java - Spring Integration 从 REST 服务获取分页结果

Question

我正在研究与 REST 服务的集成，其想法是由出站网关 marketingCategoryOutboundGateway 进行轮询。由 HttpRequestExecutingMessageHandler 实现。网关向 REST 服务发出请求并将其响应推送到 marketingCategory channel 。网关本身由 marketingCategoryPollerMessageSource 创建的消息触发。使用makeTriggeringMessage工厂方法。

问题在于该服务返回分页结果。我一些东西可以在 marketingCategory 上监听 channel ，除了我已经拥有的服务激活器之外，检查是否响应并推送一条由 makeTriggeringMessage 创建的递增页码的新消息。到marketingCategoryPoller channel ，以便代码会循环旋转，直到从 REST 服务获取所有页面。

Spring Integration是否允许创建这样的过滤器:在输入 channel 上接收一条消息，根据条件对其进行测试，并在条件为真时将新消息推送到输出 channel ？

代码:

//Responses from the REST service go to this channel
@Bean("marketingCategory")
MessageChannel marketingCategory() { return new PublishSubscribeChannel();}

//This channel is used to trigger the outbound gateway which makes a request to the REST service
@Bean
MessageChannel marketingCategoryPoller() {return new DirectChannel();}

//An adapter creating triggering messages for the gateway
@Bean
@InboundChannelAdapter(channel = "marketingCategoryPoller", poller = @Poller(fixedDelay = "15000"))
public MessageSource<String> marketingCategoryPollerMessageSource() { return () -> makeTriggeringMessage(1);}

//A factory for producing messages which trigger the gateway
private Message<String> makeTriggeringMessage(int page) {
    //make a message for triggering marketingCategoryOutboundGateway
    return MessageBuilder.withPayload("")
            .setHeader("Host", "eclinic")
            .setHeader("page", page)
            .build();
}

//An outbound gateway, makes a request to the REST service and returns the response to marketingCategory channel
@Bean
@ServiceActivator(inputChannel = "marketingCategoryPoller")
public MessageHandler marketingCategoryOutboundGateway(@Qualifier("marketingCategory") MessageChannel channel) {
    //make a request to the REST service and push the response to the marketingCategory channel
}

//handler for REST service responses
@Bean
@ServiceActivator(inputChannel = "marketingCategory")
public MessageHandler marketingCategoryHandler() {
    return (msg) -> {
        //process the categories returned by marketingCategoryOutboundGateway
    };
}

Answer 1

我根据这篇文章找到了解决方案Read and download from a paginated REST-Services with spring integration :

1. 触发与 REST 服务通信的出站网关，并使用带有轮询器的入站 channel 适配器将响应推送到 channel 。 入站 channel 适配器是一个消息源，它最初生成一条消息，该消息的 header 指示要从 REST API 获取的页码。 出站网关使用页面消息头来生成指定所需页面的 url

2. 出站网关推送 REST 服务响应的 channel 有 2 个订阅者:

   2.1。一个服务激活器，它对获取的数据执行某些操作

   2.2。一个过滤器，它检查这是否是最后一页，如果不是，它将消息进一步发送到 header 丰富器使用的另一个 channel

3. 收到消息后， header 丰富器会增加其页面 header ，并将消息进一步推送到触发出站网关的 channel ， 网关读取递增的页头并从 REST 服务获取下一页

4. 循环不断旋转，直到 REST 服务返回最后一页。过滤器不会让此消息传递到 header 丰富器，从而打破循环。

完整代码:

@Configuration
public class IntegrationConfiguration {

    private final ApiGateConfig apiGateConfig;

    IntegrationConfiguration(ApiGateConfig apiGateConfig) {
        this.apiGateConfig = apiGateConfig;
    }

    @Bean("marketingCategory")
    MessageChannel marketingCategory() {
        return new PublishSubscribeChannel();
    }

    @Bean
    MessageChannel marketingCategoryPoller() {
        return new DirectChannel();
    }

    @Bean
    MessageChannel marketingCategoryPollerNextPage() {
        return new DirectChannel();
    }

    @Bean
    @InboundChannelAdapter(channel = "marketingCategoryPoller", poller = @Poller(fixedDelay = "15000"))
    public MessageSource<RestPageImpl<MarketingCategory>> marketingCategoryPollerMessageSource() {
        return () -> makeTriggeringMessage(0);
    }

    /**
     * Build a gateway triggering message
     */
    private Message<RestPageImpl<MarketingCategory>> makeTriggeringMessage(int page) {
        return MessageBuilder.withPayload(new RestPageImpl<MarketingCategory>())
                .setHeader("Host", "eclinic")
                .setHeader("page", page)
                .build();
    }

    @Bean
    @ServiceActivator(inputChannel = "marketingCategoryPoller")
    public MessageHandler marketingCategoryOutboundGateway(@Qualifier("marketingCategory") MessageChannel channel) {

        String uri = apiGateConfig.getUri() + "/marketingCategories?page={page}";

        //the type of the payload
        ParameterizedTypeReference<RestPageImpl<MarketingCategory>> type = new ParameterizedTypeReference<>() {
        };

        //page number comes from the message
        SpelExpressionParser expressionParser = new SpelExpressionParser();
        var uriVariables = new HashMap<String, Expression>();
        uriVariables.put("page", expressionParser.parseExpression("headers.page"));

        HttpRequestExecutingMessageHandler handler = new HttpRequestExecutingMessageHandler(uri);
        handler.setHttpMethod(HttpMethod.GET);
        handler.setExpectedResponseTypeExpression(new ValueExpression<>(type));
        handler.setOutputChannel(channel);
        handler.setUriVariableExpressions(uriVariables);

        return handler;
    }

    @Bean
    @ServiceActivator(inputChannel = "marketingCategory")
    public MessageHandler marketingCategoryHandler() {
        return (msg) -> {
            var page = (RestPageImpl<MarketingCategory>) msg.getPayload();

            System.out.println("Page #" + page.getNumber());

            page.getContent().forEach(c -> System.out.println(c.getMarketingCategory()));

        };
    }

    @Filter(inputChannel = "marketingCategory", outputChannel = "marketingCategoryPollerNextPage")
    public boolean marketingCategoryPaginationFilter(RestPageImpl<MarketingCategory> page) {
        return !page.isLast();
    }

    @Bean
    @Transformer(inputChannel = "marketingCategoryPollerNextPage", outputChannel = "marketingCategoryPoller")
    HeaderEnricher incrementPage() {
        Map<String, HeaderValueMessageProcessor<?>> headersToAdd = new HashMap<>();
        Expression expression = new SpelExpressionParser().parseExpression("headers.page+1");

        var valueProcessor = new ExpressionEvaluatingHeaderValueMessageProcessor<>(expression, Integer.class);
        valueProcessor.setOverwrite(true);

        headersToAdd.put("page", valueProcessor);
        return new HeaderEnricher(headersToAdd);
    }
}