KafkaException：無法實例化類JsonDeserializer

Question

我試圖啓動與Kafka客戶端的彈簧啓動應用程序以下this reference guide，我得到下面的錯誤。
你能否提出建議如何解決？

@Bean 
public Map<String, Object> consumerConfig() { 
    final HashMap<String, Object> result = new HashMap<>(); 
    result.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, env.getProperty("spring.kafka.bootstrap.servers")); 
    result.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, LongDeserializer.class); 
    result.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, JsonDeserializer.class); 
    return result; 
} 

@Bean 
public ConsumerFactory<Long, String> consumerFactory() { 
    return new DefaultKafkaConsumerFactory<>(consumerConfig()); 
} 

@Bean 
ConcurrentKafkaListenerContainerFactory<Long, String> kafkaListenerContainerFactory() { 
    ConcurrentKafkaListenerContainerFactory<Long, String> containerFactory = new ConcurrentKafkaListenerContainerFactory<>(); 
    containerFactory.setConsumerFactory(consumerFactory()); 
    containerFactory.setConcurrency(3); 
    containerFactory.getContainerProperties().setPollTimeout(3000); 
    return containerFactory; 
} 

-

org.springframework.context.ApplicationContextException: Failed to start bean 'org.springframework.kafka.config.internalKafkaListenerEndpointRegistry'; nested exception is org.apache.kafka.common.KafkaException: Failed to construct kafka consumer 
    at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:176) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:51) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:346) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:149) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:112) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:879) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:545) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:737) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE] 
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:370) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE] 
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:314) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE] 
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1162) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE] 
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1151) [spring-boot-1.5.1.RELEASE.jar:1.5.1.RELEASE] 
    at com.ubs.wma.bmss.BmssConsumerApp.main(BmssConsumerApp.java:12) [classes/:na] 
Caused by: org.apache.kafka.common.KafkaException: Failed to construct kafka consumer 
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:703) ~[kafka-clients-0.10.1.1.jar:na] 
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:553) ~[kafka-clients-0.10.1.1.jar:na] 
    at org.springframework.kafka.core.DefaultKafkaConsumerFactory.createKafkaConsumer(DefaultKafkaConsumerFactory.java:73) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.core.DefaultKafkaConsumerFactory.createConsumer(DefaultKafkaConsumerFactory.java:69) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.<init>(KafkaMessageListenerContainer.java:305) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.<init>(KafkaMessageListenerContainer.java:230) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.listener.KafkaMessageListenerContainer.doStart(KafkaMessageListenerContainer.java:180) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.listener.AbstractMessageListenerContainer.start(AbstractMessageListenerContainer.java:202) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.listener.ConcurrentMessageListenerContainer.doStart(ConcurrentMessageListenerContainer.java:124) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.listener.AbstractMessageListenerContainer.start(AbstractMessageListenerContainer.java:202) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.config.KafkaListenerEndpointRegistry.startIfNecessary(KafkaListenerEndpointRegistry.java:287) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.kafka.config.KafkaListenerEndpointRegistry.start(KafkaListenerEndpointRegistry.java:236) ~[spring-kafka-1.1.2.RELEASE.jar:na] 
    at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:173) ~[spring-context-4.3.6.RELEASE.jar:4.3.6.RELEASE] 
    ... 12 common frames omitted 
Caused by: org.apache.kafka.common.KafkaException: Could not instantiate class org.springframework.kafka.support.serializer.JsonDeserializer 
    at org.apache.kafka.common.utils.Utils.newInstance(Utils.java:316) ~[kafka-clients-0.10.1.1.jar:na] 
    at org.apache.kafka.common.config.AbstractConfig.getConfiguredInstance(AbstractConfig.java:203) ~[kafka-clients-0.10.1.1.jar:na] 
    at org.apache.kafka.clients.consumer.KafkaConsumer.<init>(KafkaConsumer.java:632) ~[kafka-clients-0.10.1.1.jar:na] 
    ... 24 common frames omitted 
Caused by: java.lang.IllegalAccessException: Class org.apache.kafka.common.utils.Utils can not access a member of class org.springframework.kafka.support.serializer.JsonDeserializer with modifiers "protected" 
    at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:102) ~[na:1.8.0_121] 
    at java.lang.Class.newInstance(Class.java:436) ~[na:1.8.0_121] 
    at org.apache.kafka.common.utils.Utils.newInstance(Utils.java:314) ~[kafka-clients-0.10.1.1.jar:na] 
    ... 26 common frames omitted 

Answer 1

根據該文件，我們有：

對於較複雜或特殊情況下，KafkaConsumer，因此KafkaProducer，提供重載構造函數接受(De)Serializer實例分別爲鍵和/或值。

爲了符合此API，DefaultKafkaProducerFactory和DefaultKafkaConsumerFactory也提供了屬性以允許將自定義(De)Serializer注入到目標Producer/Consumer。

並進一步阿帕奇卡夫卡的JavaDoc：

/** 
* A producer is instantiated by providing a set of key-value pairs as configuration, a key and a value {@link Serializer}. 
* Valid configuration strings are documented <a href="http://kafka.apache.org/documentation.html#producerconfigs">here</a>. 
* Values can be either strings or Objects of the appropriate type (for example a numeric configuration would accept 
* either the string "42" or the integer 42). 
* @param configs The producer configs 
* @param keySerializer The serializer for key that implements {@link Serializer}. The configure() method won't be 
*      called in the producer when the serializer is passed in directly. 
* @param valueSerializer The serializer for value that implements {@link Serializer}. The configure() method won't 
*       be called in the producer when the serializer is passed in directly. 
*/ 
public KafkaProducer(Map<String, Object> configs, Serializer<K> keySerializer, Serializer<V> valueSerializer) { 

所以，你需要的是這樣的：

@Bean 
public ConsumerFactory<Long, String> consumerFactory() { 
    return new DefaultKafkaConsumerFactory<>(consumerConfig(), null, new JsonDeserializer(Foo.class)); 
} 

是JsonDeserializer無法通過反射來實例化的問題，因爲它需要要反序列化的特定類型。