Spring Framework IoC 容器示例

目标

演示 Spring IoC 容器的基本用法：Bean 定义、依赖注入、ApplicationContext 启动。

完整代码

1. 服务接口和实现

// MessageService.java
package com.example.service;

public interface MessageService {
    String getMessage();
}

// EmailService.java
package com.example.service.impl;

import com.example.service.MessageService;

public class EmailService implements MessageService {
    private String sender;

    // Setter 注入
    public void setSender(String sender) {
        this.sender = sender;
    }

    @Override
    public String getMessage() {
        return "Email from " + sender;
    }
}

// SmsService.java
package com.example.service.impl;

import com.example.service.MessageService;

public class SmsService implements MessageService {
    @Override
    public String getMessage() {
        return "SMS message";
    }
}

2. 消费者类

package com.example.consumer;

import com.example.service.MessageService;

public class NotificationConsumer {
    private MessageService messageService;

    // 构造器注入（推荐）
    public NotificationConsumer(MessageService messageService) {
        this.messageService = messageService;
    }

    public void notifyUser() {
        System.out.println(messageService.getMessage());
    }
}

3. XML 配置 beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="emailService" class="com.example.service.impl.EmailService">
        <property name="sender" value="noreply@example.com"/>
    </bean>

    <bean id="smsService" class="com.example.service.impl.SmsService"/>

    <bean id="notificationConsumer" class="com.example.consumer.NotificationConsumer">
        <constructor-arg ref="emailService"/>
    </bean>
</beans>

4. Java Config 配置（注解方式）

package com.example.config;

import com.example.service.MessageService;
import com.example.service.impl.EmailService;
import com.example.consumer.NotificationConsumer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {

    @Bean
    public MessageService messageService() {
        EmailService service = new EmailService();
        service.setSender("noreply@example.com");
        return service;
    }

    @Bean
    public NotificationConsumer notificationConsumer() {
        return new NotificationConsumer(messageService());
    }
}

5. 主程序

package com.example;

import com.example.config.AppConfig;
import com.example.consumer.NotificationConsumer;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {
    public static void main(String[] args) {
        // 方式一：XML 配置
        ApplicationContext xmlCtx =
            new ClassPathXmlApplicationContext("beans.xml");
        NotificationConsumer consumer1 =
            xmlCtx.getBean(NotificationConsumer.class);
        consumer1.notifyUser();

        // 方式二：Java 注解配置
        ApplicationContext annoCtx =
            new AnnotationConfigApplicationContext(AppConfig.class);
        NotificationConsumer consumer2 =
            annoCtx.getBean(NotificationConsumer.class);
        consumer2.notifyUser();
    }
}

运行

javac -cp "spring-context-6.1.0.jar:..." com/example/*.java com/example/**/*.java
java -cp ".:spring-context-6.1.0.jar:spring-core-6.1.0.jar:spring-beans-6.1.0.jar:spring-expression-6.1.0.jar:commons-logging-1.2.jar" com.example.Main

预期输出

Email from noreply@example.com
Email from noreply@example.com