Cannot deserialize instance of object out of START_ARRAY token in Spring 3 REST Webservice

Question

I am making use of this cool thing Spring offers: Spring RESTWebService (Version of spring is 3). If I access the URL from browser I can see the JSON response, but from a Client endpoint (Android application) iIreceive this error message:

Caused by: org.springframework.web.client.ResourceAccessException: 
    I/O error: Can not deserialize instance of MyObject out of START_ARRAY token
  at [Source: org.apache.http.conn.EofSensorInputStream@4076e940; line: 1, 
    column: 1]; nested exception is org.codehaus.jackson.map.JsonMappingException: 
    Can not deserialize instance of MyObject  out of START_ARRAY token
  at [Source: org.apache.http.conn.EofSensorInputStream@4076e940; line: 1, column: 1]
   at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:466)
   at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:414)
   at org.springframework.web.client.RestTemplate.getForEntity(RestTemplate.java:234)
   at com.be.android.locateconsultants.resources.AsyncTaskRESTServiceCaller.doInBackground(AsyncTaskRESTServiceCaller.java:43)
   at com.be.android.locateconsultants.resources.AsyncTaskRESTServiceCaller.doInBackground(AsyncTaskRESTServiceCaller.java:1)
   at android.os.AsyncTask$2.call(AsyncTask.java:252)
   at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
   ... 4 more

 Caused by: org.codehaus.jackson.map.JsonMappingException: Can not deserialize 
    instance of MyObject  out of START_ARRAY token
  at [Source: org.apache.http.conn.EofSensorInputStream@4076e940; line: 1, column: 1]
   at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:198)
   at org.codehaus.jackson.map.deser.BeanDeserializer.deserializeUsingCreator(BeanDeserializer.java:565)
   at org.codehaus.jackson.map.deser.BeanDeserializer.deserialize(BeanDeserializer.java:365)
   at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2395)
   at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1655)
   at org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.readInternal(MappingJacksonHttpMessageConverter.java:135)
   at org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:154)
   at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:74)
   at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:632)
   at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:618)
   at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:459)
   ... 10 more

MyObject structure is the same as the one from the server side application.

I have tried to request the server like this:

final String url = ".....";
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<Consultant> responseEntity = restTemplate.getForEntity(
            url, Consultant.class);

Or like this:

HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
HttpEntity<String> entity = new HttpEntity<String>(headers);
ResponseEntity<MyObject> response = restTemplate
            .exchange("....",HttpMethod.GET, entity, MyObject.class);
System.out.println("RESPONSE: " + response.getBody());

But still the same error as above. Can't figure out what I am missing at this point, any idea or hints would be great. Thank you.

What is the json structure, how MyObject looks. Not enough information. The only guess I see is that you're getting array from server and trying to map it to MyObject. — pawelzieba, May 23 '12 at 12:34
in the client: `public class Consultant { private int id; private String firstName; private String lastName; private String phoneNumber; private String jobName; private String workAddress; private Date created; private String email; getters and setters } ` — Gabriela Radu, May 23 '12 at 12:43
and the response json is this: `[{"id":1,"firstName":"first name","lastName":"last name","jobName":"programmer","created":1328133600000,"email":"test@yahoo.com","workAddress":"test","phoneNumber":"0000"},{...},{..}]` — Gabriela Radu, May 23 '12 at 12:46
Yes, then you should map it to List rather than to Consultant.class. — pawelzieba, May 23 '12 at 13:09
You are correct. Thank you. If you don't write the last comment as an answer I cannot tag your response as the correct one :D — Gabriela Radu, May 23 '12 at 14:20

pawelzieba · Answer 1 · 2012-05-23T15:36:00.463

23

You should map it to List<Consultant> rather than to Consultant.class.

edited May 23 '12 at 15:36

answered May 23 '12 at 15:08

pawelzieba

16,082
3
46
72

The tip helped me in my case also – Damilola Aug 21 '14 at 10:40
2

Could you clarify this? I get syntax error when I try List, instead I had to use MyObject[].class – otgw Oct 09 '14 at 17:45
getting syntex error in this rest.getForObject("http://localhost:8081/RestCRUDWithoutDao/country/allCountries", List); – Rajan Chauhan Mar 21 '18 at 14:23

score 18 · Accepted Answer · answered Feb 11 '15 at 08:27

18

Solution in a similar situation was to map to Consultant[].class This applies if you try to deserialize a JSON array of your mapped objects.

answered Feb 11 '15 at 08:27

Ahto Luuri

238
3
12

score 9 · Answer 3 · edited May 12 '16 at 09:10

9

This is related to Jackson and the way you're attempting to deserialize and initialize a container from an array.

While my usage context is a bit different, this may help some who get here from searching for Jackson-specific deserialization errors.

I had to do it like this:

List<Consultant> consultants = Arrays.asList(
    mapper.readValue(myJson.toString(), Consultants[].class)
);

edited May 12 '16 at 09:10

JJD

50,076
60
203
339

answered Aug 14 '15 at 15:13

NathanChristie

2,374
21
20

score 0 · Answer 4 · answered Jan 09 '18 at 01:21

a file foo.json contains a batch of data like this:

[{"A":"TYMH","B":"datab","C":"DLJQ","D":"datad"}, {"A":"TYMH","B":"datab","C":"DLJQ","D":"datad"}]

The following statement gives you an ArrayList of LinkedHashMap, where A B C D are the keys.

List list = mapper.readValue(new File("D:\\...\\foo.json"), List.class);

WesternGun · Answer 5 · 2022-12-31T16:32:21.850

If you want to serialize an array from a json like:

[
  {"foo":"bar"}, {"foo1":"bar1"}
]

You must configure the value deserializer to accept an array in the method signature.

    @Bean
    public ConsumerFactory<String, DTO[]> consumerFactory() {
        Map<String, Object> props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
                bootstrapAddress);
        props.put(ConsumerConfig.GROUP_ID_CONFIG,
                groupId);
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "latest");
        props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, true);
        props.put(ConsumerConfig.ALLOW_AUTO_CREATE_TOPICS_CONFIG, true);
        return new DefaultKafkaConsumerFactory<>(props,
                new StringDeserializer(),
                new JsonDeserializer<>(DTO[].class));
    }

    @Bean
    public ConcurrentKafkaListenerContainerFactory<String, DTO[]>
    kafkaListenerContainerFactory() {
        ConcurrentKafkaListenerContainerFactory<String, DTO[]> factory =
                new ConcurrentKafkaListenerContainerFactory<>();
        factory.setConsumerFactory(consumerFactory());
        return factory;
    }

And in your consumer:

@KafkaListener(topics = "foo-topic", groupId = "foo-group")
void listen(DTO[] dtos) {

}

No type reference or other things needed. I think underneath, ObjectArrayDeserializer is used.

Note that in this way, you will need to put all configs into java code, and (maybe) all configs by YAML will not work for consumer. I am not sure but you can try to combine code config and YAML config.

Cannot deserialize instance of object out of START_ARRAY token in Spring 3 REST Webservice

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