request.getInputStream()得不到值

用的HttpUrlConnection模拟请求

URL serverUrl = new URL("");
		HttpURLConnection conn = (HttpURLConnection) serverUrl.openConnection();

		conn.setRequestMethod("POST");
		conn.setDoOutput(true);
		
		conn.connect();
		String params = "hello";
		
		conn.getOutputStream().write(params.getBytes());
		conn.getOutputStream().flush();
		conn.getOutputStream().close();
		InputStream is = conn.getInputStream();

但是请求的接口，想获得inputStream为空，

解决方法：
新增Content-Type请求头，明确告诉服务器处理什么样的数据。

conn.setRequestProperty("content-type", "text/html");