6:21:32

方式一：InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation

源码分析

AbstractAutowireCapableBeanFactory中的createBean方法

AbstractAutowireCapableBeanFactory中的resolveBeforeInstantiation方法

AbstractAutowireCapableBeanFactory中的applyBeanPostProcessorsBeforeInstantiation方法

使用案例

方式二：Supplier

源码分析

AbstractAutowireCapableBeanFactory中的doCreateBean

AbstractAutowireCapableBeanFactory中的createBeanInstance方法

使用案例

方式三：FactoryMethod

源码分析

AbstractAutowireCapableBeanFactory中的doCreateBean

AbstractAutowireCapableBeanFactory中的createBeanInstance方法

使用案例

方式四：反射

源码分析

BeanUtils的instantiateClass方法

使用案例

方式五：FactoryBean

源码分析

FactoryBean接口

使用案例

方式一：InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation

源码分析

AbstractAutowireCapableBeanFactory中的createBean方法

Bean在实例化之前，会给个机会可以自定义创建Bean对象，如果自定义创建了Bean对象，就直接返回

AbstractAutowireCapableBeanFactory中的resolveBeforeInstantiation方法

执行Bean实例化之前的逻辑

AbstractAutowireCapableBeanFactory中的applyBeanPostProcessorsBeforeInstantiation方法

执行InstantiationAwareBeanPostProcessor的实例化之前方法回调

使用案例

定义一个组件类

package spring.demo;import org.springframework.stereotype.Component;@Component
public class People {private Long no;private String name;public void setNo(Long no) {this.no = no;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "People{" +"no=" + no +", name='" + name + '\'' +'}';}
}

自定义一个BeanPostProcessor并实现了InstantiationAwareBeanPostProcessor的实例化之前的方法

package spring.demo;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
import org.springframework.stereotype.Component;import java.lang.reflect.Constructor;@Component
public class CustomInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {@Overridepublic Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {if (beanClass == People.class) {try {// 这里自定义创建了Bean对象，并返回Constructor<?> constructor = beanClass.getDeclaredConstructor();People people = (People) constructor.newInstance();people.setNo(101L);people.setName("AAA");return people;} catch (Exception e) {throw new RuntimeException(e);}}return null;}
}

定义扫包规则

package spring.demo;import org.springframework.context.annotation.ComponentScan;@ComponentScan("spring.demo")
public class SpringConfig {
}

编写测试类并查看测试效果

package spring.demo;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class SpringMain {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);People people = applicationContext.getBean(People.class);System.out.println(people);}
}

方式二：Supplier

源码分析

AbstractAutowireCapableBeanFactory中的doCreateBean

创建Bean实例对象

AbstractAutowireCapableBeanFactory中的createBeanInstance方法

从Bean定义对象中获取Supplier，并通过Supplier中get方法的逻辑中获取Bean实例对象

使用案例

自定义一个组件类

package spring.demo;import org.springframework.stereotype.Component;@Component
public class Person {private int age;private String name;public void setAge(int age) {this.age = age;}public void setName(String name) {this.name = name;}@Overridepublic String toString() {return "Person{" +"age=" + age +", name='" + name + '\'' +'}';}
}

自定义一个BeanDefinitionRegistryPostProcessor

package spring.demo;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;
import org.springframework.beans.factory.support.GenericBeanDefinition;
import org.springframework.stereotype.Component;import java.util.function.Supplier;@Component
public class CustomBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {@Overridepublic void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {// 获取person的Bean定义对象BeanDefinition personBeanDefinition = registry.getBeanDefinition("person");if (personBeanDefinition != null && personBeanDefinition instanceof GenericBeanDefinition) {// 往person的Bean定义对象中设置SupplierSupplier<Person> supplier = () -> {Person person = new Person();person.setAge(18);person.setName("BBB");return person;};((GenericBeanDefinition) personBeanDefinition).setInstanceSupplier(supplier);}}@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
}

编写测试类并查看测试效果

package spring.demo;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class SpringMain {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);Person person = applicationContext.getBean(Person.class);System.out.println(person);}
}

方式三：FactoryMethod

源码分析

AbstractAutowireCapableBeanFactory中的doCreateBean

创建Bean实例对象

AbstractAutowireCapableBeanFactory中的createBeanInstance方法

通过工厂方法创建Bean实例对象

使用案例

定义一个普通Java类

package spring.demo;public class Toy {
}

定义一个组件类

package spring.demo;import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;@Component
public class ToyFactory {@Bean(name = "toy")public Toy create() {return new Toy();}
}

编写测试类并查看测试效果

package spring.demo;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class SpringMain {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);Toy toy = applicationContext.getBean(Toy.class);System.out.println(toy);}
}

方式四：反射

源码分析

BeanUtils的instantiateClass方法

通过反射调用构造器实例化Bean对象

使用案例

自定义组件类

package spring.demo;import org.springframework.stereotype.Component;@Component
public class Account {public Account() {System.out.println("执行Account构造器...");}
}

编写测试类并查看测试效果

package spring.demo;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class SpringMain {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);Account account = applicationContext.getBean(Account.class);System.out.println(account);}
}

方式五：FactoryBean

源码分析

FactoryBean接口

package org.springframework.beans.factory;import org.springframework.lang.Nullable;public interface FactoryBean<T> {String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";// 获取Bean实例对象@NullableT getObject() throws Exception;// Bean的类型@NullableClass<?> getObjectType();// 是否单例，默认是单例default boolean isSingleton() {return true;}
}

使用案例

定义一个普通Java类

package spring.demo;public class User {private String no;private String name;public User(String no, String name) {this.no = no;this.name = name;}@Overridepublic String toString() {return "User{" +"no=" + no +", name='" + name + '\'' +'}';}
}

自定义一个FactoryBean

package spring.demo;import org.springframework.beans.factory.FactoryBean;
import org.springframework.stereotype.Component;@Component
public class UserFactoryBean implements FactoryBean<User> {@Overridepublic User getObject() throws Exception {return new User("001", "CCC");}@Overridepublic Class<?> getObjectType() {return User.class;}
}

编写测试类并查看测试效果

package spring.demo;import org.springframework.context.annotation.AnnotationConfigApplicationContext;public class SpringMain {public static void main(String[] args) {AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(SpringConfig.class);Object bean = applicationContext.getBean("userFactoryBean");System.out.println(bean);}
}