Spring Boot 自動配置與代碼配置

       在Spring中依賴注入（dependency injection，即DI）是指容器負責創建對象和維護對象之間的依賴關係，而不是通過對象本身實現自己的創建和解決自己的依賴。在Spring中有自動配置、Java配置和XML配置，其中Java配置更爲靈活，在Spring Boot中主要採用自動配置，在某些情況下采用java配置。下面來看一下自動配置和Java配置的代碼實現，詳細代碼如下：

一、自動配置 

package com.example.demo.test.DI;

import org.springframework.stereotype.Service;

@Service
public class FunctionService {

    public String sayHello(String words){
        return "hello" + words + "!";
    }
}

package com.example.demo.test.DI;

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

@Service
public class UseFunctionService {
    @Autowired
    FunctionService functionService;

    public String sayHello(String words){
        return functionService.sayHello(words);
    }
}

 

package com.example.demo.test.DI;

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

@Configuration
@ComponentScan("com.example.demo.test.DI")
public class DiConfig {

}

自動配置測試

import com.example.demo.test.DI.DiConfig;
import com.example.demo.test.DI.UseFunctionService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class DemoApplication {

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

      UseFunctionService useFunctionService = context.getBean(UseFunctionService.class);
      System.out.println(useFunctionService.sayHello("world"));

      context.close();
   }
}

自動配置類也可不寫，在啓動類加入@ComponentScan("com.example.demo.test.DI")和@SpringBootApplication註解即可

 

二、java代碼配置

通過@Configuration和@Bean實現，其中@Configuration聲明當前類是一個配置類，相當於Spring配置的xml文件；@Bean註解在方法上，表明該方法返回一個Bean。

package com.example.demo.test.javaConfig;

public class FunctionService {

    public String sayHello(String words){
        return "hello " + words + "!";
    }
}

FunctionService類注入

package com.example.demo.test.javaConfig;

public class UseFunctionService {
    FunctionService service;

    public UseFunctionService(FunctionService functionService){
        service = functionService;
    }

    public String sayHello(String words){
        return service.sayHello(words);
    }
}

配置類

package com.example.demo.test.javaConfig;

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

@Configuration
//指定掃描範圍
@ComponentScan("com.example.demo.test.javaConfig")
public class JavaConfig {

    @Bean
    public FunctionService functionService(){
        return new FunctionService();
    }

    @Bean
    public UseFunctionService useFunctionService(FunctionService functionService){
        return new UseFunctionService(functionService);
    }
//   也可以是下面寫法
//    @Bean
//    public UseFunctionService useFunctionService(){
//        return new UseFunctionService(functionService());
//    }
}

java配置測試

package com.example.demo;

import com.example.demo.test.javaConfig.JavaConfig;
import com.example.demo.test.javaConfig.UseFunctionService;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class DemoApplication {

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

      UseFunctionService useFunctionService = context.getBean(UseFunctionService.class);
      System.out.println(useFunctionService.sayHello("world"));

      context.close();
   }
}

 

 

以上兩種方式的輸出結果都是Hello world! 這兩種方式也是最爲常用配置方式。