Spring框架中的@Conditional系列注解详解

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
public @interface Conditional {
    Class<? extends Condition>[] value();
}

public interface Condition {
    boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata);
}

//如果当前工程运行在Windows系统下，就注册Student
public class Student {}
//如果当前工程运行在Linux系统下，就注册Teacher
public class Teacher {}
// 如果是Mac OSX 系统，就注册Parent
public class Parent {}

 
public class LinuxCondition implements Condition {
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
            // 获取系统环境的属性
          String systemName = context.getEnvironment().getProperty("os.name");
          if(systemName.contains("Linux")){
              return true;
          }
          return false;
    }
}
//自定义一个判断条件
public class WindowsCondition implements Condition {
    /*
     * ConditionContext context: spring容器上下文环境
     * AnnotatedTypeMetadata metadata ：@Conditional修饰类型信息
     */
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
           String systemName = context.getEnvironment().getProperty("os.name");
           if(systemName.contains("Windows")){
               return true;
           }
        return false;
    }
}
public class OsxCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        String property = context.getEnvironment().getProperty("os.name");
        if(property.equals("Mac OS X")){
            return true;
        }
        return false;
    }
}

 
@Configuration
public class AppConfig {
    @Conditional(OsxCondition.class)
    @Bean
    public Student student(){
        return new Student();
    }
    @Conditional(LinuxCondition.class)
    @Bean
    public Teacher teacher(){
        return new Teacher();
    }
    @Conditional(WindowsCondition.class)
    @Bean
    public Parent parent(){
        return new Parent();
    }
}

 
public class ConditionTest {
 
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        String[] names = context.getBeanDefinitionNames();
        for(String name : names){
            System.out.println("name = " + name);
        }
    }
}

@Conditional(value = OsxCondition.class)

// 单纯为了测试
public class TestCondition implements Condition {
    @Override
    public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
        // 返回false，表示不匹配
        return false;
    }
}

@Conditional(value = {OsxCondition.class,TestCondition.class})

@ConditionalOnProperty(prefix = DUBBO_PREFIX, name = "enabled", matchIfMissing = true)
@Configuration
@AutoConfigureAfter(DubboRelaxedBindingAutoConfiguration.class)
@EnableConfigurationProperties(DubboConfigurationProperties.class)
@EnableDubboConfig
public class DubboAutoConfiguration {
    /**
     * Creates {@link ServiceAnnotationPostProcessor} Bean
     * dubbo.scan.base-packages
     * @param packagesToScan the packages to scan
     * @return {@link ServiceAnnotationPostProcessor}
     */
    @ConditionalOnProperty(prefix = DUBBO_SCAN_PREFIX, name = BASE_PACKAGES_PROPERTY_NAME)
    // 先找BASE_PACKAGES_BEAN_NAME 这个bean, 如果没有这个bean, 那么serviceAnnotationBeanProcessor不会被Spring装载。
    @ConditionalOnBean(name = BASE_PACKAGES_BEAN_NAME)
    @Bean
    public ServiceAnnotationPostProcessor serviceAnnotationBeanProcessor(@Qualifier(BASE_PACKAGES_BEAN_NAME)
                                                                       Set<String> packagesToScan) {
        return new ServiceAnnotationPostProcessor(packagesToScan);
    }
}

/**
 * Dubbo Relaxed Binding Auto-{@link Configuration} for Spring Boot 2.0
 *
 * @see DubboRelaxedBindingAutoConfiguration
 * @since 2.7.0
 */
@Configuration
@ConditionalOnProperty(prefix = DUBBO_PREFIX, name = "enabled", matchIfMissing = true)
@ConditionalOnClass(name = "org.springframework.boot.context.properties.bind.Binder")
@AutoConfigureBefore(DubboRelaxedBindingAutoConfiguration.class)
public class DubboRelaxedBinding2AutoConfiguration {
    public PropertyResolver dubboScanBasePackagesPropertyResolver(ConfigurableEnvironment environment) {
        ConfigurableEnvironment propertyResolver = new AbstractEnvironment() {
            @Override
            protected void customizePropertySources(MutablePropertySources propertySources) {
                Map<String, Object> dubboScanProperties = getSubProperties(environment.getPropertySources(), DUBBO_SCAN_PREFIX);
                propertySources.addLast(new MapPropertySource("dubboScanProperties", dubboScanProperties));
            }
        };
        ConfigurationPropertySources.attach(propertyResolver);
        return propertyResolver;
    }
    /**
     * The bean is used to scan the packages of Dubbo Service classes
     * 如果没有就创建
     * @param environment {@link Environment} instance
     * @return non-null {@link Set}
     * @since 2.7.8
     */
    @ConditionalOnMissingBean(name = BASE_PACKAGES_BEAN_NAME)
    @Bean(name = BASE_PACKAGES_BEAN_NAME)
    public Set<String> dubboBasePackages(ConfigurableEnvironment environment) {
        PropertyResolver propertyResolver = dubboScanBasePackagesPropertyResolver(environment);
        return propertyResolver.getProperty(BASE_PACKAGES_PROPERTY_NAME, Set.class, emptySet());
    }
    @ConditionalOnMissingBean(name = RELAXED_DUBBO_CONFIG_BINDER_BEAN_NAME, value = ConfigurationBeanBinder.class)
    @Bean(RELAXED_DUBBO_CONFIG_BINDER_BEAN_NAME)
    @Scope(scopeName = SCOPE_PROTOTYPE)
    public ConfigurationBeanBinder relaxedDubboConfigBinder() {
        return new BinderDubboConfigBinder();
    }
}

spring.datasource.type=com.zaxxer.hikari.HikariDataSource

@ConditionalOnProperty(name={cache.effect},marchIfMissing=true)
public class CacheAutoConfiguration{
   // ...
}