Java REST API: Can not deserialize instance of Object out of START_ARRAY token

Question

I have a REST API written using Java and Jersey. Below is the related code of the WEB API.

 @GET
    @Path("/getAllPhase1")
    @Produces(MediaType.APPLICATION_JSON)  
    public List<Phase1Bean> getAllPhase1()
    {
        Phase1Interface phase1Interface = new Phase1Impl();
        List<Phase1Bean> allPhase1 = phase1Interface.getAllPhase1();
        return allPhase1;
    }

In my web application's REST client, I wrote the below code.

Client client = ClientBuilder.newClient();

        client.target("http://localhost:8080/xxx/rest")
            .path("phase1/getAllPhase1")
            .request(MediaType.APPLICATION_JSON)
            .get(Phase1Bean.class);

Unfortunatly this generates the below error

Exception in thread "main" javax.ws.rs.client.ResponseProcessingException: com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of bean.Phase1Bean out of START_ARRAY token
 at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream@2fb3536e; line: 1, column: 1]
    at org.glassfish.jersey.client.JerseyInvocation.translate(JerseyInvocation.java:806)
    at org.glassfish.jersey.client.JerseyInvocation.access$700(JerseyInvocation.java:92)
    at org.glassfish.jersey.client.JerseyInvocation$2.call(JerseyInvocation.java:700)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:228)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:444)
    at org.glassfish.jersey.client.JerseyInvocation.invoke(JerseyInvocation.java:696)
    at org.glassfish.jersey.client.JerseyInvocation$Builder.method(JerseyInvocation.java:420)
    at org.glassfish.jersey.client.JerseyInvocation$Builder.get(JerseyInvocation.java:316)
    at JerseyClientGet.main(JerseyClientGet.java:32)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of bean.Phase1Bean out of START_ARRAY token
 at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream@2fb3536e; line: 1, column: 1]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:164)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:691)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:685)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromArray(BeanDeserializerBase.java:1215)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:151)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:126)
    at com.fasterxml.jackson.databind.ObjectReader._bind(ObjectReader.java:1233)
    at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:677)
    at com.fasterxml.jackson.jaxrs.base.ProviderBase.readFrom(ProviderBase.java:777)
    at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$TerminalReaderInterceptor.invokeReadFrom(ReaderInterceptorExecutor.java:256)
    at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$TerminalReaderInterceptor.aroundReadFrom(ReaderInterceptorExecutor.java:235)
    at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor.proceed(ReaderInterceptorExecutor.java:155)
    at org.glassfish.jersey.message.internal.MessageBodyFactory.readFrom(MessageBodyFactory.java:1085)
    at org.glassfish.jersey.message.internal.InboundMessageContext.readEntity(InboundMessageContext.java:874)
    at org.glassfish.jersey.message.internal.InboundMessageContext.readEntity(InboundMessageContext.java:808)
    at org.glassfish.jersey.client.ClientResponse.readEntity(ClientResponse.java:326)
    at org.glassfish.jersey.client.JerseyInvocation.translate(JerseyInvocation.java:803)
    ... 10 more
Java Result: 1

How can I solve this issue?

Matt Pearce · Accepted Answer · 2016-06-11 10:45:14Z

2

Your GET method is returning a List, rather than a single Phase1Bean object - hence the "START_ARRAY" token mentioned in the error message. You can change your client .get() method to receive a List, and then extract the Phase1Bean items from there.

client.target("http://localhost:8080/xxx/rest")
        .path("phase1/getAllPhase1")
        .request(MediaType.APPLICATION_JSON)
        .get(new GenericType<List<Phase1Bean>>(){});

An alternative would be to wrap your list in another object (Phase1BeanResponse, for example), containing the list and possibly other metadata related to the items.

edited Jun 11, 2016 at 10:45

answered Jun 11, 2016 at 9:30

Matt Pearce

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1 Comment

Paul Samsotha Over a year ago

You should instead use get(new GenericType<List<Phase1Bean>>(){});. What you are doing will give you a raw List, which will be populated with LinkedHashMaps, instead of Phase1Beans

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