【第9章】SpringBoot中Bean的扫描和注册

文章目录

前言
一、bean扫描
- [1. @SpringBootApplication](#1. @SpringBootApplication)
- [2. @ComponentScan](#2. @ComponentScan)
二、bean注册
- 1.应用bean注册
- 2.外部bean注册
- - [2.1 @Bean](#2.1 @Bean)
  - [2.2 @Import](#2.2 @Import)
- 3.bean注册条件
- - [3.1 @ConditionalOnProperty](#3.1 @ConditionalOnProperty)
  - [3.2 @ConditionalOnMissingBean](#3.2 @ConditionalOnMissingBean)
  - [3.3 @ConditionalOnBean](#3.3 @ConditionalOnBean)
总结

前言

注册bean对象相关内容。

一、bean扫描

1. @SpringBootApplication

springboot应用程序会扫描启动类同级及子目录下的java文件。

2. @ComponentScan

bash 复制代码

@Configuration
@ComponentScan(basePackages = "org.example.spring")
public class SpringBootConfig {}

二、bean注册

1.应用bean注册

在springboot应用中我们通常通过注解的形式完成bean对象的注册

注解	描述
@Component	被标识的类被spring容器管理
@Controller	控制层注解，@Component衍生类
@Service	服务层注解，@Component衍生类
@Repository	持久层注解，@Component衍生类

2.外部bean注册

将jar包中的类交由spring容器管理

2.1 @Bean

java 复制代码

@Configuration
public class DruidConfig {
    @Bean
    @ConfigurationProperties("spring.datasource.druid")
    public DataSource dataSource(){
        return new DruidDataSource();
    }
}

2.2 @Import

bash 复制代码

@MapperScan("org.example.springboot3.mybatis.mappers")
@RestController
@SpringBootApplication
@Import(DruidConfig.class)
public class SpringBoot3Application {
    private static final Logger log = LoggerFactory.getLogger(SpringBoot3Application.class);
    public static void main(String[] args) {
        ConfigurableApplicationContext run = SpringApplication.run(SpringBoot3Application.class, args);
        String appName = run.getEnvironment().getProperty("spring.application.name");
        log.info("{}启动完成",appName);
    }
    @RequestMapping("/")
    String home() {
        return "Hello SpringBoot!";
    }
}

3.bean注册条件

3.1 @ConditionalOnProperty

java 复制代码

@Bean
@ConfigurationProperties("spring.datasource.druid")
@ConditionalOnProperty(prefix = "spring.datasource.druid",value = {"driver-class-name","url","username","password"})
public DataSource dataSource(){
    return new DruidDataSource();
}

3.2 @ConditionalOnMissingBean

bash 复制代码

@Bean
@ConfigurationProperties("spring.datasource.druid")
@ConditionalOnProperty(prefix = "spring.datasource.druid",value = {"driver-class-name","url","username","password"})
@ConditionalOnMissingBean(DataSource.class)
public DataSource dataSource(){
    return new DruidDataSource();
}

3.3 @ConditionalOnBean

java 复制代码

@Bean
@ConfigurationProperties("spring.datasource.druid")
@ConditionalOnProperty(prefix = "spring.datasource.druid",value = {"driver-class-name","url","username","password"})
@ConditionalOnMissingBean(DataSource.class)
@ConditionalOnBean(com.mysql.cj.jdbc.Driver.class)
public DataSource dataSource(){
    return new DruidDataSource();
}

总结

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