@Scope设置作用域@Lazy懒加载Conditional条件限制

一、@Scope设置bean作用域，常用配置singleton(默认)、prototype，单例和原型，

singleton bean在容器启动就创建好，使用直接拿，prototype容器启动不会创建，使用时才创建

用例：

@Configuration
public class ConfigurationBean {
    @Scope(value="singleton")
    @Bean("person") 
    public Person getPerson() {
        Person person = new Person();
        person.setAge(25);
        person.setName("小东");
        System.out.println("person创建....");
        return person;
    }
}

 二、懒加载

仅针对单实例bean 即singleton作用域bean，添加了@lazy注解，则容器创建时不创建bean，使用时才创建

@Configuration
public class ConfigurationBean {
    @Lazy
    @Scope(value="singleton")
    @Bean("person") 
    public Person getPerson() {
        Person person = new Person();
        person.setAge(25);
        person.setName("小东");
        System.out.println("person创建....");
        return person;
    }
}

三、@Conditional条件限定注解

用于限制某个类或方法创建的bean的限制条件

@Configuration
public class ConfigurationBean {
    @Scope(value="singleton")
    @Bean("person") 
    public Person getPerson() {
        Person person = new Person();
        person.setAge(25);
        person.setName("小东");
        return person;
    }
    
    @Conditional(value = MyConditional.class)
    @Bean("billGates") 
    public Person getBillGates() {
        Person person = new Person();
        person.setAge(66);
        person.setName("billGates");
        return person;
    }
}

public class MyConditional implements Condition{
    @Override
    public boolean matches(ConditionContext context,
            AnnotatedTypeMetadata metadata) {
        BeanDefinitionRegistry registry = context.getRegistry();
        String[] beanNames = registry.getBeanDefinitionNames();
        System.out.println("registryBean : =" + beanNames);    //打印容器注册所有bean
        Environment env = context.getEnvironment();
        if("Windows 7".equals(env.getProperty("os.name"))) {
            Map<String, Object> map = metadata.getAnnotationAttributes("org.springframework.context.annotation.Bean");
            String[] values = (String[]) map.get("value");
            if("billGates".equals(values[0])) {
                return true;
            }
        }
        return false;
    }
}

ApplicationContext applicationContext = new AnnotationConfigApplicationContext(
                ConfigurationBean.class);
        String[] beanNames = applicationContext.getBeanNamesForType(Person.class);
        for(String beanName : beanNames) {
            System.out.println("beanName:" + beanName);
        }

打印：

beanName:person
beanName:billGates