Der Blog von Benny Neugebauer » MySQL

MySQL NOW() equivalent in Java for prepared statements

bennyn — Sun, 01 Apr 2012 20:30:59 +0000

If you are used to MySQL then you probably know the MySQL function NOW() which inserts the current date and time in a MySQL query. But if you use JDBC and prepared statements, then you can reconstruct this function with a GregorianCalendar (which is the successor of Date):

public void insertArticle(Article article) throws SQLException
{
  //query = "INSERT INTO articles(title,content,date) VALUES (?,?,NOW())";
  query = "INSERT INTO articles(title,content,date) VALUES (?,?,?)";
 
  statement = connection.prepareStatement(query);
 
  statement.setString(1, article.getTitle());
  statement.setString(2, article.getContent());
  statement.setTimestamp(3, new Timestamp(new GregorianCalendar().getTimeInMillis()));
 
  logger.info(statement);
  statement.executeUpdate();
}

Insert only in specific columns with MySQL

bennyn — Sun, 04 Mar 2012 22:08:45 +0000

If you have a big MySQL table and you want to insert data only in specific columns, then you can do this with naming the columns in parentheses after the table name:

INSERT INTO `wp_posts`(`post_author`,`post_content`,`post_title`,`post_date`) VALUES (0,'Hello World','Text...',NOW());

This works even without apostrophes:

INSERT INTO wp_posts(post_author,post_content,post_title,post_date) VALUES (0,'Hello World','Text...',NOW());

java.sql.SQLException – Value can not be represented as java.sql.Date

bennyn — Sun, 04 Mar 2012 21:20:54 +0000

If you receive an error that is similar to this:

java.sql.SQLException: Value ’0000-00-00 00:00:00′ can not be represented as java.sql.Date

Then you should check your database connection. If your connection url looks like jdbc:mysql://localhost/my_database then you should try jdbc:mysql://localhost/my_database?zeroDateTimeBehavior=convertToNull.

Other options are:
jdbc:mysql://localhost/my_database?zeroDateTimeBehavior=round
jdbc:mysql://localhost/my_database?zeroDateTimeBehavior=exception

The explanation can be found in “handling DATETIME values“.

Connecting to a MySQL Database with Java (JDBC)

bennyn — Sun, 04 Mar 2012 21:12:49 +0000

In the beginning of my study time I’ve programmed a MySQL connection in Java for a music collection. After 2 years now I have made a remake of this code to show how to use the Java Database Connectivity (JDBC). All you need is mysql-connector-java-5.0.8-bin.jar.

I’ve written a small sample for the connection with a WordPress database.

DatabaseController.java

import com.mysql.jdbc.PreparedStatement;
import com.mysql.jdbc.ResultSet;
import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.text.SimpleDateFormat;
import java.util.logging.Level;
import java.util.logging.Logger;
 
public class DatabaseController
{
 
  private String host = null;
  private String name = null;
  private String user = null;
  private String password = null;
  static final Logger logger = Logger.getLogger(DatabaseController.class.getName());
 
  public DatabaseController(String host, String name, String user, String password)
  {
    this.host = host;
    this.name = name;
    this.user = user;
    this.password = password;
  }
 
  private Connection getConnection()
  {
    Connection connection = null;
    try
    {
      Class.forName("com.mysql.jdbc.Driver");
      connection = DriverManager.getConnection("jdbc:mysql://" + host + "/" + name + "?zeroDateTimeBehavior=convertToNull", user, password);
    }
    catch (SQLException | ClassNotFoundException ex)
    {
      logger.log(Level.SEVERE, ex.getLocalizedMessage());
    }
    return connection;
  }
 
  public void printWordPressPosts() throws SQLException
  {
    Connection connection = getConnection();
    String query = "SELECT * FROM wp_posts";
    PreparedStatement statement = (PreparedStatement) connection.prepareStatement(query);
    ResultSet result = (ResultSet) statement.executeQuery();    
 
    SimpleDateFormat dateFormat = new SimpleDateFormat( "yyyy-MM-dd HH:mm:ss.S" );
 
    while (result.next())
    {
      Date date = result.getDate("post_date");
      String title = result.getString("post_title");
      String content = result.getString("post_content");
 
      if (date != null)
      {
        System.out.println("Posted on: " + dateFormat.format(date) + ", Title: " + title);
      }
    }
  }
}

Execution:

public static void main(String[] args) throws Exception
{
  DatabaseController controller = new DatabaseController("localhost", "database", "db_user", "db_password");
  controller.printWordPressPosts();
}

Datenbank-Zugriff mit PHP und PDO

bennyn — Thu, 12 May 2011 19:33:07 +0000

Beim Zugriff auf eine Datenbank sollte man mit PHP immer auf PDO (PHP Data Objects) zurückgreifen. Durch diese Abstraktionsstufe ist das Datenbank-System später einfacher austauschbar und Prepared Statements lassen sich auch ganz leicht realisieren. Hierzu ein exemplarischer Beispielcode.

Code:

database.sql

DROP DATABASE IF EXISTS `dailydjango`;
CREATE DATABASE `dailydjango` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;
USE `dailydjango`;
 
CREATE TABLE IF NOT EXISTS `feed_entries` 
(
	`id`		INT(10)	NOT NULL AUTO_INCREMENT
	,`pubdate`	DATETIME NOT NULL	
	,`title`	VARCHAR(255) NOT NULL
	,`link`		VARCHAR(255) NOT NULL
	,PRIMARY KEY(`id`)
	,UNIQUE KEY(`link`)
) ENGINE = InnoDB CHARACTER SET utf8 COLLATE utf8_general_ci;

code.php

$HOST	= 'localhost';
$DB	= 'dailydjango';
$USER	= 'root';
$PASS	= '';
$TABLE	= 'feed_entries';
 
// Test-Daten
$test_pubdate = '2011-05-01 21:30:45';
$test_title = 'Ein Titel';
$test_link = 'http://www.bennyn.de/';
 
// MySQL-Eintrag
	try 
	{
		$con	= new PDO("mysql:host=$HOST;dbname=$DB", $USER, $PASS);
		$sql	= "INSERT INTO $TABLE(id,pubdate,title,link) VALUES(NULL,:pubdate,:title,:link)";
		$stmt	= $con->prepare($sql);
		$stmt->bindParam(':pubdate',$test_pubdate);
		$stmt->bindParam(':title',$test_title);
		$stmt->bindParam(':link',$test_link);
		$stmt->execute();
		$stmt	= null;
		$con	= null;
	}
	catch(PDOException $ex)
	{
		echo $ex->getMessage();
	}
 
// MySQL-Abfrage
	try 
	{  		
		$con	= new PDO("mysql:host=$HOST;dbname=$DB", $USER, $PASS);
		$sql	= "SELECT * FROM $TABLE";
		foreach($con->query($sql) as $record)
		{
			print $record['id'].' ';
			print $record['pubdate'].' ';
			print $record['title'].' ';
			print $record['link']."\n";
		}
		$con	= null;
	}  
	catch(PDOException $ex)
	{
		echo $ex->getMessage();
	}

Hinweis: Die Datenbank-Verbindung sollte nicht immer bei jeder Datenbank-Anfrage neu aufgebaut und abgebaut werden.