I'm trying to create a JSON document by using Jackson. The hierarchy goes as follows:
Event:
class Event {
private String name = "";
private Set<Integer> admin = new HashSet<>();
private List<House> houseList = new ArrayList<>();
}
House:
class House {
private List<OG> OGList = new ArrayList<>();
private int score = 0;
private String name = "";
}
Group:
class OG {
private int score = 0;
private int id = 0;
}
Every event might comprises of a set number of houses, which in turn comprises of a set number of groups. Each house and group has a score modifier as well.
Currently, this is how I print the JSON document using the pretty print method:
ObjectMapper mapper = new ObjectMapper();
File f = new File("./db/" + dir);
if (f.exists() && !f.isDirectory()) {
return "This event name is taken. Please try again.";
}
try {
mapper.writeValue(f, event);
// Convert object to JSON string and pretty print
String jsonInString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(event);
System.out.println(jsonInString);
}
}
The resulting output is pretty ugly:
{
"name" : "test",
"admin" : [ 423766405 ],
"houseList" : [ {
"score" : 0,
"name" : "first",
"oglist" : [ {
"score" : 0,
"id" : 0
}, {
"score" : 0,
"id" : 1
}, {
"score" : 0,
"id" : 2
} ]
..
}
Is there a better way to format the output, for example:
name:
test
admin:
a
b
c
houses:
name:
first
group:
1
..
It appears like you want to output YAML, not JSON.
This answer shows how simple it is to write YAML output to a file using Jackson.
This answer shows how to read a YAML file, modify it's contents, and save it back out again.
Related
I want to create a model from JSON where key is a value. This is the exact issue described, but in iOS. I want a similar solution in Android. Basically I want to have a Decodable equivalent in Android.
I am using GSON to parse JSON to model. As of now, I have compared the JSON key (mentioned in the link) against static values.
JSON :
{
"rows" :
[
{
"_id": "5cdc0ede5c3dcb04bdb3a972",
"emp_code": 187,
"log_id": 361711,
"punch_time": "2019-05-07T04:00:33.000Z",
"pin_type": 1,
"status": 4,
"__v": 0
},
{
"_id": "5cdc40de5c3dcb04bdb3a972",
"emp_code": 111,
"log_id": 361701,
"punch_time": "2019-05-07T04:00:35.000Z",
"pin_type": 101,
"status": 4,
"__v": 0
}
],
"pin_type_text": {
"1": "In Fingerprint",
"4": "In Card",
"101": "Out Fingerprint",
"104": "Out Card"
}
}
The value of pin_type in each row refers to the record in pin_type_text mapped with it's key.
I am using GSON for creating models, and here is the model class :
class MyModel {
var length : Long = 0
var rows = ArrayList<Rows>()
var pin_type_text : String = ""
}
class PinTypeText {
var 1 : String = ""
var 4 : String = ""
var 101 : String = ""
var 104 : String = ""
}
Basically, the keys defined in class PinTypeText are the values of the key 'pin_type' obtained in Rows model as seen in the JSON shared. So in this case, the keys in 'PinTypeText' are dependent on values defined in 'rows'. Hence, i want 'PinTypeText' model to be created with respect to 'pin_type' values from 'Rows' model.
Issue : Suppose in future, the 'pin_type' values - 1, 4, 101, 104 change in the backend, how can I handle such a case without changing my model. As per this model structure, I need to change my model class every time the backend model changes
you can store the item PinTypeText as a JsonElement and not as a custom class,
so your response model will be something like this
public class Response{
#SerializedName("rows")
#Expose
private List<Row> rows = null;
#SerializedName("pin_type_text")
#Expose
private JsonElement pinTypeText;
public List<Row> getRows() {
return rows;
}
public void setRows(List<Row> rows) {
this.rows = rows;
}
public JsonElement getPinTypeText() {
return pinTypeText;
}
public void setPinTypeText(JsonElement pinTypeText) {
this.pinTypeText = pinTypeText;
}
}
and when you want to check the type you can convert it to JsonObject and get the value for the key,
example
pinTypeText= response.getPinTypeText().asJsonObject().get([your pin_type here]).toString()
I have this JSON object:
{
"maindrawer":
{
"enabled": true,
"actions":
[
{
"type": "Section",
"title": "Section 1"
},
{
"id": 1,
"type": "Primary",
"title": "Title 1",
"badge":
{
"enabled": false,
"value": 0,
"textColor": "#000000",
"badgeColor": "#ff0990"
},
"subActions":
[
{
"id": 1,
"type": "Primary",
"title": "Sub Title 1"
}
]
}
]
}
}
This is the code I'm using to access the badge -> textColor value:
public void loadJSONFromRaw(Context context, int id)
{
json = null;
try
{
//read and return json sting
InputStream is = context.getResources().openRawResource(id);
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
//convert json to object
Type type = new TypeToken<Map<String, Object>>() {}.getType();
Map<String, Object> data = new Gson().fromJson(json, type);
//access maindrawer property
Map<String, Object> maindrawer = (Map<String, Object>)data.get("maindrawer");
//access actions list
List<Object> actions = (List<Object>)maindrawer.get("actions");
//return first item in the list
Map<String, Object> action = (Map<String, Object>) actions.get(1);
//return badge object
Map<String, String> badge = (Map<String, String>) action.get("badge");
//access badge -> textColor value
String textColor = badge.get("textColor");
}
catch (IOException e)
{
e.printStackTrace();
}
}
Is there a better/faster or more dynamic way to access JSON nested properties using java/android? I'm using Gson library for this task and don't mind to switch to any other solution to make it easier as this is too much of code to write just to access a single variable.
Ideally, I'm looking for something like:
String textColor = data.get("maindrawer").get("actions").get(1).get("badge").get("textColor");
Also I'm not very interested in using POJO for now.
Lastly, I'm still new to Java so I'm probably missing something here or maybe there are some limitations? anyways thanks for you help!!
Found what I need using JsonPath library. It looks like it does similar to what I need. Here's a sample code I found:
String textColor = JsonPath.parse(json).read("$.maindrawer.actions[1].badge.textColor");
Very clean and straightforward. Hopes this will save someone else's time as well.
Since you are accessing json file locally, it means you know its structure.
So instead of using -
Map<String, Object> data = new Gson().fromJson(json, type);
You can use something like this-
Map<String, MainDrawer> data = new Gson().fromJson(json, type);
where MainDrawer is a class with member variables - enabled, actions and array of another type.
That would make easier to fetch your values like using -
mainDrawer.isEnabled()
Here are two solutions without importing a new library.
Write a simple path parser:
String textColor = (String)parse(data, "maindrawer", "actions", 1, "badge", "textColor");
//...
static Object parse(Object root, Object... params) {
Object current = root;
for (Object p : params) {
if (p instanceof Number) {
current = ((List<?>)current).get(((Number)p).intValue());
} else {
current = ((Map<?,?>)current).get(p.toString());
}
}
return current;
}
Or parse and walk through Gson's JsonElement:
JsonElement root = new Gson().fromJson(json, JsonElement.class);
String textColor = root
.getAsJsonObject().get("maindrawer")
.getAsJsonObject().get("actions")
.getAsJsonArray().get(1)
.getAsJsonObject().get("badge")
.getAsJsonObject().get("textColor")
.getAsString();
You can also do this with BSON using a single line query. You have to cast the object to the type as you go down into Nested JSON objects.
//import java.util.ArrayList;
//import org.bson.Document;
Document root = Document.parse("{ \"maindrawer\" : { \"enabled\" : true, \"actions\" : [{ \"type\" : \"Section\", \"title\" : \"Section 1\" }, { \"id\" : 1, \"type\" : \"Primary\", \"title\" : \"Title 1\", \"badge\" : { \"enabled\" : false, \"value\" : 0, \"textColor\" : \"#000000\", \"badgeColor\" : \"#ff0990\" }, \"subActions\" : [{ \"id\" : 1, \"type\" : \"Primary\", \"title\" : \"Sub Title 1\" }] }] } }");
System.out.println(((String)((Document)((Document)((ArrayList)((Document)root.get("maindrawer")).get("actions")).get(1)).get("badge")).get("textColor")));
public class Town {
private Person p;
private String hello;
private long number;
}
public class Person {
private String firstName;
private double legs;
private String lastName;
}
I am trying to write the Town class to JSON using the below code
ObjectMapper mapper = new ObjectMapper();
ObjectWriter writer = mapper.writer(new DefaultPrettyPrinter());
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(file, true)));
writer.writeValue(out, townobj);
Which produces Json like this.
{
"p" : {
"firstName" : "John",
"amount" : 6860.0,
"lastName" : "Smith"
},
"hello" : "qwiejiowcqnio",
"number" : 1380.0
}
{
"p" : {
"firstName" : "Sam",
"amount" : 623460.0,
"lastName" : "Smith"
},
"hello" : "qwiej2342io",
"number" : 1330.0
}
How do I read such an output produced from nested objects into Java with jackson?
If you want to read two objects as a list into Java, you need to write them as a list as well:
List<Town> towns = new ArrayList<>();
towns.add(townobj);
towns.add(anotherTownobj);
writer.writeValue(out, towns);
When you read that back it becomes a List again.
The output you've shown in your question as not a valid single json file. But using the above method will get you a valid single json file that looks like this:
[
{
"p" : {
"firstName" : "John",
"amount" : 6860.0,
"lastName" : "Smith"
},
"hello" : "qwiejiowcqnio",
"number" : 1380.0
},
{
"p" : {
"firstName" : "Sam",
"amount" : 623460.0,
"lastName" : "Smith"
},
"hello" : "qwiej2342io",
"number" : 1330.0
}
]
I have a JSON file and I do not know how can I parse the part of "coordinates", others done already. It seems null, others seem ok when I try to reach them. I guess, coordinates part is another class defined in cities part. Could you please help me to get coordinates of cities?
I kept my cities in a linkedlist.
"cities" : [
{
"code" : "SCL" ,
"name" : "Santiago" ,
"country" : "CL" ,
"continent" : "South America" ,
"timezone" : -4 ,
"coordinates" : {"S" : 33, "W" : 71} ,
"population" : 6000000 ,
"region" : 1
}
static List<City> allCities = new LinkedList<City>();
static List<Flight> allFlights = new LinkedList<Flight>();
static JSONArray cities;
static JSONArray flights;
FileReader reader = new FileReader("csair.json");
JSONObject CSAirData = (JSONObject) JSONValue.parse(reader);
cities = (JSONArray) CSAirData.get("cities");
flights = (JSONArray) CSAirData.get("routes");
Assuming "cities" is an attribute of variable myVar, like this
var myVar = {
"cities": [
{
"code": "SCL",
"name": "Santiago",
...
}
]
};
then you could access "coordinates" by doing
myVar.cities[0].coordinates
"cities" corresponds to an array
the first element in the array (index = 0) is an object
that object has an attribute called "coordinates", which references another object
Edit
Now that I see you are using Java code, you just need to transform this syntax into Java.
We know that "cities" is a JSONArray.
JSONObject city = cities.get(0); // Get the first city in the array (index = 0)
JSONObject coordinates = city.getJSONObject("coordinates");
int coordinates_s = coordinates.getInt("S");
int coordinates_w = coordinates.getInt("W");
I have the following JSON:
{
"registration": {
"name": "Vik Kumar",
"first_name": "Vik",
"last_name": "Kumar",
"bloodGroup": "B-",
"gender": "male",
"birthday": "10\/31\/1983",
"email": "vik.ceo\u0040gmail.com",
"cellPhone": "1234123456",
"homePhone": "1234123457",
"officePhone": "1234123458",
"primaryAddress": "jdfjfgj",
"area": "jfdjdfj",
"location": {
"name": "Redwood Shores, California",
"id": 103107903062719
},
"subscribe": true,
"eyePledge": false,
"reference": "fgfgfgfg"
}
}
I am using the following code to parse it:
JsonNode json = new ObjectMapper().readTree(jsonString);
JsonNode registration_fields = json.get("registration");
Iterator<String> fieldNames = registration_fields.getFieldNames();
while(fieldNames.hasNext()){
String fieldName = fieldNames.next();
String fieldValue = registration_fields.get(fieldName).asText();
System.out.println(fieldName+" : "+fieldValue);
}
This works fine and it print all the values except for location which is kind of another level of nesting. I tried the same trick as above code to pass json.get("location") but that does not work. Please suggest how to make it work for location.
You need to detect when you are dealing with a (nested) Object using JsonNode#isObject:
public static void printAll(JsonNode node) {
Iterator<String> fieldNames = node.getFieldNames();
while(fieldNames.hasNext()){
String fieldName = fieldNames.next();
JsonNode fieldValue = node.get(fieldName);
if (fieldValue.isObject()) {
System.out.println(fieldName + " :");
printAll(fieldValue);
} else {
String value = fieldValue.asText();
System.out.println(fieldName + " : " + value);
}
}
}
Thus, when you reach an object, such as location, you'll call the printAll recursively to print all its inner values.
org.codehaus.jackson.JsonNode json = new ObjectMapper().readTree(jsonString);
org.codehaus.jackson.JsonNode registration_fields = json.get("registration");
printAll(registration_fields);
Since location is nested within registration, you need to use:
registration_fields.get("location");
to get it. But isn't it already processed by the while-loop, why do you need to get it separately?