Daily Archives: August 30, 2020

Making sample JDBC code easier

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I’m writing a lot of small JDBC examples for our upcoming practice tests book. I got tired of writing the same code over and over so I wrote this helper class. It can:

  • Drop the table if it already there (because I run the same examples many times)
  • Run a varargs of SQL statements (to create tables and insert data)
  • Spit out the contents of a table (to confirm what happened)


import java.sql.*;
public class DerbyUtil {

    public static void dropTablesIfExist(String url, String... tables) throws SQLException {
        try (var conn = DriverManager.getConnection(url)) {
            for (String table : tables) {
                try (PreparedStatement ps = conn.prepareStatement("DROP TABLE " + table)) {
                    ps.executeUpdate();
                } catch (SQLException e) {
                    // ignore exceptions on drop since table might not exist
                }
            }
        }
    }

    public static void run(String url, String... sqlStatements) throws SQLException {
        try (var conn = DriverManager.getConnection(url)) {
            for (String stmt : sqlStatements) {
                try (PreparedStatement ps = conn.prepareStatement(stmt)) {
                    ps.executeUpdate();
                }
            }
        }
    }

    public static void outputTable(String url, String tableName) throws SQLException {
        String sql = "SELECT * FROM " + tableName;
        try (var conn = DriverManager.getConnection(url);
             var ps = conn.prepareStatement(sql);
             var rs = ps.executeQuery()) {

            var metadata = rs.getMetaData();
            int numColumns = metadata.getColumnCount();

            while (rs.next()) {
                outputRow(rs, numColumns);
            }
        }
    }

    private static void outputRow(ResultSet rs, int numColumns) throws SQLException {
        for (int i = 1; i <= numColumns; i++) {
            System.out.print(rs.getString(i));
            System.out.print('\t');
        }
        System.out.println();
    }
}