Gson turn an array of data objects into json - Android

Question

Currently I am working on a native android app with webView front end.

I have something like:

public class dataObject {   int a;   String b; } 

and in activity,

I have made an array of dataObject, say dataObject x[5];

Now i want to pass these 5 dataObject to my javascript webView interface as JSON in a callback function.

I looked through the internet, seems like most tutorials talk about how to convert fromJson(). There are not a lot about toJson(). I found one that taught me that dataObject.toJson(), would work.

But how can I pass all 5 dataObjects?

Answer 1

Here's a comprehensive example on how to use Gson with a list of objects. This should demonstrate exactly how to convert to/from Json, how to reference lists, etc.

Test.java:

import com.google.gson.Gson; import java.util.List; import java.util.ArrayList; import com.google.gson.reflect.TypeToken; import java.lang.reflect.Type;   public class Test {    public static void main (String[] args) {      // Initialize a list of type DataObject     List<DataObject> objList = new ArrayList<DataObject>();     objList.add(new DataObject(0, "zero"));     objList.add(new DataObject(1, "one"));     objList.add(new DataObject(2, "two"));      // Convert the object to a JSON string     String json = new Gson().toJson(objList);     System.out.println(json);      // Now convert the JSON string back to your java object     Type type = new TypeToken<List<DataObject>>(){}.getType();     List<DataObject> inpList = new Gson().fromJson(json, type);     for (int i=0;i<inpList.size();i++) {       DataObject x = inpList.get(i);       System.out.println(x);     }    }     private static class DataObject {     private int a;     private String b;      public DataObject(int a, String b) {       this.a = a;       this.b = b;     }      public String toString() {       return "a = " +a+ ", b = " +b;     }   }  } 

To compile it:

javac -cp "gson-2.1.jar:." Test.java 

And finally to run it:

java -cp "gson-2.1.jar:." Test 

Note that if you're using Windows, you'll have to switch : with ; in the previous two commands.

After you run it, you should see the following output:

[{"a":0,"b":"zero"},{"a":1,"b":"one"},{"a":2,"b":"two"}] a = 0, b = zero a = 1, b = one a = 2, b = two 

Keep in mind that this is only a command line program to demonstrate how it works, but the same principles apply within the Android environment (referencing jar libs, etc.)