由于腾讯限制第三方网站直接根据封面URL引用封面图片，因此，在取到封面素材id后，需再次发送HTTPS POST请求获取图片存储在本地，显示时显示的是存储在本地的图片,在这里我要骂一句 :F*和谐C*和谐K Tencent.

然后此处给出通过HttpClient获取图片存储到本地的代码:(需先引入apache的jar包:commons-io-2.6.jar)

/**
	 * 以Post方式json形式的获取文件请求
	 * @param url
	 * @param parameters
	 * @param filePath  文件存储路径(包含文件名)
	 * @throws Exception 
	 */
	public static void getFileByPost(String url,JSONObject parameters,String filePath) throws Exception {
		CloseableHttpClient httpClient = HttpClients.createDefault();
		HttpPost httpPost = new HttpPost(url);
		httpPost.addHeader(HTTP.CONTENT_TYPE, "application/json");
		httpPost.setHeader("Accept","application/json");
		StringEntity se = new StringEntity(parameters.toString());
		se.setContentType("text/json");
		httpPost.setEntity(se);
		HttpResponse response=httpClient.execute(httpPost);
		HttpEntity he = response.getEntity();
		InputStream inputStream = he.getContent();
		FileUtils.copyToFile(inputStream, new File(filePath));
	}

使用示例:

public static void main(String[] args) {
		String url = "https://api.weixin.qq.com/cgi-bin/material/get_material?access_token=这里写你的ACCESSTOKEN";
		JSONObject j = new JSONObject();
		j.put("media_id", "这里写你获取到的图片素材的ID");
		try {
			getFileByPost(url, j,"D://upload/f*ckTencent.png");
		} catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}