Spring,使用@Configuration和@Bean注释

Question

我有一个代码:

@Configuration
public class BeanSample {

    @Bean(destroyMethod = "stop")
    public SomeBean someBean() throws Exception {
        return new SomeBean("somebean name1");
    }


    class SomeBean {

        String name;

        public SomeBean(String name) {
            this.name = name;
        }

        public void stop() {
            System.out.println("stop");
        }
    }

    public static void main(String[] args) throws Exception {

        BeanSample beanSample = new BeanSample();
        SomeBean someBean1 = beanSample.someBean();

        ClassPathXmlApplicationContext appContext = new ClassPathXmlApplicationContext(
                new String[] {"appContext.xml"});

        SomeBean someBean2 = (SomeBean) appContext.getBean("someBean");

        if (someBean1 == someBean2) System.out.println("OK");

    }
}

我期待,一旦我启动应用程序,BeanSample.getSomeBean()然后SomeBean开始由'someBean'提供.

现在我有一个错误:没有定义名为'someBean'的bean

实际上,我不明白我应该用哪种app-context来挑选我的豆子？

关于@Configuration:

有什么理由,为什么我应该在这里使用@Configuration注释？(有了这个,我的IDE突出了我的类,因为它与Spring相关,所以它应该有意义)

- 好的:在我得到答案后,我的代码看起来像这样:

 public static void main(String[] args) throws Exception {

        AnnotationConfigApplicationContext appContext = new AnnotationConfigApplicationContext(BeanSample.class);

        SomeBean someBean2 = (SomeBean) appContext.getBean("someBean");

        if (someBean2 != null) System.out.println("OK");

    }

Answer 1

首先,如果您使用Java配置,则必须像下面这样实例化您的上下文:

new AnnotationConfigApplicationContext(BeanSample.class)

其次,@Configuration注释不会使bean被注释掉.只有@Bean方法用于创建bean.

如果你也想要一个BeanSamplebean,你必须创建另一个@Bean创建一个bean的方法.但话又说回来,你为什么要这样呢？我认为一个@Configuration类只应该用作配置容器而不能用于其他任何东西.

第三,默认的bean名称@Bean不遵循属性getter的约定.方法名称是直接使用的,在您的示例中,bean将被命名getSomeBean而不是someBean.将方法更改为:

@Bean(destroyMethod = "stop")
public SomeBean someBean() throws Exception {
    return new SomeBean("somebean name1");
}

最后,@Configuration不应该实例化该类.它的方法仅用于创建bean.然后Spring将处理它们的生命周期,注入属性等等.相反,如果您实例化类并直接调用方法,则返回的对象将只是与Spring无关的普通对象.

Answer 2

生产的豆子

@Bean
public SomeBean getSomeBean() 

将具有默认名称 - 这是生产者方法的名称 getSomeBean

所以你可以做两件事

@Bean
public SomeBean getSomeBean() {...}   
...
SomeBean bean = (SomeBean) appContext.getBean("getSomeBean");
if (bean != null) System.out.println("OK");

要么

@Bean(name="someBean")
public SomeBean getSomeBean() {...}  
...
SomeBean bean = (SomeBean) appContext.getBean("someBean");
if (bean != null) System.out.println("OK");

我用的一些完整的例子代替了AnnotationConfigApplicationContextClassPathXmlApplicationContext

import java.util.Arrays;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanSample {

    @Bean(name="someBean")
    public SomeBean getSomeBean() throws Exception {
        return new SomeBean("somebean name1");
    }

    class SomeBean {

        String name;

        public SomeBean(final String name) {
            this.name = name;
        }

        public void stop() {
            System.out.println("stop");
        }
    }

    public static void main(final String[] args) throws Exception {

        AnnotationConfigApplicationContext appContext = new AnnotationConfigApplicationContext(BeanSample.class);

        BeanSample beanSample = (BeanSample) appContext.getBean("beanSample");

        //next time use this to have a look at the beans in the context!
        System.out.println(Arrays.toString(appContext.getBeanDefinitionNames()));

        SomeBean bean = (SomeBean) appContext.getBean("someBean");
        if (bean != null) System.out.println("OK");

    }
}

OUTPUT:

[org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalPersistenceAnnotationProcessor ,beanSample,org.springframework.context.annotation.ConfigurationClassPostProcessor $ ImportAwareBeanPostProcessor#0,someBean] OK