Java Mail network is unreacheable connect exception

Recently I stumbled upon a weird problem while debugging a simple java application that needed to send an email

Since I was debbuging this application locally I used the FakeSMTP tool that I described in this tutorial here : Testing email sending functionality with FakeSMTP which I run locally on my machine

So after editing the configuration on my Java program and firing up the SMTP server I was quite surprised to get the following exception :

Caused by: javax.mail.MessagingException: Could not connect to SMTP host: 127.0.0.1, port: 25 (java.net.SocketException: Network is unreachable: connect)
System.setProperty("java.net.preferIPv4Stack" , "true");

So once you are sure you problem is not coming from a non running SMTP server or a network connection, you can check if the culprit is no other than Java

If you read the Oracle documentation here you will see that by default Java prefers IPv6 to IPv4 which is the problem in our case since FakeSMTP binds on IPv4

Luckily there is a way to force Java to prefer IPv4 over IPv6 using the system property java.net.preferIPv4Stack

This can either be done :

  • programmatically
  • using java options

1. Programmatically


 System.setProperty("java.net.preferIPv4Stack" , "true");

2. Using java options


java -jar myJar.jar -Djava.net.preferIPv4Stack=true

That should take care of the problem

Another solution would be to disable IPv6 networking on your machine but that may have other side effects on your system..

Heroku PostgreSQL and DBVisualiser connection using SSL

I occasionally use Heroku to deploy webapps on the cloud combined with a Postgres database to store my relational data

I recently found a multi-platform polyglot SQL client that I could use with my MAC, this product is called DbVisualiser

However since Heroku requires an SSL security on external connections after providing the usual database connection properties (url, username, password) when I tried to connect through DbVisualiser I was getting the error message :

FATAL: no pg_hba.conf entry for host "86.200.9.63", user "u4b1uljsil33m2", database "de9td8cv06p4se", SSL off

After playing a bit with the different options and reading the Postgres JDBC driver over here I found out that you can provide an Non Validating SSL factory in the connection properties to satisfy Heroku's SSL requirements

In order to configure the SSL properties in DbVisualiser you need to edit the following SSL properties in the Properties tab :

  • SSL : true
  • sslfactory : org.postgresql.ssl.NonValidatingFactory

By providing these 2 properties you should be able to connect to your Heroku database without any problems

Angular6 hiding component selector

It's sometimes useful to have angular's component selector not to be rendered in the page, as sometimes this can cause problems with...