DB2JsonThread.java

import java.io.FileWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;

public class DatabaseToJson {
    private static final int BATCH_SIZE = 10000; // Number of rows to fetch at a time
    private static final int THREAD_COUNT = 4; // Number of threads to use for extraction
    private static final String DB_URL = "jdbc:mysql://localhost:3306/mydatabase";
    private static final String DB_USER = "root";
    private static final String DB_PASSWORD = "mypassword";
    private static final String OUTPUT_FILE = "data.json";
    private static final String SELECT_QUERY = "SELECT * FROM mytable LIMIT ? OFFSET ?";

    public static void main(String[] args) throws Exception {
        long start = System.currentTimeMillis();
        JSONArray jsonArray = new JSONArray();
        int offset = 0;
        int totalRows = getTotalRows();
        ExecutorService executor = Executors.newFixedThreadPool(THREAD_COUNT);

        while (offset < totalRows) {
            executor.execute(new ExtractTask(offset, BATCH_SIZE, jsonArray));
            offset += BATCH_SIZE;
        }

        executor.shutdown();
        while (!executor.isTerminated()) {}

        try (FileWriter fileWriter = new FileWriter(OUTPUT_FILE)) {
            fileWriter.write(jsonArray.toJSONString());
        }

        long end = System.currentTimeMillis();
        System.out.println("Time taken: " + (end - start) / 1000.0 + " seconds");
    }

    private static int getTotalRows() throws SQLException {
        try (Connection connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
             PreparedStatement preparedStatement = connection.prepareStatement("SELECT COUNT(*) FROM mytable");
             ResultSet resultSet = preparedStatement.executeQuery()) {
            resultSet.next();
            return resultSet.getInt(1);
        }
    }

    private static class ExtractTask implements Runnable {
        private int offset;
        private int batchSize;
        private JSONArray jsonArray;

        public ExtractTask(int offset, int batchSize, JSONArray jsonArray) {
            this.offset = offset;
            this.batchSize = batchSize;
            this.jsonArray = jsonArray;
        }

        @Override
        public void run() {
            try (Connection connection = DriverManager.getConnection(DB_URL, DB_USER, DB_PASSWORD);
                 PreparedStatement preparedStatement = connection.prepareStatement(SELECT_QUERY)) {
                preparedStatement.setInt(1, batchSize);
                preparedStatement.setInt(2, offset);

                try (ResultSet resultSet = preparedStatement.executeQuery()) {
                    while (resultSet.next()) {
                        JSONObject jsonObject = new JSONObject();
                        jsonObject.put("id", resultSet.getInt("id"));
                        jsonObject.put("name", resultSet.getString("name"));
                        jsonObject.put("age", resultSet.getInt("age"));
                        // Add more fields as needed

                        synchronized (jsonArray) {
                            jsonArray.add(jsonObject);
                        }
                    }
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}