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json into list with Gson

I have a Json like below:
{
"searchResults": {
"searchCriteria": {
"location": {
"originalLocation": null
},
"startAndEndDate": {
"start": "2016-10-06T00:00:00",
"end": "2016-10-09T00:00:00"
},
"solution": [
{
"resultID": "O1MDc1MD",
"selected": false,
"charges": {
"localCurrencyCode": "USD",
"averagePricePerNight": 153
},
"starRating": 3.5
},
{
"resultID": "0MDc1MD",
"selected": false,
"charges": {
"localCurrencyCode": "USD",
"averagePricePerNight": 153
},
"starRating": 3.5
}
....
I have class with attributes starRating and averagePricePerNight which essentially formulates into my POJO.
class ResponseModel {
Int starRating; Int averagePricePerNight
}
I want to parse this JSON and return a List containing :
List(ResponseModel(3.5,900), ResponseModel(3.5,100), ResponseModel(4.5,1000))
I tried to get the json as a List but then i am unable to find examples to get two elements from JSon.

You can write a custom deserializer:
class Deserializers {
public static ResponseModel responseModelDeserializer(JsonElement json, Type typeOfT,
JsonDeserializationContext context) {
JsonObject obj1 = json.getAsJsonObject();
JsonObject obj2 = obj1.get("charges").getAsJsonObject();
double starRating = obj1.get("starRating").getAsDouble();
int averagePricePerNight = obj2.get("averagePricePerNight").getAsInt();
return new ResponseModel(starRating, averagePricePerNight);
}
}
Register it when building Gson:
Gson gson = new GsonBuilder()
.registerTypeAdapter(ResponseModel.class,
(JsonDeserializer<ResponseModel>) Deserializers::responseModelDeserializer
// ^^^ Cast is needed because the parameter has type Object
)
.create();
(Other options include, besides a method reference, are; lambda, anonymous class, or just a regular class. But this one is my favourite.)
Parse your json:
// Get root json object
JsonObject root = new JsonParser().parse(input).getAsJsonObject();
Type tt = new TypeToken<List<ResponseModel>>() {}.getType();
// Get array
List<ResponseModel> mo = gson.fromJson(root.get("solution"), tt);
System.out.println(mo); // [3.5 : 153, 3.5 : 153]
Where ResponseModel is:
class ResponseModel {
private final double starRating;
private final int averagePricePerNight;
public ResponseModel(double starRating, int averagePricePerNight) {
this.starRating = starRating;
this.averagePricePerNight = averagePricePerNight;
}
#Override
public String toString() {
return String.format("%s : %s", starRating, averagePricePerNight);
}
}
I made starRating a double since it seems to be one in your example.

Error java.lang.NullPointerException in JSON parsing

I am new to Java,and using below code to parse JSON,but I am getting java.lang.NullPointerException error when the offers {} node is coming with empty values ,which is public class in my code.
How to handle empty JSON nodes/keys ??
The code is able to parse JSON if there is data under "offers" like "info",but exiting with NULL exception error when JSON returns and empty as shown below.
ERROR MSG :
Exception in thread "api_temp_1.dat" java.lang.NullPointerException
at com.t.dw.dl.api.data.Pkg_Data.getCount(Pkg_Data.java:57)
at com.t.dw.dl.api.DataRetrieveRunnable.run(DataRetrieveRunnable.java:185)
Code extracts from error lines shown
public long getCount() {
if (offers != null)
return offers.getPkg().size();
return 0;
}
**Code from com.t.dw.dl.api.DataRetrieveRunnable.run(DataRetrieveRunnable.java:185)**
try
{
Pkg_Data dls = parseResult(result);
if (dls.getCount() > 0)
{
fw.write(deals.writeResults(fields, delimiter));
threadStats.increment(Stats2.COUNT_OF_ROWS_PROCESSED,
dls.getCount());
}
}
Parsing code:
private Pkg_Data parseResult( String result ) throws JsonParseException {
JsonParser parser = new JsonParser();
JsonElement jo = parser.parse(result);
Gson gson = new Gson();
Pkg_Data ehw = gson.fromJson(jo, Pkg_Data.class);
return ehw;
}
CODE:
import java.util.ArrayList;
public class offers
{
private ArrayList<PkgData> pkg;
class Pkgdata
{
Info Info;
class Info
{
String Id;
String Url;
}
public String getId() {
if (Info != null && Info.Id != null)
return Info.Id;
return "";
}
SAMPLE JSON: NOT working for this where "offers" returns empty
{
"offerInfo":{
"siteID":"1",
"language":"en_US",
"currency":"USD"
},
"offers":{ }
}

That is because offer is compared to the Class that you giving to refer so in that case Json will be wrong try with this Json it will work.
{
"offerInfo": {
"siteID": "1",
"language": "en_US",
"currency": "USD"
},
"offers": {
"siteID": " ",
"language": "",
"currency": " "
}
}
Because Compiler not able to find any field attribute in side your offer object so its giving error.
try this Json.

Parsing the nested JSON Array using Jackson library in java

I would like to know how to parse the following JSON using jackson library in java to construct the URI like http://api.statdns.com/google.com/cname
{
"status": {
"status": 200,
"msg": "SUCCESS"
},
"apicalls": [
{
"API": {
"method": "get",
"success": "200",
"baseURL": "http://api.statdns.com/",
"param1": "google.com/",
"param2": "cname",
"continue_on_fail": "1",
"add_header2": "'Accept', 'application/json'",
"add_header1": "'Content-Type', 'application/json'",
"client_id": "101"
},
"id": 1385
}
]
}
I have written bad code to parse the above json array. Following is the code i used,
public void parseJSON(String json) {
try{
JsonFactory factory = new JsonFactory();
JsonParser parser;
parser = factory.createJsonParser(json);
parser.setCodec(new ObjectMapper()); // to avoid IllegalStateException
JsonToken current;
current = parser.nextToken();
if (current != JsonToken.START_OBJECT) {
System.out.println("Error: root should be object: quiting.");
return;
}
while (parser.nextToken() != JsonToken.END_OBJECT) {
String fieldName = parser.getCurrentName();
// Move from field name to field value
current = parser.nextToken();
if (fieldName.equals("APIcalls")) {
JsonNode node = parser.readValueAsTree();
JsonNode currentJson = node.findValue("API");
System.out.println("Current JSON :: " + currentJson);
JsonNode url = currentJson.get("baseURL");
JsonNode param1 = currentJson.get("param1");
JsonNode param2 = currentJson.get("param2");
String baseURL = url.asText();
String params1 = param1.asText();
String params2 = param2.asText();
String uri = baseURL + params1 + params2;
System.out.println("URL :: " + uri);
initiateRESTCall(uri);
}
}
} catch (JsonParseException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
Could anyone help me to know parsing the JSON using jackson? Help is highly appreciated.

If you are using jackson library, then you should go something like this:
I am using response from http://api.statdns.com/google.com/cname
public void parseJSON(String json) {
JSONObject parse = new JSONObject(data);
if(parse.get("question") instanceof JSONObject){
JSONObject questionJson = (JSONObject) parse.get("question");
System.out.println("Name"+questionJson.getString("name"));
System.out.println("Type"+questionJson.getString("type"));
System.out.println("Class"+questionJson.getString("class"));
}
else if(parse.get("question") instanceof JSONArray){
JSONArray questionJson = (JSONArray) parse.get("question");
String[] nameAttrib=new String[questionJson.length()];
String[] typeAttrib=new String[questionJson.length()];
String[] classAttrib=new String[questionJson.length()];
for(int i=0;i<questionJson.length();i++){
JSONObject questionJsonData=(JSONObject)questionJson.get(i);
nameAttrib[i]=questionJsonData.getString("name");
typeAttrib[i]=questionJsonData.getString("type");
classAttrib[i]=questionJsonData.getString("class");
System.out.println("Name: "+nameAttrib[i]);
System.out.println("Type: "+typeAttrib[i]);
System.out.println("Class: "+classAttrib[i]);
}
}
else if (parse.get("question").equals(null)){
System.out.println("question"+null);
}
}
Here I am doing for "question" only, similarly you can do other as well say "answer", "authority" in case url you have mentioned http://api.statdns.com/google.com/cname.
Hopefully it helps you with your problem..!!!!

If you are confident in the JSON not changing, a quick and dirty way to simplify your code is to use JSON Pointers.
// prefer injecting your project's ObjectMapper
private static final ObjectMapper om = new ObjectMapper();
public void parseJSON(String json) throws IOException {
JsonNode jsonNode = om.readTree(json);
String uri = new StringBuilder(jsonNode.findValue("baseURL").asText())
.append(jsonNode.findValue("param1").asText())
.append(jsonNode.findValue("param2").asText())
.toString();
initiateRESTCall(uri);
}
This becomes vulnerable if multiple apicalls entries are returned.

I don't know JACKSON library but I think it is similar to GSON. You just have to make some POJO and the library will take care of filling the fields for you.
For instance to convert your string to MyJSONClass use the following classes :
class Status {
int status;
String msg;
}
class APIClass {
String method;
String success;
String baseURL;
String param1;
String param2;
String continue_on_fail;
String add_header2;
String add_header1;
String client_id;
}
class APICall {
APIClass API;
int id;
}
class MyJSONClass {
Status status;
List<APICall> apicalls;
}
This set of classes could be transformed to JSON with JACKSON library (thanks to this stackoverflow answer) like that:
ObjectWriter ow = new ObjectMapper().writer().withDefaultPrettyPrinter();
String json = ow.writeValueAsString(object);

Java - Json deserialize data []

I am new to stackoverflow.
I am creating an Java application which it will get data from a web server. The data is in json format. Example"
[
{
"item_name": "Adame",
"item_type": "Special",
"item": "Chestplate",
"item_min_lvl": "50",
"enchantment": {
"health": "0.3",
"dam": "24%",
"life": "0.1",
"xp": "24%",
"loot": "22%"
},
"def": "73"
},
{
"item_name": "Sticks'",
"item_type": "Unique",
"item": "Stick",
"item_min_lvl": "4",
"enchantment": {
"health": "0.6",
"mana": "1",
"dam": "12%",
"life": "0.3",
"xp": "17%",
"loot": "17%"
},
"min_dam": "39",
"max_dam": "34"
}
]
I know how to deserialize json using Gson. As you can see, it's started with [. I never deserialize this case before. Also, the json data is not the same(e.g. enchantment). I also searched in Google but I can't find any similar case. Can anyone help me with the code?

Try with this code. You will get the answer of your question. It's an List with 2 items.
StringBuilder builder = new StringBuilder();
BufferedReader reader = new BufferedReader(new FileReader(new File("resources/json1.txt")));
String line = null;
while ((line = reader.readLine()) != null) {
builder.append(line);
}
reader.close();
Gson gson = new Gson();
Type listType = new TypeToken<ArrayList<MyJSON>>() {
}.getType();
List<MyJSON> list = gson.fromJson(builder.toString(), listType);
// you can try this form as well
// MyJSON[] list = gson.fromJson(builder.toString(), MyJSON[].class);
for (MyJSON json : list) {
System.out.println(json.toString());
}
...
class MyJSON {
String item_name;
String item_type;
String item;
String item_min_lvl;
Enchantment enchantment;
#Override
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("\nitem_name:").append(item_name);
builder.append("\nitem_type:").append(item_type);
builder.append("\nitem:").append(item);
builder.append("\nitem_min_lvl:").append(item_min_lvl);
builder.append("\n\nEnchantment Details:");
builder.append("\nhealth:").append(enchantment.health);
builder.append("\ndam:").append(enchantment.dam);
builder.append("\nlife:").append(enchantment.life);
builder.append("\nxp:").append(enchantment.xp);
builder.append("\nloot:").append(enchantment.loot);
return builder.toString();
}
}
class Enchantment {
String health;
String dam;
String life;
String xp;
String loot;
}
output:
item_name:Adame
item_type:Special
item:Chestplate
item_min_lvl:50
Enchantment Details:
health:0.3
dam:24%
life:0.1
xp:24%
loot:22%
item_name:Sticks'
item_type:Unique
item:Stick
item_min_lvl:4
Enchantment Details:
health:0.6
dam:12%
life:0.3
xp:17%
loot:17%
EDIT
The structure of each entry is not same hence you can't use POJO for this type of JSON.
Simply use ArrayList<Map<String, Object>> and access the value based on key from the map.
Gson gson = new Gson();
Type listType = new TypeToken<ArrayList<Map<String, Object>>>() {
}.getType();
ArrayList<Map<String, Object>> list = gson.fromJson(builder.toString(), listType);
for (Map<String, Object> json : list) {
for (String key : json.keySet()) {
System.out.println(key + ":" + json.get(key));
}
System.out.println("===========");
}
output:
item_name:Adame
item_type:Special
item:Chestplate
item_min_lvl:50
enchantment:{health=0.3, dam=24%, life=0.1, xp=24%, loot=22%}
def:73
===========
item_name:Sticks'
item_type:Unique
item:Stick
item_min_lvl:4
enchantment:{health=0.6, mana=1, dam=12%, life=0.3, xp=17%, loot=17%}
min_dam:39
max_dam:34
===========

This is actually valid in Java and with GSON:
YourObject[] locs = gson.fromJson (someJsonString, YourObject[].class);
It'll parse and return an array of YourObject. Just create Java Classes that represent your JSON objects, and replace the placeholders as necessary.
EDIT:
As Braj said before, you can create a fully formed POJO, including the other, (non-symmetrical) attributes (I'm borrowing the code from from Braj's answer here):
//... snip ...
class MyJSON
{
String item_name;
String item_type;
String item;
String item_min_lvl;
Enchantment enchantment;
// Heres the other attributes
String min_dam;
String max_dam;
}
//... snip ...
GSON will parse it and set the values to null if they aren't provided in the original JSON.
However, from the other question, it seems that the JSON (Java - JSON Parser Error) for enchantment is provided inconsistently, so this will cause issues. I would recommend sending JSON for enchantment as an array for consistency, then you could structure your POJO as:
//... snip ...
class MyJSON
{
String item_name;
String item_type;
String item;
String item_min_lvl;
Enchantment[] enchantment;
// Heres the other attributes
String min_dam;
String max_dam;
}
//... snip ...

Interpreting and reading JSON with GSON

I'm having trouble trying to make sense of this JSON string.
{
"results":[
{
"user":{
"gender":"female",
"name":{
"title":"miss",
"first":"taylor",
"last":"anderson"
},
"location":{
"street":"3645 dogwood ave",
"city":"roseburg",
"state":"new hampshire",
"zip":"20963"
},
"email":"taylor.anderson49#example.com",
"username":"heavyduck595",
"password":"liverpool",
"salt":"UK`o;9a_",
"md5":"6c8db0305b4591d8d9820d9f8edfd162",
"sha1":"906df4c09f3a87899666cb57bf974bd9b1950ea6",
"sha256":"3b12f5e51688578f845bef8ae1750d3e263c2010691010a80ce632a6b2323c03",
"registered":"1359027425",
"dob":"16243995",
"phone":"(934)-888-7068",
"cell":"(727)-467-8384",
"SSN":"697-20-6143",
"picture":"http://api.randomuser.me/0.3/portraits/women/30.jpg"
},
"seed":"5eaf02877746c7e",
"version":"0.3"
}
]
}
It's the first time I've really used JSON and want to try and interpret it appropriately. This is the code i have thus far:
static class Results{
String results;
}
static class User{
String gender;
String name;
String location;
List<Results> items;
}
private static String readUrl(String urlString) throws Exception {
BufferedReader reader = null;
try {
URL url = new URL(urlString);
reader = new BufferedReader(new InputStreamReader(url.openStream()));
StringBuffer buffer = new StringBuffer();
int read;
char[] chars = new char[1024];
while ((read = reader.read(chars)) != -1)
buffer.append(chars, 0, read);
return buffer.toString();
} finally {
if (reader != null)
reader.close();
}
}
public void larry() throws Exception{
String json = readUrl("http://api.randomuser.me/");
System.out.println(json);
Gson gson = new Gson();
User page = gson.fromJson(json, User.class);
System.out.println(page.name);
for (Results item : page.items)
System.out.println(" " + item.results);
}

There is nothing particularly complicated about JSON, or mapping it to your own Java classes. You just have to understand the basic structure.
Your JSON is an object that has exactly one field; results. This is what {} means:
{ "results": ... }
That field holds an array. That's the [].
{ "results": [ ... ] }
That array holds another object (presumably you'd have more than one in an array, but the JSON you've posted just has one). That object has three fields, one of which ("user") holds another object with the other two being strings.
To map that to your own classes, you simply make them look like that JSON:
class JsonResult {
List<Result> results; // JSON arrays map to Java Lists
}
class Result {
User user;
String seed;
String version;
}
class User {
String gender;
Name name;
// and so on ...
}
class Name {
String title;
String first;
String last;
}
And so forth. You build classes to match the objects (again, denoted by {}) in the JSON, and structure everything accordingly.
As #HotLicks notes in his comment, you can decide not to map to Java classes and use a "clean" parser. In fact, Gson offers this with it's JsonParser class. This will just parse the JSON to a tree from which you can extract the info you want:
JsonElement element = new JsonParser().parse(yourJsonString);
From there you can access the JSON structure using the field names:
JsonObject root = element.getAsJsonObject();
JsonArray array = root.getAsJsonArray("results");
By accessing the JSON structure you can get to whatever you want.