Develop Reference

Check if item in text file in JSON format Android Studio

I'm trying to check if config1 exists in a text file, I'm using Google's Gson library.
My JSON file :
{
"maps":{
"config2":{
"component1":"url1",
"component2":"url1",
"component3":"url1"
},
"config1":{
"component1":"url1",
"component2":"url1",
"component3":"url1"
}
}
}
Loading :
public void load() throws IOException {
File file = getContext().getFileStreamPath("jsonfile.txt");
FileInputStream fis = getContext().openFileInput("jsonfile.txt");
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader bufferedReader = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
sb.append(line);
}
String json = sb.toString();
Gson gson = new Gson();
Data data = gson.fromJson(json, Data.class);
componentURL= data.getMap().get("config1").get("component1");
Saving :
Gson gson = new Gson();
webViewActivity.Data data = gson.fromJson(json, webViewActivity.Data.class);
Map<String, String> configTest = data.getMap().get("config1");
data.getMap().get("config1").put(component, itemUrl);
String json = gson.toJson(data);
String filename = "jsonfile.txt";
FileOutputStream outputStream;
try {
outputStream = openFileOutput(filename, Context.MODE_PRIVATE);
outputStream.write(json.getBytes());
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
Data class :
public class Data {
private Map<String, Map<String, String>> map;
public Data() {
}
public Data(Map<String, Map<String, String>> map) {
this.map = map;
}
public Map<String, Map<String, String>> getMap() {
return map;
}
public void setMap(Map<String, Map<String, String>> map) {
this.map = map;
}
}
My problem is that I need to create the file once and then check if the file exists, if it does I need to check if config1 exists if it doesn't I need to put config1 in the file.
But I can't check if config1 exists because I get :
java.lang.NullPointerException: Attempt to invoke virtual method 'java.util.Map com.a.app.ui.app.appFragment$Data.getMap()
I check if it exists by doing :
Boolean configTest = data.getMap().containsKey("config1");
if(!configTest){}
How can I create the file and check the data without getting a NullPointerException ?

I think you should modify the way you're handling things.
First create POJO for Config1 each values as:
// file Config1.java
public class Config1
{
private String component1;
private String component2;
private String component3;
public String getComponent1 ()
{
return component1;
}
public void setComponent1 (String component1)
{
this.component1 = component1;
}
public String getComponent2 ()
{
return component2;
}
public void setComponent2 (String component2)
{
this.component2 = component2;
}
public String getComponent3 ()
{
return component3;
}
public void setComponent3 (String component3)
{
this.component3 = component3;
}
#Override
public String toString()
{
return "ClassPojo [component1 = "+component1+", component2 = "+component2+", component3 = "+component3+"]";
}
}
And then after that POJO for Config2
// file Config2.java
public class Config2
{
private String component1;
private String component2;
private String component3;
public String getComponent1 ()
{
return component1;
}
public void setComponent1 (String component1)
{
this.component1 = component1;
}
public String getComponent2 ()
{
return component2;
}
public void setComponent2 (String component2)
{
this.component2 = component2;
}
public String getComponent3 ()
{
return component3;
}
public void setComponent3 (String component3)
{
this.component3 = component3;
}
#Override
public String toString()
{
return "ClassPojo [component1 = "+component1+", component2 = "+component2+", component3 = "+component3+"]";
}
}
And then you need POJO for Maps
// file Maps.java
public class Maps
{
private Config2 config2;
private Config1 config1;
public Config2 getConfig2 ()
{
return config2;
}
public void setConfig2 (Config2 config2)
{
this.config2 = config2;
}
public Config1 getConfig1 ()
{
return config1;
}
public void setConfig1 (Config1 config1)
{
this.config1 = config1;
}
#Override
public String toString()
{
return "ClassPojo [config2 = "+config2+", config1 = "+config1+"]";
}
}
And finally the class which will wrap everything up MyJsonPojo. Though you can rename it to whatever you want.
// file MyJsonPojo.java
public class MyJsonPojo
{
private Maps maps;
public Maps getMaps ()
{
return maps;
}
public void setMaps (Maps maps)
{
this.maps = maps;
}
#Override
public String toString()
{
return "ClassPojo [maps = "+maps+"]";
}
}
Finally replace your code in the loadData() method as:
public void load() throws IOException {
File file = getContext().getFileStreamPath("jsonfile.txt");
FileInputStream fis = getContext().openFileInput("jsonfile.txt");
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader bufferedReader = new BufferedReader(isr);
StringBuilder sb = new StringBuilder();
String line;
while ((line = bufferedReader.readLine()) != null) {
sb.append(line);
}
String json = sb.toString();
Gson gson = new Gson();
Data data = gson.fromJson(json, MyJsonPojo.class);
Maps maps = data.getMaps();
Config1 config1 = null;
if (maps != null) {
config1 = maps.getConfig1()
}
if (config1 != null) {
componentURL = config1.getComponent1();
}
}
For saving the values you can do this:
public void save() {
// set url here
Component1 component1 = new Component1();
component1.setComponent1(itemUrl);
// store it in maps
Maps maps = new Maps();
maps.setComponent1(component1);
// finally add it to the MyJsonPojo instance
MyJsonPojo myJsonPojo = new MyJsonPojo();
myJsonPojo.setMaps(maps);
Gson gson = new Gson();
String json = gson.toJson(maps);
String filename = "jsonfile.txt";
FileOutputStream outputStream;
try {
outputStream = openFileOutput(filename, Context.MODE_PRIVATE);
outputStream.write(json.getBytes());
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
Please note that you may have to modify the save() code as per your structure because I am quite unsure about how you have handled what in the code. I have provided the basic implementation without much proof reading my code.

Change my writeJsonFile function from GSON to Jackson

I have some code that takes in a list of descriptors and writes them to different JSON files using the GSON library. I am now trying to change that library to Jackson. I am not a Jackson expert so I'm looking for some help. Here is my code when I am using GSON:
Descriptor Class:
public class Descriptor {
#SerializedName("BatchName")
private String batchName;
#SerializedName("Metadata")
private Metadata metadata;
#SerializedName("SampleInfo")
private SampleInfoJsonModel sampleInfo;
#SerializedName("Files")
private List<String> files;
#SerializedName("ClientData")
private ClientData clientData;
#SerializedName("CaseName")
private String caseName;
public Descriptor() {
this.metadata = new Metadata();
this.sampleInfo = new SampleInfoJsonModel();
this.files = new ArrayList<String>();
this.clientData = new ClientData();
}
public String getBatchName() {
return batchName;
}
public void setBatchName(String batchName) {
this.batchName = batchName;
}
public Metadata getMetadata() {
return metadata;
}
public void setMetadata(Metadata metadata) {
this.metadata = metadata;
}
public SampleInfoJsonModel getSampleInfo() {
return sampleInfo;
}
public void setSampleInfo(SampleInfoJsonModel sampleInfo) {
this.sampleInfo = sampleInfo;
}
public List<String> getFiles() {
return files;
}
public void setFiles(List<String> files) {
this.files = files;
}
public ClientData getClientData() {
return clientData;
}
public void setClientData(ClientData clientData) {
this.clientData = clientData;
}
public String getCaseName() {
return caseName;
}
public void setCaseName(String caseName) {
this.caseName = caseName;
}
public ClientData getClientDataNoCountryCodes() {
// TODO Auto-generated method stub
return null ;
}
}
My write JSON File function:
public static void writeJsonFile(List<Descriptor> descriptors) {
try {
for(Descriptor descriptor : descriptors) {
BufferedWriter buffWrite = new BufferedWriter(new FileWriter("descriptor_"+descriptor.getCaseName()+".json"));
Gson gson = new GsonBuilder().setPrettyPrinting().create();
buffWrite.write(gson.toJson(descriptor));
buffWrite.close();
}
}
catch (IOException ioe) {
System.err.println("Error while writing to json file in writeJsonFile: ");
ioe.printStackTrace();
}
}
Here is what I have written in Jackson:
BufferedWriter buffWrite = new BufferedWriter(new FileWriter("descriptor_"+descriptor.getCaseName()+".json"));
ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
buffWrite.write(mapper.writeValueAsString(descriptor));
Is this the equivalent of the code below in GSON?
BufferedWriter buffWrite = new BufferedWriter(new FileWriter("descriptor_"+descriptor.getCaseName()+".json"));
Gson gson = new GsonBuilder().setPrettyPrinting().create();
buffWrite.write(gson.toJson(descriptor));
buffWrite.close();

I think you are looking for generating a pretty JSON output for your Object and trying to write it into a file.
You have to make sure that you are using #SerializedName equivalent annotation from jackson which is #JsonProperty on your object properties.
Also you can use following to prettify JSON using jackson ObjectMapper
mapper.writerWithDefaultPrettyPrinter().writeValueAsString( descriptorObj )
NOTE that setting SerializationFeature.INDENT_OUTPUT will also help doing the same as you are already thinking.
Also Files APIs are really useful for file related operations.
I hope this will help!

Parsing JSON and writing it to prefs as a list of custom object

I have a custom model class like this -
public class MyModel implements Parcelable {
String title;
String message;
/**
* Creator method for the Parcel to use.
*/
public static final Parcelable.Creator<MyModel> CREATOR = new Parcelable.Creator<MyModel>() {
public MyModel createFromParcel(Parcel source) {
return new MyModel(source);
}
public MyModel[] newArray(int size) {
return new MyModel[size];
}
};
public void setTitle(final String titleValue) {
title = titleValue;
}
public void setMessage(final String messageValue) {
message = messageValue;
}
public String getTitle() {
return title;
}
public String getMessage() {
return message;
}
public MyModel() {
}
#Override
public int describeContents() {
return 0;
}
#Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.title);
dest.writeString(this.message);
}
private MyModel(Parcel in) {
this.title = in.readString();
this.message = in.readString();
}
}
My JSON in assets folder is -
[
{
"title": "1",
"message": "Hi"
},
{
"title": "2",
"message": "Bye"
},
{
"title": "3",
"message": "Ciao"
}
]
I need to read and parse this JSON and write it as a list of MyModel object into the shared prefs. To write into prefs, I am doing like this -
public void setSteps(final ArrayList<MyModel> steps) {
Gson gson = new Gson();
getPrefs(mContext).edit().putString("steps", gson.toJson(steps)).apply();
}
How can I parse this JSON and write it to the prefs as a list of MyModel object?
The JSON is currently stored in my assets folder.
Later I can read from the prefs and get the list

It's quite simple:
Type listType = new TypeToken<ArrayList<YourClass>>(){}.getType();
List<YourClass> yourClassList = new Gson().fromJson(jsonArray, listType);

public ArrayList<MyModel> getSteps(){
String localData = getPrefs(mContext).getString("steps");
return new Gson().fromJson(localData , new TypeToken<ArrayList<MyModel>>(){}.getType());
}

firstly load json data from asset folder to string:
public String loadJSONFromAsset() {
// check here data available in pref or not
// if available then return string object of pref here else fetch //from asset and set into pref
String json = null;
try {
InputStream is = getActivity().getAssets().open("yourfilename.json");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
return null;
}
return json;
}
this method will return the string json file then pass your string json into this:
Type listType = new TypeToken<ArrayList<ModelClass>>(){}.getType();
List<ModelClass> yourClassList = new Gson().fromJson(yourJsonString, listType);

Write this code read JSON from your asset folder.
public String loadJSONFromAsset() {
String json = null;
try {
InputStream is = getActivity().getAssets().open("yourfilename.txt");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
return null;
}
return json;
}
Write this code to read array data from your preference file.
import java.lang.reflect.Type;
import com.google.gson.reflect.TypeToken;
...
String jsonArray = getPrefs(mContext).getString("steps","[]").apply();
Type stepType = new TypeToken<ArrayList<YourModelClass>>(){}.getType();
ArrayList<YourModelClass> yourClassList = new Gson().fromJson(jsonArray, stepType);

Let's assume that you have data.json file in data folder in your assets.
just try below code to parse your json.
private void getJsonData()
{
String json = null;
try {
InputStream is = getAssets().open("data/data.json");
int size = is.available();
byte[] buffer = new byte[size];
is.read(buffer);
is.close();
json = new String(buffer, "UTF-8");
} catch (IOException ex) {
ex.printStackTrace();
}
Type listType = new TypeToken<List<MyModel>>(){}.getType();
ArrayList<MyModel> steps = new Gson().fromJson(json, listType);
setSteps(steps);
}
public void setSteps(final ArrayList<MyModel> steps) {
Gson gson = new Gson();
Log.e("~~~~~", gson.toJson(steps));
}
Here is my logcat result :
E/~~~~~: [{"message":"Hi","title":"1"},{"message":"Bye","title":"2"},{"message":"Ciao","title":"3"}]

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

Load very heavy stream with GSON

I'm trying to read a very heavy JSON (over than 6000 objects) and store them on a hash map to insert it into my database later.
But the problem is that I face with OOM and that's cause from my heavy JSON, however GSON library should rid me from this situation, but it is not !!!
Any ideas?
public Map<String,String> readJsonStream(InputStream in) throws IOException
{
JsonReader reader = new JsonReader(new InputStreamReader(in, "UTF-8"));
Map<String,String> contentMap = new HashMap<String,String>();
Gson mGson = new Gson();
contentMap = mGson.fromJson(reader, contentMap.getClass());
reader.close();
return contentMap;
}

From my experience, yes you can use google GSON to stream JSON data this is an example how to do it :
APIModel result = new APIModel();
try {
HttpResponse response;
HttpClient myClient = new DefaultHttpClient();
HttpPost myConnection = new HttpPost(APIParam.API_001_PRESENT(
serial_id, api_key));
try {
response = myClient.execute(myConnection);
Reader streamReader = new InputStreamReader(response
.getEntity().getContent());
JsonReader reader = new JsonReader(streamReader);
reader.beginObject();
while (reader.hasNext()) {
String name = reader.nextName();
if (name.equals("result")) {
if (reader.nextString() == "NG") {
result.setResult(Util.API_001_RESULT_NG);
break;
}
} else if (name.equals("items")) {
result = readItemsArray(reader);
} else {
reader.skipValue(); // avoid some unhandle events
}
}
reader.endObject();
reader.close();
} catch (Exception e) {
e.printStackTrace();
result.setResult(Util.API_001_RESULT_NG);
}
} catch (Exception e) {
e.printStackTrace();
result.setResult(Util.API_001_RESULT_NG);
}
readItemsArray function :
// read items array
private APIModel readItemsArray(JsonReader reader) throws IOException {
APIModel result = new APIModel();
String item_name, file_name, data;
result.setResult(Util.API_001_RESULT_OK);
reader.beginArray();
while (reader.hasNext()) {
item_name = "";
file_name = "";
data = "";
reader.beginObject();
while (reader.hasNext()) {
String name = reader.nextName();
if (name.equals("name")) {
item_name = reader.nextString();
} else if (name.equals("file")) {
file_name = reader.nextString();
} else if (name.equals("data")) {
data = reader.nextString();
} else {
reader.skipValue();
}
}
reader.endObject();
result.populateModel("null", item_name, file_name, data);
}
reader.endArray();
return result;
}
API Model Class :
public class APIModel {
private int result;
private String error_title;
private String error_message;
private ArrayList<String> type;
private ArrayList<String> item_name;
private ArrayList<String> file_name;
private ArrayList<String> data;
public APIModel() {
result = -1;
error_title = "";
error_message = "";
setType(new ArrayList<String>());
setItem_name(new ArrayList<String>());
setFile_name(new ArrayList<String>());
setData(new ArrayList<String>());
}
public void populateModel(String type, String item_name, String file_name, String data) {
this.type.add(type);
this.item_name.add(item_name);
this.file_name.add(file_name);
this.data.add(data);
}
public int getResult() {
return result;
}
public void setResult(int result) {
this.result = result;
}
public String getError_title() {
return error_title;
}
public void setError_title(String error_title) {
this.error_title = error_title;
}
public String getError_message() {
return error_message;
}
public void setError_message(String error_message) {
this.error_message = error_message;
}
public ArrayList<String> getType() {
return type;
}
public void setType(ArrayList<String> type) {
this.type = type;
}
public ArrayList<String> getItem_name() {
return item_name;
}
public void setItem_name(ArrayList<String> item_name) {
this.item_name = item_name;
}
public ArrayList<String> getFile_name() {
return file_name;
}
public void setFile_name(ArrayList<String> file_name) {
this.file_name = file_name;
}
public ArrayList<String> getData() {
return data;
}
public void setData(ArrayList<String> data) {
this.data = data;
}
}
before I use the streaming API from google GSON I also got OOM error because the JSON data I got is very big data (many images and sounds in Base64 encoding) but with GSON streaming I can overcome that error because it reads the data per token not all at once. And for Jackson JSON library I think it also have streaming API and how to use it almost same with my implementation with google GSON. I hope my answer can help you and if you have another question about my answer feel free to ask in the comment :)