Spring Framework 5 Simple bean示例-为什么出现NoSuchBeanDefinitionException

Question

我是注释风格的Spring框架的新手，并且配置了一个简单的bean，无法使@ComponentScan正常工作。 bean和应用程序都在同一包中。

package springdemo;

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

@Configuration
public class Pet {
    private String name;

    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @Bean
    public Pet fido() {
        Pet p = new Pet();
        p.setName("fido");
        return p;
    }
}

以及应用：

package springdemo;

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

@Configuration
@ComponentScan
public class BeanApplication {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
        ctx.refresh();
        ctx.start();
        Pet dog = (Pet) ctx.getBean("fido");
        System.out.println(dog.getName());
        ctx.stop();
    }
}

当我运行此程序时，应用程序找不到bean（我假设组件扫描也可以拾取bean ...）：

Exception in thread "main" org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'fido' available
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanDefinition(DefaultListableBeanFactory.java:772)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getMergedLocalBeanDefinition(AbstractBeanFactory.java:1212)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:294)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1083)
    at springmvc.bean.BeanApplication.main(BeanApplication.java:15)

我可以通过scan（）方法而不是通过注释使组件扫描在代码中起作用。

Answer 1

您需要传递一个配置类，在其中提供将由Spring容器管理的bean。

没有Spring Boot的经典Spring应用程序示例

public class SpringApplication {

    public static void main(String[] args){
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);
        Pet dog = (Pet)ctx.getBean("fido");
        System.out.println(dog.getName());
    }

}


@Configuration
class AppConfig {

    @Bean
    public Pet fido() {
        Pet p = new Pet();
        p.setName("fido");
        return p;
    }
}


class Pet {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Spring启动示例：

@SpringBootApplication
public class SpringApplication {

    public static void main(String[] args) {


        ApplicationContext ctx = SpringApplication.run(SpringApplication.class, args);

        Pet dog = (Pet) ctx.getBean("fido");
        System.out.println(dog.getName());
    }
}


@Configuration
class AppConfig {

    @Bean
    public Pet fido() {
        Pet p = new Pet();
        p.setName("fido");
        return p;
    }
}


class Pet {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}