Category: coding

Determine which Tomcat version is running

Determine process id

First we determine the process id(s) of the running Tomcat instance(s).

We can grep the running process list for ‘catalina.home’:

pgrep -f 'catalina.home'

This might yield more than one pid.

Or we can search by port (8080 is the default, adjust if necessary). The following commands will likely require root privileges:

lsof -t -i :8080

Alternatively, for example if lsof is not installed:

fuser 8080/tcp

Or yet another way, using netstat (or its “ss” replacement):

netstat -nlp | grep 8080

ss -nlp | grep 8080

Determine catalina.home

For the process id(s) determined above, we look at process details:

ps -o pid,uid,cmd -p [pidlist] | cat

For each specified pid, this shows the uid (system user) and the full command line of the process.

Typically the command line will contain something like “-Dcatalina.home=[path]” and that path is the catalina.home system property of the Java process.

Alternatively – with Java 7 and later – we can use the JDK command “jcmd” to query the JVM process for its system properties:

sudo -u [uid] jcmd [pid] VM.system_properties \
   | grep '^catalina.home' \
   | cut -f2 -d'='

Determine version

Now we can finally determine which Tomcat version is installed under the catalina.home path:

[catalina.home]/bin/catalina.sh version \
   | grep '^Server number:'

Note: Please replace [catalina.home] with the path you determined above.

The final output should be something like this:

Server number: 7.0.56.0

Continuous delivery using github, travis-ci and bintray

Continuous-Delivery-schema

Let’s say you work on a Java application and want to frequently make it available for download so that user’s can easily try the latest version.

Let’s say you work primarily on your laptop or personal computer using a Java IDE and commit code changes, but you don’t want to spend time manually building jars, packaging war or zip files, testing your application or uploading files to a website, etc.

Instead you want to have a fully automated process that compiles your source code, runs automated tests and other quality control mechanisms, builds your application and uploads the result to a public website.

But you don’t want to install any infrastructure for this and not run anything besides Java and your IDE on your own machine(s).

Basically you want to use developer-friendly reliable cloud services but you don’t want to pay a single cent.

All of this is possible, as long your code is Open Source:

  • Host your source code on github
  • Let travis-ci run vour build process
  • Let travis-ci upload the build result to bintray

For details, you can take a look at one of my github projects.

Relevant config files:

Some pure CSS buttons

Do you still use gifs or other pixel graphics for buttons on web pages? I hope not. CSS3 support is available in all modern browsers, so rounded corners, gradients, shadows, etc are no problem.

See this jsfiddle for the CSS class definitions and a minimal HTML sample.

Without box shadow:

Oliver Doepner

Oliver Doepner

Oliver Doepner

With box shadow:

Oliver Doepner

Oliver Doepner

Oliver Doepner

OpenJDK builds for Windows now available from Redhat

As I mentioned in an earlier post, officially supported OpenJDK builds for non-Linux platforms have been notoriously hard to come by in the past, at least until Azul started their Zulu builds in 2013. Unofficial community builds are also available from the ojdkbuild project on Github.

Today Redhat announced that their OpenJDK offerings now include builds for the Windows platform as well.

After Google decided to use OpenJDK in Android N, I guess this is another strong indicator of OpenJDK’s value and increasingly wide adoption.

JEE Guardians petition Oracle to actively work on Enterprise Java standards again

Over the last 6 months or so, the development on Java EE 8 JSRs led by Oracle has nearly come to a stand-still. Even some spec leads working for Oracle privately admitted that they cannot do their part because Oracle has given them other priorities.

That is why the JEE Guardians group was formed by the community and that’s why I just signed this petition: “Larry Ellison: Tell Oracle to Move Forward Java EE as a Critical Part of the Global IT Industry”

If you care about the future of Enterprise Java, please get involved and sign the petition, too.

Retrieve “last modified” timestamp of web resource in UTC seconds

This command line assumes that “${url}” is the URL of the web resource:

curl -s -I "${url}" | grep 'Last-Modified:' | cut -c 16- | date -f - +'%s'

It can be useful to check the freshness of a download URL before a GET request.

You could compare the result to the last-modified timestamp of a local file and only download the remote file if it is newer than the existing local one.

Compare two Tomcat installations using rsync

Lets assume you manage multiple servers that host Java web applications using the Tomcat web server.

To quickly compare the Tomcat installations on host1 and host2, we can use the “dry-run” mode of the rsync command.

In the following example, we assume that you have ssh access to both of your Tomcat hosts, the installations are in /opt/tomcat and the “tomcat” system user has read access to all relevant files and directories of the installation:

ssh tomcat@host1
rsync --archive --checksum --dry-run --verbose --delete \
      --exclude temp --exclude work --exclude logs --exclude webapps \
      /opt/tomcat/ tomcat@host2:/opt/tomcat/

This will list

  • All files that differ in checksum
  • All files that only exist on host2 (look for ‘deleting [filename]’)

Run the same commands with host1 and host2 switched, to also see the files that only exist on host1.

We excluded the temp, work and logs directories because they are variable in nature.
We also excluded the webapps directory because we only wanted to compare the base installation.

Spotify on Debian GNU/Linux in Canada

Today I decided to try out the free ad-sponsored Spotify music streaming service. It has been available in Canada since September 2014.

After signing up you can immediately use the flash-based web player at play.spotify.com.

Installing the client app

Alternatively you can download and install the Spotify client app. I cannot say yet what the advantages or disadvantages are, maybe reading this article can be helpful.

Anyway, if you want to try the client app, for Debian (or Ubuntu) users it works like this:

  1. Add the repo key (to verify downloaded packages)
  2. Add the spotify repo to apt sources
  3. Update apt caches
  4. Install the spotify client

Here are the shell commands (requires sudo):

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys BBEBDCB318AD50EC6865090613B00F1FD2C19886
echo deb http://repository.spotify.com stable non-free | sudo tee /etc/apt/sources.list.d/spotify.list
sudo apt-get update
sudo apt-get install spotify-client

After successful installation you will find a “Spotify” entry in the “Multimedia” section of your start menu.

Using your Facebook login

If you use your Facebook account to sign into Spotify you will probably see this question:

Spotify would like to post to Facebook for you.
Who do you want to share these posts with?

It is safe to choose “Not Now” which prevents Spotify from posting to your timeline. The login will still work.

If your are using the downloaded stand-alone client app and the Facebook login fails with an error page, then simply enter the email address and password from your Facebook account into the login fields of the Spotify client app.

Spotify says that it only uses these credentials to pass through to the Facebook authentication and won’t store your password anywhere. I hope that’s true.

Decorate your thoughts my dear : Unicode 8 supports 1051 Emojis

unicode-monkey-face Have you noticed how email subjects, chat messages and other traditional “plain text” content more and more often contains smileys, ideograms, pictograms and other funny symbols?

For example, you can probably see the faces of mouse, bull, cat and monkey right here: 🐭 🐮 🐱 🐵

These expressive tiny pictures are also known as Emojis and can be seamlessly mixed into the letters, numbers, punctuation marks and few traditional “special characters” that most of us know from the computer (or even typewriter?) keyboard.

This is possible because on todays digital devices all of us, whether we know it or not, use an international standard called Unicode that supports all letters and symbols from all official languages and writing systems on our planet (and even Klingon, by the way). And as an extensible standard, Unicode keeps growing and recent versions have increasingly incorporated non-alphanumeric symbols.

For example, there is a whole Unicode block of smileys and cat faces that was added in Unicode version 8 to incorporate a set of symbols that Japanese mobile carriers had already added to the Shift JIS character encoding: 😀 😁 😂 😃 😄 😅 😆 😇 😈 😉 😊 😋 😌 😍 😎 😏 😐 😑 😒 😓 😔 😕 😖 😗 😘 😙 😚 😛 😜 😝 😞 😟 😠 😡 😢 😣 😥 😦 😧 😨 😩 😪 😫 😭 😮 😯 😰 😱 😲 😳 😴 😵 😶 😷 😸 😹 😺 😻 😼 😽 😾 😿 🙀

With the now ubiquituous support of Unicode by computer operating systems, internet services and mobile devices, we are no longer limited to the 90° tilted “ASCII emoticons” using character sequences like :^). With Unicode we can use emojis as single symbols of their own right.

This leads to the question how to enter emojis using your keyboard, be it a physical computer keyboard or through the on-screen touch keyboards on your modern mobile devices. It is possible, with varying degrees of convenience on Apple, Android, Windows or Mac computers and many other devices.

Unfortunately, UI level emoji support on GNU/Linux systems is practically non-existent which effectively limits Linux users to copy/paste from “cheatsheets” or the official Unicode 8 charts with their 1051 emoji and symbol codepoints.

One tip for Debian based systems: Make sure to have the Droid and Symbola fonts installed:

sudo apt-get install ttf-ancient-fonts fonts-droid

Then you can write a chess game for the text console using these Unicode glyphs from the “Miscellaneous Symbols” Unicode block: ♔ ♕ ♖ ♗ ♘ ♙ ♚ ♛ ♜ ♝ ♞ ♟

Or roll the dice: ⚀ ⚁ ⚂ ⚃ ⚄ ⚅

PS: All characters in this blog post are ok to recycle ☺ : ♲ ♳ ♴ ♵ ♶ ♷ ♸ ♹ ♺ ♻ ♼ ♽

As always, please feel free to respond in the comments section below.