Introduction to Error Handling in API Requests with Java

Welcome to the first lesson of Efficient API Interactions with Java. In this course, you will learn how to handle common scenarios when working with APIs more effectively. One of the key aspects of working with APIs is error handling. Handling errors gracefully not only helps in building robust applications but also enhances the user experience by providing meaningful feedback when things go wrong. Our goal in this lesson is to help you manage these outcomes effectively.

When you send a request to an API, the server responds with an HTTP status code. These codes indicate the result of your request. Understanding them is essential for effective error handling. Here's a brief overview:

• 2xx (Success): Indicates that the request was successfully received, understood, and accepted. For example, a 200 status code means OK.
• 4xx (Client Errors): Suggests that there was an error in the request made by your client. For example, 404 means the requested resource was not found.
• 5xx (Server Errors): Indicates that the server failed to fulfill a valid request. A common code here is 500, which means an internal server error.

By paying attention to these codes, you can determine whether your request succeeded or if there was a problem that needs addressing.

Java's HttpClient allows us to perform HTTP requests and manage responses manually. Unlike in some other languages, Java does not automatically throw exceptions for HTTP error status codes. Therefore, you must manually check the status codes and handle them appropriately.

Consider the following example, which fetches todo items from an API:

import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.io.IOException;

public class APIErrorHandlingExample {
    private static final String BASE_URL = "http://localhost:8000";

    public static void main(String[] args) {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
                .uri(URI.create(BASE_URL + "/todos"))
                .build();

        try {
            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

            if (response.statusCode() != 200) {
                throw new IOException("Failed to fetch todos: " + response.body());
            }

            System.out.println("Todos fetched successfully!");
        } catch (IOException | InterruptedException e) {
            System.out.println("Error occurred" + e.getMessage());
        }
    }
}

In this example, we manually check the statusCode() of the response. If it is not 200, we throw an IOException and the try-catch blocks handles it accordingly.