PHP snippet to filter AirBnB Not available events and fix the end date

I wanted to import the AirBnB calendar via ical into my Google calendar but all the blocked days were annoying. Also the end date was one day too early on all events..

So i hacked a php snippet together which filters the “Not available” events and corrects the date. Then i simply added the php URL to Google calendar and now everything works fine!

If you want to use this snippet just replace the AirBnB URL with your own.

How to fix logrotate cron job error (/etc/cron.daily/logrotate)

After migrating my database to a new server running Ubuntu 14.04.4 LTS i received an email with the following content:


Cron test -x /usr/sbin/anacron || ( cd / && run-parts –report /etc/cron.daily )


error: error running shared postrotate script for ‘/var/log/mysql.log /var/log/mysql/mysql.log /var/log/mysql/mysql-slow.log /var/log/mysql/error.log ‘
run-parts: /etc/cron.daily/logrotate exited with return code 1

The reason why i was getting this error was because i imported my old mysql tables, including the users.
This particular cron job uses a mysql user debian-sys-maint to flush the logs, but i changed the password by importing all of my old tables.

You can fix this by creating the user with the correct password which can be found in the /etc/mysql/debian.cnf file:
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How to get random unique integers in a range with Java

If you are able to use Java 8 or up you can make use of the various methods of Random that return an IntStream.

E.g. if you want to generate random distinct numbers from a range [0, 100) you can use:

OfInt iterator = ThreadLocalRandom.current().ints(0, 100).distinct().iterator();
for (int i = 0; i < 100; i++) {
  System.out.println("Next random number: " +;

Since our range contains 100 Integers and .distinct() was used we can’t draw more than 100 numbers from the stream!

How to convert a String to int / Integer in Java

When you want to convert a String to int or Integer you can use two simple methods from the Integer class.

To convert a String to primitive int use Integer.parseInt(String s)

String a = "1234";
int x = Integer.parseInt(a);

To convert a String to an instance of Integer use Integer.valueOf(String s)

String a = "1234";
Integer x = Integer.valueOf(a);

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How to compare Strings in Java

A common mistake Java novices do is using the == operator to compare Strings. This does almost certainly lead to unexpected and unwanted behaviour. There is a simple solution to this problem and a not so simple explanation why it is such a common mistake.

The simple solution is to use String.equals instead of the == operator.

So when you want to know if two String objects hold the same value instead of

String a = "Test";
String b = "Test";
if (a == b) {
  // Do something

just use this:

String a = "Test";
String b = "Test";
if (a.equals(b)) {
  // Do something

But look out for null Strings, == handles null Strings nicely but when you call

String a = null;
String b = "Test";
if (a.equals(b)) {
  // Do something

it will result in a NullPointerException!

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EML to PDF Converter

I just finished a new project, an EML to PDF Converting tool which i released for free under the Apache V2 License to github. This tool allows you to convert your E-Mails in the EML format to PDF’s, which is necessary for archivability. Since E-Mails reference external resources such as images they tend to be an impermanent medium. To deal with this they can be converted to a format which is permanent such as PDF.

You can download it for free or check out the source code at github!

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How to install a (portable) JDK in Windows without admin rights

It recently happened to me that I was stuck at work on a Windows installation without access to admin privileges. While I could use a bunch of portable apps I could not find a portable JDK. To get a portable JDK without admin privileges in Windows you have to follow three simple steps.

1. Download

Download the JDK from Oracle (e.g. JDK 8 8u111).


2. Extract

If you want to use the x86 version simply open the .exe file with 7-Zip. It contains a single file, which contains all the files we need.
Open with 7-Zip

For x64 the can be found in .rsrc\1033\JAVA_CAB10\111\

Extract the to the desired JDK directory (e.g. “D:\JavaJDK\”).
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