How to read HTTP custom error string

Question

I'm trying to read custom error message I sent along an HTTP response for a web API project using Java.

Currently, I have this piece of Java code to read Header Response,

import java.net.HttpURLConnection;
import java.net.URL;

public class URLReader {
   public static void main(String[] args) throws Exception {
        URL oracle = new URL(URL);
        HttpURLConnection connection =(HttpURLConnection)oracle.openConnection();
        connection.setRequestMethod("GET");
        connection.connect();
        System.out.println(connection.getHeaderField(0));
    }
}

An output of HTTP response header looks like this (Fiddler):

How can I get My Error Message text using Java?

To my understanding all you need is to assign a key to the header. like the other ones above yours and you will be able to use the key to retrieve the message. — Nico
– Nico, Commented Dec 22, 2016 at 13:46

Jerry Chin · Accepted Answer · 2016-12-22 07:03:35Z

2

@Abzal Kalimbetov is wrong about getErrorStream(), which will return an InputStream when an exception is raised, indicating response code >= 400 is received from the server.

Recap:

InputStream inputStream = null;
try {
    // normal operation
    inputStream = connection.getInputStream();
}
catch(IOException exception)
{
    inputStream = connection.getErrorStream();
    //@TODO you can now extract your custom error message from inputStream.
}

answered Dec 22, 2016 at 7:03

Jerry Chin

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3 Comments

Abzal Kalimbetov Over a year ago

Your approach is not so good, you are trying to get inputstream while you know it is not there when the response code is 400

Jerry Chin Over a year ago

Take a look at grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/…

Jerry Chin Over a year ago

Response statue code >= 400 will be regarded as an exception in Java, not just 404 or 410, though they're of FileNotFoundException type, more specific one.

Abzal Kalimbetov · Accepted Answer · 2016-12-22 09:05:47Z

1

If the request status is greater than or equal 400, you use getErrorStream() method

  if(connection.getResponseCode()>=400){ 
       String myErrorMessage = connection.getErrorStream();
  }

edited Dec 22, 2016 at 9:05

answered Dec 22, 2016 at 6:34

Abzal Kalimbetov

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1 Comment

rkosegi Over a year ago

Looking at implementation of HttpUrlConnection, errorStream is being used under this condition : responseCode >= 400. 1xx and 3xx status codes doesn't represent error states. Only 4xx (client error) or 5xx (server error) does.

Nico · Accepted Answer · 2016-12-22 07:20:47Z

-1

You can set a header in your server application which you then can read out very simple like this: ( Servlet usage is needed for this. )

private void test(ServletRequest request, ServletResponse response) {
HttpServletRequest httpServletRequest = (HttpServletRequest) request;
HttpServletResponse httpServletResponse = (HttpServletResponse) response;

httpServletResponse.addHeader( "myErrorMessage", "this is the message" );
String message = httpServletRequest.getHeader( "myErrorMessage" );
}

if you don't have these resources available it is possible to get the message like this:

//get all headers
Map<String, List<String>> map = connection.getHeaderFields();
for (Map.Entry<String, List<String>> entry : map.entrySet()) {
    System.out.println("Key : " + entry.getKey() +
                 " ,Value : " + entry.getValue());
}

//get header by 'key'
String server = connection.getHeaderField("Server");

answered Dec 22, 2016 at 7:20

Nico

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1 Comment

Nico Over a year ago

@Downvoter please be so kind and let me know why you downvoted so I can learn from it and improve my future answers and my general understanding of programming. Thanks...

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