Java OCR Invoice API: Enterprise Data Extraction

import java.io.IOException;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.file.Files;
import java.nio.file.Path;
import java.time.Duration;
import java.util.Base64;

public class InvoiceOcrExample {

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    private static final String API_KEY = "YOUR_API_KEY_HERE";
    private static final String API_ENDPOINT = "https://api.structocr.com/v1/invoice";

    public static void main(String[] args) {
        // Supports PDFs, local image paths, Base64 strings, or Image URLs
        String documentPath = "vendor_invoice.pdf";

        try {
            // 1. Validate File
            Path path = Path.of(documentPath);
            if (!Files.exists(path)) {
                System.err.println("Error: File not found at " + path.toAbsolutePath());
                return;
            }

            // 2. Read document and encode to Base64
            byte[] fileBytes = Files.readAllBytes(path);
            String base64Data = Base64.getEncoder().encodeToString(fileBytes);

            // 3. Construct JSON Payload (Dependency-free)
            // Ideally, use a library like Jackson or Gson for production.
            String jsonPayload = "{\"img\": \"" + base64Data + "\"}";

            // 4. Create HttpClient
            HttpClient client = HttpClient.newBuilder()
                    .version(HttpClient.Version.HTTP_1_1)
                    .connectTimeout(Duration.ofSeconds(10))
                    .build();

            // 5. Build Request
            // Important: 'x-api-key' header is required
            HttpRequest request = HttpRequest.newBuilder()
                    .uri(URI.create(API_ENDPOINT))
                    .header("Content-Type", "application/json")
                    .header("x-api-key", API_KEY)
                    .timeout(Duration.ofSeconds(30))
                    .POST(HttpRequest.BodyPublishers.ofString(jsonPayload))
                    .build();

            System.out.println("Sending invoice to " + API_ENDPOINT + "...");

            // 6. Send Request
            HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());

            // 7. Output Result
            if (response.statusCode() == 200) {
                System.out.println("✅ Extraction Successful!");
                // The response contains nested JSON: merchant, financials, line_items
                System.out.println("Response Body:");
                System.out.println(response.body());
            } else {
                System.err.println("❌ API Error: " + response.statusCode());
                System.err.println(response.body());
            }

        } catch (IOException | InterruptedException e) {
            System.err.println("Request failed: " + e.getMessage());
            Thread.currentThread().interrupt();
        }
    }
}