German Java Magazin

Thursday 04 April 2013

JavaMagazin: Himbeerkuchen mit Kaffee

Just a quick note. The german Java Magazin just published my article about extending JavaFx Applications with self-made hardware on a RaspberryPi.

JavaMagazin 05.2013 (Page 59)

You can find the source code on my GitHub Page

A Code you can Maintain or High Productivity

I have been doing a little development lately in addition to my routine task. Something that’s struck me: checking a one-line code repair requires some minutes.

Development goes in stages between maintainable and productive, typically hitting among those extremes at the same time.

The art of programs moves rapidly. Some people have taken part in Rapid Application Development (RAD), where making a modification and getting it to production happens from an IDE (or not) and takes seconds. On the other hand, we’ve all seen catastrophic production interruptions, when some developer pushes a product to production that should not exist.

In other situations we’ve done extremely maintainable development where nothing is a one-line code change and releasing what would be a one-line code modification to production is an act of sheer will with a lot of moving pieces. The software world likes to do this and makes intricacy extremely well, thank you quite.

Take a historical example of RAD. In the Java world, JBuilder utilized to be able to release to Weblogic incrementally. In the PHP world, you could modify a file on the web server or locally, then SCP it into the ideal directory. In any case, you could quickly check that file locally. In the Microsoft world, back in the VB days, you could easily make a modification, then struck Run and test it once again. Microsoft still leads in the cloud era with the auto swap, however, let’s admit it, it ain’t like it used to be.

Take the greatest historical example of software application development. Java EE abstracted you from the hardware and, in exchange, needed you to create about 20 embedded Zip files (OK, a small exaggeration) and 15 different XML descriptors (not an exaggeration in a considerable app) to check a one-line code modification in your Design 2 controller. On the one hand: Look ma, say goodbye to someone-did-something-by-mistake in production! And say goodbye to buffer under/overruns. On the contrary: it was a productivity suck.

Fast-forward to today, as well as the language efficiency for a full stack application, is an intriguing performance suck. Adding a small detail in a Java servlet or C# app is nothing compared to an entirely practical shows monster. No more will you pull a header from an injected environment thing, oh no, we need to determine how to do this in an entirely stateless manner that stays “functional” throughout.


RaspberryPi with Faytech Touchscreen

Wednesday 13 February 2013

Just a quick note for anybody who’s struggling with Touchscreens on the RaspberryPi.

I just downloaded the latest Raspbian Image and started it. My Faytech 7” Touchscreen just works out of the box and it even works with JavaFX applications. No more kernel compilation!

One tiny thing you might want to do is to calibrate the touch controller. xinput_calibrator will do the job but you have to compile it yourself.

sudo apt-get install libx11-dev libxext-dev libxi-dev x11proto-input-dev
sudo make install

Touch the points until the application closes. Follow the instructions on the console output and create the configuration for X11. The directory for the configuration file is /usr/share/X11/xorg.conf.d instead of the directory shown by xinput_callibrator.

Reboot and you’re done!

JUnit Rules!

Monday 11 February 2013

Some weeks ago at Devoxx in Belgium I heard about the JUnit feature called Rules. The feature got introduced without causing a stir but it’s exactly what I was waiting for!

package org.junit.rules;
import org.junit.runner.Description;
import org.junit.runners.model.Statement;

public interface TestRule {
* Modifies the method-running {@link Statement} to implement this
* test-running rule.
* @param base The {@link Statement} to be modified
* @param description A {@link Description} of the test implemented in
*        {@code base}
* @return a new statement, which may be the same as {@code base},
*         a wrapper around {@code base}, or a completely new Statement.
Statement apply(Statement base, Description description);

Well, I have to admit that when I looked at this interface for the first time I had clue what this can be useful for. Looking at the implementations shipped with JUnit made things clear. It’s just perfect for solving the test-case inheritance mess and @Before and @After stuff that makes tests less readable. Rules reduce your tests code, setup and teardown code can be moved into separate classes.

An example

Itegrationtests so far:

public void find() throws Exception {
  // Assemble
  PersonDao dao = new PersonDao();
  Person expectedPerson = new Person("Dummy");;
  try {
    // Activate
    Person actualPerson = dao.find(expectedPerson.getName());
    // Assert
    assertThat(actualPerson, equalTo(expectedPerson));
  } finally {
   // Cleanup

and pimped with @Rules:

public PersonRule personCreator = new PersonRule();
public void find() throws Exception {
  // Assemble
  Person expectedPerson = personCreator.createPerson("Dummy");
  PersonDao dao = new PersonDao();
  // Activate
  Person actualPerson = dao.find(expectedPerson.getName());
  // Assert
  assertThat(actualPerson, equalTo(expectedPerson));

Try-catch has been disappeared! And best is, it didn’t even move into the PersonRule!

import java.util.ArrayList;
import java.util.List;
import org.junit.rules.ExternalResource;
public class PersonRule extends ExternalResource {
  private List<Person> persons = new ArrayList<>();
  protected void after() {
    System.out.println("Cleaning up");
    for (Person p : persons) {
  private void delete(Person p) {
    System.out.println(String.format("Delete %s from database", p));
    new PersonDao().delete(p);
  public Person createPerson(String name) {
    System.out.println(String.format("Create %s in database", name));
    Person p = new Person(name);
    new PersonDao().save(p);
    return p;

As you can see the code implements an after() method where the cleanup is done. The base class is implemented in a way that the after() method gets called after each test exactly as methods annotated with @Afterare.

There’s more

JUnit comes with some handy base classes providing template methods for different purposes. One of these base classes is ExternalResource which provides the template methods before() and after(). Working with the base classes is much easier than implementing the TestRule on your own. Don’t forget to have a look at the other classes!

  • ExternalResource
    before(), after()
  • TestWatcher
    starting(), succeeded(), finished(), skipped(), failed()
  • Verifier

Also have a look at the ExpectedException Rule which enables you to look in detail at exceptions thrown by your test. Use it if @Test(expected=Exception.class) is not enough!

public ExpectedException thrown= ExpectedException.none();

public void throwsNullPointerExceptionWithMessage() {
  throw new NullPointerException("What happened?");

So long, happy testing!

Dangerous drop-in replacement Jars

Monday 04 February 2013

Have you ever put an updated jar into your classpath, eg. a new version of a library for your webapp? In this post I’d like to show you something you should be aware of, especially if you get strange behavior after a simple jar update.

The riddle

Create an interface:

public interface MyInterface {
String GREETING = "Hello World";

Now we compile the interface and pack it into a jar.

> javac
> jar -cf lib.jar MyInterface.class

Next is a simple demo application

public class App {
public static void main(String[] args) {
System.out.println("Greeting: " + MyInterface.GREETING);

The app gets compiled using the library-jar we created before and pack it.

> javac -cp lib.jar
> jar -cf app.jar App.class

Now that the demo app is ready we start it with the command:

> java -cp app.jar:lib.jar App

What a suprise, the output is as expected:

Greeting: Hello World

Now the fun starts. Edit the MyInterface, change the value of GREETING.

public interface MyInterface {
    String GREETING = "Good Bye";

Recompile and repack our interface

> javac
> jar -cf drop-in.jar MyInterface.class

And now, here comes the million dollar question! What will we get if we start our app with the new drop-in-jar instead of the old lib.jar in the classpath?

> java -cp app.jar:drop-in.jar App


What do you guess? Greeting: Good Bye? Wrong! We still get Greeting: Hello World even though our interface in the classpath says good bye!

What did just happen?

For optimization reasons the java compiler writes our constant value directly into the App bytecode. Java doesn’t read it from the interface at runtime! Therefore, the value from the drop-in jar is never read at runtime.


When using drop-in replacement jars keep in mind that changed constant values of the library will only make it into the runtime if you recompile your code!