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【第9章】SpringBoot中Bean的扫描和注册

news 来源：原创 2024/9/29 17:36:19

文章目录

前言
一、bean扫描
- 1. @SpringBootApplication
- 2. @ComponentScan
二、bean注册
- 1.应用bean注册
- 2.外部bean注册
- - 2.1 @Bean
  - 2.2 @Import
- 3.bean注册条件
- - 3.1 @ConditionalOnProperty
  - 3.2 @ConditionalOnMissingBean
  - 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

@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

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

2.2 @Import

@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

@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

@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

@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();
}