Java Database Connectivity

I’ll start off with a small example and then give a couple of pointers regarding JDBC.



This example connects to a MySQL database. I’m querying the superhero database which originally contains 2 rows:

id, name, first_name, last_name, good

The code queries the database for all the names of the superheros. It prints out all of these names.

Then, a new superhero is added. The number of rows affected is printed.

Finally the database is queried again and the names are printed (including the newly inserted record).

import java.sql.*;

public class UseJDBC {

    public static void main(String[] args) throws SQLException {
        String url = "jdbc:mysql://localhost:3306/demo";

        try(Connection conn = DriverManager.getConnection(url, "demouser", "demopass");
            Statement stmt = conn.createStatement())

            ResultSet rs = stmt.executeQuery("select name from superhero");
            showColumnContent(rs, 1);

            int result = stmt.executeUpdate("insert into superhero (name, first_name, good) values ('Goku', 'Kakarot', 1)");
            System.out.println("result: rows affected = " + result);

            ResultSet rs2 = stmt.executeQuery("select name from superhero");
            showColumnContent(rs2, 1);


    private static void showColumnContent(ResultSet rs, int columnIndex) throws SQLException {


result: rows affected = 1


Extra ++

Now I’ll dive a little deeper in working with JDBC:

  • JDBC has four key interfaces: Driver, Connection, Statement, Resultset
  • A Driver creates a Connection
  • On the Connection you can create a Statement
  • When executing a statement it can return a ResultSet
  • If you want to automatically close the sql Resources instantiate them in a try block
    try(Connection conn = DriverManager.getConnection(url, "demouser", "demouser");
        Statement stmt = conn.createStatement();
        PreparedStatement pstmt = conn.prepareStatement("select last_name from superhero where first_name = ?");
        ResultSet rs = stmt.executeQuery("select name from superhero"))
  • The classes that implement these interfaces come from an external JDBC driver
  • The drivers are specific to the type of database (MySQL, Postgress..)
  • You can download a jar that contains these concrete classes
  • You have to run your program with that new jar file on the classpath. java -cp /path/to/driver/jar MyProgram
  • A JDBC url needs to be in a specific format: jdbc:ProductName://ConnectionDetails. For example:
    • jdbc:mysql://localhost:3306/database
    • when you do not specify localhost, localhost will be the default location
  • When you look into a driver JAR file there is a directory META-INF/services. This directory has a file java.sql.Driver containing the path to the concrete class that implements the Driver interface. This way Java knows where to locate the driver implementation.
  • You can create a statement like
    • conn.createStatement();
    • conn.createStatement(int ResultSetType, int ResultSetConcurrency);
      • Type: specify how you can navigate trough your ResultSet.
      • Concurrency: specify whether or not you can do updates on the ResultSet
  • To execute a statement there are three methods:
    • execute():
      • supports: SELECT, INSERT, DELETE, UPDATE
      • returns: boolean (true for select, false for other)
    • executeQuery():
      • supports: SELECT
      • returns: ResultSet
    • executeUpdate():
      • supports: INSERT, DELETE, UPDATE
      • returns: int (the number of rows returned)
  • You can get read results from a ResultSet with methods like getInt(int index), getString(int index) which take the column number as method argument
  • The indexes of the columns in a ResultSet start from 1!
  • DATE, TIME and TIMESTAMP are retrieved from a ResultSet with getDate(), getTime(), getTimeStamp() and return java.sql.Date, java.sql.Time, java.sql.TimeStamp. These can be converted to LocalDate, LocalTime and LocalDateTime with the methods toLocalDate(), toLocalTime() and toLocalDateTime();
  • To navigate forward one row in a ResultSet call next() on the ResultSet object
    • If the ResultSetType allows it (eg. ResultSet.TYPE_SCROLL_INSENSITIVE) you can also use methods like beforeFirst(), afterLast(), previous(), last(), first(), absolute(int row), relative(int row). They all return a boolean except for afterLast() and beforeFirst() which return void.
  • if rs is a ResultSet then rs.absolute(0) returns falls because cursor is positioned before the first row.
  • You need to close database resources to avoid memory leaks
  • When you close a Connection the Statement and ResultSet will be automatically closed.
  • When executing on a statement the previous ResultSet of that statement is automatically closed.

Leave a Reply

Your email address will not be published.