java在springboot中将protobuf作为JSON发送

2 年，1 月 Questions & Answers 5448

我使用protobufs来定义这个具体的定义

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

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

我想将它作为JSON与我的spring boot应用程序一起发送。我已将此包添加到我的gradle依赖项中：

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

当我尝试使用以下代码输出哈希生成的对象时：

@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;
    }
}

它抛出了一个终极例外：

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。它将散列数据类型（https://redis.io/topics/data-types）解析为proto中定义的散列对象。其中哈希->；category是hash的主键，hash redis数据类型中的值被转换为proto中定义的KVPair。我不能显示所有的源代码，因为它调用其他系统，并且源代码很长

kvService返回有效的散列对象，但当我返回此散列对象并spring尝试将其转换为JSON时，会发生异常

我的构建中的重要依赖项。格拉德尔：

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',
]

依赖关系{

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中所看到的，它的定义不是任何自引用

有什么可能的方法来解决这个问题吗

共 (3) 个答案

# 1 楼答案
要将protobuf对象转换为JSON，应该使用包com.google.protobuf.util.JsonFormat中的以下类作为：
```
JsonFormat.printer().print()
```

# 2 楼答案

如果您使用的是SpringWebFlux并试图produces{}，那么您可以这样做，以使其适用于所有返回protobuf消息的映射类型：

@Configuration
@EnableWebFlux
public class WebConfig implements WebFluxConfigurer {

@Override
public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
    configurer.defaultCodecs().jackson2JsonEncoder(
        new Jackson2JsonEncoder(Jackson2ObjectMapperBuilder.json().serializerByType(
                Message.class, new JsonSerializer<Message>() {
                    @Override
                    public void serialize(Message value, JsonGenerator gen, SerializerProvider serializers) throws IOException {
                        String str = JsonFormat.printer().omittingInsignificantWhitespace().print(value);
                        gen.writeRawValue(str);
                    }
                }
        ).build())
    );
}

# 3 楼答案

类UnknownFieldSet（通过生成的方法Hash.getUnknownFields()到达）包含getter getDefaultInstanceForType()，它返回UnknownFieldSet的单例实例。此单例实例在getDefaultInstanceForType()中引用自身，Jackson databind无法自动处理此问题（请参见下面的edit2）

您可能希望使用来自com.google.protobuf:protobuf-java-util的JsonFormat，它使用canonical encoding而不是Jackson

祝你好运

编辑>；春天有ProtobufJsonFormatHttpMessageConverter

编辑部2>；当然，您可以使用Mix-in Annotations处理这种情况，但IMHO JsonFormat绝对是一种解决方法

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java在springboot中将protobuf作为JSON发送

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