How do I query records from a table?

By Wayan in JDBC 0 Comment 
package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

public class JdbcQueryExample {
    // Database connection information
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        // Get a connection to database.
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            // Create a statement object.
            Statement statement = connection.createStatement();

            // Executes a query command to select isbn and the book title
            // from books table. The execute query returns a ResultSet
            // object which is the result of our query execution.
            String query = "SELECT isbn, title, published_year FROM book";
            ResultSet books = statement.executeQuery(query);

            // To get the value returned by the statement.executeQuery we
            // need to iterate the books object until the last items.
            while (books.next()) {
                // To get the value from the ResultSet object we can call
                // a method that correspond to the data type of the column
                // in database table. In the example below we call
                // books.getString("isbn") to get the book's ISBN 
                // information.
                System.out.println(books.getString("isbn") + ", " +
                        books.getString("title") + ", " +
                        books.getInt("published_year"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.1.0</version>
</dependency>

Maven Central

How do I create a connection to database?

By Wayan in JDBC 0 Comment

This post is about an example for obtaining a connection to MySQL database. For connecting to other database all you have to do is change the url to match to url format for a particular database and of course you have to register a correct JDBC driver of the database you are using.

Here are the steps:

  • Define the JDBC url of your database. Below is the format of JDBC url for MySQL database. localhost is your database address and kodejava is the database name.
private static final String URL = "jdbc:mysql://localhost/kodejava";
  • Define the username and password for the connection.
private static final String USERNAME = "kodejava";
private static final String PASSWORD = "s3cr*t";
  • Register the database JDBC driver to be used by our program. Below is the driver for MySQL database.
Class.forName("com.mysql.cj.jdbc.Driver");

The driver registration step above is not required anymore for modern JDBC drivers (JDBC 4.0 / since JDK 6). The JDBC driver class will be located using the service provider mechanism. So you can remove the Class.forName() statement above and all you need to do is place the JDBC driver in your classpath, and the driver will be loaded automatically.

  • We can open a connection to the database.
Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
  • Do any database operation such as select, insert, update and delete.
  • Finally don’t forget to close the Connection object. We usually do this in the finally block of the try-catch block`
if (connection != null) {
    connection.close();
}

But in the code snippet below instead of manually close the connection object we use the try-with-resource statement, this statement will automatically close the connection for us.

Here is the complete code snippet.

package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class ConnectionSample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "kodejava";
    private static final String PASSWORD = "s3cr*t";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            System.out.println("connection = " + connection);

            String sql = "SELECT isbn, title, published_year FROM book";
            PreparedStatement stmt = connection.prepareStatement(sql);

            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                System.out.println(rs.getString("isbn") + ", " +
                        rs.getString("title") + ", " +
                        rs.getInt("published_year"));
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Maven Dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.1.0</version>
</dependency>

Maven Central