前面有写过HttpPost上传文件，结果不久又遇到要用java代码去下载文件的需求；代码中的url是文件的访问地址

    public static byte[] get(String url, Map<String, String> headers) throws ClientProtocolException, IOException {
        logger.info("Ready Get Request Url[{}]", url);
        HttpGet get = new HttpGet(url);
        setHttpHeaders(get, headers);
        HttpResponse response = HttpClients.createDefault().execute(get);
        if (null == response || response.getStatusLine() == null) {
            logger.info("Post Request For Url[{}] is not ok. Response is null", url);
            return null;
        } else if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK) {
            logger.info("Post Request For Url[{}] is not ok. Response Status Code is {}", url,
                    response.getStatusLine().getStatusCode());
            return null;
        }
        return EntityUtils.toByteArray(response.getEntity());
    }