How do you use the Android Volley API?

Edit: finally here it is an official training about "Volley library"

I found some examples about Volley library

• 6 examples by Ognyan Bankov :

  • Simple request
  • JSON request
  • Gson request
  • Image loading
  • with newer external HttpClient (4.2.3)
  • With Self-Signed SSL Certificate.

• one good simple example by Paresh Mayani

• other example by HARDIK TRIVEDI

• (NEW) Android working with Volley Library by Ravi Tamada

Hope this helps you

This is an illustration for making a POST request using Volley. StringRequest is used to get response in the form of String.
Assuming your rest API returns a JSON. The JSON response from your API is received as String here, which you can covert again to JSON and process it further. Added comments in code.

StringRequest postRequest = new StringRequest(Request.Method.POST, "PUT_YOUR_REST_API_URL_HERE",
            new Response.Listener<String>() {
                @Override
                public void onResponse(String response) {
                    try {
                        final JSONObject jsonObject = new JSONObject(response);
                        // Process your json here as required
                    } catch (JSONException e) {
                        // Handle json exception as needed
                    }
                }
            },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    String json = null;
                    NetworkResponse response = error.networkResponse;
                    if(response != null && response.data != null){
                        switch(response.statusCode) {
                            default:
                                String value = null;
                                try {
                                    // It is important to put UTF-8 to receive proper data else you will get byte[] parsing error.
                                    value = new String(response.data, "UTF-8");
                                } catch (UnsupportedEncodingException e) {
                                    e.printStackTrace();
                                }
                                json = trimMessage(value, "message");
                                // Use it for displaying error message to user 
                                break;
                        }
                    }
                    loginError(json);
                    progressDialog.dismiss();
                    error.printStackTrace();
                }  
                public String trimMessage(String json, String key){
                    String trimmedString = null;
                    try{
                        JSONObject obj = new JSONObject(json);
                        trimmedString = obj.getString(key);
                    } catch(JSONException e){
                        e.printStackTrace();
                        return null;
                    }
                    return trimmedString;
                }
            }
    ) {
        @Override
        protected Map<String, String> getParams() {
            Map<String, String> params = new HashMap<>();
            params.put("abc", "pass abc");
            params.put("xyz", "pass xyz");
            // Pass more params as needed in your rest API
    // Example you may want to pass user input from EditText as a parameter
    // editText.getText().toString().trim()
            return params;
        }  
        @Override
        public String getBodyContentType() {
            // This is where you specify the content type
            return "application/x-www-form-urlencoded; charset=UTF-8";
        }
    };

    // This adds the request to the request queue
    MySingleton.getInstance(YourActivity.this)
.addToRequestQueue(postRequest);

// Below is MySingleton class

public class MySingleton {
    private static MySingleton mInstance;
    private RequestQueue mRequestQueue;
    private static Context mCtx;  
    private MySingleton(Context context) {
        mCtx = context;
        mRequestQueue = getRequestQueue();
    }

    public static synchronized MySingleton getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new MySingleton(context);
        }
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
            // getApplicationContext() is key, it keeps you from leaking the
            // Activity or BroadcastReceiver if someone passes one in.
            mRequestQueue = Volley.newRequestQueue(mCtx.getApplicationContext());
        }
        return mRequestQueue;
    }

    public <T> void addToRequestQueue(Request<T> req) {
        getRequestQueue().add(req);
    }
}

Unfortunately there is no documentation for a Volley library like JavaDocs until now. Only repo on github and several tutorials across the Internet. So the only good docs is source code :) . When I played with Volley I read this tutorial.

About post/get you can read this : Volley - POST/GET parameters

Hope this helps