Introduction
Volley is a reliable HTTP (HyperText Transfer Protocol) library that helps in making networking swift and efficient. It was produced by Google; it came into existence during Google I/O 2013 and was announced by Ficus Kirkpatrick.
There was a dire need for a networking class that could work abstractly, without producing any interference in the user experience, in the Android SDK. Earlier, Volley was an integral component of the Android Open Source Project (AOSP). The first instance at which was the Volley Library was by the Play Store team in Play Store Application. Later, in January 2017, Google declared Volley an independent library.
The volley library comes with some superior features like automated and scheduled network requests and numerous concurrent connections; we can prioritize requests in case of conflicts, inhibit or revert specific requests, it allows offer a higher degree of customization, and mainly allows us to manage user interface with higher ease using the asynchronously fetched data from the network.
There is no need to write boilerplate codes using AsyncTask to fetch responses from Web API and display the relevant data in the user interface. Developers can easily skip the tedious process of writing network-based codes using AsyncTask. This reduces the overall size of the source code and makes the repository easy to maintain and debug. This is the main reason that developers prefer Volley over AsyncTask.

Working of Async class
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For instance, if we employ Asynctask to fetch an image and its corresponding description from a native JSON array created in server API. The data is fetched and displayed in the user interface, but now if the user rotates the screen and toggles to landscape mode. The previous activity is cleared from the stack, and the data needs to be fetched again. Since multiple network requests are being created for the same data set, it leads to unnecessary congestion at the server and provides a bad user experience due to the latency.
Volley library utilizes the device's cache memory to improve the App performance by reducing the remote server's memory requirement, congestion, and bandwidth. Whenever a recurring data request is made by the user, rather than fetching the data from the server, Volley directly brings it from the cache-saving resource and improves the overall user experience. However, the Volley library is not compatible with large-sized downloads or high quality-streaming operations as it saves all responses in memory while parsing data.

Working of Volley Library
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Volley has two default methods that allow us to synchronize pre and post-execute activities, namely the onPreExecute() and onPostExecute() methods. The prerequisites of a network request can be written in the onPreExecute() method, such as fetching the parameters required to make the network request and the post-actions, such as the setting of dialogs, alerts, progress bars, etc. These methods produce distinct and uniform networking codes and eliminate the need for writing BaseTask classes for implementing and managing post operations.
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Working of Volley Library
Pre-requisites
Step 1:
Open build.Gradle(Module: app) and add the following dependency and rebuild the project after syncing of the Gradle:
dependencies{
//…
implementation ‘com.android.volley:volley:1.0.0’
}
Step 2:
In AndroidManifest.xml add the internet permission:
Volley requests can be made by creating two classes in our Android Project:
- RequestQueue: The network requests are stored in a queue in sequential order. A queue works on the FIFO strategy(First in, first out). So the requests made first are attended to first unless no priority is specified.
- A Request: Based on our requirements, we must pass the suitable parameters and call the specific API from the web server; we must create valid network requests.
A network request can be of various types:
- StringRequest: To retrieve the response body from the API as a String.
- JsonArrayRequest: To fetch a JSON Array as a response from the server after the API call.
- JsonObjectRequest: To send and receive JSON Objects from the server via network requests.
- ImageRequest: To receive an image from the server as a response.
Parameters that should be passed into the constructor to create a network request:
- First parameter, The Request Method: The method of the created request should be specified, such as GET, POST, PUT, and DELETE.
- Second parameter URL: String of the URL of the required object.
- Third parameter ResponseListener: Response Listener, whose callback method contains the response received from the API.
- Fourth parameter ErrorListener: A Response.ErrorListener, whose callback method will deal with any error generated while executing the network request.