【Spring】导入配置文件

方式1：通过XML方式指定配置文件路径，用于XML文件中属性

Book.java

@Component
@Getter
@Setter
@Data
public class Book {private String name;
}

beans.xml   <context:property-placeholder location="classpath:db.properties" />

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

    <context:property-placeholder location="classpath:db.properties" />

    <bean id="book" class="com.example.ioc.pojo.Book">
        <property name="name" value="${user}"/>
    </bean>

</beans>

Main.java

        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Book book = applicationContext.getBean("book", Book.class);

        System.out.println(book);

方式2：@PropertySource + @Value("${xxxx}")

   src/main/resouces/db.properties

   user=root

使用 BeanConfig (@PropertySource("classpath:db.properties")  导入外部文件

@Configuration
@PropertySource("classpath:db.properties")
public class BeanConfig {
    @Bean
    public Book book() {
        return new Book();
    }
}

Book.java  @Value("${user}")

@Getter
@Setter
@Data
public class Book {
    @Value("${user}")
    private String name;
}

Main.java

 public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext
            = new AnnotationConfigApplicationContext();
        annotationConfigApplicationContext.register(BeanConfig.class);
        annotationConfigApplicationContext.refresh();
        Book book = annotationConfigApplicationContext.getBean(Book.class);

        System.out.println(book);
    }

说明：引入外部属性配置文件 @PropertySouce 和 @PropertySources

针对springboot：1）src/main/resouces/application.properies被自动检测到，不需要配置；2）java -jar app.jar --spring.config.location=config/*/

@Configuration
@PropertySource("classpath:/annotations.properties")
@PropertySource("classpath:/vehicle-factory.properties")
class VehicleFactoryConfig {}

或 
@Configuration
@PropertySources({ 
    @PropertySource("classpath:/annotations.properties"),
    @PropertySource("classpath:/vehicle-factory.properties")
})
class VehicleFactoryConfig {}

关于@Value的更多用法

1、@Value("${unknown.param:some default}")  提供默认值

2、配置文件中value配置项value通过逗号分隔，传入数组

3、@Value("#{${valuesMap}['unknownKey']}")

4、作为构造器注入

   

 5、通过setter注入