Ujjwal's Blog: June 2012

Thursday, June 28, 2012

Liferay goes Dropbox: Liferay Sync

Liferay announced a powerful feature that reminds me of Dropbox: Document synchronization.

It will allow you to access your files on- and offline on a various list of devices. Read the press release here: Liferay Sync

If you have any questions then feel free to comment..

Cheers..

Ujjwal Soni

Friday, June 22, 2012

Difference between FetchType LAZY and EAGER in Java persistence

Sometimes you have two entities and there's a relationship between them. For example, you might have an entity called University and another entity called Student.

The University entity might have some basic properties such as id, name, address, etc. as well as a property called students:

public class University {
 private String id;
 private String name;
 private String address;
 private List students;

 // setters and getters
}

Now when you load a University from the database, JPA loads its id, name, and address fields for you. But you have two options for students: to load it together with the rest of the fields (i.e. eagerly) or to load it on-demand (i.e. lazily) when you call the university's getStudents() method.

When a university has many students it is not efficient to load all of its students with it when they are not needed. So in suchlike cases, you can declare that you want students to be loaded when they are actually needed. This is called lazy loading.

Thursday, June 14, 2012

Display link mailto / Href in alert box javascript

Hi,

Below is the code i implemented for displaying link in href alert box ::

<!doctype html>
<html>
 <meta charset="utf-8">
 <title>Basic usage of the jQuery UI dialog</title>

 <link rel="stylesheet" type="text/css" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.7.1/themes/base/jquery-ui.css">

 <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
 <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.7.1/jquery-ui.min.js"></script>
 <script type="text/javascript">
 $(document).ready(function() {
  var $dialog = $('<div></div>')
   .html('Welcome, Please click on the Link to display blog <a href='http://ujjwalbsoni.blogspot.com'>Visit blog</a>')
   .dialog({
    autoOpen: false,
    title: 'Basic Dialog'
   });

  $('#opener').click(function() {
   $dialog.dialog('open');
   // prevent the default action, e.g., following a link
   return false;
  });
 });
 </script>
</head>
<body>

<p>This is an example from the Ujjwal's Blog</a>.</p>

<button id="opener">Show Dialog</button>

</body>
</html>

Wednesday, June 13, 2012

Beginning Liferay - Installation and Execution

Hi,

I recently begin my Liferay learning by installing letest version of Liferay Portal 6.1 Community Edition from www.liferay.com. I downloaded and extracted it in macosx. I downloaded tomcat bundled installation.

After extracting it in a specific folder run the below file from terminal (in mac osx)::

LIFERAY_PORTAL/liferay-portal-6.1.0-ce-ga1/tomcat-7.0.23/bin/startup.sh

If you are running it in windows, you can run startup.bat file.

I have just installed liferay on my machine, now i will begin learning portlets and development using life ray.

Keep reading my blog for more updates

thanks,

Ujjwal soni

Monday, June 11, 2012

org.hibernate.InvalidMappingException: Could not parse mapping document

Hi,

If you get below exception in your struts hibernate application

org.hibernate.InvalidMappingException: Could not parse mapping document from resource ujjwal/home/homes.hbm.xml

The reason behind this exception could be

1) wrong package name in hibernate.cfg.xml file

2) wrong package name in homes.hbm.xml

for example

<class name="ujjwal.homes.Homes" table="homes" schema="myhomes">

As you can see in above example, we are having package name ujjwal.homes.Homes under class name which is totally incorrect, it should be ujjwal.home.homes.Homes instead.

If you still face this issue, feel free to comment

Thanks,

Ujjwal Soni

java.lang.NoSuchMethodError: antlr.collections.AST.getLine() Struts Hibernate exception

Hi,

I recently got an error java.lang.NoSuchMethodError: antlr.collections.AST.getLine()

This error comes when there is a conflict in antlr jar file with struts 1.3 and hibernate 3. You need to remove antlr 2.7.2 jar file from struts 1.3 by clicking on myeclipse preferences > libraries.

If any questions, feel free to comment.

Thanks,

Ujjwal Soni

Saturday, June 9, 2012

Killing idle sessions in Postgresql

Recently, i faced an issue with Postgresql with one table where it got locked due to some reason. I followed below steps to unlock it ::

1) connect to Postgresql using below command

ssh -L 5432:127.0.0.1:5432 DEMO@server.com

2) Find idle processes using below command

ps -ef | grep postgres

Identify the process and note its id

3) connect to database using PG Admin tool

Fire below command from sql window

pg_cancel_backend(‘procpid’)

Thanks,

Ujjwal Soni

Friday, June 1, 2012

Playing movies and music over SSH

If you want to remotely access your SSH account (e.g. NAS in home) and listen to the music or watch some movies without downloading them in the first place, you can use the following command:

ssh user@your.host.com cat mediaFile.avi | mplayer -

It will connect to your.host.com, log into the user account, invoke the cat command on the given mediaFile.avi and transfer the output (stream of bytes) to your local mplayer.

The mplayer - says that it should read the data from the standard input — which in this case is the result of the cat command.
When you finish watching or listening — just break the connection and no traces are left on your local device.

Alternatively, you can also mount your remote ssh location using the sshfs.

Executing SSH commands from ANT

ou can easily achieve remote command invocation, using an ANT Task sshexec. An example of its usage could be this snippet (note that remote.* variables are taken from the *.properties file in this case):

<sshexec host="${remote.host}"
         username="${remote.user}"
         password="${remote.pass}"
         trust="true"
         command="rm -rf ${remote.webapps.path}/ROOT*" />

You can read about more detailed examples here.

To add this feature to your ANT installation, you need to download the JSch – Java Secure Channel library and include the jsch jar file into ANT classpath (i.e. in your ANT_HOME/lib/ or — if you’re using an Eclipse — into Eclipse Ant classpath).

I found this feature quite useful as it reduced time I needed to build and deploy an application.

Compiling Java Source File From Running Java Application

Hi All,

id you know that you can compile Java source code from your running Java Application? It’s not even so hard and the JavaCompiler javadoc is quite verbose.
Try it for yourself:

package com.piotrnowicki.javacompiler; 

 

import javax.tools.JavaCompiler;
import javax.tools.ToolProvider; 

public class Executor {
    public static void main(String[] args) {
        JavaCompiler jcp = ToolProvider.getSystemJavaCompiler(); 

        // Compile pointed *.java file
        jcp.run(null, null, null, "/home/piotr/MyClass.java");
    }
}

Now imagine that you can compile your Java code from a Java application that compiles your Java code. Why…? Because we can and because it’s so inception!

Fun with music in Java

Music programming in Java is now easy with jfugue.

Step 1. Download

Go to jfugue.org → Download → jfugue-4.0.3.jar

Step 2. Place it in the classpath

Eclipse: Project > Java Build Path > Libraries > Add External JARs…
Netbeans: File > “Project” Properties > Libraries > Add JAR/Folder
JDeveloper: Tools > Project Properties… > Libraries and Classpath > Add JAR/Directory…

Step 3. Have fun

Play a note

new Player().play("C");

Play a note on a different octave

// 7th octave of the piano
new Player().play("C7");

Play a note with different duration

// w means whole = 4/4
new Player().play("Cw");

Play two notes

new Player().play("C D");

Use a rest

new Player().play("C R D");

Play some notes together

// h means half = 2/4
new Player().play("C5h+E5h+G5h+C6h");

Pick a different instrument

new Player().play("I[HARMONICA] C D E");

Play a simple song

new Player().play("I[BLOWN_BOTTLE] Gh Eq Cq | Gw | Gh Eq Cq | Gw");

Play a simple song with different tempo

new Player().play("T[220] I[KALIMBA] Gh Eq Cq | Gw | Gh Eq Cq | Gw");

Create a rythm!

Rhythm rhythm = new Rhythm();
rhythm.setLayer(1, "...*...*...*...*");
rhythm.setLayer(2, "----------------");
rhythm.addSubstitution('.', "Ri");
rhythm.addSubstitution('*', "[SKAKUHACHI]i");
rhythm.addSubstitution('-', "[PEDAL_HI_HAT]s Rs");
new Player().play(rhythm.getPattern());

Conclusion

At last, it’s easy to program some music for our games and create sounds for our applications.
The sound API of JDK really needed this comfortable boost. Congratulations to David Koelle for creating this tool!