cron is a UNIX tool that has been around for a long time, so its scheduling capabilities are powerful and proven. The CronTrigger class is based on the scheduling capabilities of cron.

Got more details from following sites:

• CronTrigger Tutorial
• List of Sample Cron Expressions To Define Simple And Complex Scheduling

Problem: Last day, I got stuck on repo sync. I was unable to sync as git gave error – “It looks like git-am is in progress. Cannot rebase.”

Solution: I’ve deleted rebase-apply directory on .git, finally succeed in repo syncing. Following command I’ve used:

rm -rf .git/rebase-apply

Notes About

How I configured Jboss mail service to use Gmail as an SMTP server from spring application.

Jboss Mail Service Configuration

The JBossAS deploy/mail-service.xml configures a JavaMail session binding into JNDI. Configured the file to work with Gmail, as follows:

<server>
    <mbean code="org.jboss.mail.MailService" name="jboss:service=GMail">
        <attribute name="JNDIName">java:/GMail</attribute>
        <attribute name="User">someuser@gmail.com</attribute>
        <attribute name="Password">myPassword</attribute>
        <attribute name="Configuration">
        <configuration>
            <property name="mail.smtp.host" value="smtp.gmail.com">
            <property name="mail.smtp.port" value="465">
            <property name="mail.smtp.auth" value="true">
            <property name="mail.smtp.ssl.enable" value="true">
        </configuration>
        </attribute>
        <depends>jboss:service=Naming</depends>
    </mbean>
</server>

Spring Bean Definition

For my spring apps i’ve used spring mail api and JNDI bound mail session.

<bean id="mailSender">
    <property name="session"><ref bean="mailSession"></property>
</bean>

<bean id="mailSession">
    <property name="jndiName"><value>java:/GMail</value></property>
</bean>

Helpful References:

• https://community.jboss.org/wiki/JavaMail
• http://wheelersoftware.com/articles/spring-javamail.html
• http://achorniy.wordpress.com/2009/12/15/jboss-mail-service-with-ssl-smtp/

What i need to know?

Both delete and truncate command can be used to delete all the rows from a table. But significent differences between this two sql statements should have clear understanding.

Delete From <Table_name>

DELETE command is used to remove rows from a table. A WHERE clause can be used to remove only some rows. If no WHERE condition is specified, all rows will be removed. For example:

To delete a row with id 10 from mytable, the sql delete query would be like,

DELETE FROM mytable WHERE id = 10;

To delete all the rows from mytable, the query would be like,

DELETE FROM mytable;

It is a DML command. As why, After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it.

Truncate Table <Table_name>

Truncate command is used to delete all the rows from the table and free the storage containing the table. Truncate is DDL coammand. So TRUNCATE operations cannot be rolled back. For Example:

To delete all the rows from mytable, the query would be like,

TRUNCATE TABLE mytable;

TRUNCATE is much faster than DELETE. Why?

When you type DELETE mytable all the data get copied into the Rollback Tablespace first. Then delete operation get performed. That’s why when you type ROLLBACK after deleting a table, you can get back the data(The system get it for you from the Rollback Tablespace). All this process take time. But when you type TRUNCATE,it removes data directly without copying it into the Rollback Tablespace. Thatswhy TRUNCATE is faster. Once you Truncate you cann’t get back the data.

If there Exist Foreign key Constraints

You can’t TRUNCATE a table that is referenced by foreign key constraints. Disabling foreign key constraints won’t work. You have to drop the foreign key constraint from Child Table that references the Master Table to be truncated, then after only you are able to truncate the Master Table.

On other hand, if you use ON DELETE CASCADE, Delete command remove all the records from master table and child as well.

TRUNCATE command resets the High Water Mark for the table but DELETE does not.

Don’t know High Water Mark? HWM is the upper boundary of the storage area of a table. HWM is basically the max space a particular table as occupied till that pt. that doesn’t mean that one cannot insert records more than a HWM. Once HWM is crossed a new HWM is set for a table.

When TRUNCATE is used on the table, all the rows of that table is deleted and the HWM is decreased to the minimum size-ZERO. But when DELETE is issued on the table, the rows are deleted and nothing is done on the HWM. Thats is, the HWM is never decreased even after the no of rows for the table is less or none. Thats is this keeps some space always with its own.

In a statement: The TRUNCATE TABLE mytable statement is logically (though not physically) equivalent to the DELETE FROM mytable statement (without a WHERE clause).

Engilish translation of a touchy song from hindi movie Murder 2 naming ‘Aye khuda…’

What are these empty spaces in my heart,
Now commit sins has become my nature..
I am the one who fell from Thy Mercy
Aye khoda… I fell… i fell…
Ever since I parted from you…
I lost everything…

The burden of many mistakes you carry, It seems as if wealth is your god,
You spend every moment like a wind blowing under the shadow of sins
like a ocean you were always in motion
you always did what you pleased
you are guilty to your own self

Aye khoda… I fell… i fell…
Ever since I parted from you…
I lost everything…..

Why you collect so worldly materials
One day this all will pass away
No matter how much accumulate
One day all this will surely slip away from your hands
Every person is made of dust and finally will be reduced to dust
This is the inevitable truth, you must realize this
Why you turn away from reality?
Fulfill any desire of yours
The destiny will never stop
your existence will be erased
But you heart will never be full (you will never satisfied)

Aye khoda… I fell… i fell…
Ever since I parted from you…
I lost everything…..

If you think you have fallen
Hold my hand and rise
I am standing at your hearts gates
Make me yours…
You say you are surrounded by shadows,
I am the light of your paths
I take your sins upon myself
In my eyes you are innocent(almighty is the forgiver)

Show me such a sight
Make me meet such a person
Let such a heart hear my tale
The heart which is free from all these wounds

Aye khoda… I fell… i fell…
Ever since I parted from you…
I lost everything…..

I was desparately needed to update Centos to version 6.2 during my office hour. Usually, yum hammers internet connection consuming maximum bandwidth. To prevent blockage by system admin, I set a speed limit on yum by adding the following line to the file /etc/yum.conf

On this sleepy rainy day, I’ve recalled some elementary knowledge on linux file system and permission. Following articles help me a lot.

• Unix and Linux File system Inodes
• Understanding Linux User Permissions
• Understanding Linux File Ownership
• How to change file ownership on a Linux server
• Granting Users Access to Privileged Files
• Why and How to Use Sticky Bit on Directory and File
• Another helpful post to understand Sticky bit
• SUDO vs SU: What Really Matters

I had written a post on chmod and chown before too.

In java, Array or List can be initialized on creation time. Such as:

int[] array = new int[] {1,2,5};

But on create initialization of Set collection needs some kind of hackish way.

Following way works fine.
Set <String> s = new HashSet<String>(Arrays.asList(new String[]{"1", "2", "5"}));

Another way to initialize Set on creation which is more readable:
Set s = new HashSet() {{
add("1");
add("2");
add("5");
}};

How To

Source code

[user]
name = Jamund Ferguson
email = jamund@gmail.com
[color]
branch = auto
diff = auto
status = auto
[color "branch"]
current = yellow reverse
local = yellow
remote = green
[color "diff"]
meta = yellow bold
frag = magenta bold
old = red
new = cyan
[color "status"]
added = yellow
changed = green
untracked = cyan