10.Spring配置方式

 

Spring配置

第一阶段：xml配置

Spring 1.x

第二阶段：注解配置

Spring 2.x，基本配置（如数据库配置）用xml，业务配置用注解

第三阶段：Java配置

Spring 3.x，Spring Boot

无论是xml配置，注解配置还是Java配置，都被称为配置元数据，元数据即描述数据的数据。元数据本身不具备任何可执行的能力，只能通过外界代码来对这些元数据进行解析后，才能进行一些有意义的操作。

Java配置

Java配置是通过@Configuration和@Bean来实现的。

• @Configuration声明当前类是一个配置类，相当于一个Spring配置的xml文件

• @Bean注解在方法上，声明当前方法的返回值为一个Bean

全局配置使用Java配置（如数据库相关配置、MVC相关配置），业务Bean的配置使用注解配置（@Service,@Component,@Repository,@Controller）

public class FunctionService {

    public String sayHello(String word){
        return "Hello "+word+" !";
    }
}

public class UseFunctionService {
    FunctionService functionService;

    public void setFunctionService(FunctionService functionService) {
        this.functionService = functionService;
    }

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

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

@Configuration
public class JavaConfig {

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

    @Bean
    public UseFunctionService useFunctionService() {
        UseFunctionService useFunctionService = new UseFunctionService();
        useFunctionService.setFunctionService(functionService());
        return useFunctionService;
    }


}

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Main {

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

        UseFunctionService useFunctionService = context.getBean(UseFunctionService.class);

        System.out.println(useFunctionService.sayHello("java config"));

        context.close();
    }
}

output:

09:34:41.367 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Refreshing org.springframework.context.annotation.AnnotationConfigApplicationContext@1e81f4dc
09:34:41.473 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalConfigurationAnnotationProcessor'
09:34:41.999 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerProcessor'
09:34:42.001 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.event.internalEventListenerFactory'
09:34:42.003 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalAutowiredAnnotationProcessor'
09:34:42.005 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'org.springframework.context.annotation.internalCommonAnnotationProcessor'
09:34:42.085 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'javaConfig'
09:34:42.092 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'functionService'
09:34:42.112 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating shared instance of singleton bean 'useFunctionService'
Hello java config !
09:34:42.246 [main] DEBUG org.springframework.context.annotation.AnnotationConfigApplicationContext - Closing org.springframework.context.annotation.AnnotationConfigApplicationContext@1e81f4dc, started on Thu Mar 26 09:34:41 CST 2020

Process finished with exit code 0

Spring框架的四大原则

1. 使用POJO进行轻量级和最小侵入式开发。

2. 通过依赖注入和基于接口编程实现松耦合。

3. 通过AOP和默认习惯进行声明式编程。

4. 使用AOP和模板（template）减少模式化代码。