PostMultipart.java

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.file.Files;
import java.util.Map;

public class PostMultipart
{
    private final static String API_KEY = "helloworld";         // TODO: Change this to your own API key
    private final static String IMAGE_FILE = "test.png";        // TODO: Change this to your own image file
    private final static String OCR_URL = "https://api.ocr.space/parse/image"; // OCR API Endpoint
    private final static String USER_AGENT = "Mozilla/5.0";     // User-Agent to use for HTTP requests
    private final static String PARSE_LANG = "eng";             // Language to be used for parsing
    private final static String USE_OVERLAY = "true";           // Request overlay information

    private final String boundary = "*****";
    private final String crlf = "\r\n";
    private final String twoHyphens = "--";
    private final HttpURLConnection httpConn;
    private final DataOutputStream requestStream;

    public static void main(String[] args) throws IOException
    {
        long startTime = System.currentTimeMillis();

        PostMultipart multipartUtility = new PostMultipart(OCR_URL, null);
        multipartUtility.addFormField("apikey", API_KEY);
        multipartUtility.addFormField("language", PARSE_LANG);
        multipartUtility.addFormField("isOverlayRequired", USE_OVERLAY);
        multipartUtility.addFormField("apikey", API_KEY);
        multipartUtility.addFilePart("file", new File (IMAGE_FILE));

        JSONObject jsonData = multipartUtility.finish();
        //System.out.println(jsonData.toString());
        handleJSONResponse(jsonData);

        System.out.println("Elapsed time: " + (System.currentTimeMillis() - startTime) + " ms");
    }

    private static void handleJSONResponse(JSONObject response) throws JSONException
    {
        if (response.has("ParsedText"))
        {
            JSONArray overlay = response.getJSONObject("TextOverlay").getJSONArray("Lines");
            System.out.println("TextOverlay returned " + overlay.length() + " Lines");
            for (int i = 0; i < overlay.length(); i++)
            {
                JSONObject currObj = overlay.getJSONObject(i);
                JSONArray words = currObj.getJSONArray("Words");
                System.out.println("Line " + i + " (" + words.length() + " words) -> " + currObj.getString("LineText") + " (H:" + currObj.getInt("MaxHeight") + " T:" + currObj.getInt("MinTop") + ")");
                for (int x = 0; x < words.length(); x++)
                    System.out.println("Line " + i + ", Word " + x + ": " + words.getJSONObject(x).getString("WordText") + " (L:" + words.getJSONObject(x).getInt("Left") + ", T:" + words.getJSONObject(x).getInt("Top") + ", H:" + words.getJSONObject(x).getInt("Height") + ", W:" + words.getJSONObject(x).getInt("Width") + ")");
            }
            // System.out.println("ParsedText: " + response.getString("ParsedText"));
        }
        else if (response.has("ErrorMessage"))
        {
            String error = response.getString("ErrorMessage");
            System.out.println("ErrorMessage: " + error);
        }
    }

    /**
     * This constructor initializes a new HTTP POST request with content type is set to multipart/form-data
     */
    public PostMultipart(String requestURL, Map<String, String> requestProps) throws IOException
    {
        // creates a unique boundary based on time stamp
        URL url = new URL(requestURL);
        httpConn = (HttpURLConnection) url.openConnection();
        httpConn.setUseCaches(false);
        httpConn.setDoOutput(true); // indicates POST method
        httpConn.setDoInput(true);

        httpConn.setRequestMethod("POST");
        httpConn.setRequestProperty("Connection", "Keep-Alive");
        httpConn.setRequestProperty("Cache-Control", "no-cache");
        httpConn.setRequestProperty("User-Agent", USER_AGENT);

        if (requestProps != null)
        {
            for (Map.Entry<String, String> entry : requestProps.entrySet())
            {
                httpConn.setRequestProperty(entry.getKey(), entry.getValue());
            }
        }

        httpConn.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + this.boundary);
        requestStream = new DataOutputStream(httpConn.getOutputStream());
    }

    /**
     * Adds a form field to the request
     */
    public void addFormField(String name, String value) throws IOException
    {
        requestStream.writeBytes(this.twoHyphens + this.boundary + this.crlf);
        requestStream.writeBytes("Content-Disposition: form-data; name=\"" + name + "\"" + this.crlf);
        requestStream.writeBytes("Content-Type: text/plain; charset=UTF-8" + this.crlf);
        requestStream.writeBytes(this.crlf);
        requestStream.writeBytes(value + this.crlf);
        requestStream.flush();
    }

    /**
     * Adds an upload file section to the request
     *
     * @param fieldName  name attribute in <input type="file" name="..." />
     * @param uploadFile a File to be uploaded
     */
    public void addFilePart(String fieldName, File uploadFile) throws IOException
    {
        String fileName = uploadFile.getName();
        requestStream.writeBytes(this.twoHyphens + this.boundary + this.crlf);
        requestStream.writeBytes("Content-Disposition: form-data; name=\"" + fieldName + "\";filename=\"" + fileName + "\"" + this.crlf);
        requestStream.writeBytes(this.crlf);

        byte[] bytes = Files.readAllBytes(uploadFile.toPath());
        requestStream.write(bytes);
        requestStream.flush();
    }

    /**
     * Completes the request and returns the JSON response from the server.
     */
    public JSONObject finish() throws IOException
    {
        String responseMessage;

        requestStream.writeBytes(crlf);
        requestStream.writeBytes(twoHyphens);
        requestStream.writeBytes(boundary);
        requestStream.writeBytes(twoHyphens);
        requestStream.writeBytes(crlf);

        requestStream.flush();
        requestStream.close();

        // checks server's status code first
        int responseStatus = httpConn.getResponseCode();
        if (responseStatus == HttpURLConnection.HTTP_OK)
        {
            InputStream responseStream = new BufferedInputStream(httpConn.getInputStream());
            BufferedReader responseStreamReader = new BufferedReader(new InputStreamReader(responseStream));

            String line;
            StringBuilder stringBuilder = new StringBuilder();

            while ((line = responseStreamReader.readLine()) != null)
            {
                stringBuilder.append(line).append("\n");
            }
            responseStreamReader.close();

            responseMessage = stringBuilder.toString();
            httpConn.disconnect();
        }
        else
        {
            throw new IOException("Server returned non-OK status: " + responseStatus);
        }

        JSONObject jsonData = new JSONObject(responseMessage);

        // Filter the return values to results and errors
        if (jsonData.has("ParsedResults"))
            return jsonData.getJSONArray("ParsedResults").getJSONObject(0);
        else if (jsonData.has("IsErroredOnProcessing") && jsonData.getBoolean("IsErroredOnProcessing"))
            return jsonData;
        return null;
    }
}