Detailed introduction to Spring4

The demo of this article is based on the spring official website entry case. Of course, I made some changes.

My maven web project structure is as follows:

Add spring dependencies in pom.xml:

接下来我们开始创建需要用到的类：

package com.mm.service;

public interface MessageService {
	String getMessage();
}

package com.mm.service.impl;

import com.mm.service.MessageService;

public class MessageServiceImpl implements MessageService{
	@Override
	public String getMessage() {
		return "hello mm";
	}
}

I don’t need injection in the form of spring configuration file, so I created a new configuration file class

package com.mm.main.spring;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import com.mm.service.MessageService;
import com.mm.service.impl.MessageServiceImpl;

@Configuration
@ComponentScan(basePackages = "com.mm")
public class ApplicationConfig {
    @Bean
    MessageService messageService() {
        return new MessageServiceImpl();
    }
}

Create a new bean to call the service

package com.mm.main.spring;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import com.mm.service.MessageService;

@Component
public class MessagePrinter {
	@Autowired
	private MessageService messageService;
	public void printMessage() {
        System.out.println(this.messageService.getMessage());
    }
}

Finally complete the writing of the client

package com.mm.main.spring;

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

public class Client {
	public static void main(String[] args) {
		ApplicationContext context=new AnnotationConfigApplicationContext(ApplicationConfig.class);
		MessagePrinter messagePrinter=context.getBean(MessagePrinter.class);
		messagePrinter.printMessage();
	}
}

The background print is as follows:

Next we use annotations to inject, first remove the MessageService bean in the configuration file class

@Configuration
@ComponentScan(basePackages = "com.mm")public class ApplicationConfig {//    @Bean//    MessageService messageService() {//        return new MessageServiceImpl();//    }}

Add annotations to MessageServiceImpl

@Service//注解方式public class MessageServiceImpl implements MessageService{
    @Overridepublic String getMessage() {return "hello mm";
    }
}

The same complete output

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