java - 如何判断是否需要用@Bean进行注解

Question

如何确定在 Spring 集成中，我需要使用 @Bean 进行注释？

例如，让我们看一下 @Transformer 注释。

考虑以下代码片段:

1.

    @AllArgsConstructor
    @Getter
    @Setter
    @ToString
    private static class Person {
        private String firstName;
        private String lastName;
        private String phone;
    }

    @Override
    public void run(ApplicationArguments args) {
        firstChannel.send(MessageBuilder.withPayload(new Person("s", "f", null)).build());
    }

    // without bean
    @Transformer(inputChannel = FIRST_CHANNEL, outputChannel = SECOND_CHANNEL)
    public ContentEnricher contentEnricher() {
        ContentEnricher contentEnricher = new ContentEnricher();
        contentEnricher.setPropertyExpressions(ImmutableMap.of("phone", new ValueExpression("123")));
        return contentEnricher;
    }

    @ServiceActivator(inputChannel = SECOND_CHANNEL)
    private void fromSecondChannel(Message<?> message) {
        System.out.println(message.getPayload());
    }

和

2.

    // with bean
    @Bean
    @Transformer(inputChannel = FIRST_CHANNEL, outputChannel = SECOND_CHANNEL)
    public HeaderEnricher headerEnricher() {
        return new HeaderEnricher(ImmutableMap.of("key1", new StaticHeaderValueMessageProcessor<>("value1")));
    }

没有 @Bean 的代码片段 nr 2 的输出是:

GenericMessage [payload=org.springframework.integration.transformer.HeaderEnricher@15a3b42, headers={id=76d24f2c-8b64-a254-8733-8b5911871cce, timestamp=1590856526985}]

对于 @Bean 来说是:

GenericMessage [payload=DemoApplication11.Person(firstName=s, lastName=f, phone=null), headers={key1=value1, id=55e5b4b7-9a4b-8822-4398-b42755bc7697, timestamp=1590856617667}]

Answer 1

没有 @Bean 意味着转换器被作为 POJO 方法调用。

@Transformer(...)
public String transform(String in) {
    return in.toUpperCase();
}

如果转换器实际上是 Transformer 的实现(例如 header 丰富器)，则需要 @Bean。

ContentEnricher 不是一个转换器，它是一个 MessageHandler，因此必须用 @ServiceActivator 和 @Bean 注解.

参见the documentation和 here .

Starting with version 4.0, you can configure messaging annotations on @Bean method definitions in @Configuration classes, to produce message endpoints based on the beans, not the methods. It is useful when @Bean definitions are “out-of-the-box” MessageHandler instances (AggregatingMessageHandler, DefaultMessageSplitter, and others), Transformer instances (JsonToObjectTransformer, ClaimCheckOutTransformer, and others), and MessageSource instances (FileReadingMessageSource, RedisStoreMessageSource, and others). The following example shows how to use messaging annotations with @Bean annotations ...