While integrating Volley into a project, I encountered several common issues worth documenting. The following does not apply to Android 2.3 and below.

Adding Request Parameters

Override getParams:

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@Override
protected Map<String, String> getParams() {
    return mParams;
}

Using Cookies

HttpURLConnection natively supports cookie management via CookieHandler:

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CookieHandler.setDefault(new CookieManager());
CookieHandler.setDefault(new CookieManager(null, CookiePolicy.ACCEPT_ALL));

Cookies are carried in request headers and parsed from set-cookie in responses. See the HttpURLConnection documentation.

Cache.Entry NullPointerException

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Attempt to read from field com.android.volley.Cache$Entry
com.android.volley.Response.cacheEntry on a null object reference
    at com.android.volley.NetworkDispatcher.run(NetworkDispatcher.java:126)

Cause: Passing null as the second parameter in parseNetworkResponse causes a NPE when NetworkDispatcher reads the cache entry.

Fix: Always return valid cache headers.

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@Override
protected Response<String> parseNetworkResponse(NetworkResponse response) {
    // ...
    return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
}

statusCode NullPointerException

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int statusCode = statusLine.getStatusCode(); // NullPointerException

This can occur when constructor parameters (e.g., listener) are null. Ensure all required parameters are non-null.

Setting Timeout

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myRequest.setRetryPolicy(new DefaultRetryPolicy(
    MY_SOCKET_TIMEOUT_MS,
    DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
    DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));

References