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Jackson ObjectMapper from MongoDB BSON

I got a JSON that I serialize to a MongoDB BasicDBObject and insert it into the DB:
String serialized = "";
try {
serialized = OBJECT_MAPPER.writeValueAsString(customEx.getOut().getBody());
} catch (JsonProcessingException e) {
e.printStackTrace();
}
collection.update(upsertQuery, BasicDBObject.parse(serialized), true, false);
On reading the DBObject from the DB I want to convert it to a POJO using the ObjectMappers' readValue() with a given class:
public static <T> T fromDB(DBObject o, Class<T> clazz) {
try {
return OBJECT_MAPPER.readValue(o.toString(), clazz);
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
The class I want to convert it to is generated from an xsd sheme and also contains timestamps/long values as following:
#XmlRootElement(name = "ItemType")
public class ItemType {
#XmlSchemaType(name = "dateTime")
protected XMLGregorianCalendar date;
[...]
However this worked fine for older Java MongoDB versions. Now the long values are serialized as BSON looking like this:
"date": {
"$numberLong": "1551172199214"
}
When I try to deserialize this using jacksons ObjectMapper I get
Cannot deserialize instance of javax.xml.datatype.XMLGregorianCalendar out of START_OBJECT token
The reason for this is clear to me because the long value is in an own BSON - Style object.
So far I already tried using BsonDocument like this:
public static <T> T fromDB(DBObject o, Class<T> clazz) {
try {
BsonDocument parse = BsonDocument.parse(o.toString());
return OBJECT_MAPPER.readValue(parse.toJson(), clazz);
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
But that still does not convert the BSON parts to JSON.
Is there any way to deserialize the BSON to a given Class using Jacksons ObjectMapper?
Or just convert it to a DBObject without using BSON parts?

If calendar field is wrapped we need to unwrap it. We can extend already implemented CoreXMLDeserializers.GregorianCalendarDeserializer:
class XmlGregorianCalendarDeserializer extends CoreXMLDeserializers.GregorianCalendarDeserializer {
#Override
public XMLGregorianCalendar deserialize(JsonParser jp, DeserializationContext ctxt)
throws IOException {
jp.nextToken(); // Skip FIELD_NAME
jp.nextToken(); // Skip VALUE_STRING
XMLGregorianCalendar calendar = super.deserialize(jp, ctxt);
jp.nextToken(); // Skip END_OBJECT
return calendar;
}
}
If XMLGregorianCalendar is always wrapped we can register this deserialiser using SimpleModule. See below example:
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ext.CoreXMLDeserializers;
import com.fasterxml.jackson.databind.module.SimpleModule;
import java.io.IOException;
import javax.xml.datatype.XMLGregorianCalendar;
public class Test {
public static void main(String[] args) throws Exception {
SimpleModule wrappedCalendarModule = new SimpleModule();
wrappedCalendarModule.addDeserializer(XMLGregorianCalendar.class, new XmlGregorianCalendarDeserializer());
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(wrappedCalendarModule);
String json = "{\n"
+ " \"date\":{\n"
+ " \"$numberLong\":\"1551172199214\"\n"
+ " },\n"
+ " \"name\":\"Rick\"\n"
+ "}";
System.out.println(mapper.readValue(json, Wrapper.class));
}
}
class Wrapper {
private XMLGregorianCalendar date;
private String name;
// getters, setters, toString
}
Above code prints:
Wrapper{date=2019-02-26T09:09:59.214Z, name='Rick'}

It looks like you need to configure the ObjectMapper to deserialize the XMLGregorianCalendar differently:
public class XMLGregorianCalendarDeserializer extends JsonDeserializer<XMLGregorianCalendar> {
private ObjectMapper objectMapper = new ObjectMapper();
#Override
public XMLGregorianCalendar deserialize(
JsonParser jsonParser, DeserializationContext deserializationContext)
throws IOException, JsonProcessingException {
Map<String, String> bsonStringAsMap =
objectMapper.readValue(
jsonParser.readValueAsTree().toString(), new TypeReference<Map<String, String>>() {});
String timestampString = bsonStringAsMap.get("$numberLong");
if (timestampString != null && !timestampString.isEmpty()) {
long timestamp = Long.parseLong(timestampString);
Date date = new Date(timestamp);
GregorianCalendar gregorianCalendar = new GregorianCalendar();
gregorianCalendar.setTime(date);
return DatatypeFactory.newInstance().newXMLGregorianCalendar(gregorianCalendar);
}
return null;
}
}
Then you can annotate the field with this and deserialize as you have been:
#JsonDeserialize(using=XMLGregorianCalendarDeserializer.class)
#XmlSchemaType(name = "dateTime")
protected XMLGregorianCalendar date;

How to parsing JSON like this?

I have json data format like
{
"status":200,
"message":"ok",
"response": {"result":1, "time": 0.0123, "values":[1,1,0,0,0,0,0,0,0]
}
}
I want to get one value of values array and put it on textView in eclipse. Look my code in eclipse
protected void onPostExecute (String result){
try {
JSONobject json = new JSONObject(result);
tv.setText(json.toString(1));
}catch (JSONException e){
e.printStackTrace();
}
}

You can use GSON
Create a POJO for your response
public class Response{
private int result;
private double time;
private ArrayList<Integer> values;
// create SET's and GET's
}
And then use GSON to create the object you desire.
protected void onPostExecute (String result){
try {
Gson gson = new GsonBuilder().create();
Response p = gson.fromJson(result, Response.class);
tv.setText(p.getValues());
}catch (JSONException e){
e.printStackTrace();
}
}

You can use jackson library for json parsing.
ObjectMapper mapper = new ObjectMapper();
Map map = mapper.readTree(json);
map.get("key");
You can use readTree if you know json is an instance of JSONObject class else use typeref and go with readValue to get the map.

protected void onPostExecute (String result){
try {
JSONObject json = new JSONObject(result);
JSONObject resp = json.getJSONObject("response");
JSONArray jarr = resp.getJSONArray("values");
tv.setText(jarr.get(0).toString(1));
}catch (JSONException e){
e.printStackTrace();
}
}

Unchecked cast warning in code

My code:
private List<Day> readDays(File file) {
List<Day> days = new ArrayList<>();
try {
ObjectInputStream in = new ObjectInputStream(new FileInputStream(file));
days.addAll((List<Day>) in.readObject());
} catch (IOException | ClassNotFoundException e) {
Logger.logError(LOG_TAG, e);
}
return days;
}
Unchecked cast problem in this code
days.addAll((List<Day>) in.readObject());
And this is a problem, in some cases the app crashes.

if your problem is cast object; you can define a convertor to convert your object to your class and handle exceptions.
if your stream return json string, You can use ObejctMapper and convert json string to your class as follow method by using jackson library:
//create ObjectMapper instance
ObjectMapper objectMapper = new ObjectMapper();
//convert json string to object
Day day = objectMapper.readValue(jsonData, Day.class);
// use day class now
so converting object, depend on your file data format.

gson list object attributes are null

I am trying get a list object from json file usiong gson. It returning list with objects but all attributes are null. How to get the objects properly?
json file:
[{"PeriodEndP":"2014-04-06T00:00:00","SiteKeyP":"00035"},{"PeriodEndP":"2014-04-06T00:00:00","SiteKeyP":"00035"}]
ScheduleDTO.java
public class ScheduleDTO {
String periodEndP;
String siteKeyP;
}
GsonEx.java
public class GsonEx {
public static void main(String[] args) {
try
{
JsonReader jsonReader = new JsonReader(new FileReader("F:/schedule.txt"));
Gson gson = new Gson();
Type ScheduleMsgDestType = new TypeToken<List<ScheduleDTO>>(){}.getType();
List<ScheduleDTO> ScheduleList = gson.fromJson(jsonReader, ScheduleMsgDestType);
for(ScheduleDTO t :ScheduleList )
{
System.out.println(t.periodEndP);
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
}

Make PeriodEndP to periodEndP
and same for SiteKeyP which will be siteKeyP
The names should be the same in the json and code.

How to parse a JSON Input stream

I am using java to call a url that returns a JSON object:
url = new URL("my URl");
urlInputStream = url.openConnection().getInputStream();
How can I convert the response into string form and parse it?

I would suggest you have to use a Reader to convert your InputStream in.
BufferedReader streamReader = new BufferedReader(new InputStreamReader(in, "UTF-8"));
StringBuilder responseStrBuilder = new StringBuilder();
String inputStr;
while ((inputStr = streamReader.readLine()) != null)
responseStrBuilder.append(inputStr);
new JSONObject(responseStrBuilder.toString());
I tried in.toString() but it returns:
getClass().getName() + '#' + Integer.toHexString(hashCode())
(like documentation says it derives to toString from Object)

All the current answers assume that it is okay to pull the entire JSON into memory where the advantage of an InputStream is that you can read the input little by little. If you would like to avoid reading the entire Json file at once then I would suggest using the Jackson library (which is my personal favorite but I'm sure others like Gson have similar functions).
With Jackson you can use a JsonParser to read one section at a time. Below is an example of code I wrote that wraps the reading of an Array of JsonObjects in an Iterator. If you just want to see an example of Jackson, look at the initJsonParser, initFirstElement, and initNextObject methods.
public class JsonObjectIterator implements Iterator<Map<String, Object>>, Closeable {
private static final Logger LOG = LoggerFactory.getLogger(JsonObjectIterator.class);
private final InputStream inputStream;
private JsonParser jsonParser;
private boolean isInitialized;
private Map<String, Object> nextObject;
public JsonObjectIterator(final InputStream inputStream) {
this.inputStream = inputStream;
this.isInitialized = false;
this.nextObject = null;
}
private void init() {
this.initJsonParser();
this.initFirstElement();
this.isInitialized = true;
}
private void initJsonParser() {
final ObjectMapper objectMapper = new ObjectMapper();
final JsonFactory jsonFactory = objectMapper.getFactory();
try {
this.jsonParser = jsonFactory.createParser(inputStream);
} catch (final IOException e) {
LOG.error("There was a problem setting up the JsonParser: " + e.getMessage(), e);
throw new RuntimeException("There was a problem setting up the JsonParser: " + e.getMessage(), e);
}
}
private void initFirstElement() {
try {
// Check that the first element is the start of an array
final JsonToken arrayStartToken = this.jsonParser.nextToken();
if (arrayStartToken != JsonToken.START_ARRAY) {
throw new IllegalStateException("The first element of the Json structure was expected to be a start array token, but it was: " + arrayStartToken);
}
// Initialize the first object
this.initNextObject();
} catch (final Exception e) {
LOG.error("There was a problem initializing the first element of the Json Structure: " + e.getMessage(), e);
throw new RuntimeException("There was a problem initializing the first element of the Json Structure: " + e.getMessage(), e);
}
}
private void initNextObject() {
try {
final JsonToken nextToken = this.jsonParser.nextToken();
// Check for the end of the array which will mean we're done
if (nextToken == JsonToken.END_ARRAY) {
this.nextObject = null;
return;
}
// Make sure the next token is the start of an object
if (nextToken != JsonToken.START_OBJECT) {
throw new IllegalStateException("The next token of Json structure was expected to be a start object token, but it was: " + nextToken);
}
// Get the next product and make sure it's not null
this.nextObject = this.jsonParser.readValueAs(new TypeReference<Map<String, Object>>() { });
if (this.nextObject == null) {
throw new IllegalStateException("The next parsed object of the Json structure was null");
}
} catch (final Exception e) {
LOG.error("There was a problem initializing the next Object: " + e.getMessage(), e);
throw new RuntimeException("There was a problem initializing the next Object: " + e.getMessage(), e);
}
}
#Override
public boolean hasNext() {
if (!this.isInitialized) {
this.init();
}
return this.nextObject != null;
}
#Override
public Map<String, Object> next() {
// This method will return the current object and initialize the next object so hasNext will always have knowledge of the current state
// Makes sure we're initialized first
if (!this.isInitialized) {
this.init();
}
// Store the current next object for return
final Map<String, Object> currentNextObject = this.nextObject;
// Initialize the next object
this.initNextObject();
return currentNextObject;
}
#Override
public void close() throws IOException {
IOUtils.closeQuietly(this.jsonParser);
IOUtils.closeQuietly(this.inputStream);
}
}
If you don't care about memory usage, then it would certainly be easier to read the entire file and parse it as one big Json as mentioned in other answers.

For those that pointed out the fact that you can't use the toString method of InputStream like this see https://stackoverflow.com/a/5445161/1304830 :
My correct answer would be then :
import org.json.JSONObject;
public static String convertStreamToString(java.io.InputStream is) {
java.util.Scanner s = new java.util.Scanner(is).useDelimiter("\\A");
return s.hasNext() ? s.next() : "";
}
...
JSONObject json = new JSONObject(convertStreamToString(url.openStream());

If you like to use Jackson Databind (which Spring uses by default for its HttpMessageConverters), then you may use the ObjectMapper.readTree(InputStream) API. For example,
ObjectMapper mapper = new ObjectMapper();
JsonNode json = mapper.readTree(myInputStream);

use jackson to convert json input stream to the map or object http://jackson.codehaus.org/
there are also some other usefull libraries for json, you can google: json java

Use a library.
GSON
Jackson
or one of many other JSON libraries that are out there.

Kotlin version with Gson
to read the response JSON:
val response = BufferedReader(
InputStreamReader(conn.inputStream, "UTF-8")
).use { it.readText() }
to parse response we can use Gson:
val model = Gson().fromJson(response, YourModelClass::class.java)

This example reads all objects from a stream of objects,
it is assumed that you need CustomObjects instead of a Map:
ObjectMapper mapper = new ObjectMapper();
JsonParser parser = mapper.getFactory().createParser( source );
if(parser.nextToken() != JsonToken.START_ARRAY) {
throw new IllegalStateException("Expected an array");
}
while(parser.nextToken() == JsonToken.START_OBJECT) {
// read everything from this START_OBJECT to the matching END_OBJECT
// and return it as a tree model ObjectNode
ObjectNode node = mapper.readTree(parser);
CustomObject custom = mapper.convertValue( node, CustomObject.class );
// do whatever you need to do with this object
System.out.println( "" + custom );
}
parser.close();
This answer was composed by using : Use Jackson To Stream Parse an Array of Json Objects and Convert JsonNode into Object

I suggest use javax.json.Json factory as less verbose possible solution:
JsonObject json = Json.createReader(yourInputStream).readObject();
Enjoy!

if you have JSON file you can set it on assets folder then call it using this code
InputStream in = mResources.getAssets().open("fragrances.json");
// where mResources object from Resources class

{
InputStream is = HTTPClient.get(url);
InputStreamReader reader = new InputStreamReader(is);
JSONTokener tokenizer = new JSONTokener(reader);
JSONObject jsonObject = new JSONObject(tokenizer);
}