Spring 使用指南 ~ 1、Spring 的 IOC 和 DI 简介

一、IOC && DI

1、概念介绍

• IOC：控制反转，即把类的实例化交给 Spring 来管理
• DI：依赖注入，即通过 Spring 为应用中被 Spring 管理的类实例注入其依赖的实例和其他信息

2、使用 XML 形式

1）、构造函数注入

package com.luo.spring.guides.iocdi.xml.constructorconfusion;

import org.springframework.context.support.GenericXmlApplicationContext;

/**
* @author : archer
* @date : Created in 2022/11/30 14:46
* @description :
*/
public class ConstructorConfusion {

   private String someValue;

   public ConstructorConfusion(String someValue) {
       System.out.println("ConstructorConfusion(String) called");
       this.someValue = someValue;
   }

   public ConstructorConfusion(int someValue) {
       System.out.println("ConstructorConfusion(int) called");
       this.someValue = "Number: " + Integer.toString(someValue);
   }

   public String toString() {
       return someValue;
   }
}

app-context-xml.xml

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

    <bean id="constructorConfusion"
          class="com.luo.spring.guides.iocdi.xml.constructorconfusion.ConstructorConfusion">
        <constructor-arg type="int">
            <value>90value>
        constructor-arg>
    bean>
beans>

测试

package com.luo.spring.guides.iocdi.xml.constructorconfusion;

import org.springframework.context.support.GenericXmlApplicationContext;

/**
 * @author : archer
 * @date : Created in 2022/11/30 14:51
 * @description :
 */
public class Main {
    public static void main(String... args) {
        GenericXmlApplicationContext ctx = new GenericXmlApplicationContext();
        ctx.load("classpath:iocdi/app-context.xml");
        ctx.refresh();
        ConstructorConfusion cc = (ConstructorConfusion) ctx.getBean("constructorConfusion");
        System.out.println(cc);
        ctx.close();
    }
}

输出

ConstructorConfusion(int) called
Number: 90

2）、setter 注入

package com.luo.spring.guides.iocdi.xml.setter;

public class Dependency {

    @Override
    public String toString() {
        return "Dependency{}";
    }
}

package com.luo.spring.guides.iocdi.xml.setter;

public class SetterInjection {

	private Dependency dependency;

	public void setDependency(Dependency dependency) {
		this.dependency = dependency;
	}

	@Override
	public String toString() {
		return dependency.toString();
	}
}

app-context-xml.xml

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:c="http://www.springframework.org/schema/c"
       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">


    <bean id="dependency" class="com.luo.spring.guides.iocdi.xml.setter.Dependency"/>

    <bean id="setterInjection" class="com.luo.spring.guides.iocdi.xml.setter.SetterInjection"
          p:dependency-ref="dependency"/>
beans>

测试

package com.luo.spring.guides.iocdi.xml.setter;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * @author : archer
 * @date : Created in 2022/11/30 15:22
 * @description :
 */
public class Main {
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext
                ("iocdi/injection/setter/app-context-xml.xml");

        SetterInjection mr = ctx.getBean("setterInjection", SetterInjection.class);
        System.out.println(mr);
    }
}

输出

Dependency{}

3、使用注解形式

1）、构造函数注入

package com.luo.spring.guides.iocdi.annotation.constructorconfusion;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.support.GenericXmlApplicationContext;
import org.springframework.stereotype.Service;

@Service("constructorConfusion")
public class ConstructorConfusion {

	private String someValue;

	public ConstructorConfusion(String someValue) {
		System.out.println("ConstructorConfusion(String) called");
		this.someValue = someValue;
	}

	@Autowired
	public ConstructorConfusion(@Value("90") int someValue) {
		System.out.println("ConstructorConfusion(int) called");
		this.someValue = "Number: " + Integer.toString(someValue);
	}

	public String toString() {
		return someValue;
	}
}

app-context-annotation.xml

<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:c="http://www.springframework.org/schema/c"
       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">

    <context:component-scan 
          base-package="com.luo.spring.guides.iocdi.annotation"/>

    <bean id="message" class="java.lang.String"
          c:_0="I hope that someone gets my message in a bottle"/>

    <bean id="message2" class="java.lang.String"
          c:_0="I know I won't be injected :("/>
beans>

测试

package com.luo.spring.guides.iocdi.annotation.constructorconfusion;

import org.springframework.context.support.GenericXmlApplicationContext;

/**
 * @author : archer
 * @date : Created in 2022/11/30 14:51
 * @description :
 */
public class Main {
    public static void main(String... args) {
        GenericXmlApplicationContext ctx = new GenericXmlApplicationContext();
        ctx.load("classpath:iocdi/app-context-annotation.xml");
        ctx.refresh();

        ConstructorConfusion cc = (ConstructorConfusion) ctx.getBean("constructorConfusion");
        System.out.println(cc);
        ctx.close();
    }
}

输出

ConstructorConfusion(int) called
Number: 90

2）、setter 注入

package com.luo.spring.guides.iocdi.annotation.setter;

import org.springframework.stereotype.Component;

@Component("dependency")
public class Dependency {

    @Override
    public String toString() {
        return "Dependency{}";
    }
}

package com.luo.spring.guides.iocdi.annotation.setter;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component("setterInjection")
public class SetterInjection {

	private Dependency dependency;

	@Autowired
	public void setDependency(Dependency dependency) {
		this.dependency = dependency;
	}

	@Override
	public String toString() {
		return dependency.toString();
	}
}

配置类

package com.luo.spring.guides.iocdi.annotation.setter;

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

/**
 * @author : archer
 * @date : Created in 2022/11/30 15:32
 * @description :
 */
@ComponentScan(basePackages = {"com.luo.spring.guides.iocdi.annotation"})
@Configuration
public class SetterInjectionConfiguration {
}

测试

package com.luo.spring.guides.iocdi.annotation.setter;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

/**
 * @author : archer
 * @date : Created in 2022/11/30 15:33
 * @description :
 */
public class Main {
    public static void main(String... args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext
                (SetterInjectionConfiguration.class);
        SetterInjection mr = ctx.getBean("setterInjection", SetterInjection.class);
        System.out.println(mr);
    }
}

输出

Dependency{}

3）、字段注入

package com.luo.spring.guides.iocdi.annotation.field;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * Created by iuliana.cosmina on 2/15/17.
 */
@Service("singer")
public class Singer {

	@Autowired
	private Inspiration inspirationBean;

	public void sing() {
		System.out.println("... " + inspirationBean.getLyric());
	}
}

package com.luo.spring.guides.iocdi.annotation.field;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

/**
 * Created by iuliana.cosmina on 2/15/17.
 */
@Component
public class Inspiration {

	private String lyric = "I can keep the door cracked open, to let light through";

	public Inspiration(@Value("For all my running, I can understand") String lyric) {
		this.lyric = lyric;
	}

	public String getLyric() {
		return lyric;
	}

	public void setLyric(String lyric) {
		this.lyric = lyric;
	}
}

测试

package com.luo.spring.guides.iocdi.annotation.field;

import com.luo.spring.guides.iocdi.annotation.InjectionConfiguration;
import com.luo.spring.guides.iocdi.annotation.setter.SetterInjection;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.GenericXmlApplicationContext;

/**
 * @author : archer
 * @date : Created in 2022/11/30 20:46
 * @description :
 */
public class Main {

    public static void main(String... args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext
                (InjectionConfiguration.class);
        Singer singer = ctx.getBean("singer", Singer.class);

        Singer singerBean = ctx.getBean(Singer.class);
        System.out.println(singer == singerBean);
        singerBean.sing();
        singer.sing();
    }
}

输出

ConstructorConfusion(int) called
true
… For all my running, I can understand
… For all my running, I can understand