How to read a blob field in Java?

One way to read Blob fields in Java is by using the methods provided by the java.sql.Blob interface. Here is a simple example:

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
public class BlobReader {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String username = "root";
        String password = "password";
        try {
            Connection conn = DriverManager.getConnection(url, username, password);
            String sql = "SELECT blob_column FROM my_table WHERE id = ?";
            PreparedStatement statement = conn.prepareStatement(sql);
            statement.setInt(1, 1);
            ResultSet result = statement.executeQuery();
            if (result.next()) {
                Blob blob = result.getBlob("blob_column");
                InputStream inputStream = blob.getBinaryStream();
                FileOutputStream outputStream = new FileOutputStream("output_file.txt");
                int bytesRead;
                byte[] buffer = new byte[4096];
                while ((bytesRead = inputStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, bytesRead);
                }
                inputStream.close();
                outputStream.close();
            }
            conn.close();
        } catch (SQLException | IOException e) {
            e.printStackTrace();
        }
    }
}

In the example above, connecting to a database via JDBC and executing a SELECT statement to retrieve a Blob field. Then, using the getBinaryStream() method of the Blob object to get the input stream, and then writing it to a file output stream. Note: In actual use, need to replace `url`, `username`, `password`, `sql`, and the output file path. Additionally, proper handling of exceptions and closing connections is also required.