Waking up Heroku app

Deployment is not enough to wake it up. I just hit the URL in the browser :) Unfortunately if you use a free dyno for a hugbot that is integrated with slack, you need to wake your dyno up after recharging period.

young-sands-45836.herokuapp.com

Oracle PLSQL alert table add not null column with default value throws exception

I was trying to run following script:

alter table qrtz_blob_triggers add sched_name varchar(120) not null DEFAULT 'TestScheduler';

I kept receiving a following exception:

alter table qrtz_blob_triggers add sched_name varchar(120) not null DEFAULT 'TestScheduler'
Error report -
SQL Error: ORA-30649: missing DIRECTORY keyword
30649.0000 -  "missing DIRECTORY keyword"
*Cause:    DEFAULT DIRECTORY clause missing or incorrect.
*Action:   Provide the DEFAULT DIRECTORY.

I had to change the order of a query (default before not null):

alter table qrtz_blob_triggers add sched_name varchar(120) DEFAULT 'TestScheduler' not null;

I will keep this as an example for people that keep telling me that SQL is a declarative/functional language, and not something that Scarily Qualifies as a Language

Maven command to run tests in a selected module and ignore failures and redirect output to a file

This is useful when I want to see all the failed tests, and I want to have it in file so I can easily navigate thru entire output - for example to search for errors.

mvn -f system-tests/pom.xml -Dmaven.test.failure.ignore=true clean install > myout.txt

NoClassDefFoundError - classloaders in Java

Key concepts

1. There is a hierarchy of classloaders
2. Class loader may delegate to its parent
3. Parent may load class
4. If none of loaders loaded the class -> NoClassDefFoundError

Jenkins: Couldn't find any revision to build. Verify the repository and branch configuration for this job.

If you see following error in Jenskins build and you are using git:

ERROR: Couldn't find any revision to build. Verify the repository and branch configuration for this job.

It is because someone moved some git branches around, and they are missing. Instead of selecting a branch in Jenkins config modify advance input with:

+refs/heads/foo/bar:refs/remotes/origin/foo/bar

Maven command to run System tests from CI

I keep system tests in a separate module. Command run by CI to run them is following:

mvn -X -B -f system-tests/reservationsWS/pom.xml --fail-at-end verify install deploy:deploy

Maven install skipping tests

It speeds up install when I just want to recompile everything:

mvn clean install -DskipTests -DskipITs -DskipSystemTests

UNMET PEER DEPENDENCY kerberos@~0.0, while installing mongoose

I am not sure why it is not in a mongoose documentation, but when you run:

npm install --save mongoose

You receive a following error

UNMET PEER DEPENDENCY kerberos@~0.0

I had to install first kerberos in order for mongoose to success.

npm install --save kerberos mongoose

XOR swap - or how to swap two numbers

It used to be explain in multiple books that I read in university, but I do not see a clear and easy to follow explanation in the internet.

Let's say that we have two variables:

x = 5
y = 7

and we want to change the value of these numbers w/o using additional variable. We can achieve it by using using simple basic operation:

x := x + y = 5 + 7 = 12
y := x - y = 12 - 7 = 5
x := x - y = 12 - 5 = 7

But there is a different technique that is more efficient in IT because all the data is kept in binary format, it make sense to take advantage of a simple xor operation to do the work.

x= 101 in binary = 5 in decimal
y= 111 in binary = 7 in decimal


x=101
y=111
------ x xor y
x=010

x=010
y=111
------ x xor y
y=101 = 5 in decimal

x=101
y=010
------ x xor y
x=111 = 7 in decimal

One more note. You don't want to code it, because compile should optimize it for you - even when you use additional variable to swap the values compiler should use xor technique to do the job.

Enabling debugging for TomEE+

The simplest way is to edit bin\startup.bat file. Add following two lines:

set JPDA_ADDRESS=8000
set JPDA_TRANSPORT=dt_socket

Modify following line:

call "%EXECUTABLE%" start %CMD_LINE_ARGS%

to.

call "%EXECUTABLE%" jpda start %CMD_LINE_ARGS%

Config options explained on Trifork blog.

Nuget repository only looks at Microsoft repository

Recently few things changed in Nuget word. Currently when I run:

get-packages -ListAvailable

It only shows packages from Microsoft.
To be able to use Nuget repo again and be able to install typical libriaries like NUnit one has to add NuGet.Config to a folder that holds the solution file.

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="NuGet official package source" value="https://nuget.org/api/v2/" />
    <add key="local" value="C:\development\PathToYourLocalNugetRepositoryIfYouNeedIt\NugetLocal" />
  </packageSources>
</configuration>

After modification, Manage NuGet Packages tool should show All, NuGet official package source, local, Microsoft and .NET.

gulp-jshint@2.0.0 requires a peer of jshint@2.x but none was installed

Just like in title. When you try to run

npm install

In freshly created mean folder

cd  && npm install

You will probably first see

├── UNMET PEER DEPENDENCY jshint@2.x

Error and then at the very end

npm WARN EPEERINVALID gulp-jshint@2.0.0 requires a peer of jshint@2.x but none was installed.

In order to fix this issue you need to run

npm install --save-dev jshint gulp-jshint

It will show some invalid operations in a console

But at the end it will work.