Issue with application/json reponse being escaped in Spring Integration 4.2

问题

Creating an HTTP proxy in Spring Integration 4.2.1.RELEASE. Environment is using the latest 2.0.0.RELEASE platform BOM, including a spring-webmvc layer - running on Tomcat7.

Calls are "application/json", passed through the web layer to a different REST server endpoint (the setupUrl method rewrites the URL). The code successfully calls the external server, gets good response, then mangles the response before it returns to the caller.

@Bean
    public IntegrationFlow httpProxyFlow()  {
        return IntegrationFlows
            .from((MessagingGateways g) ->
                    g.httpGateway("/my-service/**")
                            .messageConverters(new MappingJackson2HttpMessageConverter())
                        .payloadFunction(httpEntity ->
                                ((ServletRequestAttributes) RequestContextHolder.currentRequestAttributes())
                                        .getRequest()
                                        .getQueryString())
                        .requestPayloadType(String.class))
                        .handleWithAdapter(a ->
                                a.httpGateway(this::setupUrl)
                                        .httpMethodFunction(this::getMethodFunction)
                                        .errorHandler(new PassThroughErrorHandler())
                                        .encodeUri(false)
                                        .expectedResponseType(String.class)
                        ).get();
    }

The call directly to the REST endpoint returns

{"affiliate":"test","producer":"TST","products"...

While the call through Spring Integration returns

"{\"affiliate\":\"test\",\"producer\":\"TST\",\"products\":[{\"

Tried a lot of combinations of adding StringHttpMessageConverter to the outbound adapter. Messing with the encodings (UTF-8 rather than ISO-8859-1). Something is messing with the response string, and it seems to be AFTER it leaves Spring Integration as near as I can tell. The last time Integration touches it is HttpRequestHandlingMessagingGateway.handleRequest() line 117. It still looks correct in the response object there.

It's possible the issue is really with spring-mvc, that is the first place I see the mangled string in debugging.

回答1:

Best guess is some problem with the accept (inbound) or content-type (outbound).

I just changed the http sample like so...

<int-http:inbound-gateway request-channel="proxyChannel"
                            reply-channel="reply"
                            path="/receiveGateway"
                            supported-methods="POST"/>

<int:channel id="reply" />

<int-http:outbound-gateway request-channel="proxyChannel"
                reply-channel="reply"
                expected-response-type="java.lang.String"
                url="http://localhost:8080/http/receiveGateway2"/>

<int-http:inbound-gateway request-channel="receiveChannel"
                            path="/receiveGateway2"
                            supported-methods="POST"/>

<int:channel id="receiveChannel"/>

<int:chain input-channel="receiveChannel">
    <int:header-filter header-names="content-type" />
    <int:service-activator expression='{"foo" : "bar"}'/>
</int:chain>

The payload being returned to the first gateway is type String; it works for me with an inbound accept of text/plain or application/json.

Since the StringHttpMessageConverter is ahead of the JSON message converter in the list, and the payload is a String, it is chosen because the type is String and that converter can handle */* accept, so there's no double JSON encoding.

{"foo":"bar"} is received by my client.

If you can't figure it out with DEBUG logging and/or the debugger, you could try reconfiguring the inbound gateway with just a StringHttpMessageConverter.

Set a breakpoint at line 151 (current release) in HttpRequestHandlingMessagingGateway to see which outbound message converter is being selected.

来源：https://stackoverflow.com/questions/33924009/issue-with-application-json-reponse-being-escaped-in-spring-integration-4-2