没有名为xxx的bean可用

Question

It is a very simple program that has a main class as JavaLoader , one interface Student . Student is implemented by two classes. I have also made a configuration class. When I instantiate the bean from the main class and call a method on Samir . A NoSuchBeanDefinitionException is thrown.

Main class ( JavaLoader ):

package spring;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class JavaLoader {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext appContext = new
                AnnotationConfigApplicationContext("StudentConfig.class");

        Student samir = (Student) appContext.getBean("samir", Student.class);
        System.out.println(samir.readsBook());
    }
}

StudentConfig class:

package spring;

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

@Configuration
@ComponentScan("spring")
public class StudentConfig {

}

Samir class:

package spring;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.stereotype.Component;

@Component("samir")
public class Samir implements Student{
    @Autowired
    @Qualifier("history")
    Book book;

    public Samir(Book book){
        this.book = book;
    }
    public String readsBook(){
        return book.readBook();
    }
}

The expected output is that the method samir.readsBook() on JavaLoader should be executed

Answer 1

You need to provide a Class instance to the AnnotationConfigApplicationContext constructor:

 new AnnotationConfigApplicationContext(StudentConfig.class);

note that StudentConfig.class is not the same as the string "StudentConfig.class" .

Note that AnnotationConfigApplicationContext has a string-constructor as well (that's why your code still compiles), but that string is interpreted as a base package for auto-scanning rather than the configuration class name.