BufferedWriter, BufferedReader 데이터 읽고 쓰기

HttpURLConnection conn = (HttpURLConnection)url.openConnection();

conn.setRequestMethod("POST");
conn.setRequestProperty("Access-Control-Allow-Origin", "*");
conn.setRequestProperty("Content-Type", "application/json");
conn.setRequestProperty("Accept", "application/json");
conn.setDoInput(true);
conn.setDoOutput(true);

BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(conn.getOutputStream()));
bw.write(obj.toString());
bw.flush();
bw.close();

// 서버로부터 데이터 읽어오기
BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
StringBuilder sb = new StringBuilder();
String line = null;

while((line = br.readLine()) != null) {
sb.append(line);
}