优化 springboot 启动速度

前言： springboot的starter功能很强大，但是也导致了springboot 项目启动缓慢。在一定场景下，我们可能需要springboot项目尽量小，启动速度尽可能的快。

分析原因：

默认情况下, 我们会使用@SpringBootApplication注解来自动获取应用的配置信息. 这样会有一些副作用. 其中一个就是组件扫描@ComponentScan . 它会拖慢应用启动的速度, 也会加载一些不必要的bean.

改进方法：

1.不使用@SpringBootApplication，用 @Configuration和@EnableAutoConfiguration代替

  /**
   * @author cphovo
   */
  @Configuration
  @EnableAutoConfiguration
  // @SpringBootApplication
  public class MiniSpringbootApplication {

      public static void main(String[] args) {
          SpringApplication.run(MiniSpringbootApplication.class, args);
      }

  }

2.但是这样也引发了问题 -> 无法扫描到我们编写的组件类，如 @Controller、@Service、@Mapper 等标记的组件无法被扫描到。
解决办法：用@Bean显式进行配置这些类，但是要注意依赖关系，被依赖的需要先配置

@Configuration
public class BeansConfig {

    @Resource
    private SqlSessionFactory sqlSessionFactory;

    @Bean
    public MapperFactoryBean<UserMapper> userMapper() {
        MapperFactoryBean<UserMapper> mapperFactoryBean = new MapperFactoryBean<>();
        mapperFactoryBean.setMapperInterface(UserMapper.class);
        mapperFactoryBean.setSqlSessionFactory(sqlSessionFactory);
        return mapperFactoryBean;
    }

    @Bean
    public UserServiceImpl userService() {
        return new UserServiceImpl();
    }

    @Bean
    public UserController userController() {
        return new UserController();
    }
}

进一步优化

使用 @Configuration和@EnableAutoConfiguration其实还有可以优化启动速度的地方，@EnableAutoConfiguration会扫描所有 @Configuration的组件，这也导致启动速度变慢。
1.在application.properties配置logging.level.org.springframework.boot.autoconfigure=DEBUG，查看哪些是必要的Bean

============================
CONDITIONS EVALUATION REPORT
============================


Positive matches:
-----------------

   AopAutoConfiguration matched:
      - @ConditionalOnProperty (spring.aop.auto=true) matched (OnPropertyCondition)

   AopAutoConfiguration.ClassProxyingConfiguration matched:
      - @ConditionalOnMissingClass did not find unwanted class 'org.aspectj.weaver.Advice' (OnClassCondition)
      - @ConditionalOnProperty (spring.aop.proxy-target-class=true) matched (OnPropertyCondition)

   DataSourceAutoConfiguration matched:
      - @ConditionalOnClass found required classes 'javax.sql.DataSource', 'org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType' (OnClassCondition)
      - @ConditionalOnMissingBean (types: io.r2dbc.spi.ConnectionFactory; SearchStrategy: all) did not find any beans (OnBeanCondition)

   DataSourceAutoConfiguration.PooledDataSourceConfiguration matched:
      - AnyNestedCondition 1 matched 1 did not; NestedCondition on DataSourceAutoConfiguration.PooledDataSourceCondition.PooledDataSourceAvailable PooledDataSource found supported DataSource; NestedCondition on DataSourceAutoConfiguration.PooledDataSourceCondition.ExplicitType @ConditionalOnProperty (spring.datasource.type) did not find property 'type' (DataSourceAutoConfiguration.PooledDataSourceCondition)
      - @ConditionalOnMissingBean (types: javax.sql.DataSource,javax.sql.XADataSource; SearchStrategy: all) did not find any beans (OnBeanCondition)
   ...

• 关注Positive matches下的AutoConfiguration，把需要的自动配置用@Import显示引入。

@Configuration
@Import({
        DataSourceAutoConfiguration.class,
        DispatcherServletAutoConfiguration.class,
        ErrorMvcAutoConfiguration.class,
        HttpEncodingAutoConfiguration.class,
        HttpMessageConvertersAutoConfiguration.class,
        JacksonAutoConfiguration.class,
        MybatisAutoConfiguration.class,
        ServletWebServerFactoryAutoConfiguration.class,
        WebMvcAutoConfiguration.class,
        BeansConfig.class
})
//@EnableAutoConfiguration
//@SpringBootApplication
public class MiniSpringbootApplication {

    public static void main(String[] args) {
        SpringApplication.run(MiniSpringbootApplication.class, args);
    }

}

2.使用springboot全局懒加载，设置spring.main.lazy-initialization=true
3.关闭springboot JMX监控，设置spring.jmx.enabled=false
4.设置JVM参数-noverify，不对类进行验证