无法解码Spring云流中的json类型DefaultKafkaHeaderMapper

Question

我们正在使用spring cloud stream，并计划升级我们的Kafka版本
我们的应用程序使用apache kafka服务器1.0.1的spring cloud stream:2.0.0（spring kafka 2.1.7），还使用spring cloud sleuth:2.0.0进行跟踪
我们将把Kafka服务器升级到2.3.0版，因此需要升级到spring boot 2.2版。x（霍克斯顿）与春云侦探：2.2.0和春云流：3.0.3（Horsham.SR3）
我们有约200个使用Kafka的应用程序，因此升级将逐步进行，因此作为中间状态，我们将有更新版本的生产者和使用旧版本的消费者
我们的消费者正在使用@StreamListener。

在我们的测试中，我们遇到了一个问题：解析大多数类型为String的标题，并获得以下信息：

ERROR 27448 --- [container-0-C-1] o.s.c.s.b.k.KafkaMessageChannelBinder$4  : Could not decode json type: ecb89ccb3e79418b for key: X-B3-TraceId
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'ecb89ccb3e79418b': was expecting ('true', 'false' or 'null')
 at [Source: (byte[])"ecb89ccb3e79418b"; line: 1, column: 33]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1804) ~[jackson-core-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:679) ~[jackson-core-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._reportInvalidToken(UTF8StreamJsonParser.java:3526) ~[jackson-core-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._handleUnexpectedValue(UTF8StreamJsonParser.java:2621) ~[jackson-core-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser._nextTokenNotInObject(UTF8StreamJsonParser.java:826) ~[jackson-core-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.core.json.UTF8StreamJsonParser.nextToken(UTF8StreamJsonParser.java:723) ~[jackson-core-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectMapper._initForReading(ObjectMapper.java:4141) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4000) ~[jackson-databind-2.9.6.jar:2.9.6]
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3091) ~[jackson-databind-2.9.6.jar:2.9.6]
    at org.springframework.kafka.support.DefaultKafkaHeaderMapper.lambda$toHeaders$1(DefaultKafkaHeaderMapper.java:233) ~[spring-kafka-2.1.7.RELEASE.jar:2.1.7.RELEASE]
    at java.lang.Iterable.forEach(Iterable.java:75) ~[na:1.8.0_221]
    at org.springframework.kafka.support.DefaultKafkaHeaderMapper.toHeaders(DefaultKafkaHeaderMapper.java:216) ~[spring-kafka-2.1.7.RELEASE.jar:2.1.7.RELEASE]
    at org.springframework.cloud.stream.binder.kafka.KafkaMessageChannelBinder$4.toHeaders(KafkaMessageChannelBinder.java:554) ~[spring-cloud-stream-binder-kafka-2.0.0.RELEASE.jar:2.0.0.RELEASE]
    at org.springframework.kafka.support.converter.MessagingMessageConverter.toMessage(MessagingMessageConverter.java:106) ~[spring-kafka-2.1.7.RELEASE.jar:2.1.7.RELEASE]
    at org.springframework.kafka.listener.adapter.MessagingMessageListenerAdapter.toMessagingMessage(MessagingMessageListenerAdapter.java:229) ~[spring-kafka-2.1.7.RELEASE.jar:2.1.7.RELEASE]
...

而类型标题是：

{spanTraceId=java.lang.String, spanId=java.lang.String, spanParentSpanId=java.lang.String, nativeHeaders=org.springframework.util.LinkedMultiValueMap, X-B3-SpanId=java.lang.String, X-B3-ParentSpanId=java.lang.String, scst_partition=java.lang.Integer, X-B3-Sampled=java.lang.String, X-B3-TraceId=java.lang.String, spanSampled=java.lang.String, contentType=java.lang.String}

例如，Sleuth添加的X-B3-SpanId类型为String，值为：ecb89ccb3e79418b，不是JSON字符串，因此ObjectMapper在转换为String对象时失败：

headers.put(h.key(), getObjectMapper().readValue(h.value(), type))

看起来当我们有字符串类型时，它不应该使用ObjectMapper，因此我们的旧消费者失败了。

在使用新生产者和旧消费者时，有没有办法防止这个问题？

Answer 1

您可以将DefaultKafkaHeaderMapper配置为与旧版本兼容：

    /**
     * Set to true to encode String-valued headers as JSON ("..."), by default just the
     * raw String value is converted to a byte array using the configured charset. Set to
     * true if a consumer of the outbound record is using Spring for Apache Kafka version
     * less than 2.3
     * @param encodeStrings true to encode (default false).
     * @since 2.3
     */
    public void setEncodeStrings(boolean encodeStrings) {
        this.encodeStrings = encodeStrings;
    }

也看到https://docs.spring.io/spring-cloud-stream-binder-kafka/docs/3.0.10.RELEASE/reference/html/spring-cloud-stream-binder-kafka.html#_kafka_binder_properties

spring。云流动Kafka。粘合剂headerMapperBeanName