singleton：spring ioc容器中只会存在一个共享的bean实例，并且对所有语法，只要id与该bean定义相匹配，就可以返回bean的同一实例
prototype：对于每次getBean请求，都会创建一个新的Bean实例，相当于new
@Component("name")：相当于把普通pojo实例化到spring容器中
以下是实例
BeanTest.java
package tryBean;
import org.junit.Test;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
@Service
//@Component("getBean")
@Configuration
public class BeanTest {
public BeanTest() {
}
@Bean
@Scope("prototype")
public BeanTest getBean(){
BeanTest bean = new BeanTest();
System.out.println("调用方法："+bean);
return bean;
}
}
Main,java
package tryBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
public static void main(String[] args) {
ApplicationContext context = new AnnotationConfigApplicationContext(BeanTest.class);
Object bean1 = context.getBean("getBean"); // wrong!
System.out.println(bean1);
Object bean2 = context.getBean("getBean");
System.out.println(bean2);
((AbstractApplicationContext) context).close();
}
}
运行结果：
调用方法：tryBean.BeanTest@7e9a5fbe
tryBean.BeanTest@7e9a5fbe
调用方法：tryBean.BeanTest@71623278
tryBean.BeanTest@71623278
那么如果把@scope("prototype")改变为@scope("singleton")结果会是什么呢？
运行结果:
调用方法：tryBean.BeanTest@47db50c5
tryBean.BeanTest@47db50c5
tryBean.BeanTest@47db50c5
如果@scope("prototype") 并且把@Component("getBean")的注释去掉呢？
运行结果：
tryBean.BeanTest$$EnhancerBySpringCGLIB$$cf0e9586@646007f4
tryBean.BeanTest$$EnhancerBySpringCGLIB$$cf0e9586@646007f4
如果@scope("singleton")并且把@Component("getBean")`的注释去掉呢？
运行结果：
tryBean.BeanTest$$EnhancerBySpringCGLIB$$cf0e9586@646007f4
tryBean.BeanTest$$EnhancerBySpringCGLIB$$cf0e9586@646007f4
可以看到：singleton会打印一次“调用方法”，而prototype会打印两次，说明singleton只有第一次创建了实例，而prototype两次都创建了实例。那么为什么加了@Component("getBean")之后就不再打印“调用方法”了呢？
原因是该注解将名为getBean的POJO实例化到spring容器中，从而每次实例化是无效的
