Java 如果服务器返回502错误，如何读取HTTP响应？

我使用

URLConnection

向服务器发送POST请求，并使用以下代码读取响应：

String line;
BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));   
while ((line = reader.readLine()) != null) {
    response += line;
}
reader.close();

但是，服务器有时会返回一个502错误，并在响应中包含一条有意义的错误消息，我希望获得这条消息。我的问题是，在这种情况下尝试创建

BufferedReader

将导致

java.io.IOException

：

Server returned HTTP response code: 502 for URL: <url>

服务器为URL返回了HTTP响应代码：502:

---

如何绕过此问题？

根据这些行修改代码，以便获得errorstream而不是抛出IOException

HttpURLConnection httpConn = (HttpURLConnection)connection;
InputStream is;
if (httpConn.getResponseCode() >= 400) {
    is = httpConn.getErrorStream();
} else {
    is = httpConn.getInputStream();
}

BufferedReader reader = new BufferedReader(new  InputStreamReader(is));   
while ((line = reader.readLine()) != null) {
     response += line;
}
reader.close();

---

沿着这些行修改代码，以便获得errorstream，而不是抛出IOException

HttpURLConnection httpConn = (HttpURLConnection)connection;
InputStream is;
if (httpConn.getResponseCode() >= 400) {
    is = httpConn.getErrorStream();
} else {
    is = httpConn.getInputStream();
}

BufferedReader reader = new BufferedReader(new  InputStreamReader(is));   
while ((line = reader.readLine()) != null) {
     response += line;
}
reader.close();