example of using generics

JsonTest.java

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONTokener;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.ViewGroup;
import android.widget.TextView;

import com.loopj.android.http.AsyncHttpResponseHandler;

public class JsonTest extends Activity {
    private TextView mTextView;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        mTextView = createTextView();
        
        test();
    }
    
    private void test() {
        String jsonArray = "[1,\"hello\"]";
        String jsonObject = "{\"2\":[1,\"hello\"],\"a\":\"b\"}";
        
        // passing array type works
        new MyJsonHttpResponseHandler<JSONArray>() {
            @Override
            public void onSuccess(JSONArray response) {
                appendLog("onSuccess", response);
            }
            @Override
            public void onFailure(Throwable throwable, String message) {
                appendLog("onFailure", throwable, message);
            }
        }.handleSuccessMessage(jsonArray);
        
        // passing wrong type
        new MyJsonHttpResponseHandler<JSONArray>() {
            @Override
            public void onSuccess(JSONArray response) {
                appendLog("onSuccess", response);
            }
            @Override
            public void onFailure(Throwable throwable, String message) {
                appendLog("onFailure", throwable, message);
            }
        }.handleSuccessMessage(jsonObject);
    }
    
    private TextView createTextView() {
        int fillParent = ViewGroup.LayoutParams.FILL_PARENT;
        ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(fillParent, fillParent);
        TextView textView = new TextView(this);
        textView.setTextColor(Color.WHITE);
        addContentView(textView, params);
        return textView;
    }
    
    private void appendLog(Object...messages) {
        StringBuilder messageBuilder = new StringBuilder();
        for (Object message : messages) {
            messageBuilder.append(message.toString())
                          .append(' ');
        }
        {// replace the last space with newline
            int len = messageBuilder.length();
            messageBuilder.replace(len - 1, len, "\n");
        }
        mTextView.append(messageBuilder);
    }
    
    private static class MyJsonHttpResponseHandler<JSONType> extends AsyncHttpResponseHandler {
        public  void onSuccess(JSONType response) { }
        @Override
        protected void handleSuccessMessage(String responseBody) {
            super.handleSuccessMessage(responseBody);
            
            try {
                onSuccess(parseResponse(responseBody));
            } catch(JSONException e) {
                // in case, json is malformed
                onFailure(e, responseBody);
            } catch (ClassCastException e) {
                // in case, the expected type is wrong.
                onFailure(e, responseBody);
            }
        }
        @SuppressWarnings("unchecked")
        protected JSONType parseResponse(String responseBody) throws JSONException {
            return (JSONType) new JSONTokener(responseBody).nextValue();
        }
    }
}