Bean的加载控制

编程式

public class MyImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {

        try {
            Class<?> clazz = Class.forName("com.itheima.bean.Mouse");
            if(clazz != null){
                return new String[]{"com.itheima.bean.Cat"};
            }
        } catch (ClassNotFoundException e) {
//            throw new RuntimeException(e);
            return new String[0];
        }
        return null;
    }
}

注解式@ConditionalOn***

使用@Conditional注解的派生注解设置各种组合条件控制bean的加载

@Component("tom")
@ConditionalOnBean(name = "com.itheima.bean.Mouse")
//@ConditionalOnNotWebApplication
@ConditionalOnWebApplication
public class Cat {
}

组合条件

应用一下，根据是否使用 jdbc来决定加载不加载对应的bean

//@Import(MyImportSelector.class)
@ComponentScan("com.itheima.bean")
public class SpringConfig {

/*
    @Bean
//    @ConditionalOnClass(Mouse.class)  //ConditionalOnClas是Conditional的注解下面的，可以Ctrl + h查看到
//    @ConditionalOnClass(name = "com.itheima.bean.Mouse")  //ConditionalOnClas是Conditional的注解下面的，可以Ctrl + h查看到
//    @ConditionalOnMissingClass("com.itheima.bean.Wolf")   // 点进去看看，人家让写String
//    @ConditionalOnBean(name = "com.itheima.bean.Mouse")
    @ConditionalOnNotWebApplication
    public Cat tom(){
        return new Cat();
    }
 */

    @Bean
    @ConditionalOnClass(name = "com.mysql.jdbc.Driver")
    public DruidDataSource dataSource(){
        return new DruidDataSource();
    }

}