@Autowired Spring @Component 和 @ConditionalOnProperty

Question

我可以使用 @Autowired Spring 4.x @Component 和 @ConditionalOnProperty 来选择 Feature[=35 的实现吗=] 基于 featuretoggles.properties 文件?

public class Controller { @Autowired private Feature feature; } @Component @ConditionalOnProperty(name = "b", havingValue = "off") public class A implements Feature { } @Component @ConditionalOnProperty(name = "b", havingValue = "on") public class B implements Feature { } @Configuration @PropertySource("classpath:featuretoggles.properties") public class SomeRandomConfig { }

使用 src/main/resources/featuretoggles.properties 文件：

b = on

(切换的名称 "b" 和 class "B" 匹配的名称是巧合；我的目的不是让它们相等，切换可以有任何姓名。)

这无法在 Controller 中使用 UnsatisfiedDependencyException 自动连接 feature，表示 "No qualifying bean of type 'Feature' available: expected at least 1 bean that qualifies as autowire candidate"。

我知道我可以通过 @Configuration class 实现这一点，根据属性选择 @Bean。但是，当我这样做时，每次添加功能切换时我都必须添加一个新的配置 class，并且这些配置 class 将非常相似：

@Configuration @PropertySource("classpath:featuretoggles.properties") public class FeatureConfig { @Bean @ConditionalOnProperty(name = "b", havingValue = "on") public Feature useB() { return new B(); } @Bean @ConditionalOnProperty(name = "b", havingValue = "off") public Feature useA() { return new A(); } }

Answer 1

我按照 this guide 做了你想做的事。第一步是写一个 Condition...

public class OnEnvironmentPropertyCondition implements Condition
{
  @Override
  public boolean matches(ConditionContext ctx, AnnotatedTypeMetadata meta)
  {
    Environment env = ctx.getEnvironment();
    Map<String, Object> attr = meta.getAnnotationAttributes(
                                 ConditionalOnEnvProperty.class.getName());

    boolean shouldPropExist = (Boolean)attr.get("exists");
    String prop = (String)attr.get("value");

    boolean doesPropExist = env.getProperty(prop) != null;

    // doesPropExist    shouldPropExist    result
    //    true             true             true
    //    true             false            false
    //    false            true             false
    //    true             false            true
    return doesPropExist == shouldPropExist;
  }
}

...然后是使用该条件的注释。

/*
 * Condition returns true if myprop exists:
 * @ConditionalOnEnvProperty("myprop")
 *
 * Condition returns true if myprop does not exist
 * @ConditionalOnEnvProperty(value="myprop", exists=false)
 */
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Conditional(OnEnvironmentPropertyCondition.class)
public @interface ConditionalOnEnvProperty
{
  public String value();
  public boolean exists() default true;
}

您可以使用 @PropertySource 注释将 featuretoggles.properties 添加到环境中。

@Autowired Spring @Component 和 @ConditionalOnProperty

@Autowired Spring @Component with @ConditionalOnProperty

spring

autowired

featuretoggle