Max Korytko's Blog

Grails MySQL connection problem – java.net.ConnectException: Connection refused

maxkorytko — Wed, 27 Apr 2011 15:43:52 +0000

I have recently run into the java.net.ConnectException: Connection refused exception trying to connect MySQL server with Grails.

The resolution turned out to be pretty easy. Here is what my set up was:

Max OS X 10.6

XAMPP

GRAILS 1.3.7

After configuring the data source to connect MySQL server (regular stuff) and running grails run-app command, I was getting tons of exceptions. All of them were related to MySQL server connection problem.

Caused by: java.net.ConnectException: Connection refused
	at java.net.PlainSocketImpl.socketConnect(Native Method)
	at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
	at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
	at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
	at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:432)
	at java.net.Socket.connect(Socket.java:529)
	at java.net.Socket.connect(Socket.java:478)
	at java.net.Socket.(Socket.java:375)
	at java.net.Socket.(Socket.java:218)
	at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:254)
	at com.mysql.jdbc.MysqlIO.(MysqlIO.java:295)

Here is how I was able to fix the problem thanks to this blog post: Hydronitrogen.com

Open file /Applications/XAMPP/xamppfiles/etc/my.cnf
Comment the following line: skip-networking

The problem should be fixed.
If not, try replacing localhost with 127.0.0.1 in your DataSource.groovy.

Configure log4net

maxkorytko — Mon, 17 Jan 2011 20:28:18 +0000

Here is how I configured log4net to log to a file.
Place lo4net configuration to web.config.

Refer to this documentation page to find more details regarding PatternLayout.

Java

maxkorytko — Tue, 17 Aug 2010 14:16:48 +0000

MacOS X comes with its own version of Java.
There is a program called Java Preferences in Applications->Utilities, which you can use to manage your JVMs.

If you need to find out where Java home is, run the following script:
/usr/libexec/java_home

Good to know technologies

maxkorytko — Wed, 28 Apr 2010 17:42:43 +0000

BlazeDS

BlazeDS is the server-based Java remoting and web messaging technology for Adobe Flex and AIR applications.

FlourineFX

FluorineFx provides an implementation of Flex/Flash Remoting, Flex Data Services and real-time messaging functionality for the .NET framework.

JMeter

Java desktop application designed to load test functional behavior and measure performance.

Apache Lucene

Apache Lucene is a high-performance, full-featured text search engine library written entirely in Java.

File upload in CakePHP

maxkorytko — Wed, 10 Mar 2010 21:26:53 +0000

Refer to this blog post:
CakePHP file upload

CakePHP Console

maxkorytko — Thu, 11 Feb 2010 20:32:05 +0000

CakePHP console lets you create scripts executable from the command line. This might be useful if you need to create a cron task for your project, for example. In this post I’ll summarize my experience with building console scripts.
You can also read about the Cake console in the Cake book under Developing with CakePHP->The CakePHP Console.
There are two artifacts that you can build: shells and tasks. Usually you create a shell which executes the tasks. Refer to the documentaion for mode details.
Most likely when building console scripts, you’ll want to use Cake’s methods related to models (find, save, etc). In order to do it, you’ll need to import related classes. As you know in controllers you use the uses, components arrays. In shells and tasks it’s a bit different. In the example below, I’m importing a model, controller, view and the Email component.
App::import('Core', 'Controller'); App::import('Core', 'View'); App::import('Model', 'MyModel'); App::import('Component', 'Email');

Once you’ve imported all you need you can start writing the task class. It’s your job to create the objects you’ve imported.
class MyTask extends Shell { protected $Controller; protected $Email; protected $MyModel;

function initialize() { $this->Controller =& new Controller(); $this->Email =& new EmailComponent(null); $this->Email->startup($this->Controller); $this->MyModel =& new MyModel(); } }

That’s pretty much it. You can now use the model methods as you would in the contoller.

function execute() { $this->MyModel->find('all');


// the Email component will also work

$this->Email->layout = 'my_email_layout';

$this->Email->template = 'my_email_template'; // make sure you create my_email_template.ctp in /app/views/email/html|plain/

$this->Email->sendAs('html');

$this->Email->charset('UTF-8');

$this->Controller->set('myVar', 'my value'); // will be available in the email template $success = $this->Email->send(); }

In order to be able to use this task in a shell, make sure you add it to the task list:
class MyShell extends Shell { var $tasks = array('MyTask');

function main() { $this->out('Executing My task'); $this->MyTask->execute(); } }

MySQL server character encodings and collations

maxkorytko — Wed, 13 Jan 2010 17:37:29 +0000

Quite often there is a requirement to build a localized web site. The challenge I keep facing is how to store, select, and display string values that require different character encoding. I’ve taken some time to read the MySQL server documentation on the topic, and this post is just a quick summary of what I read. The complete documentation is located here: MySQL Server Localization

To store character values MySql server provides CHAR, VARCHAR, and TEXT data types. Each uses a character set and collation.

Character set is a set of symbols and encodings.
Collation is a set of rules for comparing characters in a character set.

It’s clearly explained in the mysql server reference document. You can read it here.

Display the list of character sets MySQL server supports
mysql> show character set;

Display the list of collations
mysql> show collation;
mysql> show collation like ‘latin1%’;

Specify character sets and collations
Can be specified for:

server
database
table
column

The table character set and collation are MySQL extensions, and will not work in standard SQL.

Change the character set for all column of an existing table
mysql> ALTER TABLE tbl_name CONVERT TO CHARACTER SET charset_name [COLLATE collation_name];
If the character sets are incompatible, there may be data loss.

Determine the character set and collation for the selected database
mysql> show variables like ‘character_set_database’
mysql> show variable like ‘collation_server’

URL rewriting in Grails 1.1

maxkorytko — Thu, 07 Jan 2010 17:00:31 +0000

To store data between requests we use sessions. With every request the browser sends session id to the server, so that the request is identified and session scope is assigned to it. On the client side, the browser stores the session id in a cookie. If the browser doesn’t support cookies (mobile browser) or they are turned off, we can use URL rewriting to append session id to each URL on all pages of the website. So with cookies turned on some URL might look like this: /shop/promos.
To append a session id at the end of the URL you would write something like this in JSP: response.encodeURL(“/shop/promos”) . The resulting URL will look like this: /shop/promos;jsessionid=G32898fdaGagda098890.

To enable URL rewriting in Grails views, add this line line to Config.groovy:
grails.views.enable.jsessionid = true
I tested this in Grails 1.1.

Then, URLs generated by Grails tags (link, createLink, etc) will be url encoded only when cookies are disabled.

CakePHP tips and tricks

maxkorytko — Fri, 11 Dec 2009 17:49:05 +0000

Change the configuration settings programmatically

configure::write('debug', 0);

Collections in GORM

maxkorytko — Tue, 24 Nov 2009 21:12:17 +0000

Grails allows several data types to be used to store the data on the programmatic level for 1:m and m:n relationships.
If you read Grails documentation, you’ll find out that by default Grails uses an object of the java.util.Set class to store objects of the associated class. For example:

class Person
{
  String name
  City city
  static belongsTo = City
}

class City
{
  String name
  static hasMany = [people:Person]
}

The data type of the people instance field will be java.util.Set.
If you want to use List instead, and access the associated objects by index, you need to declare the people field as List.


class City
{
  String name
  List people
  static hasMany = [people:Person]
}

To make this work, Grails will ad the people_idx column to the person table. The values in this column are important. The first record will have its value set to 0, the next 1, and so forth.

Pay attention to the following quote, taken from the Grails user guide

When using a List, elements must be added to the collection before being saved, otherwise Hibernate will throw an exception (org.hibernate.HibernateException: null index column for collection):



// This won't work!

def book = new Book(title: 'The Shining')

book.save()

author.addToBooks(book)

// Do it this way instead. def book = new Book(title: 'Misery') author.addToBooks(book) author.save()

When you write city.people, Grails will construct the list of people based on the values of the persons_idx column. If the sequence is broken, you’ll end up with nulls in the list.

Examples
Suppose the people_idx sequence is like so: 0 1 2 3
city.people will be equal to [personA, personB, personC, personD]

Suppose the poople_idx sequence is like so: 0 1 4 5
city.people will be equal to [personA, personB, null, null, personC, personD]

To avoid breaking the sequnce, make sure you remove the associated object from its owner when deleting the associated object.

When deleting a person do the following:

def person = Person.get(params.id)
person.delete()
City.get(person.city.id)?.removeFromPeople(person)