January 23, 2017

Elliptic Curve Keys with OpenSSL

List pre-defined curves in OpenSSL:

Generate private key:

Generate public key:

Reference: https://wiki.openssl.org/index.php/Command_Line_Elliptic_Curve_Operations

January 12, 2017

Jackson Standard JSON library for Java


Jackson is build up by the following modules:

  • Streaming: "jackson-core"
  • Annotations: "jackson-annotations"
  • Databind: "jackson-databind" implements data-binding (and object serialization)


Jackson JSON Parser and Generator

To do JSON parsing and generation you only need one class com.fasterxml.jackson.databind.ObjectMapper.

To parse a json file.

And to generate json.

Different ObjectMapper#readValue(...) and ObjectMapper#writeValue(...)

Different parse methods:

  • com.fasterxml.jackson.databind.ObjectMapper.readValue(File, Class)
  • com.fasterxml.jackson.databind.ObjectMapper.readValue(URL, Class)
  • com.fasterxml.jackson.databind.ObjectMapper.readValue(String, Class)
  • com.fasterxml.jackson.databind.ObjectMapper.readValue(Reader, Class)
  • com.fasterxml.jackson.databind.ObjectMapper.readValue(InputStream, Class)
  • com.fasterxml.jackson.databind.ObjectMapper.readValue(byte[], Class)
  • com.fasterxml.jackson.databind.ObjectMapper.readValue(DataInput, Class)

Different generation methods:

  • com.fasterxml.jackson.databind.ObjectMapper.writeValue(File, Object)
  • com.fasterxml.jackson.databind.ObjectMapper.writeValue(OutputStream, Object)
  • com.fasterxml.jackson.databind.ObjectMapper.writeValue(DataOutput, Object)
  • com.fasterxml.jackson.databind.ObjectMapper.writeValue(Writer, Object)
  • com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(Object)
  • com.fasterxml.jackson.databind.ObjectMapper.writeValueAsBytes(Object)

Configure ObjectMapper

January 6, 2017

BDD Testing with Cucumber, Java and JUnit


BDD (Behaviour-Driven Development) is about designing code by defining your application in terms of behavior.

You start by gathering Tester, Developer and Product Owner (The Three Amigos) and define User Stories. These User Stories are given a Feature name and each Feature is broken down into a Scenario with Steps defines with the keywords: Given, When and Then


Now in Cucumber you write your User Stories (=Feature) in a language called Gherkin. Example:

Feature: Cash withdrawal 

Scenario: Withdrawal from an account in credit 
    Given I have deposited $100.00 in my account 
    When I withdraw $20 
    Then $20 should be dispensed 

Maven Dependency

Cucumber Code Structure

All code (production code, test code and gherkin code) must be placed in the same catalog structure.

  • Production Code - src/main/java/se/magnuskkarlsson/examples/cucumber/Account.java
  • Test Code - src/test/java/se/magnuskkarlsson/examples/cucumber/AccountTest.java
  • Test Code - src/test/java/se/magnuskkarlsson/examples/cucumber/AccountSteps.java
  • Gherkin Code - src/test/resources/se/magnuskkarlsson/examples/cucumber/cash_withdrawal.feature

Cucumber Test Code

We need two classes: one JUnit wrapper class and one Cucumber class that implements the steps in your Gherkin Code.


You can now either run you JUnit test class AccountTest inside your IDE or run complete test from command line as usual in maven: mvn clean install.

January 5, 2017

JDK Logger/Java Logging API


Since JDK 1.4 there is a default Logging API in Java. The entire Logging API is contained in the package java.util.logging.

Reference: https://docs.oracle.com/javase/8/docs/technotes/guides/logging/overview.html


Default Logging Configuration

Java comes with a default logging configuration file, that only contains a ConsoleHandler and writes to standard error.



To change default configuration, create a new configuration file and add a system property java.util.logging.config.file to you java process, which point to yours configuration file. Example:

The available handlers/appenders and their configuration are:

Log Levels

Java Logging API has the following levels: OFF, SEVERE, WARNING, INFO, CONFIG, FINE, FINER, FINEST, ALL

You define a global log level with .level, then if you need specific configuration you add: <package>[.class].level=<level>

NOTE: ConsoleHandler is special, for that you need to set ConsoleHandler.level for others you don't!

Log Formatter

There exists only two formatter and you typically want to use the SimpleFormatter.

NOTE: Most handlers uses the SimpleFormatter as default, but some do not. For them you need to set the formatter configuration.

Configure java.util.logging.SimpleFormatter

The default format is quite odd, so you want to change that.

The configuration is done with java.util.logging.SimpleFormatter.format. And the value is for the java call in java.util.logging.SimpleFormatter.format(LogRecord)

To understand the java.lang.String.format(String, Object...) syntax, read https://docs.oracle.com/javase/8/docs/api/java/util/Formatter.html#syntax.

Configuration in Java EE 6


Dependency Injection has come strong in Java EE 6, which is widely influenced from Spring Framework.

You can use the same pattern to handle configuration.


And to use it

And finally you need to add and empty WEB-INF/beans.xml to your achieve to make CDI work.