Jackson JsonParser无法读取Json中的数组

Question

I have a Json Structure something like this

{
"name" : "abcd",
"details" : [{"city":"string", "zipcode":"integer"}],

"name" : "qwert",
"details" : [{"address":"long", "state":"string"}]
}

And my java code looks like below

public class JsonTest {

    public static void main(String[] args) throws JsonParseException, IOException {

        JsonFactory jf = new JsonFactory(); 
        JsonParser jp = jf.createParser(new File("C:\\sample.json"));

        while (jp.nextToken() != JsonToken.END_OBJECT)
        {
            String jsonField = jp.getCurrentName();

            if ("name".equalsIgnoreCase(jsonField))
            {
                jp.nextToken();
                System.out.println(jp.getText());
            }

            if ("details".equalsIgnoreCase(jsonField))
            {
                jp.nextToken();
                while (jp.nextToken() != JsonToken.END_ARRAY)
                {
                    jp.nextToken();
                    String field = jp.getText();
                    System.out.println(field);
                }
            }
        }           
    }

}

All am trying to do is parse the whole json token by token and get the text. But the line while (jp.nextToken() != JsonToken.END_OBJECT) fails when it encounters a '}' in the array. Am just stuck here since yesterday and experimenting with several other tricks but nothing works out. Do we have another way doing this? Is my JSON structure looks okay? Please tell me where am going wrong. Thanks!

Answer 1

First of all:

[Doe]s my JSON structure look[s] okay?

Yes and no. while your JSON is legal, you are going to have a problem because of duplicate keys:

{
    "name": "xxx",
    "name": "yyy"
}

The behaviour of a JSON parser in this event is unpredictable, even RFC 7159 says so (yes, RFC 4627 has been superseded). Unfortunately, duplicate keys are still not forbidden.

So, it is legal, but not sane. Use an array instead:

[ { "name": "xxx", "details": "whatever" }, "etc" ]

This aside, reading JSON with Jackson is done as this:

final ObjectMapper mapper = new ObjectMapper();
final JsonNode node = mapper.readTree(yourFileHere);

You can then use the full power of JsonNode .

Answer 2

You cannot have fields with the same name in a json, well you can but it could not be parsed as in your case.

I assume you have an array of users with name and details fileds for each user.

Here is a candidate Java class corresponding to your User class :

public class TestUser implements Serializable {
    String name;
    List<Map<String, String>> details = new ArrayList<Map<String, String>>();

    TestUser() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Map<String, String>> getDetails() {
        return details;
    }

    public void setDetails(List<Map<String, String>> details) {
        this.details = details;
    }
}

with reverse engineering lets see how is a list of users are de-serialized;

public static void main(String[] args) throws IOException {
    List<TestUser> testUsers = new ArrayList<TestUser>();

    TestUser testUser1 = new TestUser();
    testUser1.name = "abcd";
    HashMap<String, String> detailsHashMap = new HashMap<String, String>();
    detailsHashMap.put("city", "string");
    detailsHashMap.put("zipcode", "integer");
    testUser1.details.add(detailsHashMap);
    testUsers.add(testUser1);

    TestUser testUser2 = new TestUser();
    testUser2.name = "qwert";
    detailsHashMap = new HashMap<String, String>();
    detailsHashMap.put("address", "long");
    detailsHashMap.put("state", "string");
    testUser2.details.add(detailsHashMap);
    testUsers.add(testUser2);

    ObjectMapper mapper = new ObjectMapper();

    System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(testUsers));

}

and the outcome of the users list is:

[ {
  "name" : "abcd",
  "details" : [ {
    "zipcode" : "integer",
    "city" : "string"
  } ]
}, {
  "name" : "qwert",
  "details" : [ {
    "address" : "long",
    "state" : "string"
  } ]
} ]

As you can see it is different from your JSON string.

UPDATE If you want to hold names and details in two separate containers...;

public static class Container {
    List<String> names = new ArrayList<String>();
    Map<String, String> details = new HashMap<String, String>();

    public Container() {
    }

    public List<String> getNames() {
        return names;
    }

    public void setNames(List<String> names) {
        this.names = names;
    }

    public Map<String, String> getDetails() {
        return details;
    }

    public void setDetails(Map<String, String> details) {
        this.details = details;
    }
}

....
public static void main(String[] args) throws IOException {

    Container container = new Container();
    container.names.add("abcd");
    container.names.add("qwert");
    container.details.put("city", "string");
    container.details.put("zipcode", "integer");
    container.details.put("address", "long");
    container.details.put("state", "string");

    ObjectMapper mapper = new ObjectMapper();
    System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(container));
}

and the outcome JSON is;

{
  "names" : [ "abcd", "qwert" ],
  "details" : {
    "address" : "long",
    "zipcode" : "integer",
    "state" : "string",
    "city" : "string"
  }
}