android-async-http/android-async-http · error · IllegalArgumentException

ResponseHandler must not be null

Error message

ResponseHandler must not be null

What it means

sendRequest throws IllegalArgumentException when the ResponseHandler passed in is null. AsyncHttpClient relies on the handler to process the HTTP response on the caller's looper thread; without one it cannot deliver results. The guard fails fast instead of crashing when the response arrives.

Solutions

1. Pass a non-null AsyncHttpResponseHandler (e.g. new TextHttpResponseHandler(){...}) to the request method
2. If no result handling is needed, still supply an empty handler implementation
3. Verify any handler-producing helper cannot return null

Example fix

// before
client.get(url, (RequestParams) null, null);
// after
client.get(url, (RequestParams) null, new AsyncHttpResponseHandler() {
    @Override public void onSuccess(int statusCode, Header[] headers, byte[] responseBody) {}
    @Override public void onFailure(int statusCode, Header[] headers, byte[] responseBody, Throwable error) {}
});

if (handler == null) { handler = new AsyncHttpResponseHandler() {
    @Override public void onSuccess(int s, Header[] h, byte[] b) {}
    @Override public void onFailure(int s, Header[] h, byte[] b, Throwable t) {}
}; }

boolean hasHandler = (responseHandler instanceof ResponseHandlerInterface); // null check before request call
if (!hasHandler) { /* create default handler */ }

try { client.get(url, params, handler); } catch (IllegalArgumentException e) { Log.e(TAG, "handler missing", e); }

When it happens

Trigger: Calling get/post/delete/put with a null ResponseHandlerInterface; passing a handler variable that was never initialized; API misuse where the developer expected the client to work fire-and-forget without a handler.

Common situations: Forgetting to instantiate an AsyncHttpResponseHandler subclass; a factory method returning null on failure; code paths where the handler is only assigned in one branch.

Related errors

• HttpUriRequest must not be null
• Synchronous ResponseHandler used in AsyncHttpClient. You…
• File too large to fit into available memory
• File too large to fit into available memory
• HTTP entity too large to be buffered in memory

AI-assisted analysis of android-async-http/android-async-http@018a0b8d96 (2026-09-09). Data as JSON: /api/errors/75b5ab7caea3a2fc. Report an issue: GitHub.

Appendix: source

Thrown at library/src/main/java/com/loopj/android/http/AsyncHttpClient.java:1540

    /**
     * Puts a new request in queue as a new thread in pool to be executed
     *
     * @param client          HttpClient to be used for request, can differ in single requests
     * @param contentType     MIME body type, for POST and PUT requests, may be null
     * @param context         Context of Android application, to hold the reference of request
     * @param httpContext     HttpContext in which the request will be executed
     * @param responseHandler ResponseHandler or its subclass to put the response into
     * @param uriRequest      instance of HttpUriRequest, which means it must be of HttpDelete,
     *                        HttpPost, HttpGet, HttpPut, etc.
     * @return RequestHandle of future request process
     */
    protected RequestHandle sendRequest(DefaultHttpClient client, HttpContext httpContext, HttpUriRequest uriRequest, String contentType, ResponseHandlerInterface responseHandler, Context context) {
        if (uriRequest == null) {
            throw new IllegalArgumentException("HttpUriRequest must not be null");
        }

        if (responseHandler == null) {
            throw new IllegalArgumentException("ResponseHandler must not be null");
        }

        if (responseHandler.getUseSynchronousMode() && !responseHandler.getUsePoolThread()) {
            throw new IllegalArgumentException("Synchronous ResponseHandler used in AsyncHttpClient. You should create your response handler in a looper thread or use SyncHttpClient instead.");
        }

        if (contentType != null) {
            if (uriRequest instanceof HttpEntityEnclosingRequestBase && ((HttpEntityEnclosingRequestBase) uriRequest).getEntity() != null && uriRequest.containsHeader(HEADER_CONTENT_TYPE)) {
                log.w(LOG_TAG, "Passed contentType will be ignored because HttpEntity sets content type");
            } else {
                uriRequest.setHeader(HEADER_CONTENT_TYPE, contentType);
            }
        }

        responseHandler.setRequestHeaders(uriRequest.getAllHeaders());
        responseHandler.setRequestURI(uriRequest.getURI());

        AsyncHttpRequest request = newAsyncHttpRequest(client, httpContext, uriRequest, contentType, responseHandler, context);

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