Converting Java objects to JSON with Jackson

Converting Java objects to JSON with Jackson - java

I want my JSON to look like this:
{
"information": [{
"timestamp": "xxxx",
"feature": "xxxx",
"ean": 1234,
"data": "xxxx"
}, {
"timestamp": "yyy",
"feature": "yyy",
"ean": 12345,
"data": "yyy"
}]
}
Code so far:
import java.util.List;
public class ValueData {
private List<ValueItems> information;
public ValueData(){
}
public List<ValueItems> getInformation() {
return information;
}
public void setInformation(List<ValueItems> information) {
this.information = information;
}
#Override
public String toString() {
return String.format("{information:%s}", information);
}
}
and
public class ValueItems {
private String timestamp;
private String feature;
private int ean;
private String data;
public ValueItems(){
}
public ValueItems(String timestamp, String feature, int ean, String data){
this.timestamp = timestamp;
this.feature = feature;
this.ean = ean;
this.data = data;
}
public String getTimestamp() {
return timestamp;
}
public void setTimestamp(String timestamp) {
this.timestamp = timestamp;
}
public String getFeature() {
return feature;
}
public void setFeature(String feature) {
this.feature = feature;
}
public int getEan() {
return ean;
}
public void setEan(int ean) {
this.ean = ean;
}
public String getData() {
return data;
}
public void setData(String data) {
this.data = data;
}
#Override
public String toString() {
return String.format("{timestamp:%s,feature:%s,ean:%s,data:%s}", timestamp, feature, ean, data);
}
}
I just missing the part how I can convert the Java object to JSON with Jackson:
public static void main(String[] args) {
// CONVERT THE JAVA OBJECT TO JSON HERE
System.out.println(json);
}
My Question is: Are my classes correct? Which instance do I have to call and how that I can achieve this JSON output?

To convert your object in JSON with Jackson:
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectWriter;
ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
String json = ow.writeValueAsString(object);

I know this is old (and I am new to java), but I ran into the same problem. And the answers were not as clear to me as a newbie... so I thought I would add what I learned.
I used a third-party library to aid in the endeavor: org.codehaus.jackson
All of the downloads for this can be found here.
For base JSON functionality, you need to add the following jars to your project's libraries:
jackson-mapper-asl
and
jackson-core-asl
Choose the version your project needs. (Typically you can go with the latest stable build).
Once they are imported in to your project's libraries, add the following import lines to your code:
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
With the java object defined and assigned values that you wish to convert to JSON and return as part of a RESTful web service
User u = new User();
u.firstName = "Sample";
u.lastName = "User";
u.email = "sampleU#example.com";
ObjectMapper mapper = new ObjectMapper();
try {
// convert user object to json string and return it
return mapper.writeValueAsString(u);
}
catch (JsonGenerationException | JsonMappingException e) {
// catch various errors
e.printStackTrace();
}
The result should looks like this:
{"firstName":"Sample","lastName":"User","email":"sampleU#example.com"}

Just follow any of these:
For jackson it should work:
ObjectMapper mapper = new ObjectMapper();
return mapper.writeValueAsString(object);
//will return json in string
For gson it should work:
Gson gson = new Gson();
return Response.ok(gson.toJson(yourClass)).build();

You could do this:
String json = new ObjectMapper().writeValueAsString(yourObjectHere);

This might be useful:
objectMapper.writeValue(new File("c:\\employee.json"), employee);
// display to console
Object json = objectMapper.readValue(
objectMapper.writeValueAsString(employee), Object.class);
System.out.println(objectMapper.writerWithDefaultPrettyPrinter()
.writeValueAsString(json));

You can use Google Gson like this
UserEntity user = new UserEntity();
user.setUserName("UserName");
user.setUserAge(18);
Gson gson = new Gson();
String jsonStr = gson.toJson(user);

Well, even the accepted answer does not exactly output what op has asked for. It outputs the JSON string but with " characters escaped. So, although might be a little late, I am answering hopeing it will help people! Here is how I do it:
StringWriter writer = new StringWriter();
JsonGenerator jgen = new JsonFactory().createGenerator(writer);
jgen.setCodec(new ObjectMapper());
jgen.writeObject(object);
jgen.close();
System.out.println(writer.toString());

Note: To make the most voted solution work, attributes in the POJO have to be public or have a public getter/setter:
By default, Jackson 2 will only work with fields that are either
public, or have a public getter method – serializing an entity that
has all fields private or package private will fail.
Not tested yet, but I believe that this rule also applies for other JSON libs like google Gson.

public class JSONConvector {
public static String toJSON(Object object) throws JSONException, IllegalAccessException {
String str = "";
Class c = object.getClass();
JSONObject jsonObject = new JSONObject();
for (Field field : c.getDeclaredFields()) {
field.setAccessible(true);
String name = field.getName();
String value = String.valueOf(field.get(object));
jsonObject.put(name, value);
}
System.out.println(jsonObject.toString());
return jsonObject.toString();
}
public static String toJSON(List list ) throws JSONException, IllegalAccessException {
JSONArray jsonArray = new JSONArray();
for (Object i : list) {
String jstr = toJSON(i);
JSONObject jsonObject = new JSONObject(jstr);
jsonArray.put(jsonArray);
}
return jsonArray.toString();
}
}

Related

GSON: JSON deserialization to variable type (List/String)

At this point it's already an old question and I've probably read every related topic on SO.
But to the point. I need some advice or correction maybe?
For some reason we have generatable Jsons of 2 types:
{"data": {"id": "value"}} and {"data":[{"id": "value"}]}
Object and Array. There are also other params but they doesn't matter here. "id" is differ for every request. Sometimes it's userId, portfolioId etc. So I get "id" and pass it to related var.
For a long time I was working with the first case. And created POJO like this:
Data.class
public class Data {
#SerializedName("id")
#Expose
private String id;
public Data() {
}
public Data(String id) {
super();
this.id = id;
}
protected String getId() {
return id;
}
And I adress "data" paramets via User.class.
#JsonAdapter(UserDeserializer.class)
public Data data;
public Data getData() {
return data;
}
public void setData(Data data) {
this.data = data;
}
public User() {
}
public User(Data data) {
super();
this.data = data;
}
Gson gson = new Gson();
public String getPortfolioList(String tokenId, String userId) {
Call<User> call = apiRequest.getPortfolioList(userId, tokenId);
try {
User newResult = gson.fromJson(String.valueOf(call.execute().body()), User.class);
System.out.println(newResult.getData().getId());
} catch (IOException e) {
e.printStackTrace();
}
return getPortfolioId();
}
Deserializer.class
public class UserDeserializer implements JsonDeserializer<User> {
private Type listType = new TypeToken<List<Data>>(){}.getType();
#Override
public User deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
User user = new User();
JsonElement jsonElement;
if (json.isJsonArray()) {
jsonElement = json.getAsJsonArray();
user.data = context.deserialize(jsonElement,listType);
// user.data = new Gson().fromJson(jsonElement, new TypeToken<List<Data>>() {}.getType());
} else {
jsonElement = json.getAsJsonObject();
user.data = context.deserialize(jsonElement, Data.class);
// user.setData(new Gson().fromJson(jsonElement, new TypeToken<Data>() {}.getType()));
}
return user;
}
}
Gson builder in BaseApi class just in case:
Gson gson = new GsonBuilder().registerTypeAdapter(UserDeserializer.class, new UserDeserializer()).setLenient().create();
Without custom deserialization and Array JSON issue this would work perfectly. But now I have to determine "data" 's exact type I get.
In above case I get java.lang.ClassCastException: java.util.ArrayList cannot be cast to auto.Rest.Data
I assume I have to create another Data class (for example there will be DataObject & DataArray) and describe every parameter as I did before in Data.class to get this work? I think I do something wrong during deserialization but I'm not sure where tbh.
Or am I wrong and it is possible to invoke Data as List and Data as an Object of the same class?
I'm working on this for several days already(?) and was thinking about use generics instead of Gson help, yeah, I'm desperate. So any help appreciated.

if there is always one object, just add
json.getAsJsonArray().get(0);
public class UserDeserializer implements JsonDeserializer<User> {
private Type listType = new TypeToken<List<Data>>(){}.getType();
#Override
public User deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
User user = new User();
JsonElement jsonElement;
if (json.isJsonArray()) {
jsonElement = json.getAsJsonArray().get(0);
user.data = context.deserialize(jsonElement,listType);
// user.data = new Gson().fromJson(jsonElement, new TypeToken<List<Data>>() {}.getType());
} else {
jsonElement = json.getAsJsonObject();
user.data = context.deserialize(jsonElement, Data.class);
// user.setData(new Gson().fromJson(jsonElement, new TypeToken<Data>() {}.getType()));
}
return user;
}
}
if there are more objects, change field data to the list
public class UserDeserializer implements JsonDeserializer<User> {
private Type listType = new TypeToken<List<Data>>(){}.getType();
#Override
public User deserialize(JsonElement json, Type type, JsonDeserializationContext context) throws JsonParseException {
User user = new User();
JsonElement jsonElement;
if (json.isJsonArray()) {
jsonElement = json.getAsJsonArray();
user.data = context.deserialize(jsonElement,listType);
// user.data = new Gson().fromJson(jsonElement, new TypeToken<List<Data>>() {}.getType());
} else {
jsonElement = json.getAsJsonObject();
List<Data> data = new ArrayList<Data>();
data.add(context.deserialize(jsonElement, Data.class)) ;
user.data = data ;
// user.setData(new Gson().fromJson(jsonElement, new TypeToken<Data>() {}.getType()));
}
return user;
}
}
and change User.class field data to List
public List<Data> data;
this is a similar topic in kotlin language link

If you always have object or one-element array you can write custom deserialiser as below:
class OneOrElementJsonDeserializer<T> implements JsonDeserializer<T> {
#Override
public T deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
if (json instanceof JsonArray) {
final JsonArray array = (JsonArray) json;
final int size = array.size();
if (size == 0) {
return null;
}
return context.deserialize(array.get(0), typeOfT);
}
return context.deserialize(json, typeOfT);
}
}
Your example model after simplification looks like below:
class User {
#JsonAdapter(OneOrElementJsonDeserializer.class)
private Data data;
public User() {
}
public User(Data data) {
super();
this.data = data;
}
public Data getData() {
return data;
}
public void setData(Data data) {
this.data = data;
}
#Override
public String toString() {
return "User{" +
"data=" + data +
'}';
}
}
class Data {
private String id;
protected String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
#Override
public String toString() {
return "Data{" +
"id='" + id + '\'' +
'}';
}
}
Example usage:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.annotations.JsonAdapter;
import java.io.File;
import java.io.FileReader;
import java.lang.reflect.Type;
public class GsonApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
Gson gson = new GsonBuilder()
.setPrettyPrinting()
.create();
User root = gson.fromJson(new FileReader(jsonFile), User.class);
System.out.println(root);
}
}
Above code for below JSON payload:
{
"data": [
{
"id": "c87ca3fe85781007869b83f"
}
]
}
prints:
User{data=Data{id='c87ca3fe85781007869b83f'}}
And for object case JSON payload:
{
"data": {
"id": "c87ca3fe85781007869b83f"
}
}
prints:
User{data=Data{id='c87ca3fe85781007869b83f'}}
In case your property could contain JSON object or multi-element array see my answer to this question Mapping Json Array to Java Models. There is implemented deserialiser which handle cases like this.

Having issue collecting Json object and array with java

First of all, i am new to this so please pardon me. Have been working on a music app and I am trying to parse JSON code from a streaming link and display "artist" name and "title" of song to my app users. But i am having issues collecting the data.
Here is my JSON code from the streaming link:
{"type":"result","data":[{"title":"My Stream ","song":"Unknown - The Authorised One","track":{"artist":"Unknown Artist","title":"The Authorised One","album":"Unknown","royaltytrackid":181938.0000,"started":1498151105,"id":181938,"length":0,"playlist":{"id":3520,"title":"Rev Arome E. Adah"},"buyurl":"https:\/\/itunes.apple.com\/us\/album\/the-unknown-god\/id772022436?uo=4","imageurl":"http:\/\/is5.mzstatic.com\/image\/thumb\/Music5\/v4\/d7\/6d\/52\/d76d52df-db43-7130-0e37-62241ff50a21\/source\/100x100bb.jpg"},"bitrate":"128 Kbps","server":"Online","autodj":"Online","source":"Yes","offline":false,"summary":"<a href=\"http:\/\/cp9.serverse.com:2199\/tunein\/-stream\/svhxmwhp.pls\">Eloti Designs Stream - Unknown - The Authorised One<\/a>","listeners":0,"maxlisteners":1000,"reseller":0,"serverstate":true,"sourcestate":true,"sourceconn":1,"date":"Jun 22, 2017","time":"07:06 PM","rawmeta":"Unknown - The Authorised One ","mountpoint":"\/stream","tuneinurl":"http:\/\/209.133.216.3:7550\/stream","directtuneinurl":"","proxytuneinurl":"http:\/\/209.133.216.3\/proxy\/svhxmwhp?mp=\/stream","tuneinformat":"mp3","webplayer":"muses","servertype":"ShoutCast2","listenertotal":0,"url":"http:\/\/cp9.serverse.com:2199\/rpc"}]
I used this code to post "artist" name of "Unkwown Artist" to my text field but it didn't work for me.
JSONObject parentObject = new JSONObject(finalJson);
JSONArray parentArray = parentObject.getJSONArray("data");
JSONObject finalObject = parentArray.getJSONObject(0);
String songName = finalObject.getString("artist");
return songName;

track is a jsonobject containing artist and track is inside first jsonobject of
data array so fetch track then fetch artist from it
String songName = finalObject.getJSONObject("track").getString("artist");
{
"type":"result",
"data":[ // fetch JSONArray
{ // fetch first JSONObject
"title":"My Stream ","song":"Unknown - The Authorised One",
"track":{ // fetch track JSONObject
"artist":"Unknown .." // fetch string

Have you tried the jackson parser? It's super easy to use and can easily parse the string above. All you need to do is create 3/4 POJO classes that map your structure and then apply the readValue function of the Mapper to the outer class. Following is a small example with a List and one inner class:
import java.io.IOException;
import java.util.List;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
class OutterPojo {
public String aString;
public List<InnerPojo> aList;
public String getaString() {
return aString;
}
public void setaString(String aString) {
this.aString = aString;
}
public List<InnerPojo> getaList() {
return aList;
}
public void setaList(List<InnerPojo> aList) {
this.aList = aList;
}
#Override
public String toString() {
return new StringBuilder().append("{ #OutterPojo# ").append("aString:").append(aString).append(", ").append("aList:")
.append(aList).append(" }").toString();
}
}
class InnerPojo {
public String anotherString;
public String getanotherString() {
return anotherString;
}
public void setanotherString(String anotherString) {
this.anotherString = anotherString;
}
#Override
public String toString() {
return new StringBuilder().append("{ #InnerPojo# ").append("anotherString:").append(anotherString).append(" }")
.toString();
}
}
public class Test {
public static void main(String args[]) throws JsonParseException, JsonMappingException, IOException {
String jsonData = "{\"aString\":\"s\",\"aList\":[{\"anotherString\":\"ss\"},{\"anotherString\":\"sss\"}]}";
ObjectMapper objectMapper = new ObjectMapper();
OutterPojo testObject = objectMapper.readValue(jsonData, OutterPojo.class);
System.out.println(testObject);
}
}
As to dependencies all you need for this to work is jackson-core, jackson-databind and jackson-annotations - here's the link to maven:
https://mvnrepository.com/artifact/com.fasterxml.jackson.core
Hope it helps! :)

Gson- Parsing a JSON array of JSON objects to ArrayList<org.json.JSONObject>

I have a JSON string like this:
{
"r": [
{
"pic": "1.jpg",
"name": "Name1"
},
{
"pic": "2.jpg",
"name": "Name2"
},
{
"pic": "3.jpg",
"name": "Name3"
}
]
}
I want to parse to this POJO model:
public class Catalog {
#SerializedName("r")
#Expose
private List<JSONObject> r = new ArrayList<JSONObject>();
public List<JSONObject> getR() {
return r;
}
public void setR(List<JSONObject> r) {
this.r = r;
}
}
I am parsing this way:
Catalog cat = new Gson().fromJson(jsonString,Catalog.class);
But finally am getting this json
{
"r": [
{
"nameValuePairs": {}
},
{
"nameValuePairs": {}
},
{
"nameValuePairs": {}
}
]
}
Please note that I don't want to use com.google.gson.JsonObject.
I want to use org.json.JSONObject. How to achieve this because almost all of my code uses it?

As it was already mentioned in other answer and comments, you probably might not really want to use org.json.JSONObject for several reasons. But if it's a must for you, you just have to create your org.json.JSONObject-aware Gson instance.
final class JSONObjectJsonDeserializer
implements JsonDeserializer<JSONObject> {
// The implementation is fully thread-safe and can be instantiated once
private static final JsonDeserializer<JSONObject> jsonObjectJsonDeserializer = new JSONObjectJsonDeserializer();
// Type tokens are immutable values and therefore can be considered constants (and final) and thread-safe as well
private static final TypeToken<Map<String, Object>> mapStringToObjectTypeToken = new TypeToken<Map<String, Object>>() {
};
private JSONObjectJsonDeserializer() {
}
static JsonDeserializer<JSONObject> getJsonObjectJsonDeserializer() {
return jsonObjectJsonDeserializer;
}
#Override
public JSONObject deserialize(final JsonElement jsonElement, final Type type, final JsonDeserializationContext context) {
// Convert the input jsonElement as if it were a Map<String, Object> (a generic representation for JSON objectS)
final Map<String, Object> map = context.deserialize(jsonElement, mapStringToObjectTypeToken.getType());
// And forward the map to the JSONObject constructor - it seems to accept it nice
return new JSONObject(map);
}
}
Gson is designed thread-safe and does not need to be instantiated every time serialization or deserialization is necessary:
private static final Gson gson = new GsonBuilder()
.registerTypeAdapter(JSONObject.class, getJsonObjectJsonDeserializer())
.create();
And finally:
final Catalog catalog = gson.fromJson(jsonString, Catalog.class);
out.println(catalog.getR());
with the following result:
[{"name":"Name1","pic":"1.jpg"}, {"name":"Name2","pic":"2.jpg"}, {"name":"Name3","pic":"3.jpg"}]
Anyway, I would suggest you to redesign your mappings model.

I think you don't need JSONObject.
Try this
// is wrapped class for serialized json.
public class JsonExample
{
List<Catalog> r;
}
public class Catalog {
private String pic;
private String name;
public String getPic() {
return pic;
}
public String getName() {
return name;
}
}
JsonExample example = new Gson().fromJson(json, JsonExample.class);
Additional - using JSONObject
JSONObject obj = new JSONObject(json);
JSONArray arr = obj.getJSONArray("r");
List<Catalog> cataList = new ArrayList<>();
for(int i = 0 ; i < arr.length() ; ++i)
{
cataList.add(new Catalog(arr.getJSONObject(i)));
}
public class Catalog {
private String pic;
private String name;
public Catalog(JSONObject obj) throws JSONException
{
pic = obj.getString("pic");
name = obj.getString("name");
}
public String getPic() {
return pic;
}
public String getName() {
return name;
}
}

I think in your case, usage of gson library is not required at all.
Only org.json can solve the entire problem.
E.g.:
JSONObject json = new JSONObject(jsonString);
JSONArray jsonArray = json.getJSONArray("r");
List<JSONObject> jsonList = new ArrayList<>();
for (int i = 0; i < jsonArray.length(); i++) {
jsonList.add(jsonArray.getJSONObject(i));
}
Catalog catalog = new Catalog();
catalog.setR(jsonList);

How to Gson to convert JSON to POJO with custom field names

I recently started using GSON and i am facing an issue in deserialising this json. The issue is at below json element which contains spaces in field names
{
longDescriptionNonHTML: {
What it is:: " An oil-free, color-tinted moisturizer."
What it does:: " This lightweight foundation can be reapplied as necessary and offers moisturizing, oil-control coverage for sensitive or acne prone skin."
}
{
SKUType: "restricted"
brandName: "Laura Mercier"
brandId: 5809
skuID: "1228139"
availableInStore: 0
topSellerRank: 8297
productName: "Tinted Moisturizer - Oil Free"
shade_description: "Porcelain"
shortDescription: "What it is: An oil-free, color-tinted moisturizer.What it does: This lightweight foundation can be reapplied as necessary and offers moisturizing, oil-control coverage for sensitive or acne prone skin."
size: "1.7 oz"
listPrice: 0
salePrice: 0
image: "http://www.sephora.com/productimages/sku/s1228139-main-hero.jpg"
rating_product: 4.3
online_store: "http://www.sephora.com/tinted-moisturizer-oil-free-P310929?skuId=1228139&lang=en"
imageBrand: "http://www.sephora.com/contentimages/brands/lauramercier/5809_logo_279.png"
productId: "P310929"
formulation: "Liquid"
spf: ""
coverage: "Sheer, Medium"
finish: "Matte, Natural"
ingredients: "Vitamin C"
skintype: "Combination, Normal, Oily"
longDescription: "<b>What it is:</b><br> An oil-free, color-tinted moisturizer.<br><br><b>What it does:</b><br> This lightweight foundation can be reapplied as necessary and offers moisturizing, oil-control coverage for sensitive or acne prone skin."
longDescriptionNonHTML: {
What it is:: " An oil-free, color-tinted moisturizer."
What it does:: " This lightweight foundation can be reapplied as necessary and offers moisturizing, oil-control coverage for sensitive or acne prone skin."
}-
skintone: "2Y03"
longIngredientsDesc: ""
language: "en"
isPrimarySkintone: 1
isDefaultSku: 0
storeonly: 0
}
I wrote below POJO
public class LongDescriptionNonHTML {
#SerializedName("What it is:")
private String whatItIs;
#SerializedName("What it does:")
private String whatItDoes;
public LongDescriptionNonHTML(String a,String b){
whatItDoes=a;
whatItDoes=b;
}
public String getWhatItIs() {
return whatItIs;
}
public void setWhatItIs(String whatItIs) {
this.whatItIs = whatItIs;
}
public String getWhatItDoes() {
return whatItDoes;
}
public void setWhatItDoes(String whatItDoes) {
this.whatItDoes = whatItDoes;
}
}
Also for deserialise it I wrote below code
Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonReader reader = new JsonReader(new FileReader(fileName));
LongDescriptionNonHTML obj=gson.fromJson(reader, LongDescriptionNonHTML.class);
System.out.println(obj.getWhatItDoes());
But it is printing null value.

It may be useful for you to convert JSON to POJO Class.
public static <T> T convertJSON2POJOClass(String json, Class<T> type)
{
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.serializeNulls();
try{
return (T) gson.fromJson(json, type);
} catch (Exception expJSONToClassConvertor) {
baseDAO.getInstance().logAnError("common", baseDAO.getInstance().stackTraceToString(expJSONToClassConvertor));
return null;
}

If what you posted is the actual JSON and your whole actual POJO code then you have a mismatch between your JSON and POJO structure:
You are asking Gson to produce a LongDescriptionNonHTML from your JSON.
But your JSON is not just that - it actually is some other object that contains a LongDescriptionNonHTML as the value for the key longDescriptionNonHTML.

I solved it
public class LongDescriptionNonHTML {
//#SerializedName("What it is:")
private String whatItIs;
//#SerializedName("What it does:")
private String whatItDoes;
public LongDescriptionNonHTML(String a,String b){
whatItDoes=a;
whatItDoes=b;
}
public String getWhatItIs() {
return whatItIs;
}
public void setWhatItIs(String whatItIs) {
this.whatItIs = whatItIs;
}
public String getWhatItDoes() {
return whatItDoes;
}
public void setWhatItDoes(String whatItDoes) {
this.whatItDoes = whatItDoes;
}
Then created a deserializer
public class FooDeserializer implements JsonDeserializer{
#Override
public LongDescriptionNonHTML deserialize(JsonElement json, Type typeOfT,
JsonDeserializationContext context)
throws JsonParseException {
JsonObject jo = (JsonObject)json;
String a =jo.get("What it is:").getAsString();
String b =jo.get("What it does:").getAsString();
return new LongDescriptionNonHTML(a,b);
}
}
and then finally tested it
public class jsonTest {
#Test
public void testJson() throws FileNotFoundException{
String fileName="/Users/User/Documents/workspace/simulator/book.json";
Gson gson = new GsonBuilder().setPrettyPrinting().registerTypeAdapter(LongDescriptionNonHTML.class, new FooDeserializer()).create();
JsonReader reader = new JsonReader(new FileReader(fileName));
LongDescriptionNonHTML obj=gson.fromJson(reader, LongDescriptionNonHTML.class);
System.out.println(obj.getWhatItDoes());
}
}

How to extract array values within nested JSON data

I have JSON data in the following format:
{
"data": {
"id": 14810798216415,
"name": "crescentbahuman.com",
"is_organization": true,
"email_domains": [
"crescentbahuman.com"
]
}
}
I want to get the string in the "email_domains" field. I wrote the following code as my attempt:
JSONObject dataObject2= (JSONObject)jsonObject2.get("data");
long id = (long) dataObject2.get("id");
System.out.println("worksapce id is: " + id);
String name = (String) dataObject2.get("name");
System.out.println("The worksapce name is: " + name);
boolean is_organization = (boolean) dataObject2.get("is_organization");
System.out.println("The workspace is organization: " + is_organization);
JSONArray email_domains = (JSONArray) jsonObject2.get("email_domains");
Iterator<String> iterator = email_domains.iterator();
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
In this code to get "email_domains" only, a JSON Array object is created that get data from the JSON object and then its iterator is used to get values from within the array. However, it throws a NullPointerException on this line:
Iterator<String> iterator = email_domains.iterator();
I am stuck due to this problem. Can anyone kindly suggest a solution?

If you are using the JSON library from http://www.json.org/java/, then you should not be using JSONObject.get() so frequently. The library has other methods to get specific types, such as getLong(), getJSONArray(), and so forth. For your case with the "email_domains" field, you should try:
JSONArray array = dataObject2.getJSONArray("email_domains");
String value = array.getString(0);

org.json.JSONArray email_domains = (org.json.JSONArray) json.get("email_domains");
int length = email_domains.length();
for(int i = length-1; i > 0; i--) {
org.json.JSONObject jsonData = (org.json.JSONObject) email_domains.get(i);
System.out.println(jsonData);
}

My solution? I hate to be someone to offer a solution in another library... but look into google collections and the Gson helper. It can turn your Json into a map for you, and then back to json again when you are done.
Map map = gson.fromJson(jsonText, Map.class);
JsonArray's can then be cast into List's

try this to fetch "email_domains"
JSONArray email_domains = ((JSONArray) jsonObject).get("email_domains");
or
JSONObject obj = new JSONObject(jsonObject.Tostring());
JSONArray email_domains = obj.optJSONArray("email_domains");

"email_address" is JSONArray so we need to fetch this like
JSONArray email_domains = (JSONArray) dataObject2.getJSONArray("email_domains");
email_domains.get(0); // this will return crescentbahuman.com

Use this implementation
import java.lang.reflect.Field;
import java.util.List;
import com.google.gson.ExclusionStrategy;
import com.google.gson.FieldAttributes;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class JsonConvertor {
private static GsonBuilder gsonBuilder;
private static Gson gson;
private JsonConvertor() {
}
public static Object fromJson(String json, Class clz)
{
gson=new Gson();
return gson.fromJson(json,clz);
}
public static String toJson(Object obj) {
gsonBuilder = new GsonBuilder();
gsonBuilder = gsonBuilder
.addSerializationExclusionStrategy(new CustomIclusionStrategy(
obj.getClass()));
gson = gsonBuilder.create();
String json = gson.toJson(obj);
return json;
}
}
class CustomIclusionStrategy implements ExclusionStrategy {
private Class classToIclude;
private Field[] declaredFields;
private List<FieldAttributes> fields;
public CustomIclusionStrategy(List<FieldAttributes> fields) {
this.fields = fields;
}
public CustomIclusionStrategy(Class classToIclude) {
this.classToIclude = classToIclude;
this.declaredFields=classToIclude.getDeclaredFields();
}
// called only if shouldSkipClass returns false
#Override
public boolean shouldSkipField(FieldAttributes f) {
try {
classToIclude.getSuperclass().getDeclaredField(f.getName());
System.out.println(f.getName());
return true;
} catch (Exception e) {
}
return false;
}
#Override
public boolean shouldSkipClass(Class<?> clazz) {
// if returns false shouldSkipField will be called, otherwise
//shouldSkipField will not be called
return false;
}
}
public class Org {
private Data data;
public Org(Data data) {
super();
this.data = data;
}
public Data getData() {
return data;
}
public void setData(Data data) {
this.data = data;
}
public String toJson()
{
return JsonConvertor.toJson(this);
}
public static void main(String[] args) {
String json="{\"data\": {\"id\":\"1\",\"name\":\"org1\",\"is_organization\":true,\"email_domains\": [\"email1\",\"email2\",\"email3\",\"email4\"]}}";
Org o=(Org) JsonConvertor.fromJson(json, Org.class);
System.out.println(o.getData().getEmail_domains());
}
}

Develop Reference

Java is a programming language and computing platform first released by Sun Microsystems in 1995.

Converting Java objects to JSON with Jackson - java

To convert your object in JSON with Jackson: import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.ObjectWriter; ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter(); String json = ow.writeValueAsString(object);

Just follow any of these: For jackson it should work: ObjectMapper mapper = new ObjectMapper(); return mapper.writeValueAsString(object); //will return json in string For gson it should work: Gson gson = new Gson(); return Response.ok(gson.toJson(yourClass)).build();

You could do this: String json = new ObjectMapper().writeValueAsString(yourObjectHere);

This might be useful: objectMapper.writeValue(new File("c:\\employee.json"), employee); // display to console Object json = objectMapper.readValue( objectMapper.writeValueAsString(employee), Object.class); System.out.println(objectMapper.writerWithDefaultPrettyPrinter() .writeValueAsString(json));

You can use Google Gson like this UserEntity user = new UserEntity(); user.setUserName("UserName"); user.setUserAge(18); Gson gson = new Gson(); String jsonStr = gson.toJson(user);

Related

GSON: JSON deserialization to variable type (List/String)

Having issue collecting Json object and array with java

Gson- Parsing a JSON array of JSON objects to ArrayList<org.json.JSONObject>

How to Gson to convert JSON to POJO with custom field names

How to extract array values within nested JSON data

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