关于Java：在Spring Boot中将protobuf作为JSON发送

Sending protobuf as JSON in spring-boot

我正在使用带有此具体定义的protobufs。

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message Hash {
string category = 1;
repeated KVPair content = 2;
}

message KVPair {
string key = 1;
string value = 2;
}

我想通过spring-boot应用程序将其作为JSON发送。
我将此程序包添加到了gradle依赖项中：

1	compile group: 'com.google.protobuf', name: 'protobuf-java', version: '3.6.1'

当我尝试使用此代码输出哈希生成的对象时：

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@RestController
@RequestMapping("/api/crm/")
public class KVController {

private final KVService kvService;

public KVController(KVService kvService) {
this.kvService = kvService;
}

@GetMapping("kv/{category}")
public Hash getHash(@PathVariable String category) {
Hash hash = kvService.retrieve(category);
return hash;
}
}

它引发了这个最终的异常：

Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Direct self-reference leading to cycle (through reference chain: com.blaazha.crm.proto.Hash["unknownFields"]->com.google.protobuf.UnknownFieldSet["defaultInstanceForType"])
at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1191) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter._handleSelfReference(BeanPropertyWriter.java:944) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:721) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1396) ~[jackson-databind-2.9.6.jar:2.9.6]
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:913) ~[jackson-databind-2.9.6.jar:2.9.6]
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:286) ~[spring-web-4.3.18.RELEASE.jar:4.3.18.RELEASE]
... 58 common frames omitted

kvService仅从redis返回数据。它将Hash数据类型(https://redis.io/topics/data-types)解析为proto中定义的Hash对象。其中Hash-> category是hash的主键，而hash redis数据类型中的值将转换为proto中定义的KVPair。我无法显示所有源代码，因为它会调用其他系统并且源代码很长。

kvService返回有效的Hash对象，但是当我返回此Hash对象并且spring尝试将其转换为JSON时发生异常。

我的build.gradle中的重要依赖项：

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def versions = [
logback: '1.2.3',
owner: '1.0.10',
jackson: '2.9.6',

guava: '25.1-jre',
guice: '4.2.0',
grpc: '1.9.1',
protoc: '3.5.1',

redis: '2.9.0',
]

依赖项{

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compile group: 'ch.qos.logback', name: 'logback-classic', version: versions.logback
compile group: 'org.aeonbits.owner', name: 'owner', version: versions.owner

compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: versions.jackson
compile group: 'com.fasterxml.jackson.core', name: 'jackson-annotations', version: versions.jackson
compile group: 'com.fasterxml.jackson.dataformat', name: 'jackson-dataformat-yaml', version: versions.jackson

compile group: 'com.google.guava', name: 'guava', version: versions.guava
compile group: 'com.google.inject', name: 'guice', version: versions.guice
compile group: 'io.grpc', name: 'grpc-netty', version: versions.grpc
compile group: 'io.grpc', name: 'grpc-protobuf', version: versions.grpc
compile group: 'io.grpc', name: 'grpc-stub', version: versions.grpc
compile 'org.glassfish:javax.annotation:10.0-b28'

compile group: 'javax.xml.bind', name: 'jaxb-api', version: '2.2.1'
compile group: 'javax.activation', name: 'activation', version: '1.1.1'

compile group: 'redis.clients', name: 'jedis', version: versions.redis

}

正如您在我的protobuf定义中所看到的，它不是任何自引用。

有没有可能解决此问题的方法？