# Volley — Android HTTP Networking Library by Google

> An HTTP library for Android that makes networking faster and easier by handling request queuing, caching, and response parsing on background threads.

## Install

Save as a script file and run:

# Volley — Android HTTP Networking Library by Google

## Quick Use
```groovy
// build.gradle (app module)
dependencies {
    implementation 'com.android.volley:volley:1.2.1'
}
```
```java
// Make a simple GET request
RequestQueue queue = Volley.newRequestQueue(context);
String url = "https://api.example.com/data";

JsonObjectRequest request = new JsonObjectRequest(
    Request.Method.GET, url, null,
    response -> {
        // Handle JSON response
        Log.d("Volley", response.toString());
    },
    error -> {
        // Handle error
        Log.e("Volley", error.toString());
    }
);

queue.add(request);
```

## Introduction
Volley is an HTTP networking library developed by Google for Android applications. It was introduced at Google I/O 2013 to simplify common networking tasks like fetching JSON, loading images, and making API calls, while providing automatic request scheduling, transparent disk and memory caching, and cancellation support.

## What Volley Does
- Manages a queue of HTTP requests with automatic scheduling and prioritization on background threads
- Provides transparent response caching using both in-memory and disk caches based on HTTP cache headers
- Delivers parsed responses to the main thread, eliminating manual Handler or runOnUiThread calls
- Includes built-in request types for strings, JSON objects, JSON arrays, and images
- Supports request cancellation by tag, allowing cleanup when Activities or Fragments are destroyed

## Architecture Overview
Volley operates through a RequestQueue that dispatches requests to a pool of network threads. Each request passes through a cache check first; if a valid cached response exists, it is returned immediately without hitting the network. Cache misses go to the network dispatcher, which uses an HttpStack (HttpURLConnection or OkHttp-backed) to perform the actual HTTP call. Responses are parsed on the background thread by the request's parseNetworkResponse method, then delivered to the caller's listener on the main thread via a ResponseDelivery. The architecture is designed for many small, concurrent requests rather than large downloads or streaming.

## Self-Hosting & Configuration
- Add the Volley dependency to your app-level build.gradle and sync the project
- Create a singleton RequestQueue, typically in an Application subclass, to avoid creating multiple queues
- Add the INTERNET permission to AndroidManifest.xml if not already present
- Configure cache size by passing a custom DiskBasedCache or setting max cache entries on the RequestQueue
- For HTTPS with custom certificates or pinning, provide a custom HurlStack with a configured SSLSocketFactory

## Key Features
- Automatic request scheduling with concurrent network threads and priority support
- Transparent HTTP response caching with in-memory LRU cache and disk-based cache
- Request cancellation by tag for clean lifecycle management in Activities and Fragments
- Built-in image loading with NetworkImageView and ImageLoader for efficient bitmap handling
- Retry policy with configurable timeout, max retries, and backoff multiplier per request

## Comparison with Similar Tools
- **OkHttp** — lower-level HTTP client by Square; more control over connections, interceptors, and HTTP/2 but requires more setup for Android-specific patterns
- **Retrofit** — type-safe REST client built on OkHttp; annotation-based API definitions with less boilerplate for structured endpoints
- **Ktor Client** — Kotlin multiplatform HTTP client; modern coroutine-based API but not Android-specific
- **Fuel** — lightweight Kotlin HTTP client; simpler API than OkHttp but smaller community and fewer features

## FAQ
**Q: Is Volley still recommended for new Android projects?**
A: Volley is maintained by Google and works well for apps making many small HTTP requests (API calls, image loading). For new projects, many developers prefer Retrofit with OkHttp for its type-safe API and coroutine support, but Volley remains a valid choice for simpler networking needs.

**Q: Can Volley handle large file downloads?**
A: Volley is not designed for large downloads or streaming. It holds the entire response in memory during parsing. For large files, use DownloadManager, OkHttp, or WorkManager with a streaming approach.

**Q: How do I use Volley with OkHttp as the transport layer?**
A: Create a custom HurlStack or use the OkHttp3Stack adapter, then pass it when creating the RequestQueue. This gives you OkHttp's connection pooling and HTTP/2 support while keeping Volley's request management.

**Q: Does Volley support request authentication?**
A: Yes. Override the getHeaders() method on your request subclass to add Authorization headers, or use a custom RetryPolicy for token refresh logic.

## Sources
- https://github.com/google/volley
- https://developer.android.com/training/volley

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Author: Script Depot