Spring boot 官网学习笔记 - Configuration Class（@import）

2021-08-12 10:25:53

推荐使用 Java-based configuration ，也可以使用xml
we generally recommend that your primary source be a single @Configuration class. Usually the class that defines the main method is a good candidate as the primary @Configuration

Importing Additional Configuration Classes

You need not put all your @Configuration into a single class. 
The @Import annotation can be used to import additional configuration classes. 
Alternatively, you can use @ComponentScan to automatically pick up 
all Spring components, including @Configuration classes.

示例

Car.java

package javabeat.net.basic;

public interface Car {

    public void print();

}

Toyota.java

package javabeat.net.basic;

import org.springframework.stereotype.Component;

@Component

public class Toyota implements Car{

    public void print(){

        System.out.println("I am Toyota");

    }

}

Volkswagen.java

package javabeat.net.basic;

import org.springframework.stereotype.Component;

@Component

public class Volkswagen implements Car{

    public void print(){

        System.out.println("I am Volkswagen");

    }

}

JavaConfigA.java

package javabeat.net.basic;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

@Configuration

public class JavaConfigA {

    @Bean(name="volkswagen")

    public Car getVolkswagen(){

        return new Volkswagen();

    }

}

JavaConfigB.java

package javabeat.net.basic;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

@Configuration

public class JavaConfigB {

    @Bean(name="toyota")

    public Car getToyota(){

        return new Toyota();

    }

}

ParentConfig.java

package javabeat.net.basic;

import org.springframework.context.annotation.Configuration;

import org.springframework.context.annotation.Import;

@Configuration

@Import({JavaConfigA.class,JavaConfigB.class})

public class ParentConfig {

    //Any other bean definitions

}

ContextLoader.java

 package javabeat.net.basic;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class ContextLoader {

    public static void main (String args[]){

        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(ParentConfig.class);

        Car car = (Toyota)context.getBean("toyota");

        car.print();

        car = (Volkswagen)context.getBean("volkswagen");

        car.print();

        context.close();

    }

}

If you run the above example,the printed output will be,

Importing XML Configuration

If you absolutely must use XML based configuration,
 we recommend that you still start with a @Configuration class. 
You can then use an @ImportResource annotation to load XML configuration files.

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