无法使用泛型与 Jackson 反序列化动态 json

Unable to deserialise dynamic json with Jackson using generics

我正在尝试使用 Jackson 在 Java 中解析 Debezium CDC 消息。但是我在进行反序列化时遇到了强制转换异常。我正在使用泛型,因为对象是动态的,并且会改变不同的 kafka 主题,因为每个 table 有不同的主题是 MySQL.

Json 输入

{"schema":{"type":"struct","fields":[{"type":"struct","fields":[{"type":"int32","optional":false,"field":"id"},{"type":"string","optional":false,"field":"first_name"},{"type":"string","optional":false,"field":"last_name"},{"type":"string","optional":false,"field":"email"}],"optional":true,"name":"dbserver1.inventory.customers.Value","field":"before"},{"type":"struct","fields":[{"type":"int32","optional":false,"field":"id"},{"type":"string","optional":false,"field":"first_name"},{"type":"string","optional":false,"field":"last_name"},{"type":"string","optional":false,"field":"email"}],"optional":true,"name":"dbserver1.inventory.customers.Value","field":"after"},{"type":"struct","fields":[{"type":"string","optional":false,"field":"version"},{"type":"string","optional":false,"field":"connector"},{"type":"string","optional":false,"field":"name"},{"type":"int64","optional":false,"field":"ts_ms"},{"type":"string","optional":true,"name":"io.debezium.data.Enum","version":1,"parameters":{"allowed":"true,last,false"},"default":"false","field":"snapshot"},{"type":"string","optional":false,"field":"db"},{"type":"string","optional":true,"field":"table"},{"type":"int64","optional":false,"field":"server_id"},{"type":"string","optional":true,"field":"gtid"},{"type":"string","optional":false,"field":"file"},{"type":"int64","optional":false,"field":"pos"},{"type":"int32","optional":false,"field":"row"},{"type":"int64","optional":true,"field":"thread"},{"type":"string","optional":true,"field":"query"}],"optional":false,"name":"io.debezium.connector.mysql.Source","field":"source"},{"type":"string","optional":false,"field":"op"},{"type":"int64","optional":true,"field":"ts_ms"},{"type":"struct","fields":[{"type":"string","optional":false,"field":"id"},{"type":"int64","optional":false,"field":"total_order"},{"type":"int64","optional":false,"field":"data_collection_order"}],"optional":true,"field":"transaction"}],"optional":false,"name":"dbserver1.inventory.customers.Envelope"},"payload":{"before":{"id":1004,"first_name":"Anne","last_name":"Kretchmar","email":"annek@noanswer.org"},"after":{"id":1004,"first_name":"Anne","last_name":"old and new","email":"annek@noanswer.org"},"source":{"version":"1.4.1.Final","connector":"mysql","name":"dbserver1","ts_ms":1614335758000,"snapshot":"false","db":"inventory","table":"customers","server_id":223344,"gtid":null,"file":"mysql-bin.000003","pos":2150,"row":0,"thread":2,"query":null},"op":"u","ts_ms":1614335758726,"transaction":null}}

根目录

@JsonIgnoreProperties(ignoreUnknown = true)
public class DebeziumCDCMessage<S,D> {
    
    private S schema;
    private DebeziumPayload<D>  payload;
    
    @JsonCreator
    DebeziumCDCMessage( @JsonProperty("schema") S _schema,
                        @JsonProperty("payload") DebeziumPayload<D>  _payload){
        this.schema=_schema;
        this.payload=_payload;
    }

    public S getSchema() {
        return schema;
    }

    public void setSchema(S schema) {
        this.schema = schema;
    }

    public DebeziumPayload<D> getPayload() {
        return payload;
    }

    public void setPayload(DebeziumPayload<D> payload) {
        this.payload = payload;
    }
    

}

DebeziumPayload Pojo

@JsonIgnoreProperties(ignoreUnknown = true)
public class DebeziumPayload<D> {

    private D before;
    private D after;
    private String op;
    private String ts_ms;
    private Object source;
    @JsonCreator
    DebeziumPayload(    @JsonProperty("before") D _before,
                        @JsonProperty("after") D _after,
                        @JsonProperty("op") String _op,
                        @JsonProperty("ts_ms") String _ts_ms,
                        @JsonProperty("source") Object _source
                         ){
        this.before=_before;
        this.after=_after; 
        this.op=_op;
        this.ts_ms=_ts_ms;
        this.setSource(_source);
    }

    public D getBefore() {
        return before;
    }

    public void setBefore(D before) {
        this.before = before;
    }

    public D getAfter() {
        return after;
    }

    public void setAfter(D after) {
        this.after = after;
    }

    public String getOp() {
        return op;
    }

    public void setOp(String op) {
        this.op = op;
    }

    public String getTs_ms() {
        return ts_ms;
    }

    public void setTs_ms(String ts_ms) {
        this.ts_ms = ts_ms;
    }

    public Object getSource() {
        return source;
    }

    public void setSource(Object source) {
        this.source = source;
    }
    
    
}

Pojo 之前和之后(仅适用于共享 JSON,每个主题将有不同的目标对象)

@JsonIgnoreProperties(ignoreUnknown = true)
public class Customer {

    private Integer id;
    private String first_name;
    private String last_name;
    private String email;
    
    @JsonCreator
    Customer(@JsonProperty("id") Integer _id,
            @JsonProperty("first_name") String _first_name,
            @JsonProperty("last_name") String _last_name,
            @JsonProperty("email") String _email){
        this.id=_id;
        this.first_name=_first_name;
        this.last_name=_last_name;
        this.email=_email;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getFirst_name() {
        return first_name;
    }

    public void setFirst_name(String first_name) {
        this.first_name = first_name;
    }

    public String getLast_name() {
        return last_name;
    }

    public void setLast_name(String last_name) {
        this.last_name = last_name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
    
    
}

最终反序列化代码

@Service
public class CustomersCDCConsumer {

    @SuppressWarnings("unchecked")
    @KafkaListener(topics = "dbserver1.inventory.customers", groupId = "group_id")
    public void listenGroupFoo(String message) {
        try {
            DebeziumCDCMessage<Object,Customer> respo=new ObjectMapper().readValue(message, DebeziumCDCMessage.class);
            DebeziumPayload<Customer> customer=respo.getPayload();
            System.out.println("data as recieved="+customer.getAfter().getLast_name());
        } catch (JsonMappingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (JsonProcessingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

我在 运行 代码时遇到错误。

org.springframework.kafka.listener.ListenerExecutionFailedException: Listener method 'public void com.licious.kafa2sfwrapper.kafkacosumers.CustomersCDCConsumer.listenGroupFoo(java.lang.String)' threw exception; nested exception is java.lang.ClassCastException: class java.util.LinkedHashMap cannot be cast to class com.licious.kafa2sfwrapper.model.tables.Customer (java.util.LinkedHashMap is in module java.base of loader 'bootstrap'; com.licious.kafa2sfwrapper.model.tables.Customer is in unnamed module of loader org.springframework.boot.loader.LaunchedURLClassLoader @5010be6); nested exception is java.lang.ClassCastException: class java.util.LinkedHashMap cannot be cast to class com.licious.kafa2sfwrapper.model.tables.Customer (java.util.LinkedHashMap is in module java.base of loader 'bootstrap'; com.licious.kafa2sfwrapper.model.tables.Customer is in unnamed module of loader org.springframework.boot.loader.LaunchedURLClassLoader @5010be6)
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.decorateException(KafkaMessageListenerContainer.java:2114) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeErrorHandler(KafkaMessageListenerContainer.java:2102) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeRecordListener(KafkaMessageListenerContainer.java:2001) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeWithRecords(KafkaMessageListenerContainer.java:1928) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeRecordListener(KafkaMessageListenerContainer.java:1814) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeListener(KafkaMessageListenerContainer.java:1531) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.pollAndInvoke(KafkaMessageListenerContainer.java:1178) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.run(KafkaMessageListenerContainer.java:1075) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) ~[na:na]
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) ~[na:na]
    at java.base/java.lang.Thread.run(Thread.java:832) ~[na:na]
Caused by: java.lang.ClassCastException: class java.util.LinkedHashMap cannot be cast to class com.licious.kafa2sfwrapper.model.tables.Customer (java.util.LinkedHashMap is in module java.base of loader 'bootstrap'; com.licious.kafa2sfwrapper.model.tables.Customer is in unnamed module of loader org.springframework.boot.loader.LaunchedURLClassLoader @5010be6)
    at com.licious.kafa2sfwrapper.kafkacosumers.CustomersCDCConsumer.listenGroupFoo(CustomersCDCConsumer.java:22) ~[classes!/:0.0.1-SNAPSHOT]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:564) ~[na:na]
    at org.springframework.messaging.handler.invocation.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:171) ~[spring-messaging-5.3.4.jar!/:5.3.4]
    at org.springframework.messaging.handler.invocation.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:120) ~[spring-messaging-5.3.4.jar!/:5.3.4]
    at org.springframework.kafka.listener.adapter.HandlerAdapter.invoke(HandlerAdapter.java:48) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.adapter.MessagingMessageListenerAdapter.invokeHandler(MessagingMessageListenerAdapter.java:330) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.adapter.RecordMessagingMessageListenerAdapter.onMessage(RecordMessagingMessageListenerAdapter.java:86) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.adapter.RecordMessagingMessageListenerAdapter.onMessage(RecordMessagingMessageListenerAdapter.java:51) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeOnMessage(KafkaMessageListenerContainer.java:2069) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.invokeOnMessage(KafkaMessageListenerContainer.java:2051) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    at org.springframework.kafka.listener.KafkaMessageListenerContainer$ListenerConsumer.doInvokeRecordListener(KafkaMessageListenerContainer.java:1988) ~[spring-kafka-2.6.6.jar!/:2.6.6]
    ... 8 common frames omitted

而不是通用数据类型,

我建议您创建一个基础 class,其中包含公共字段和多个用于不同消息的子 pojo classes。

并在 class 基础上添加:

@JsonSubTypes

注解并指定里面所有的子classes,这样jackson会找到合适的子时间反序列化json.

您可以在此处找到简单示例:https://www.tutorialspoint.com/jackson_annotations/jackson_annotations_jsonsubtypes.htm

好吧,我已经很接近了,只需要告诉 Jackson 通用目标的类型信息 class。基本上不得不更换

 DebeziumCDCMessage<Object,Customer> respo=new ObjectMapper().readValue(message, DebeziumCDCMessage.class);

DebeziumCDCMessage<Object,Customer> respo=new ObjectMapper().readValue(message, new TypeReference<DebeziumCDCMessage<Object,Customer>>() {});