how to read JSON files using Gson

[saeid jamali]

I am trying to read a Jason file but nothing happens when I press the read button there is not even an exception.
I'm using Gson and my Jason reader is

public class JASONReader {
	Datalist list = new Datalist();
	public List<Sensor> readjason(String jasonfile) throws IOException{
		Gson gsonRead = new Gson();
		InputStream in = new FileInputStream(jasonfile);
		BufferedReader buffer=new BufferedReader(new InputStreamReader(in));
		
		Datalist out = gsonRead.fromJson(buffer, Datalist.class);
		
		list = out;
		return list.getsList();	
}

}

and the code for my user interface is

//rest of the code above
else if(fc.getFileFilter().getDescription() == ("JSON")){
					File file = fc.getSelectedFile();
					JASONReader read = new JASONReader();
					try {
						List<Sensor> readJason = read.readjason(file.getAbsolutePath());
						for(Sensor data:readJason){
							textArea.append(data+"\n\n");
						}
					} catch (IOException e1) {
						// TODO Auto-generated catch block
						e1.printStackTrace();
					}
				}
//rest of the code below

The datalist class is an arraylist which I use for all the files instead of having separate arraylists. Can anybody see the problem in my code please?
Thanks a lot

[Christian Klugesherz]

Hi Saeid

Here a simple example to test the JSON read and write. (Also reference where I got the info)
Just to change the name of destination file in the 2 class below.
Hope it will help.

package pacp.test;
// http://www.java2blog.com/2013/11/jsonsimple-example-read-and-write-json.html
import java.io.FileNotFoundException;  
import java.io.FileReader;  
import java.io.IOException;  
import java.util.Iterator;  
import org.json.simple.JSONArray;  
import org.json.simple.JSONObject;  
import org.json.simple.parser.JSONParser;  
import org.json.simple.parser.ParseException;  


public class JSONReadingFile {  

	public static void main(String[] args) {  

		JSONParser parser = new JSONParser();  

		try {  
			JSONObject jsonObjectL1;
			JSONObject jsonObjectL2;
			JSONArray jsonArrayL1; 
			
			Object obj = parser.parse(new FileReader("D:/Users/kluges1/Downloads/test.cfg"));  
			System.out.println(obj);  

			// Object level 1 (whole)
			jsonObjectL1 = (JSONObject) obj;  
			System.out.println(jsonObjectL1);
			
			// Object level 2 (+1 deeper)
			jsonObjectL2 = (JSONObject) jsonObjectL1.get("Cfg");  
			System.out.println(jsonObjectL2);
			System.out.println(jsonObjectL2.get("Lang"));  
			System.out.println(String.valueOf(jsonObjectL2.get("Empty")));  
			
			// Object level 2 (+1 deeper) is AN Array !!
			JSONArray jsonObjectScrollL = (JSONArray) jsonObjectL1.get("Scroll");
			System.out.println(	"Array -- >"+ jsonObjectScrollL);

			// Read ARRAY List !
			Iterator<?> iteratorscroll = jsonObjectScrollL.iterator();  
			while (iteratorscroll.hasNext()) {  
				jsonObjectL2 = (JSONObject)iteratorscroll.next();
				System.out.println(String.valueOf(jsonObjectL2));
				System.out.println("AVR = " + String.valueOf(jsonObjectL2.get("AVR")));  
			}  
			
			// ARRAY Get 1 element
			jsonObjectL2 = (JSONObject) jsonObjectScrollL.get(0);  
			System.out.println(jsonObjectL2);
			System.out.println(String.valueOf(jsonObjectL2.get("AVR")));  
			System.out.println(String.valueOf(jsonObjectL2.get("EE")));  

			jsonObjectL2 = (JSONObject) jsonObjectL1.get("Measure");  
			System.out.println(jsonObjectL2);

			jsonArrayL1 = (JSONArray) jsonObjectL2.get("T1T2T3T4");
			System.out.println(jsonArrayL1);
			
			Iterator<?> iterator = jsonArrayL1.iterator();  
			while (iterator.hasNext()) {  
				System.out.println(String.valueOf(iterator.next()));  
			}  
			
			jsonArrayL1 = (JSONArray) jsonObjectL2.get("H1H2H3H4");
			System.out.println(jsonArrayL1);
			System.out.println(String.valueOf(jsonArrayL1.get(0)));
			System.out.println(String.valueOf(jsonArrayL1.get(2)));
			

		} catch (FileNotFoundException e) {  
			e.printStackTrace();  
		} catch (IOException e) {  
			e.printStackTrace();  
		} catch (ParseException e) {  
			e.printStackTrace();  
		}  

	}  
}  

package pacp.test;
//http://www.java2blog.com/2013/11/jsonsimple-example-read-and-write-json.html
//https://www.tutorialspoint.com/json/json_java_example.htm
import java.io.File;  
import java.io.FileWriter;  
import java.io.IOException;  
import org.json.simple.JSONArray;  
import org.json.simple.JSONObject;  


public class JSONWritingFile {  

	@SuppressWarnings("unchecked")
	public static void main(String[] args) {  
		
		JSONArray listOfScroll = new JSONArray();
		JSONObject ObjScroll = new JSONObject();  
		ObjScroll.put("AVR", 10);
		ObjScroll.put("EE", 100);		
		listOfScroll.add(ObjScroll);

		JSONObject ObjScroll2 = new JSONObject();  
		ObjScroll2.put("AVR", 100);
		ObjScroll2.put("EE", 1000);	
		listOfScroll.add(ObjScroll2);

		
		JSONObject ObjCfg = new JSONObject();  
		ObjCfg.put("Lang", "French");
		ObjCfg.put("Empty", 1);
		
		JSONObject ObjMeasure = new JSONObject();  
		JSONArray listOfH = new JSONArray();  
		listOfH.add(100);  
		listOfH.add(200);  
		listOfH.add(300);  
		listOfH.add(400);  
		ObjMeasure.put("H1H2H3H4", listOfH);  

		JSONArray listOfT = new JSONArray();  
		listOfT.add(1);  
		listOfT.add(2);  
		listOfT.add(3);  
		listOfT.add(4);  
		ObjMeasure.put("T1T2T3T4", listOfT);  

		JSONObject ObjPacTool = new JSONObject();  
		ObjPacTool.put("Scroll", listOfScroll);  
		ObjPacTool.put("Cfg", ObjCfg);  
		ObjPacTool.put("Measure", ObjMeasure);

		try {  
			// Writing to a file  
			File file=new File("D:/Users/kluges1/Downloads/test.cfg");  
			file.createNewFile();  
			FileWriter fileWriter = new FileWriter(file);  
			System.out.println("Writing JSON object to file");  
			System.out.println("-----------------------");  
			System.out.print(ObjPacTool);  

			fileWriter.write(ObjPacTool.toJSONString());  
			fileWriter.flush();  
			fileWriter.close();  

		} catch (IOException e) {  
			e.printStackTrace();  
		}  

	}  
}  

Regards

Christian

[saeid jamali]

I prefer to use Gson and I'm sure my code is almost done and I'm just missing something small. I have three file readers which two of them are done I'm just stuck at reading Jason

[Ron McLeod]

Can post you an example of what the contents of a file with JSON-encoded sensor data looks like?

[saeid jamali]

Ron McLeod wrote:Can post you an example of what the contents of a file with JSON-encoded sensor data looks like?

{
"logdata":
[
	{
		"millis": "1000",
		"stamp": "1273010254",
		"datetime": "2010/5/4 21:57:34",
		"light": "333",
		"temp": "78.32",
		"vcc": "3.54"
	},
	{
		"millis": "2000",
		"stamp": "1273010255",
		"datetime": "2010/5/4 21:57:35",
		"light": "333",
		"temp": "78.32",
		"vcc": "3.92"
	},

[Ron McLeod]

The problem is that  in the JSON data, the list of sensor data is named logdata, but there is no field named logdata in your Datalist class (by default, when deserializing, Gson will try and match the JSON attribute name with a Java field name).

Use the SerializedName annotation to indicate that the annotated field is for the JSON data named logdata.

For example (using your code from another topic):

import java.util.List;
import com.google.gson.annotations.SerializedName;

public class Datalist {
	@SerializedName("logdata")
	private List<Sensor> sList;

	public List<Sensor> getsList() {
		return sList;
	}

	public void setsList(List<Sensor> sList) {
		this.sList = sList;
	}
}

[Ron McLeod]

Also, there is no need to create an instance of Datalist in your JASONReader class (unless it is used for something else).

public class JASONReader {
	// Datalist list = new Datalist();
	public List<Sensor> readjason(String jasonfile) throws IOException {
		Gson gsonRead = new Gson();
		InputStream in = new FileInputStream(jasonfile);
		BufferedReader buffer = new BufferedReader(new InputStreamReader(in));

		Datalist out = gsonRead.fromJson(buffer, Datalist.class);

		// list = out;
		// return list.getsList();
		return out.getsList()
	}
}

[Ron McLeod]

Also, you can simplify your reader.

public class JASONReader {
	public List<Sensor> readjason(String jasonfile) throws IOException {
		Gson gsonRead = new Gson();
		Reader reader = new FileReader(jasonfile);
		Datalist out = gsonRead.fromJson(reader, Datalist.class);
		return out.getsList();
	}	
}

[Rob Spoor]

saeid jamali wrote:and the code for my user interface is

//rest of the code above
else if(fc.getFileFilter().getDescription() == ("JSON")){

Don't use ==, use equals. Otherwise the block will not get executed if your description is equal to JSON but is a different String instance.

else if ("JSON".equals(fc.getFileFilter().getDescription())) {

[Rob Spoor]

And two more things:
1) It's JSON, not JASON (so also not jason).
2) Make sure to close your streams. Using Ron's simplified code:

public class JSONReader {
	public List<Sensor> readjson(String jsonfile) throws IOException {
		Gson gsonRead = new Gson();
		try (Reader reader = new FileReader(jsonfile)) {
			Datalist out = gsonRead.fromJson(reader, Datalist.class);
			return out.getsList();
		}
	}	
}