【spring学习】bean的三种实例化方法

1. 先创建三个类

public class BeanClass {
  public String message;
  public BeanClass(){
      message="构造方法实例化";
  }
  public BeanClass(String s)
  {
      message = s;
  }
}


public class BeanInstanceFactory {
    public BeanClass createBeanClassFactory(){
        return new BeanClass("实例工厂实例化");
    }
}

public class BeanStaticFactory {
    public static BeanClass beanClass = new BeanClass("静态工厂实例化bean");
    public static BeanClass createInstance(){
        return beanClass;
    }
}

2.编写config类

public class BeanConfig {
    //使用@Bean定义三个bean
    @Bean(value= "beanclass")
    public BeanClass getBeanClass(){
        return new BeanClass();
    }
    @Bean(value = "beanStaticFactory")
    public BeanClass getBeanStaticFactory(){
        return BeanStaticFactory.createInstance();
    }
    @Bean(value = "beanInstanceFactory")
    public BeanClass getBeanInstanceFactory(){
        BeanInstanceFactory beanInstanceFactory = new BeanInstanceFactory();
        return beanInstanceFactory.createBeanClassFactory();
    }
}

3.测试：

public class TestBean {
    public static void main(String[] args) {
        //初始化spring容器ApplicationContext
        AnnotationConfigApplicationContext app = new AnnotationConfigApplicationContext(BeanConfig.class);
      //对应config中的  @Bean(value= "beanclass")
        BeanClass bi = (BeanClass) app.getBean("beanclass");
        System.out.println(bi+bi.message);
        BeanClass b2 = (BeanClass) app.getBean("beanStaticFactory");
        System.out.println(b2+b2.message);
        BeanClass b3 = (BeanClass) app.getBean("beanInstanceFactory");
        System.out.println(b3+b3.message);
    }
}

输出：