如何在 Spring 云数据流处理器“http-request”中指定标头表达式？

Question

We are trying to pass the basic authentication header when using the SCDF prebuilt processor " http-request " to call an external service. From my understanding, the message http headers are not automatically carried over in making the call, we need to populate the " headers-expression " property instead. The following is the the call processor step of the stream definition:

http-request --body-expression=payload
--url-expression='headers.reportURL' --http-method-expression='headers.httpMethod' --headers-expression='headers.Authorization'

We already had set the message header " Authorization " as " Basic <base64encoded("user:password")> " in previous step so " headers.Authorization " has the correct Basic Authentication header value when the message arrives to " http-request " processor. However, this doesn't work, the stream log has the following error:

org.springframework.expression.spel.SpelEvaluationException: EL1001E: Type conversion problem, cannot convert from java.lang.String to java.util.Map at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:75) at org.springframework.expression.common.ExpressionUtils.convertTypedValue(ExpressionUtils.java:57)

From the error message, it appears we need to pass a map? Something like " Authorization: headers.Authorization "? (The stream wasn't even deployed successfully by coding this way). We don't want to hard-code the " headers.Authorization " as the literal Basic Auth base64 string. Also how to specify more than one header (like adding " content-type ") in the " headers-expression "? We have searched the SCDF documentation and online but can't seem to find an example of how to do it.

Thanks.

Answer 1

If you say that you have already set those headers upfront, consider just that expression like this: --headers-expression='headers'. The --headers-expression='headers'. The headers property of the Message is a Map` by itself.

If that still doesn't fit your requirements, consider to use an in-line map syntax for SpEL: https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#expressions-inline-maps