WittyReader: More than a speed reading tool

WittyReader is a reading tool and provide the possibility to you to read web pages, blogs, twitter feeds, text books, rss feeds on your smartphone while traveling. Forget the zooming, scrolling, positioning, With WittyReader it’s just a single tip and you can enjoy reading.

Read more on WittyReader.com

Follow me on Tumblr

Follow me on Tumblr and read about Groovy and Grails, SmartBiobank and view my photos: szpetip.tumblr.com.

Developing in Groovy and Grails

In the last two years, I abandoned the pure Java EE as primary developing framework, this is the main reason, why this blog doesn't have new posts.
We had to face with new challenges and the pure Java EE technology was not flexible enough to support our development processes. We thought, we should try one of the new dynamic web application framework. The Groovy on Grails was the chosen one.
It was a big decision. Migration to a new technology in a country, where nobody knows nothing except .NET and Java was not an easy task. Our developer team was really enthusiastic, we made some pilot projects and drawn the consequences: Let's do it!
Our first live project with Groovy and Grails was the SmartBiobank (http://smartbiobank.com).

SmartBiobank is a free, online biobank software designed to help clinicians, lab biologists and researchers to integrate translational research elements into one single system. SmartBiobank can store, manage and analyze biospecimen data, clinical data as well as experimental data. SmartBiobank is fully customizable. Users can choose from several types of questions and then build forms freely from these questions. Forms are then linked to patients or samples creating the basic structure of the project.

SmartBiobank's development is continuous, but I'm absolutely sure:

Changing to Groovy and Grails was a brilliant idea!

I can tell you our experiences about Groovy and Grails:

• Our development process is five-six times as fast! Just imagine, you can work as fast as a complete team.
• Source code is more transparent and no sucks with jar files, application layouts, rigid EE design patterns.

But of course, there are some disadvantages:

• Only experienced developers should use Groovy and Grails and other dynamic languages: No compiler errors, less code competition, typeless objects, closures.
• We posted a job advertisement and got a call from the advertising company, what a hell is this "Groovy on Grails developer", this is a fake position or a kind of Java or .NET developer.
• Of course, nobody applied the job.

If you are curious,  try out Groovy and Grails and check out SmartBiobank!

Grails: The search is over!

SmartBiobank: The most intelligent digital biobank system

Last post

Unfortunately I'm closing my blog this week. I can't spend time with posting and moderating out Chinese people who write junk comments all the time.

I have had ~9000 visitor from 111 country all over the world in the last two year, thanks for it!


Bye,


...szpetip

String puzzle

A short, but interesting puzzle.

Question
What does the following program print:



Answer
When you run the code, you get the answer: 2.

Why?
The compiler translates Unicode escapes into the characters they represent before it parses the program into tokens, such as strings literals. As you see, NetBeans IDE doesn't know it, it present the code like a string with a length() method.

NetBeans 6.5.1 generates invalid web.xml

If you use NetBeans 6.5.1 and you want to add a new servlet to the project, the IDE generate an invalid web.xml file and you will be not able to deploy the application.

The problem
If you try to deploy the web application into an application container, then you get an exception like this:

org.apache.catalina.startup.ContextConfig applicationWebConfig
SEVERE: Parse error in application web.xml file at jndi:/localhost/XXXXXX/WEB-INF/web.xml
java.lang.IllegalArgumentException: Servlet mapping specifies an unknown servlet name XXXXXX

The solution
Solving this problem is very easy:

1. Open your web.xml file and choose the XML view to see the xml code.
2. Cut all <servlet-mapping> tags and put them back after the <servlet> tags.

After you redistribute and deploy your application, it will be start successfully.

Solve MySQL server drops and close connections in connection pool

If you get "Last packet sent to the server was XX ms ago." error in your application that want to access MySQL database or you want to know, how to create a connection pool using Tomcat server and DataSource then this is your post.

Connection pooling with MySQL
Using connection pool is a good way to increase your web application speed. If you create a connection pool in your application, using a MySQl server, in the first morning you will see, the database server drops all of the connections in the pool.

This is because MySQL drops connections after 8 hours idle period. There are many solution in the web, some are working, some aren't working, but the most of them are hacking.

I present an elegant solution to this typically problem, caused by MySQL server.

The best solution - Commons DBCP

Download Commons DBCP
The Apache Commons project has a very useful connection pool implementation, called Commons DBCP.

To use Commons DBCP,

• download the required jar file from the project page (DBCP Download),
• copy it into the lib directory in your Tomcat server and add to your project, where you want to use the connection pool.

Configuring datasource - Tomcat server, server.xml
In my solution, the datasource is defined as a global resource in the server.xml of the Tomcat. To do this, edit the server.xml file in the conf directory in your Tomcat server and add some code line like this between the <GlobalNamingResources> </GlobalNamingResources> tags:

<resource name="jdbc/sampleDB" auth="Container" type="javax.sql.DataSource" maxActive="15" maxidle="10" maxwait="10000" timeBetweenEvictionRunsMillis="10000" minEvictableIdleTimeMillis="60000" factory="org.apache.commons.dbcp.BasicDataSourceFactory" username="XXXXXXXX" password="XXXXXXX" driverClassName="com.mysql.jdbc.Driver" url="jdbc:mysql://localhost/sampledatabase" testOnBorrow="true" testOnReturn="true" validationQuery="select count(*) from TABLENAME" />

Parameters descriptions are availables here, in nutshell:
name - The datasource will be registred with this name in the naming context.
auth - The authentication type of the resource. Set to Container.
type - The resource type. Set to javax.sql.DataSource to create a datasource.
maxAcive - The maximum number of active connections that can be allocated from this pool at the same time, or negative for no limit.
maxIdele - The maximum number of connections that can remain idle in the pool, without extra ones being released, or negative for no limit.
maxWait - The maximum number of milliseconds that the pool will wait (when there are no available connections) for a connection to be returned before throwing an exception, or -1 to wait indefinitely.
timeBetweenEvictionRunsMillis - The number of milliseconds to sleep between runs of the idle object evictor thread. When non-positive, no idle object evictor thread will be run.
minEvictableIdleTimeMillis - The minimum amount of time an object may sit idle in the pool before it is eligable for eviction by the idle object evictor (if any).
factory - The factory, that provide the connections, to use Commons DBCP, use org.apache.commons.dbcp.BasicDataSourceFactory.
userName - The user name to access your database.
password - The password to access your database.
driverClassName - The driver class to access the database, in this case com.mysql.jdbc.Driver. The driver file must be copied into the lib directory of the Tomcat server.
url - The database url.
testOnBorrow - The indication of whether objects will be validated before being borrowed from the pool. If the object fails to validate, it will be dropped from the pool, and we will attempt to borrow another. Set to true.
testOnReturn - The indication of whether objects will be validated before being returned to the pool. Set to true.
validationQuery - The SQL query that will be used to validate connections from this pool before returning them to the caller. If specified, this query must be an SQL SELECT statement that returns at least one row.

Configuring datasource - Web application, context.xml
To access the defined global resource, modify the context.xml file in your web application. Open the context.xml with your favorite editor and put the following code between the <Context> </Context> tags:

<ResourceLink global="jdbc/sampleDB" name="jdbc/sampleDB" type="javax.sql.DataSource"/>

The global parameter is the global name of the defined resource in the server.xml, the name parameter is the name of the resource in our context, type is like in server.xml, the type of the resource, in this case javax.sql.DataSource.

Getting a connection from the pool
We're ready to get a connection from the pool and use it in a Hibernate transaction. The code:

...
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.sql.DataSource;
import java.sql.Connection;
...

public void someMethod() throws Exception {
//Getting the initial context.
Context initCtx = new InitialContext();
//Getting the env context from the initial context,
// where the resources are defined.
Context envCtx = (Context) initCtx.lookup("java:comp/env");
//Getting the datasource from the env context.
//The lookup parameter must be the name parameter
// of the ResourceLink tag in the application's context,xml.
DataSource dataSource = (DataSource) envCtx.lookup("jdbc/sampleDB");
//Getting a connection from the datasource.
Connection connection = dataSource.getConnection();
//sessionFactory must be set before use here, setting
// sessiobFactory is depend on the type of Hibernate
// type and version.
try {
Session session = sessionFactory.openSession(connection);
...
//Use the session
...
} catch(Exception ex) {
//Very important exception handling methods comes here
...
} finally {
//finally statement is very important if you use connection
// from datasource. if you don't use then the connection
// can be stuck and it will be not more available.
try {
//If you use datasource, closing the sessions are as important as
// opeining them.
session.close();
} catch(Excedption ex) { ... }
}
...

Tips
You must restart your Tomcat server after you copy something into lib directory or edit the server.xml file.