IOC（Inversion of Control，控制反转）是Spring框架核心概念之一。它是一种设计原则，用来实现对象的松耦合和依赖管理。在传统的编程中，对象负责创建或查找其依赖对象，而在IOC模式下，这些职责被移交给一个容器，由容器来负责对象的创建和管理。

本文章将介绍几种实现IOC的方式

目录

一.前提准备

二.基于xml的方式

三.基于注解的方式

四.基于配置类的方式

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一.前提准备

1)引入Spring的相关依赖:

2)创建示例类(要交给Spring管理的类):

@Data
public class DataConfig {
   
    private String url;
    
    private String driverName;
    
    private String userName;
   
    private String password;

}

注意:@Data注解是由Lombok提供的

Lombok 是一个用于 Java 编程的开源库，旨在通过自动生成常见代码来简化开发过程。其主要功能是减少样板代码（boilerplate code），如 getter、setter、构造函数、equals 和 hashCode 方法等，从而使代码更加简洁和易于维护。 

二.基于xml的方式

首先在src/main/resources目录下创建xml文件,文件名可自定义,但是后缀为.xml

将xml文件用来定义Bean时为固定格式,示例如下:

<?xml version="1.0" encoding="UTF-8"?>
<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"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <!-- 配置 User 对象 -->
    <bean class="com.example.spring_demo.ioc.DataConfig" id="config">
        //里面写要定义的属性
        //id用来给要管理的对象取名
    </bean>

</beans>

我们将要配置的属性写进去:

<?xml version="1.0" encoding="UTF-8"?>
<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"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <!-- 配置 User 对象 -->
    <bean class="com.example.spring_demo.ioc.DataConfig" id="config">
        <property name="driverName" value="Driver"></property>
        <property name="url" value="localhost:8080"></property>
        <property name="userName" value="root"></property>
        <property name="password" value="root"></property>
    </bean>

</beans>

最后通过IOC容器ApplicationContext来管理和获取Bean。

public class Test {
    public static void main(String[] args) {

        ApplicationContext context1=new ClassPathXmlApplicationContext("springIoc.xml");

        System.out.println(context1.getBean("config"));
        
    }
}

结果如下:

23:35:58.074 [main] DEBUG org.springframework.context.support.ClassPathXmlApplicationContext - Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1c655221
23:35:58.201 [main] DEBUG org.springframework.beans.factory.xml.XmlBeanDefinitionReader - Loaded 1 bean definitions from class path resource [springIoc.xml]
23:35:58.228 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'config'

DataConfig(url=localhost:8080, driverName=Driver, userName=root, password=root)

Process finished with exit code 0

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三.基于注解的方式

使用注解的方式相对简单,只需要给目标类添加 @Component 即可

@Data
@Component("config2")
public class DataConfig {
    @Value("localhost:3306")
    private String url;
    @Value("Driver")
    private String driverName;
    @Value("root")
    private String userName;
    @Value("root")
    private String password;
}

//@Component注解告知Spring这个类交给ioc容器管理

//"config"是给要管理的对象取的名字

//@Value给管理的对象注入初始值

接着通过IOC容器ApplicationContext来管理和获取Bean

public class Test {
    public static void main(String[] args) {

        ApplicationContext context3=new AnnotationConfigApplicationContext("com.example.spring_demo.ioc");

        System.out.println(context3.getBean("config2"));
    }
}

//"com.example.spring_demo.ioc"是要扫描的类所在的包,Spring会查找该包有无要管理的类

结果如下:

23:44:44.345 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@53e25b76
23:44:44.362 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
23:44:44.448 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
23:44:44.450 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
23:44:44.451 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
23:44:44.452 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
23:44:44.458 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'beanConfiguration'
23:44:44.462 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'config1'
23:44:44.469 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'config2'

DataConfig(url=localhost:3306, driverName=Driver, userName=root, password=root)

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四.基于配置类的方式

这种方式和xml的原理一样,只不过是使用java代码的形式来实现的,它定义了一个的专门的配置类来存放我们要管理的类,配置类要加上@Configuration注解

首先创建配置类

@Configuration
public class BeanConfiguration {

    //默认id是方法名,id可使用name属性来配置
    @Bean(name="config2")
    public DataConfig dataConfig(){
        DataConfig dataConfig=new DataConfig();
        dataConfig.setDriverName("Driver");
        dataConfig.setUrl("localhost:3306/spring_demo");
        dataConfig.setUserName("root");
        dataConfig.setPassword("root");
        return dataConfig;
    }
}

接着通过IOC容器ApplicationContext来管理和获取Bean

public class Test {
    public static void main(String[] args) {

       ApplicationContext context2=new AnnotationConfigApplicationContext("com.example.spring_demo.ioc");

        System.out.println(context2.getBean("config1"));

       
    }
}

结果如下:

23:56:29.299 [main] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [D:\code\blog_code\target\classes\com\example\spring_demo\ioc\BeanConfiguration.class]
23:56:29.301 [main] DEBUG org.springframework.context.annotation.ClassPathBeanDefinitionScanner - Identified candidate component class: file [D:\code\blog_code\target\classes\com\example\spring_demo\ioc\DataConfig.class]
23:56:29.313 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@53e25b76
23:56:29.329 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
23:56:29.413 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
23:56:29.415 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
23:56:29.416 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
23:56:29.417 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
23:56:29.423 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'beanConfiguration'
23:56:29.428 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'config1'
23:56:29.435 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'config2'

DataConfig(url=localhost:3306, driverName=Driver, userName=root, password=root)

Process finished with exit code 0

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到这里关于SpringIOC实现的三种方式就介绍完了~