class HttpClientDownloader extends AbstractDownloader {

    @Override
    public Page download(Request request, Task task) {
        if (task == null || task.getSite() == null) {
            throw new NullPointerException("task or site can not be null");
        }
        CloseableHttpResponse httpResponse = null;
        CloseableHttpClient httpClient = getHttpClient(task.getSite());
        Proxy proxy = proxyProvider != null ? proxyProvider.getProxy(task) : null;
        HttpClientRequestContext requestContext = httpUriRequestConverter.convert(request, task.getSite(), proxy);
        Page page = Page.fail();
        try {
            httpResponse = httpClient.execute(requestContext.getHttpUriRequest(), requestContext.getHttpClientContext());
            page = handleResponse(request, request.getCharset() != null ? request.getCharset() : task.getSite().getCharset(), httpResponse, task);
            onSuccess(request);
            logger.info("downloading page success {}", request.getUrl());
            return page;
        } catch (IOException e) {
            logger.warn("download page {} error", request.getUrl(), e);
            onError(request);
            return page;
        } finally {
            if (httpResponse != null) {
                //ensure the connection is released back to pool
                EntityUtils.consumeQuietly(httpResponse.getEntity());
            }
            if (proxyProvider != null && proxy != null) {
                proxyProvider.returnProxy(proxy, page, task);
            }
        }
    }

}