Mapping JSON to Java POJO Class with Jackson Mapper

Question

Trying to map JSON data (see data.json below) to a Java POJO Class using Jackson Mapper. Getting the following error during de-serialization. I am not sure what it means. Please advise.

org.springframework.http.converter.HttpMessageNotReadableException: Could not read JSON: Can not deserialize instance of org.springframework.social.test.api.impl.AccountList out of START_OBJECT token
 at [Source: java.io.BufferedInputStream@c3020c; line: 2, column: 3]; nested exception is org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of org.springframework.social.test.api.impl.AccountList out of START_OBJECT token
 at [Source: java.io.BufferedInputStream@c3020c; line: 2, column: 3]
    at org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.readJavaType(MappingJacksonHttpMessageConverter.java:169)
    at org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.read(MappingJacksonHttpMessageConverter.java:161)
    at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:94)
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:491)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:460)
    at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:228)
    at org.springframework.social.test.api.impl.AccountTemplate.getAccounts(AccountTemplate.java:44)
    at org.springframework.social.test.api.impl.AccountTemplateTest.getAccounts_current_user(AccountTemplateTest.java:24)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:601)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of org.springframework.social.test.api.impl.AccountList out of START_OBJECT token
 at [Source: java.io.BufferedInputStream@c3020c; line: 2, column: 3]
    at org.codehaus.jackson.map.JsonMappingException.from(JsonMappingException.java:163)
    at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:219)
    at org.codehaus.jackson.map.deser.StdDeserializationContext.mappingException(StdDeserializationContext.java:212)
    at org.codehaus.jackson.map.deser.std.CollectionDeserializer.handleNonArray(CollectionDeserializer.java:246)
    at org.codehaus.jackson.map.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:204)
    at org.codehaus.jackson.map.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:194)
    at org.codehaus.jackson.map.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:30)
    at org.codehaus.jackson.map.ObjectMapper._unwrapAndDeserialize(ObjectMapper.java:2802)
    at org.codehaus.jackson.map.ObjectMapper._readMapAndClose(ObjectMapper.java:2730)
    at org.codehaus.jackson.map.ObjectMapper.readValue(ObjectMapper.java:1923)
    at org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.readJavaType(MappingJacksonHttpMessageConverter.java:166)
    ... 31 more


JUnit Test Class

@Test
    public void getAccounts() {
        mockServer.expect(requestTo("api"))
        .andExpect(method(GET))
        .andExpect(header("Authorization", "Bearer someAccessToken"))
        .andRespond(withSuccess(jsonResource("data.json"), MediaType.APPLICATION_JSON));

        List<Account> accounts = tester.operations().getAccounts();
        assertEquals(4, accounts.size());

        Account account = accounts.get(0);

        assertEquals(new Long(9880), account.getId());
        assertEquals("My Account", account.getAlias());
        assertEquals("FULL", account.getPermissions());
        assertEquals("USER", account.getType());
        assertEquals(new Character('U'),account.getStatus());

        Account account1 = accounts.get(1);
        assertEquals(new Long(9887),account1.getId());
        assertEquals("Account",account1.getAlias());
        assertEquals("FULL",account1.getPermissions());
        assertEquals("USER",account1.getType());
        assertEquals(new Character('U'),account1.getStatus());

        Account account2 = accounts.get(2);
        assertEquals(new Long(00008),account2.getId());
        assertEquals("Mom's Account",account2.getAlias());
        assertEquals("FULL",account2.getPermissions());
        assertEquals("USER",account2.getType());
        assertEquals(new Character('U'),account2.getStatus());

        Account account3 = accounts.get(3);
        assertEquals(new Long(00009),account3.getId());
        assertEquals("Steph's Account",account3.getAlias());
        assertEquals("FULL",account3.getPermissions());
        assertEquals("USER",account3.getType());
        assertEquals(new Character('U'),account3.getStatus());

//The method used to configure ObjectMapper

    @Override
    protected MappingJacksonHttpMessageConverter getJsonMessageConverter() {
            MappingJacksonHttpMessageConverter converter = super.getJsonMessageConverter();
            objectMapper = new ObjectMapper();
            //UnComment if root element is not required
            objectMapper.enable(DeserializationConfig.Feature.UNWRAP_ROOT_VALUE);
            objectMapper.registerModule(new TestModule());
            converter.setObjectMapper(objectMapper);
            return converter;
    }

The above error goes away and It works if the following 3 lines are removed from data.json

The lines causing problem.

{
  "accounts": {
    "account":



Entire data json File

{
  "accounts": {
    "account": [
      {
        "id": "9880,
        "alias": "My Account",
        "permissions": "FULL",
        "type": "USER",
        "status": "U"
      },
      {
        "id": "9887",
        "alias": "Account",
        "permissions": "FULL",
        "type": "USER",
        "status": "U"
      },
      {
        "id": "00008",
        "alias": "Mom's Account",
        "permissions": "FULL",
        "type": "USER",
        "status": "U"
      },
      {
        "id": "00009",
        "alias": "Steph's Account",
        "permissions": "FULL",
        "type": "USER",
        "status": "U"
      }
    ]
  }
}

jon hanson · Accepted Answer · 2013-02-23 10:50:59Z

1

Jackson is attempting to deserialise the JSON into the AccountList type. I'm guessing this type maps to an array in JSON, so Jackson is expecting a '[' next in the stream, however your JSON begin with a '{' (aka the START_OBJECT token).

Basically your JSON doesn't match the type you're trying to deserialise into. For it to match I'd expect the target type to be something like:

class SomeClassName {
    AccountList accounts;
    [...]
}

edited Feb 23, 2013 at 10:50

answered Feb 22, 2013 at 21:40

jon hanson

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3 Comments

user1377822 Over a year ago

AccountList Class is a sub class of ArrayList e.g. AccountList extends ArrayList<Account>. Maybe this is the wrong approach for the given json data structure?

jon hanson Over a year ago

Then it will get serialised as a JSON array, but your JSON is an object at the outer level, not an array. The JSON needs to be serialised into a class which has an accounts field. I've updated my answer.

user1377822 Over a year ago

class AccountList{ private List<Account> account; /** Accessor **/ is the solution.

user1377822 · Accepted Answer · 2013-02-23 11:06:34Z

0

The solution is:

@JsonRootName(value="accounts")
public class AccountList implements Serializable{

    private static final long serialVersionUID = 1L;
private ArrayList<Account> account;

public AccountList(ArrayList<Account> account){
    this.account = account;
}
public ArrayList<Account> getAccount() {
    return account;
}

public void setAccount(ArrayList<Account> account) {
    this.account = account;
}

answered Feb 23, 2013 at 11:06

user1377822

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