学习笔记051——SpringBoot学习2

Spring Boot 原理

Spring Boot 可以自动读取配置文件，将项目所需要的组件全部自动加载到 IoC 容器中，包括两部分

• 开发者自定义组件（Controller、Service、Repository）
• 框架自带的组件（DispatcherServlet、SqlSessionFactory）

Spring Boot 启动类注解 @SpringBootApplication 是由 3 个注解组成

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan

1、@SpringBootConfiguration

@SpringBootConfiguration 本质上就是一个 @Configuration

@Configuration 的作用是标注一个配置类，将一个 Java 类标注成为一个配置类，用来取代 XML 的，向 IoC 容器中注入对象的。

基于 XML 的配置方式

package com.southwind.entity;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;@Data
@AllArgsConstructor
@NoArgsConstructor
public class Account {private String username;private String password;
}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:context="http://www.springframework.org/schema/context"xmlns:p="http://www.springframework.org/schema/p"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"><!-- 配置一个对象 --><bean id="account" class="com.southwind.entity.Account"><property name="username" value="tom"></property><property name="password" value="123"></property></bean></beans>

package com.southwind;import org.springframework.context.support.ClassPathXmlApplicationContext;public class Test {public static void main(String[] args) {ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");System.out.println(applicationContext.getBean("account"));}
}

@Configuration

配置类，Java 类相当于 XML 文件

package com.southwind.configure;import com.southwind.entity.Account;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
public class AccountConfiguration {@Beanpublic Account account(){return new Account("cat","456");}
}

2、@ConfigurationProperties

可以直接读取 YAML 文件中的数据，并封装到 bean 中，给 bean 的属性赋值。

package com.southwind.entity;import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;@Data
@ConfigurationProperties(prefix = "people")
public class People {private Integer id;private String name;private String tel;
}

package com.southwind.configure;import com.southwind.entity.People;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Configuration;@Configuration
@EnableConfigurationProperties(People.class)
public class PeopleConfiguration {
}

people:id: 1name: 张三tel: 123456789

3、@ComponentScan

将开发者自定义的组件进行扫描注入

4、@EnableAutoConfiguration

将框架自带的组件进行扫描注入

@AutoConfigurationPackage

@Import

@Import 注入 bean，结合一个选择器来注入，选择器提供要注入的 bean 的信息，@Import 实现注入

package com.southwind.entity;import lombok.Data;@Data
public class User {private String cardId;private Double score;
}

package com.southwind.selector;import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.type.AnnotationMetadata;public class UserSelector implements ImportSelector {@Overridepublic String[] selectImports(AnnotationMetadata annotationMetadata) {String[] names = {"com.southwind.entity.User"};return names;}
}

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.southwind.configure.ImportConfig