h:messages for a4j requests

Well, it's simple: validation errors are not displayed on the page when they apear while processing a Richfaces AJAX request.

To correct this you have to decorate the h:messages tag like this:

<a4j:outputPanel ajaxRendered="true">
 <h:messages/>
</a4j:outputPanel>

Why doesn't it work otherwise?

• h:messages component is not inserted in the JSF component tree the first time the page is loaded (with an empty form);
• Richfaces AJAX calls can not work with components which are not already in the JSF component tree.
  

Why does the decorated version work?

• a4j:outputPanel inserts in the component tree even non-present child components.
  
• ajaxRendered attribute sets the outputPanel (with all its child components) to be rendered with the new values after each AJAX request processing.

Using JDBC with MySQL

To write Java programs that use a MySQL database you need to do four things:

1. Install MySQL Server (there will come an article on this in the future)
   
2. Install JDK and Eclipse
   
3. Install the MySQL Connector/J
4. Write a test program

In this article details steps 3 and 4.


Install the MySQL Connector/J

The package java.sql in the JDK provides interfaces for working with the database. The implementation of this interfaces is particular to each Database Mangement System (DBMS) (i.e. Oracle, MsSql, MySQL, etc.) and is provided through drivers. In this way your code is independent of DBMS. When you decide to change the DBMS you just need to change the driver, while your code stays the same.

MySQL Connector/J is a native Java driver that converts JDBC (Java Database Connectivity) calls into the network protocol used by the MySQL database.

Installing MySQL Connector/J:

• download MySQL Connector/J 5.0 (or other version)
• unpack the archive and copy mysql-connector-java-5.0.8-bin.jar in jre1.6.0_02\lib\ext directory. (jre1.6.0_02 can have different sufix depending on the JDK version you have installed; you can find it in the directory where you installed the JDK.)
  

This is all what it takes to install the driver for MySQL. Information was taken from the driver archive: \docs\README.txt (1.2.2. Installing the Driver and Configuring the CLASSPATH).


Write a test program

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

/**
* Test connection to a MySQL database installed on local machine.
*
* @author Mihai Ionut Rus
*/
public class TestMySQL {

public static void main(String[] args) {
try {
Statement stmt;

// Register the JDBC driver for MySQL.
Class.forName("com.mysql.jdbc.Driver");

String url = "jdbc:mysql://localhost:3306/mysql";

/*
* Get a connection to the database for a user named root with a blank
* password. If have a password for root, you must provide it.
*/
Connection con = DriverManager.getConnection(url, "root", "");

System.out.println("URL: " + url);
System.out.println("Connection: " + con);

//Create a test database
stmt = con.createStatement();
stmt.executeUpdate("CREATE DATABASE JunkDB");

con.close();
} catch (Exception e) {
e.printStackTrace();
}
}

}

A humble programmer's wish

Who am I?

I'm just a simple programmer - IT is not the love of my life. I make my living out of programming but I don't see programming as the goal of my life.

I'm not into abstract theories. I like keeping things simple and practical. I like to think of myself as being lazy, not stupid.


Why & How?

I've created this blog to prove that anything can be simple if explained in the right way. A heavy task which I intend to accomplish by:

• using "Don't let me think!" approach (not that I do not encourage you to think, but I would like you to think about how to use the information not trying to understand it);
• cutting out any unnecessary information;
• focusing on a single topic at once;
• revealing the source of my knowledge;
  
• including any prerequisite information;
• answering your questions;

Hopping to succeed in this idealistic task, at least in 60%, I welcome you to this blog and wish you happy readding!