无法将消息从 Json 字符串转换为对象。 类转换异常

Question

I'm using SpringXD where I have a Rabbit Source with outputType application/json. Next module receive it and convert it to Java Object. RabbitMq is my transport bus.

My configuration is pretty standard like:

@EnableIntegration
@ImportResource("classpath:some.xml")
@ComponentScan(basePackages = "com.something")
public class MyConfigClass {

    @Autowired
    private Jackson2JsonObjectMapper jackson2JsonObjectMapper;  


    @Bean
    public MessageChannel input() {
        return new DirectChannel();
    }

    @Bean
    public MessageChannel inputObject() {
        return new DirectChannel();
    }  

    @Bean
    public MessageChannel output() {
        return new DirectChannel();
    }

    @Bean
    public MessageChannel outputObject() {
        return new DirectChannel();
    }

    @Bean
    public Jackson2JsonObjectMapper objectMapper() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new JodaModule());
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        return new Jackson2JsonObjectMapper(mapper);
    }

    @Bean
    @Transformer(inputChannel = "input", outputChannel = "inputObject")
    public JsonToObjectTransformer jsonToObjectTransformer() {
        return new JsonToObjectTransformer(someTargetClass.class, jackson2JsonObjectMapper);
    }

    @Bean
    @Transformer(inputChannel = "outputObject", outputChannel = "output")
    public ObjectToJsonTransformer objectToJsonTransformer() {
        return new ObjectToJsonTransformer(jackson2JsonObjectMapper);
    }
}

Then in another class I have something like this:

public class AnotherClass {


    @Transformer(inputChannel = "inputObject", outputChannel = "outputObject")
    public Message<someTargetClass> transform(Message<someTargetClass> incoming) {

        //Here I'm getting Caused by: org.springframework.messaging.MessageHandlingException: nested exception is java.lang.ClassCastException: java.lang.String cannot be cast to com.whatever.someTargetClass

        SomeTargetClass messagePayload = incoming.getPayload();
    }
} 

So the flow is input->inputObject-outputObject->output

But somehow I'm getting a classCastException as Input payload coming as a String and not as a Java Object (someTargetClass type).

 Caused by: org.springframework.messaging.MessageHandlingException: nested exception is java.lang.ClassCastException: java.lang.String cannot be cast to com.whatever.someTargetClass at org.springframework.integration.handler.MethodInvokingMessageProcessor.processMessage(MethodInvokingMessageProcessor.java:96) ~[spring-integration-core-4.2.5.RELEASE.jar:na] at org.springframework.integration.transformer.AbstractMessageProcessingTransformer.transform(AbstractMessageProcessingTransformer.java:90) ~[spring-integration-core-4.2.5.RELEASE.jar:na] at org.springframework.integration.transformer.MessageTransformingHandler.handleRequestMessage(MessageTransformingHandler.java:89) ~[spring-integration-core-4.2.5.RELEASE.jar:na] ... 52 common frames omitted

So, Somehow looks like the flow through the channels is not working properly. What am I missing?

Answer 1

My theory is that the source is producing a string, the fact that is json is not being transmitted, when the transformer receives the string can not convert it to SomeTargetClass. If this is true, this should fix it:

In the transform method change:

SomeTargetClass messagePayload = incoming.getPayload();

to :

String jsonString = incoming.getPayload();
SomeTargetClass messagePayload = (SomeTargetClass) JSON.std.beanFrom(SomeTargetClass.class, jsonString);

This is using Jackson Jr, but I am sure you can find the replacement in Jackson.