Develop Reference

Parsing JSON using Java JSONParser

I'm trying to parse a JSON File. I wrote the code below to parse using Java JSONParser:
public static void parseJSONResponse(JSONObject jsonObj) {
for (Object keyObj : jsonObj.keySet()) {
String key = (String) keyObj;
Object valObj = jsonObj.get(key);
if (valObj instanceof JSONObject) {
parseJSONResponse((JSONObject) valObj);
} else if (valObj instanceof JSONArray) {
System.err.println("ARRAY");
} else {
System.out.println(key + " -> " + valObj.toString());
}
}
}
public static void main(String[] args) {
try {
FileReader reader = new FileReader("C:\\Users\\extract.json");
JSONParser parser = new JSONParser();
Object obj = (JSONObject) parser.parse(reader);
JSONObject object = (JSONObject) (obj);
parseJSONResponse(object);
} catch (IOException | ParseException e) {
e.printStackTrace();
}
}
It returns me a response like this:
description -> For testing purposes only
indexUpdatedAt -> 1420751985
flags -> ["default","restorable","restorePossibleForType"]
data -> [["row-mfpy.gr8q.cpii","00000000-0000"],["00009","9BCA"]]
columns -> [{"renderTypeName":"meta_data","fieldName":":sid"},{"renderTypeName":"meta_data"}]
I need to further parse "flags", "data" & "columns" to retrieve the values individually. How can i modify my "parseJSONResponse" method to achieve this?

Can't read json file

Here's my method where im reading json file.
private void LoadTabaksFromJson() {
InputStream raw = mContext.getResources().openRawResource(R.raw.tabaks);
Reader reader = new BufferedReader(new InputStreamReader(raw));
ListOfTabaks listOfTodos = new Gson().fromJson(reader, ListOfTabaks.class);
List<Tabak> todoList = listOfTodos.getTodoArrayList();
for (Tabak item: todoList){
mDataBase.insert(TabakTable.NAME,null,getContentValues(item));
}
}
public class ListOfTabaks {
protected ArrayList<Tabak> tabakArrayList;
public ArrayList<Tabak> getTodoArrayList(){
return tabakArrayList;
}
}
And Exeption
Caused by: java.lang.NullPointerException: Attempt to invoke interface
method 'java.util.Iterator java.util.List.iterator()' on a null object
reference
at
com.hookah.roma.hookahmix.TabakLab.LoadTabaksFromJson(TabakLab.java:61)
at com.hookah.roma.hookahmix.TabakLab.(TabakLab.java:32)
at com.hookah.roma.hookahmix.TabakLab.get(TabakLab.java:37)
at
com.hookah.roma.hookahmix.TabakListFragment.updateUI(TabakListFragment.java:38)
at
com.hookah.roma.hookahmix.TabakListFragment.onCreateView(TabakListFragment.java:32)
at
android.support.v4.app.Fragment.performCreateView(Fragment.java:2184)
at
android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1298)
at
android.support.v4.app.FragmentManagerImpl.moveFragmentsToInvisible(FragmentManager.java:2323)
at
android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2136)
And json file :
{
"tabaksArrayList":[
{
"name":"Абрикос",
"description":"Со вкусом Абрикоса",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
{
"name":"Ананас",
"description":"Со вкусом Ананаса",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
{
"name":"Апельсин",
"description":"Со вкусом Апельсина",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},
{
"name":"Апельсин с мятой",
"description":"Со вкусом Апельсина с мятой",
"rating":"4.1",
"favourite":"1",
"family":"Al fakher"
},

It looks like your json schema issue, i'm guessing listOfTodos return null. You can refer to this to generate your schema.
But sometimes that tools can make us confuse so i tried to create your schema manually like this:
TabakRoot.java
public class TabakRoot {
#SerializedName("tabaksArrayList")
private List<TabakItem> tabakItem = null;
public List<TabakItem> getTabakItem() {
return tabakItem;
}}
TabakItem.java
public class TabakItem {
#SerializedName("family")
#Expose
private String tabakFamily;
public String getTabakFamily() {
return tabakFamily;
}}
finally
TabakRoot listOfTodos = new Gson().fromJson(reader, TabakRoot.class);
List<TabakItem> todoList = listOfTodos.getTabakItem();

Looks like you are not initialising your ArrayList, try changing:
protected ArrayList<Tabak> tabakArrayList;
for:
protected ArrayList<Tabak> tabakArrayList = new ArrayList<>();

Please put your json file in assets folder
use AsyncTask to protect from ANR like situtation
onBackground(){
String json = null;
try {
InputStream stream = activity.getAssets().open("ur_json_file_in_assets_folder.json");
int size = stream.available();
byte[] buffer = new byte[size];
stream.read(buffer);
stream.close();
json = new String(buffer, "UTF-8");
} catch (IOException e) {
e.printStackTrace();
return null;
}
return json;
}
then parse in
onPostExecute(String str){
JsonObject object = new JsonObject(str);
JsonArray arr = object.getJsonArray("tabaksArrayList");
...}
more details at ParseJsonFileAsync.java

You're not initialising tabakArrayList, add a constructor to your ListOfTabaks as following
public ListOfTabaks{
tabakArrayList = new ArrayList<>();
}
and you should be fine

How to handle non-existent data in JSONParser in Java

I have a JSONParser method like this :
public ArrayList<Meaning> parseMeaning (JSONObject object)
{
ArrayList<Meaning> arrayList = new ArrayList<Meaning>();
try
{
JSONObject value = object.getJSONObject("Value");
JSONArray meaningArray = value.getJSONArray("Meanings");
JSONObject meaningobj = null;
for(int i = 0; i < meaningArray.length(); i++) {
meaningobj = meaningArray.getJSONObject(i);
Meaning myMeaning = new Meaning();
myMeaning.MeaningID = meaningobj.getInt("MeaningID");
myMeaning.Type1 = meaningobj.getInt("Type1");
myMeaning.Type2= meaningobj.getInt("Type2");
arrayList.add(myMeaning);
}
}
catch (JSONException e)
{
Log.d("JSONParser=>parseMeaning", e.getMessage());
}
return arrayList;
}
My meaning class is like this :
public class Meaning {
public int MeaningID;
public Integer Type1;
public Integer Type2;
}
When I run the code, some JSON Objects don't have Type2 value (because they were null in the database). So I get this exception :
D/JSONParser=>parseMeaning﹕ No value for Type2
Can you tell me how I should handle such situations when there is no value for a field? Thanks.

You can use has method of JSONObject.
E.g. :
if(meaningobj.has("Type2")){
myMeaning.Type2= meaningobj.getInt("Type2");
}

Java - JSONObject Parsing only 1 string?

I'm fairly new to JSON parsing in Java but when I try and parse this JSON String & find out it's "ID", it repeats the same one twice.
[
{"id":"{ID1}","time":123},
{"id":"{ID2}","time":124}
]
This is my Java code:
// v = json string, c = "id"
String output = v.replace("[", "").replace("]", "");
JSONObject obj = new JSONObject(output);
ArrayList<String> list = new ArrayList<String>();
for(int i = 0 ; i < obj.length(); i++){
System.out.println(obj.getString(c));
list.add(obj.getString(c));
}
return list.get(1);
it returns ID1 twice or more. Please help

Your JSON represents an array - so that's how you should parse it. You can then easily get the id property from each JSONObject within the array. For example:
import org.json.*;
public class Test {
public static void main(String[] args) throws JSONException {
String json =
"[{\"id\":\"{ID1}\",\"time\":123}, {\"id\":\"{ID2}\",\"time\":124}]";
JSONArray array = new JSONArray(json);
for (int i = 0; i < array.length(); i++) {
JSONObject o = array.getJSONObject(i);
System.out.println(o.getString("id"));
}
}
}
Output:
{ID1}
{ID2}

I fixed my code by using it as a JSONArray(Thanks #HotLicks)
JSONArray obj = new JSONArray(v);
ArrayList<String> list = new ArrayList<String>();
for(int i = 0 ; i < obj.length(); i++){
Logger.WriteOutput(obj.getJSONObject(i).getString(c), Logger.LogLevel.Info);
}

Try this :
// This line is useless
// String output = v.replace("[", "").replace("]", "");
JSONArray arr = new JSONArray(output);
ArrayList<String> list = new ArrayList<String>();
for(int i = 0 ; i < arr.length(); i++){
System.out.println(arr.getJSONObject(i).getString(c));
list.add(arr.getJSONObject(i).getString(c));
}

First create a java bean for your json (for example here):
public class Item {
#JsonProperty("id")
private String id;
#JsonProperty("time")
private Integer time;
public final String getId() {
return id;
}
public final void setId(String id) {
this.id = id;
}
public final Integer getTime() {
return time;
}
public final void setTime(Integer time) {
this.time = time;
}
}
If you are using Jackson Java JSON-processor, you can create a List from JSON-String this way:
ObjectMapper objectMapper = new ObjectMapper();
try {
List<Item> items = objectMapper.readValue(
yourJSONString,
objectMapper.getTypeFactory().constructCollectionType(List.class, Item.class));
for (Item item : items) {
System.out.println(item.getId());
}
} catch (IOException e) {
e.printStackTrace();
}

use below code
String v = "[{\"id\":\"ID1\",\"time\":123},{\"id\":\"ID2\",\"time\":124}]";
String c = "id";
JSONArray obj = null;
try {
obj = new JSONArray(v);
ArrayList<String> list = new ArrayList<String>();
for (int i = 0; i < obj.length(); i++) {
JSONObject j = (JSONObject) obj.get(i);
System.out.println(j.getString(c));
list.add(j.getString(c));
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
note that i have slightly corrected the json structure too
before
[
{"id":"{ID1}","time":123},
{"id":"{ID2}","time":124}
]
after
[
{"id":"ID1","time":123},
{"id":"ID2","time":124}
]

How to gather data from a JSON URL and display it

I am trying to write an automated Java test where the code will go to a specified URL, read the JSON data and print it up.
Here is the JSON I am trying to access;
{
"status": "success",
"records": [
{
"timestamp": 1381222871868,
"deviceId": "288",
"temperature": 17
},
{
"timestamp": 1381222901868,
"deviceId": "288",
"temperature": 17
},
{
"timestamp": 1381222931868,
"deviceId": "288",
"temperature": 17
},
]}
As you can see I only have 3 elements, Timestamp, DeviceId and Temperature.
What I am ultimately aiming for it to be able to get 2 Timestamp values and take one value away from the other, if that is possible.
Anyway I have been trying to do this all day and am having no luck whatsoever. I was recommended to use Gson and I have included the jar files into my classpath.
If anyone knows anything or can help me in any way it would be much appreciated as I have exhausted Google and myself trying to work this out.
Here is the code I have to display the full list, but I do not fully understand it and so far can't manipulate it to my advantage;
public static void main(String[] args) throws Exception
{
String jsonString = callURL("http://localhost:8000/eem/api/v1/metrics/temperature/288");
System.out.println("\n\njsonString: " + jsonString);
// Replace this try catch block for all below subsequent examples
/*try
{
JSONArray jsonArray = new JSONArray(jsonString);
System.out.println("\n\njsonArray: " + jsonArray);
}
catch (JSONException e)
{
e.printStackTrace();
}*/
try
{
JSONArray jsonArray = new JSONArray(jsonString);
int count = jsonArray.length(); // get totalCount of all jsonObjects
for(int i=0 ; i< count; i++)
{ // iterate through jsonArray
JSONObject jsonObject = jsonArray.getJSONObject(i); // get jsonObject # i position
System.out.println("jsonObject " + i + ": " + jsonObject);
}
}
catch (JSONException e)
{
e.printStackTrace();
}
}
public static String callURL(String myURL)
{
//System.out.println("Requested URL:" + myURL);
StringBuilder sb = new StringBuilder();
URLConnection urlConn = null;
InputStreamReader in = null;
try
{
URL url = new URL(myURL);
urlConn = url.openConnection();
if (urlConn != null)
{
urlConn.setReadTimeout(60 * 1000);
}
if (urlConn != null && urlConn.getInputStream() != null)
{
in = new InputStreamReader(urlConn.getInputStream(),
Charset.defaultCharset());
BufferedReader bufferedReader = new BufferedReader(in);
if (bufferedReader != null)
{
int cp;
while ((cp = bufferedReader.read()) != -1)
{
sb.append((char) cp);
}
bufferedReader.close();
}
}
in.close();
}
catch (Exception e)
{
throw new RuntimeException("Exception while calling URL:"+ myURL, e);
}
return sb.toString();
}
Cheers

I had read the values from file but you can read from URL, the extracting process code is present inside extractJson() method.
public static void main(String [] args)
{
try
{
FileInputStream fis=new FileInputStream("testjson.json");
int b=0;
String val="";
while((b=fis.read())!=-1)
{
val=val+(char)b;
}
extractJson(val);
}
catch(Exception e)
{
e.printStackTrace();
}
}
public static void extractJson(String json)
{
try
{
JSONObject jobject=new JSONObject(json);
System.out.println("Json object Length: "+jobject.length());
System.out.println("Status: "+jobject.getString("status"));
JSONArray jarray=new JSONArray(jobject.getString("records"));
System.out.println("Json array Length: "+jarray.length());
for(int j=0;j<jarray.length();j++)
{
JSONObject tempObject=jarray.getJSONObject(j);
System.out.println("Timestamp: "+tempObject.getString("timestamp"));
System.out.println("Device Id: "+tempObject.getString("deviceId"));
System.out.println("Temperature: "+tempObject.getString("temperature"));
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
You could use ArrayList to store the values which will be available inside for loop. From your question you need to pass jsonString this variable to the extractJson() method. Use org.json jar file to process json. If you could alter this for gson then it'll be good for your requirement.

here's how to do it via Google-Gson
class MyRecord
{
private long timestamp;
private String deviceId;
private Integer temperature;
//Getters & setters
}
public static void main(String... args){
String myJsonString=callUrl("http://mydomain.com/x.json");
JsonParser jp = new JsonParser();
JsonElement ele = jp.parse(myJsonString);
Gson gg = new Gson();
Type type = new TypeToken<List<MyRecord>>() {
}.getType();
List<MyRecord> lst= gg.fromJson(ele.getAsJsonObject().get("records"), type);
//Now the json is parsed in a List of MyRecord, do whatever you want to with it
}

An "high-level" Gson parsing answer:
package stackoverflow.questions.q19252374;
import java.util.List;
import com.google.gson.Gson;
public class Q19252374 {
class Record {
Long timestamp;
String deviceId;
Long temperature;
}
class Container {
List<Record> records;
}
public static void main(String[] args) {
String json = "{ \"status\": \"success\", \"records\": [{\"timestamp\": 1381222871868,\"deviceId\": \"288\",\"temperature\": 17 },{\"timestamp\": 1381222901868,\"deviceId\": \"288\",\"temperature\": 17 },{\"timestamp\": 1381222931868,\"deviceId\": \"288\",\"temperature\": 17 } ]} ";
Gson g = new Gson();
Container c = g.fromJson(json, Container.class);
for (Record r : c.records)
System.out.println(r.timestamp);
}
}
Of course this is the result:
1381222871868
1381222901868
1381222931868