springboot成神之——ioc容器（依赖注入）

• springboot成神之——ioc容器（依赖注入）
  • spring的ioc功能
  • 文件目录结构
  • lang
  • Chinese
  • English
  • GreetingService
  • MyRepository
  • MyComponent
  • AppConfiguration
  • DemoApplication
  • 运行结果

springboot成神之——ioc容器（依赖注入）

spring,maven环境请自行搭建，本文重点放在ioc容器的工作原理

spring的ioc功能

一个对象的实例和字段的值被一个特殊的对象从外部注入，这个特殊的对象就是ioc

ioc容器包含了所有的Spring Beans

文件目录结构

lang

// 定义此接口，用来作为Chinese和English类的公共实现接口

package com.springlearn.learn.lang;

public interface Language{
    public String getGreeting();
    public String getBye();
}

Chinese

// 具体功能实现类

package com.springlearn.learn.langimpl;
import com.springlearn.learn.lang.Language;

public class Chinese implements Language{
    @Override
    public String getGreeting(){
        return "你好";
    }

    @Override
    public String getBye() {
        return "再见";
    }
}

English

// 具体功能实现类

package com.springlearn.learn.langimpl;
import com.springlearn.learn.lang.Language;

public class English implements Language{
    @Override
    public String getGreeting(){
        return "Hello";
    }

    @Override
    public String getBye() {
        return "Bye bye";
    }
}

GreetingService

// 此类就是ioc容器中的一个bean，内部属性通过外部注入
// @Service的作用就是声明他是一个bean
// @Autowired的作用就是依赖注入

package com.springlearn.learn.bean;
import com.springlearn.learn.lang.Language;

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

@Service
public class GreetingService{

    @Autowired
    private Language language;

    public GreetingService() {

    }

    public void sayGreeting() {
        String greeting = language.getGreeting();
        System.out.println("Greeting:" + greeting);
    }
}

MyRepository

// @Repository声明此类是一个bean，主要用于内部数据注入到其他bean中，比如MyComponent.java

package com.springlearn.learn.bean;

import java.util.Date;

import org.springframework.stereotype.Repository;

@Repository
public class MyRepository{
    public String getAppName(){
        return "Hello my first Spring App";
    }

    public Date getSystemDateTime() {
        return new Date();
    }
}

MyComponent

// @Component声明这是一个bean，并且字面上表示这个类是个组件依赖于其他的bean，也就是上面定义的Repository

package com.springlearn.learn.bean;

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

@Component
public class MyComponent {
    @Autowired
    private MyRepository repository;

    public void showAppInfo(){
        System.out.println("Now is:" + repository.getSystemDateTime());
        System.out.println("App Name" + repository.getAppName());
    }
}

AppConfiguration

// 此类是一个定义bean和集中bean的文件
// @Configuration声明这个类是定义bean的
// @ComponentScan扫描bean目录
// @Bean(name="language") 定义了一个名为language的bean，只要访问此bean就会自动调用getLanguage方法

package com.springlearn.learn.config;

import com.springlearn.learn.lang.Language;
import com.springlearn.learn.langimpl.Chinese;

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

@Configuration
@ComponentScan({"com.springlearn.learn.bean"})
public class AppConfiguration{

    @Bean(name="language")
    public Language getLanguage() {
        return new Chinese();
    }
}

DemoApplication

// 此类是程序的启动类
// AnnotationConfigApplicationContext会调用配置类
// 通过调用context.getBean("language");会创建Chinese类实例
// context.getBean("greetingService");greetingService其中的@Autowired会将language实例注入

package com.springlearn.learn;

import com.springlearn.learn.bean.GreetingService;
import com.springlearn.learn.bean.MyComponent;
import com.springlearn.learn.config.AppConfiguration;
import com.springlearn.learn.lang.Language;

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

public class DemoApplication {
	public static void main(String[] args) {
		ApplicationContext context = new AnnotationConfigApplicationContext(AppConfiguration.class);

		System.out.println("-------------");

		Language language = (Language)context.getBean("language");
		System.out.println("Bean Language: "+ language);
		System.out.println("Call language.sayBye(): "+ language.getBye());

		GreetingService service = (GreetingService) context.getBean("greetingService");
		service.sayGreeting();
		System.out.println("----------");

		MyComponent myComponent = (MyComponent) context.getBean("myComponent");
		myComponent.showAppInfo();
	}
}

运行结果

-------------
Bean Language: com.springlearn.learn.langimpl.Chinese@258d79be
Call language.sayBye(): 再见
Greeting:你好
----------
Now is:Sun Sep 09 13:48:45 CST 2018
App NameHello my first Spring App