Saturday, January 24, 2015

How to make Java Timer to execute tasks concurrently?

What is Java Timer?    Java Timer is used to schedule tasks for future execution in a background thread. Tasks may be scheduled for one-time execution, or for repeated execution at regular intervals.

How are tasks executed by Timer object?    Each timer object has a single background thread that is used to execute all of the timer's tasks, sequentially.

Can Timer execute more than one task at a time?
    The default implementation of Timer will execute the task only in sequential order. For example, if you've scheduled two task at 7 PM and 8 PM respectively. And if the first task takes 5 hours to complete, then the second task will only be executed only after 12'o clock.

How to make Java Timer to execute tasks concurrently?
Solution 1:
    Create multiple timers. Each timer will execute one task at time. If you want to run three tasks subsequently, you need to create three different timer objects.

Solution 2:
    Run all the tasks in a separate Thread. In the example given above, Timer thread will create one worker thread to execute the fist task at 7 PM and second task at 8 PM respectively. 

Sample Code (Solution 2):

import java.util.*;

public class JavaTimer {

public static void main(String[] args) {
Timer timer = new Timer();

timer.schedule(new Task1(), Calendar.getInstance().getTime());
timer.schedule(new Task2(), Calendar.getInstance().getTime());
timer.schedule(new Task3(), Calendar.getInstance().getTime());

class TaskBase extends TimerTask
public String getName()
return this.getClass().getName();

public void run() {
                //Creates a new thread for each task.
new Thread() {
public void run() {

public void runInAnotherThread() {
System.out.println(getName()+" Scheduled Time: "+new Date(this.scheduledExecutionTime()));
System.out.println(getName()+" Executed Time: "+new Date());


public void doTask()
System.out.println("Will be implemented by sub classes");

class Task1 extends TaskBase
public void doTask()
System.out.println("DoTask of Task1");
try {
} catch (InterruptedException e) {
System.out.println("End of DoTask of Task1");

class Task2 extends TaskBase
public void doTask()
System.out.println("DoTask of Task2");
try {
} catch (InterruptedException e) {
System.out.println("End of DoTask of Task2");

class Task3 extends TaskBase
public void doTask()
System.out.println("DoTask of Task3");
try {
} catch (InterruptedException e) {
System.out.println("End of DoTask of Task3");


Tuesday, November 25, 2014

Update the existing git tag in remote repository

Generally GIT tags are used to mark release points. Every time we make a release in our project, we tag it using the command:
git tag -a VER_7_5_0 -m "Version 7.5.0 tagged"
then push it to central repository to share with others.
 git push --tags
Often times this tag has to be altered to include/exclude a fix from the release, before make it to the customer.
Here are the steps to update the existing tag in remote repository:
Step 1: Update a tag in local repository using -f option.
            git tag -a -f VER_7_5_0 -m "Version 7.5.0 tagged"
Step 2: Remove a tag from remote repository.
            git push origin :refs/tags/VER_7_5_0
Step 3: Push the updated tag to remote repo.
            git push --tags
To view remote tags:
git ls-remote --tags origin

Caution: If someone already pulled your tags into their local repo, they will not get the updated one unless they delete the old one. If you are not sure about this, you better create a new tag instead of updating the existing one.

Saturday, October 18, 2014

How to rename a GIT tag in the remote repo?

Some times we would have added a tag, pushed it to remote and then realized that we’d named it wrong. 
Ex. VER_7_2_0 instead of VER_7_1_2. 

Here is quick tip to rename a git tag in the remote repo. 

Step 1: Create a new tag on the same commit point of old tag and push it, 
git tag new_tag old_tag 
git push --tags 

Step 2: Delete the old tag from local repo. 
git tag -d old_tag 

Step 3: Delete the old tag from remote repo. 
git push origin :refs/tags/old_tag 

You can verify the changes made, by executing the below command. It shows all remote tags: 
git ls-remote --tags origin

Saturday, October 4, 2014

Configuring Git Email Notifications via Post-receive hook

Here I'm going to explain how to configure Git to send email notifications when 'central' repo is updated on Linux and windows machines. 
Step 1: Copy (or symlink) the post-receive script, or download it here. The script must be in the ‘hooks’ directory like this:
Make sure it is named “post-receive” so that Git recognizes it.
Step 2: Make sure that the script is executable:
chmod a+x $GIT_DIR/hooks/post-receive
Step 3: Edit the first line of $GIT_DIR/description to be your repository name. This will be in the subject of the email.
Step 4: Edit $GIT_DIR/config with some email settings such as recipient / sender email and subject-line prefix. Here’s some basic settings (read the script for all possible settings).
mailinglist = ","
envelopesender =
emailprefix = "[GIT] "
Note: you can also set these by using git-config:
git-config hooks.mailinglist ","
git-config hooks.envelopesender
git-config hooks.emailprefix "[GIT] "
That’s it ! Try doing a git-push to your shared repository, and see if you get email notifications.
STEP 1: Same as Linux.
STEP 2: The post-receive script is using 'sendmail' for sending mails. But Git for Windows provides msmtp not sendmail. So we need to configure smtp server and use it in the script. Replace sendmail with msmtp in the post-receive script as follows
    if [ -n "$envelopesender" ]; then
        msmtp --host="$smtpserver" -t -f "$envelopesender"
        msmtp --host="$smtpserver" -t

And finally, near the end of the file is a section that reads in the git config variable so add a new line to read server values:

smtpserver=$(git config sendemail.smtpserver)

STEP 3: Same as Linux.
STEP 4: It requires all configuration as mentioned in step 4 Linux. Apart from that it requires one more variable to configure "sendemail.smtpserver"
git-config sendemail.smtpserver
That's it for windows!.

Sunday, September 14, 2014

The default behavior of 'git push'...

Whenever we decide to share our work, we do push our changes to a remote repository.
If you are working only in a single branch then you don't need to worry about this topic. But if you have many branches, you must aware the default behavior of 'git push'. This command actually pushes all branches (not only your current branch) to the corresponding remote branches.
But, mostly we want to push only the current branch to the remote repo. We can configure GIT to change the default behavior.
git config push.default upstream
It means git will update only the current branch to it's upstream, when you do git push.
Other valid options are:
nothing : Do not push anything.
matching : Push all matching branches (default).
upstream: Push the current branch to its upstream branch. (the branch git pull would pull from)
tracking : Deprecated, use upstream instead.
current : Push the current branch to the remote branch of the same name.


Since git version 1.7.11, A new mode, "simple", which is a cross between "current" and "upstream", has been introduced. "git push" without any refspec will push the current branch to the remote branch with the same name, only when it is set to track the remote branch. This mode is the new default value when push.default is not configured.

Sunday, August 10, 2014

GIT --everything-is-local

One of the advantage of GIT over CVS is, in GIT almost everything is local.
It means, you do not need to be connected with the server all the time, because 95% of git commands can be executed in the local repository.
Comparing different version of files, Getting the history of files, Committing the changes to the files - all are LOCAL and FAST in GIT.
There are very few commands, which are not local.  But they have reasons for that :-)
git pull/fetch - Pull/fetch changes from the server. (remote repo)
git push - Push the changes to the server.
git clone - Clone a remote repository.
git ls-remote - List references in a remote repo.
git remote show - Gives info about a remote repo.
git remote prune - Deletes all stale remote-tracking branches.
git remote update - Updates group of remote-tracking branches.

Sunday, July 20, 2014

Using Winmerge as a diff tool in GIT

Step 1:
Install Winmerge.

Step 2:
Create a file named ‘’ under your repository.

Step 3:
Write this into ‘’ file.
echo Launching WinMergeU.exe: $1 $2
"PathToWinMerge" -e -ub -dl "Base" -dr "Mine" "$1" "$2"
Path To Winmerge: Ex:  C:/Program Files/WinMerge/WinMergeU.exe

Step 4:
Update your .gitconfig file (will be under your user folder C:\Documents and Settings\YourName)
            tool = winmerge
            prompt = false
[difftool "winmerge"]
            cmd = $LOCAL $REMOTE

Step 5:
Using winmerge:
git difftool ReleativeFilePath/FileName