How to Parse the Response Body in Java for HTTP Status 401

Question

How can I effectively parse the response body in Java when encountering an HTTP 401 Unauthorized status?

// Example of handling HTTP 401 in Java with HttpURLConnection
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpClientExample {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com/protected-resource");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            int responseCode = conn.getResponseCode();

            if (responseCode == HttpURLConnection.HTTP_UNAUTHORIZED) {
                BufferedReader in = new BufferedReader(new InputStreamReader(conn.getErrorStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

                while ((inputLine = in.readLine()) != null) {
                    response.append(inputLine);
                }
                in.close();

                // Print response body
                System.out.println("Response Body: " + response.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Answer

When receiving a 401 Unauthorized status, it's important to gracefully handle the response in your Java application. The following guide outlines the process of parsing the response body to extract useful information, which can help in troubleshooting or informing the user about authentication issues.

// Complete code snippet demonstrating handling and parsing of 401 Unauthorized response
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpUnauthorizedExample {
    public static void main(String[] args) {
        String urlString = "http://example.com/protected-resource";
        try {
            URL url = new URL(urlString);
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

            int responseCode = connection.getResponseCode();
            if (responseCode == HttpURLConnection.HTTP_UNAUTHORIZED) {
                BufferedReader reader = new BufferedReader(new InputStreamReader(connection.getErrorStream()));
                StringBuilder response = new StringBuilder();
                String line;
                while ((line = reader.readLine()) != null) {
                    response.append(line);
                }
                reader.close();

                // Output the response body received from the server
                System.out.println("Error Response:");
                System.out.println(response.toString());
            } else {
                // Handle other response codes if necessary
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Causes

Invalid credentials provided in the HTTP request.
Access to the requested resource is prohibited without proper authentication.
Expired session tokens or lack of session cookies.

Solutions

Check and correct the authentication credentials being used in the request.
Verify that the API endpoint is correctly configured to accept the provided authentication method.
Implement proper error handling to read the response body and extract additional information regarding the failure.

Common Mistakes

Mistake: Not correctly checking the HTTP response code before accessing the response body.

Solution: Always check the response code returned by the server before attempting to read the response. Use a conditional structure like 'if' to handle specific errors.

Mistake: Ignoring error streams when a request fails.

Solution: Utilize the connection's getErrorStream() method to retrieve the response body for error statuses.

Mistake: Overlooking exception handling, which can lead to crashes on network errors.

Solution: Implement a try-catch block around network calls to handle possible exceptions gracefully.

Helpers

Java parse response body
HTTP 401 unauthorized body parsing
Java error handling HTTP requests
HTTP response handling in Java