Java with MySql

1. Java Database Connectivity (JDBC)

The interface for accessing relational databases from Java is JDBC. Via JDBC you maintain the databases connection, issue database queries and updates and receive the results.

JDBC is an interface independently of any database. For each database you require the database specific implementation of the JDBC driver.

2. Introduction to MySQL

To learn to install and use MySQL please see MySQL - Tutorial.

The following will assume that you have successfully installed MySQL and know how to access MySQL via the command line.

3. MySQL JDBC driver

To connect to MySQL from Java you have to use the JDBC driver from MySQL. The MySQL JDBC driver is called "MySQL Connector/J". You should be able to find the latest MySQL JDBC driver on this pagehttp://dev.mysql.com/downloads/connector/j .

The download contains a jar file which we require later.

4. Create example database

Start the MySQL command line client and paste the following SQL script into it to create a sample database which we can use as an example.

create database feedback;
use feedback;
CREATE USER sqluser IDENTIFIED BY 'sqluserpw'; 
grant usage on *.* to sqluser@localhost identified by 'sqluserpw'; 
grant all privileges on feedback.* to sqluser@localhost;

CREATE TABLE COMMENTS (id INT NOT NULL AUTO_INCREMENT, 
    MYUSER VARCHAR(30) NOT NULL,
    EMAIL VARCHAR(30), 
    WEBPAGE VARCHAR(100) NOT NULL, 
    DATUM DATE NOT NULL, 
    SUMMERY VARCHAR(40) NOT NULL,
    COMMENTS VARCHAR(400) NOT NULL,
    PRIMARY KEY (ID));

INSERT INTO COMMENTS values (default, 'lars', 'myemail@gmail.com','http://www.vogella.com', '2009-09-14 10:33:11', 'Summery','My first comment'); 

5. Java JDBC

Create a Java project and a package "de.vogella.mysql.first".

Create a folder "lib" and copy the JDBC driver into this folder. Add the JDBC driver to your classpath. SeeAdding jars to the classpath for details.

Create the following class to connect to the MySQL database and perform queries, inserts and deletes. It also prints the metadata (table name, column names) of a query result.

package de.vogella.mysql.first;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Date;

public class MySQLAccess {
  private Connection connect = null;
  private Statement statement = null;
  private PreparedStatement preparedStatement = null;
  private ResultSet resultSet = null;

  public void readDataBase() throws Exception {
    try {
      // This will load the MySQL driver, each DB has its own driver
      Class.forName("com.mysql.jdbc.Driver");
      // Setup the connection with the DB
      connect = DriverManager
          .getConnection("jdbc:mysql://localhost/feedback?"
              + "user=sqluser&password=sqluserpw");

      // Statements allow to issue SQL queries to the database
      statement = connect.createStatement();
      // Result set get the result of the SQL query
      resultSet = statement
          .executeQuery("select * from FEEDBACK.COMMENTS");
      writeResultSet(resultSet);

      // PreparedStatements can use variables and are more efficient
      preparedStatement = connect
          .prepareStatement("insert into  FEEDBACK.COMMENTS values (default, ?, ?, ?, ? , ?, ?)");
      // "myuser, webpage, datum, summery, COMMENTS from FEEDBACK.COMMENTS");
      // Parameters start with 1
      preparedStatement.setString(1, "Test");
      preparedStatement.setString(2, "TestEmail");
      preparedStatement.setString(3, "TestWebpage");
      preparedStatement.setDate(4, new java.sql.Date(2009, 12, 11));
      preparedStatement.setString(5, "TestSummary");
      preparedStatement.setString(6, "TestComment");
      preparedStatement.executeUpdate();

      preparedStatement = connect
          .prepareStatement("SELECT myuser, webpage, datum, summery, COMMENTS from FEEDBACK.COMMENTS");
      resultSet = preparedStatement.executeQuery();
      writeResultSet(resultSet);

      // Remove again the insert comment
      preparedStatement = connect
      .prepareStatement("delete from FEEDBACK.COMMENTS where myuser= ? ; ");
      preparedStatement.setString(1, "Test");
      preparedStatement.executeUpdate();
      
      resultSet = statement
      .executeQuery("select * from FEEDBACK.COMMENTS");
      writeMetaData(resultSet);
      
    } catch (Exception e) {
      throw e;
    } finally {
      close();
    }

  }

  private void writeMetaData(ResultSet resultSet) throws SQLException {
    //   Now get some metadata from the database
    // Result set get the result of the SQL query
    
    System.out.println("The columns in the table are: ");
    
    System.out.println("Table: " + resultSet.getMetaData().getTableName(1));
    for  (int i = 1; i<= resultSet.getMetaData().getColumnCount(); i++){
      System.out.println("Column " +i  + " "+ resultSet.getMetaData().getColumnName(i));
    }
  }

  private void writeResultSet(ResultSet resultSet) throws SQLException {
    // ResultSet is initially before the first data set
    while (resultSet.next()) {
      // It is possible to get the columns via name
      // also possible to get the columns via the column number
      // which starts at 1
      // e.g. resultSet.getSTring(2);
      String user = resultSet.getString("myuser");
      String website = resultSet.getString("webpage");
      String summery = resultSet.getString("summery");
      Date date = resultSet.getDate("datum");
      String comment = resultSet.getString("comments");
      System.out.println("User: " + user);
      System.out.println("Website: " + website);
      System.out.println("Summery: " + summery);
      System.out.println("Date: " + date);
      System.out.println("Comment: " + comment);
    }
  }

  // You need to close the resultSet
  private void close() {
    try {
      if (resultSet != null) {
        resultSet.close();
      }

      if (statement != null) {
        statement.close();
      }

      if (connect != null) {
        connect.close();
      }
    } catch (Exception e) {

    }
  }

} 

Create the following main program to test your class.

package de.vogella.mysql.first.test;

import de.vogella.mysql.first.MySQLAccess;

public class Main {
  public static void main(String[] args) throws Exception {
    MySQLAccess dao = new MySQLAccess();
    dao.readDataBase();
  }


}