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，其思想是由出站网关MarketingCategoryOutboundGateway轮询，该网关由HttpRequestExecutingMessageHandler实现。网关向REST服务发出请求，并将其响应推送到MarketingCategory通道。网关本身由MarketingCategoryPollerMessageSource使用MaketRiggeringMessage工厂方法创建的消息触发。

问题是服务返回分页结果。除了我已经拥有的服务激活器之外，我还会监听MarketingCategory通道，检查响应并将带有由MaketriggeringMessage创建的递增页码的新消息推送到MarketingCategoryPoller通道，这样代码就会在循环中旋转，直到从REST服务获取所有页面。

Spring Integration是否允许制作这样的过滤器，在输入通道上接收一条消息，根据一个条件对其进行测试，并在条件为真的情况下将一条新消息推送到输出通道？

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

我已经找到了一个基于这篇文章的解决方案，从带有spring集成的分页REST服务中阅读和下载：

>

触发与REST服务对话的出站网关，并使用带轮询器的入站通道适配器将响应推送到通道。入站通道适配器是一个消息源，它最初生成一个消息，消息头指示要从REST API获取的页码。出站网关使用页面消息头生成指定所需页面的url

出站网关向其推送REST服务响应的信道有2个订户：

2.2.筛选器，检查这是否是最后一页，如果不是，则将消息进一步发送到header enricher使用的另一个通道

接收到消息后，报头充实器增加其页头并将该消息进一步推送到触发出站网关的通道，网关读取增加的页头并从REST服务获取下一页

循环一直旋转，直到REST服务返回最后一页。过滤器不让此消息传递到header，从而打破了循环。

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);
    }
}