jsonrpc.java

package com.example.jsonrpc;

import android.content.Context;
import android.util.Log;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.HashMap;
import java.util.Map;

public class JSONRPC {

    public static final String TAG = JSONRPC.class.getName();

    static final String END_POINT = "http://jsonrpc.example.com";

    //----------------------------------------
    // Singleton
    private static JSONRPC mInstance = new JSONRPC();
    private JSONRPC() {}
    public static JSONRPC getInstance() { return mInstance; }

    //----------------------------------------
    // Interfaces

    public static class Error extends Exception {
        public Error(String message) {
            super(message);
        }
    }

    public interface Handler {
        JSONObject buildParams() throws JSONException;
        void success(JSONObject result);
        void failure(Error error);
    }

    //----------------------------------------
    // Public Methods

    public static void call(String method, final Handler handler) {
        JSONObject body = new JSONObject();
        try {
            body.put("id", "Generated ID");
            body.put("jsonrpc", "2.0");
            body.put("method", method);
            body.put("params", handler.buildParams());
        } catch (JSONException e) {
            handler.failure(new Error(e.toString()));
            return;
        }
        Log.i(TAG, "Request to '" + END_POINT + "': " + body.toString());
        JsonObjectRequest req = new JsonObjectRequest(Request.Method.POST, END_POINT, body, new Response.Listener<JSONObject>() {
            @Override
            public void onResponse(JSONObject response) {
                Log.i(TAG, "Response: " + response.toString());
                try {
                    if (response.has("error")) {
                        handler.failure(new Error(response.getJSONObject("error").toString()));
                    } else {
                        handler.success(response.getJSONObject("result"));
                    }
                } catch (JSONException e) {
                    handler.failure(new Error(e.toString()));
                }
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                handler.failure(new Error(error.networkResponse.toString()));
            }
        }) {
            @Override
            public Map<String, String> getHeaders() throws AuthFailureError {
                Map<String, String> headers = new HashMap<String, String>();
                headers.put("Content-Type", "application/json");
                return headers;
            }
        };
        if (!getInstance().addRequest(req)) {
            handler.failure(new Error("Request queue has not been created."));
        }
    }

    //----------------------------------------
    // Private Methods

    private RequestQueue mQueue;

    private boolean addRequest(Request req) {
        if (mQueue == null) {
            Context context = App.getInstance().getContext(); // Application Context
            if (context == null) {
                return false;
            }
            mQueue = Volley.newRequestQueue(context);
        }
        mQueue.add(req);
        return true;
    }

}