28 Jun 2017
Objenesis went out last week partly because Google App Engine is now supporting Java 8 in
beta. And they are no security manager anymore preventing Objenesis to work.
The problem was that Objenesis was checking if it was running on GAE to pick an instantiating strategy. So it was still running in degraded
more on GAE Java 8. It is now fixed.
However, Spring uses an embedded version of Objenesis. So they need to upgrade. Luckily, they are super fast to do so. You can follow the
issue but it will be in Spring 4.3.10 and Spring Boot 1.5.5.
Meanwhile, you might be eager to test your shiny new app on this new Google App Engine platform and would be really happy to make it work.
I have a solution for you. It isn’t pretty but it works.
In Java, in case you don’t know, you just need to put your class file in front of another one in the classpath to “shadow” it. It means your
class will be used instead of the original implementation. In a war, everything in WEB-INF/classes
goes before WEB-INF/lib
. So you can
easily shadow a class.
That’s what I did. My SpringObjenesis.java
version shadows Spring one. It delegates to the real Objenesis implementation instead of the Spring embedded one. You only need to add the latest
Objenesis (2.6) as a dependency to your project.
Voilà!
20 Jun 2017
An all new shiny Objenesis is out. The framework everybody uses without even knowing it.
It had fun playing with the brand new Google App Engine platform supporting Java 8. They dropped the terrible security manager they used to
have to know Objenesis is working perfectly on it. This was brought to my attention by GAE developers. They are now testing mainstream frameworks
on their platform to make sure it works. This should make GAE adoption easier.
Java 9 was pretty much already working but I got rid of all the “Illegal accesses”. Not that obvious since in Objenesis, this is how we roll.
Finally, a bit of cleanup in the serialization specification was done. So now a serializing instantiator should instantiate a class by calling
the no-arg constructor of the first non-serializable class in the hierarchy. And do nothing else. See the documentation
for details.
Change log
02 Jun 2017
I’ve mentioned already why I am now using a mac after years of beloved Windows.
But I’m still complaining about the really bad UI behavior of macOS (I’m on Sierra). And the ca_fr keyboard that should have had the exact
same layout that Windows had for years instead of trying to be wiser… But that’s hardware so there’s nothing I can do about it.
During my last round of complains I was ask to write an article about it. So
here it is.
First, one of the first thing I’ve fixed is the random behavior of Home and End keys. By default, depending on the app you are in, the behave
differently. This is plainly insane. Here is the fix:
cd ~/Library
mkdir KeyBindings
cd KeyBindings
vi DefaultKeyBinding.dict
Put these lines in that file, including the curly braces:
{
/* Remap Home / End keys to be correct */
"\UF729" = "moveToBeginningOfLine:"; /* Home */
"\UF72B" = "moveToEndOfLine:"; /* End */
"$\UF729" = "moveToBeginningOfLineAndModifySelection:"; /* Shift + Home */
"$\UF72B" = "moveToEndOfLineAndModifySelection:"; /* Shift + End */
"^\UF729" = "moveToBeginningOfDocument:"; /* Ctrl + Home */
"^\UF72B" = "moveToEndOfDocument:"; /* Ctrl + End */
"$^\UF729" = "moveToBeginningOfDocumentAndModifySelection:"; /* Shift + Ctrl + Home */
"$^\UF72B" = "moveToEndOfDocumentAndModifySelection:"; /* Shift + Ctrl + End */
}
Then, macOS is lacking Windows docking. So I’ve installed BetterTouchTool for that.
Back to complaining. Here are the things I wasn’t able to fix so far.
Cmd+Tab
should bring to front the requested window. Always. It doesn’t matter if the window is minimized, in background or whatever. Just bring it in front
Cmd+Tab
should bring the last used window of an application to the front. Not my 6 Chrome windows. Only the latest one
Cmd+ù
should behave as Cmd+`
when using a ca-fr keyboard. I can probably use the remap trick for that. I tried BTT, it doesn’t work
- When switching desktop, it shouldn’t matter where my mouse is. Especially to access the dashboard. It should just switch all screens. It there a shortcut to switch screen 1?
Cmd+X
should cut everywhere. Cmd+C
and then Cmd+Alt+V
is just not the way my brain works. I think about copy or cut when seeing the file. Not when pasting it. Am I the only one?
- I use 2 keyboard layouts (US-en and CA-fr). Because of the dumb keyboard. macOS should remember which application is using which keyboard. However, I don’t need it for each Chrome tab
That’s it for the day. Can you help me?
20 Feb 2017
When living in France, I started to help Devoxx4kids France a little bit. I think
it is an amazing idea that will give kids skills that they will definitely needs later.
It also shows them that Facebook on your phone hasn’t appeared by magic. It took a lot of people for hundred of years
to discover and master the required technologies.
Now that I live in Montreal, I’ve joined Devoxx4kids Québec. Last time I’ve brought my
3 years old. He played with a LEGO Mindstorm robot he built. I was amazed to see him enjoy it even though Mindstorm are 10+.
Anyway, all this is not the theme of this post :-)
This is a post that will evolve in time where I want to put all the cool learning tools I’ve encountered. And try to comment on them.
This is mostly a selfish post that will prevent me from forgetting things. But you might found it useful. So here we go.
First, the official Devoxx4kids material.
Then my personal list (I haven’t tried everything. It’s just a list of cool stuff for me to remember).
Games
- Robot Turtles: A board game teaching young children how to program without having them notice
- The Bugs: Another board game teaching young children how to program without having them notice (note that Magik Square official website seems dead)
- RetroPie: To play old games on a Raspberry Pi
- Minecraft: Building, creating and programming worlds
Robots
- Blue-Bot: A cute mouse that can be programmed directly or from a tablet to follow a path
- Code & Go Robot mouse: Similar to Blue-Bot but comes with tiles and obstacles. The mouse can’t be programmed from a tablet. There are cards to tell the path and it recognizes a cheese at the end. Pretty fun
- mBot: Little robot on wheels that you can program using Scratch. Uses a bit too much batteries and in fact can’t do much
- Ozobot: Little robot that you can program with color markers
Programming
- Greenfoot: To program easily little games in Java
- Scratch: Visual programming games by drag & dropping
- Scratch jr: Same a Scratch but for younger kids
- Code Combat: A nice game where you learn how to code along the levels
Construction
- LEGO Mindstroms: Lego with captors and engines that you can problem using their interface. Quite complex to create models
- LEGO WeDo: Like Mindstorms but simpler and for younger kids. They a quick to build and oriented for science workshops
- LEGO Boost: A bit like WeDo but for home. Boost is long to assemble and then offers many programming possibilities
Computers
- Raspberry Pi: A really powerful mini-computer which boots on Linux and can do electronics
- Arduino: A little micro-controller that can be easily programmed to do many things
Electronics
- littleBits: Really cool bricks to build electronic systems
- Makey Makey: Fun chipset and electrodes to interact with the computer using everyday objects
- MakerBloks: Other really cool bricks to build electronic systems
- Arduino: A full-fledged electronic board to play with
- FreeNove: Multiple electronic kits with straightforward explanations
09 Feb 2017
UPDATE (2017-02-15): Spring is correctly handling the null
from getMissingCache
. So you won’t have to overload it. I was misled
by a framework that was incorrectly layering the JCacheCacheManager
. I stand corrected and the article as well. Thanks to
Stéphane Nicoll for his vigilance.
UPDATE (2017-02-16): Spring has a JCacheCacheConfiguration
that configure a JCache CacheManager
using a list of cache names and a
default cache configuration. By default, it uses new MutableConfiguration<>()
so the article was updated accordingly.
UPDATE (2017-04-07): My Hibernate PR has been accepted. So you now have an elegant
solution with the latest Hibernate versions. The article was updated accordingly.
I played a lot with JCache connectors lately. To plug Ehcache 3 to different things.
I noticed one really dangerous thing. Frameworks tend to spontaneously create caches that were not explicitly defined. I
think it is coming from the JCache spirit that there should be a default cache configuration. It is nonetheless a bad idea.
Let’s look at two examples
Spring
Caching in Spring is implemented by spring-cache
. To plug JCache to spring-cache
you use the JCacheCacheManager
. By default
when a cache isn’t available in the CacheManager
, Spring calls JCacheCacheManager.getMissingCache
. So far so good.
The default implementation for this method returns null
when a cache doesn’t exist. This null
will then be handled at
higher levels to throw a nice exception.
If you want to explicitly support spontaneous cache creation, getMissingCache
is where you should put your creation code.
However, watch out if you do that. You might lost track of all the existing caches. And please, never do the following.
@Override
protected Cache getMissingCache(String name) {
Cache cache = super.getMissingCache(name);
if(cache == null) {
return new JCacheCache(cacheManager.createCache(name, new MutableConfiguration<>()));
}
return cache;
}
It returns a cache configured using default. It is never what you want.
Then, as usual, Spring tries to be nice with us. So if you enable caching (@EnableCaching
), that the JSR-107 API is in
the classpath and that you do not expose any CacheManager
, Spring will create one for you.
The JCacheCacheConfiguration
will get a default JSR-107 CacheManager
and add a list of caches taken from the cache property
spring.cache.cache-names
. These caches are by default created using a new MutableConfiguration<>()
. As we said above, this
is not a correctly configured cache.
The solution is to expose the wanted cache configuration in a bean.
@Bean
public javax.cache.configuration.Configuration<Object, Object> cacheConfiguration() {
CacheConfiguration<Object, Object> cacheConfiguration = CacheConfigurationBuilder
.newCacheConfigurationBuilder(Object.class, Object.class, ResourcePoolsBuilder
.newResourcePoolsBuilder().heap(100))
.build();
javax.cache.configuration.Configuration<Object, Object> configuration =
Eh107Configuration.fromEhcacheCacheConfiguration(cacheConfiguration);
return configuration;
}
This bean will be magically used as cache default. You should always do this and never let ``new MutableConfiguration<>()`
be used.
Hibernate
To use JCache with Hibernate we need to use the JCacheRegionFactory
. The problem with JCacheRegionFactory
is that by
default if a cache is not found, it will spontaneously create a cache by passing new MutableConfiguration()
. This means
that instead of using a properly configured cache, you end up with some random default configuration (infinite on heap for
Ehcache).
This is really bad because it is pretty hard to detect.
What I recommend in this case is, again, to override the default. In the latest Hibernate versions (5.2.8+) (thanks to
https://github.com/hibernate/hibernate-orm/pull/1783[HHH-1783], we can do the following
@Override
protected Cache<Object, Object> createCache(String regionName, Properties properties, CacheDataDescription metadata) {
throw new IllegalArgumentException("Unknown hibernate cache: " + regionName);
}
In older versions, sadly, there is no straightforward cache creation method to override. The best we have is
newDefaultConfig
which provides the default configuration. One sad thing is that you don’t have the actual cache name
here. You will need to debug to know it.
@Override
protected Configuration<Object, Object> newDefaultConfig(Properties properties, CacheDataDescription metadata) {
throw new IllegalArgumentException("Unknown hibernate cache: " + metadata);
}
Again, an alternative solution would be to provide a meaningful default cache configuration in this method.
Conclusion
I do understand that frameworks do not like to fail with exceptions. This helps the feeling that they are working out of
the box.
But I still think silently not caching or providing random default configuration is dangerous. Using my two workarounds should
prevent you a lot of headaches.
30 Nov 2016
Yesterday, I was playing with interruption. At some point I ended up with this code.
public <T> T uninterruptibleGet(Future<T> future) throws ExecutionException {
while(true) {
try {
return future.get();
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
}
This is bad code. Don’t do that. It should be an infinite loop. For those not playing with interruption daily
here’s why:
- Waiting on
get
- Be interrupted
- Catch the exception and set the interruption state back (
Thread.currentThread().interrupt()
)
- Go back to
get
- Notice we are interrupted (the interruption state is on)
- Throw an
InterruptedException
- Go to 4
The thing is that when running the code, there was no infinite loop.
So I wanted to know why.
The answer is in FutureTask.get()
.
public V get() throws InterruptedException, ExecutionException {
int s = state;
if (s <= COMPLETING) // here
s = awaitDone(false, 0L);
return report(s);
}
The get
method first look at the state, if done, it just returns. If not, then it interrupts. Here we go,
job done.
Then it goes to the Continuous Integration. And goes in an infinite loop. Whaaat???
At first I thought it was some race condition that was happening with other tests (they are run in parallel).
But no. The answer is much simpler than that: JDK 6
The FutureTask
code above is from JDK 8. The JDK 6 code is different. It first starts to check the
interrupt. So infinite loop it is.
Now, was is the right idiom for an uninterruptibleGet
?
To get the long answer, I highly suggest that you go read Java Concurrency in Practice
(chapter 7) right now. It is a must read for any Java programmer.
The short answer is this:
public <T> T uninterruptibleGet(Future<T> future) throws ExecutionException {
boolean interrupted = false;
try {
while (true) {
try {
return future.get();
} catch (InterruptedException e) {
interrupted = true;
}
}
} finally {
if (interrupted)
Thread.currentThread().interrupt();
}
}
20 Oct 2016
These days, I’m a bit annoyed about Java generics. Because it seems that when you want to be clean, you pretty
much always get in troubles.
I’ll give you an example. The method to create a mock with EasyMock is currently typed like this:
public static <T> T mock(Class<T> toMock)
This seems quite straightforward.
But it is also quite annoying to use. For example, let’s try to mock a generic type:
List<String> list = mock(List.class);
It looks like something we would like to easily do but you get this nice warning:
Warning:(51, 33) java: unchecked conversion
required: java.util.List<java.lang.String>
found: java.util.List
And there’s no way to get around it. Here are some attempts:
List<String> list = mock(List<String>.class); // no allowed (won't compile)
List<String> list = EasyMock.<String>mock(List.class); // won't compile either because the parameter type doesn't match)
List<String> list = (List<String>) mock(List.class); // still get a warning
So what’s the way out?
To be less accurate.
Yes. I can’t see any other way out. (Do you?)
So my plan is to change EasyMock typing with this:
public static <T> T mock(Class<?> toMock)
No relation anymore between the parameter and the returned type. WAT!!! Are you crazy?!?
So yes, this will compile without complaints :-( (but I can check the type coherence at runtime)
String list = mock(Integer.class);
But this will now work without any warning :-)
List<String> list = mock(List.class);
You can’t have your cake and eat it it seems. But as usual, I will be happy to be proved wrong.
18 Sep 2016
My favorite stress tool has been Gatling for many years now.
Scenarios are
- Easy to construct, It’s just code
- Easy to version. It’s just code
- Easy to run. It’s a simple command line that you launch in remote if needed
- Having great result graphs
- Easy to datamine. There is a
simulation.log
file that let’s you do some more digging when needed
My only complaints are
- You can’t change the running scenario
- It’s in Scala
The first one might be addressed by Gatling Frontline. I haven’t tried.
The second one is a bit more complicated to solve :-)
In fact, I don’t care that’s in Scala. But I would love to be able to core my scenario in Java.
So just for fun, I did a thought experiment. I’ve coded the Gatling API in Java and then coded the BasicScenario
example using this API.
It’s not working for real
The API is just an emply shell. To know how different it would be from the Scala DSL.
The answer is: Not much.
My expectations were that I would need to rely on plenty of Java 8 features to get something close
to the Scala DSl. But in fact, not even.
The main differences are:
- Variables are typed
- I’ve added a
build
method. But it’s just for style. I can get rid of it
- A bunch of semi-colons
- No syntactic sugar to create a map
- I’m using
Duration
is used to time units
- I need a
run
method where the setUp
method is
That’s quite joyful and probably can be improved.
I’m now wondering if I could have used the Scala classes directly. I’m not good at making Java and Scala
interacting.
So if someone is and want to try, please do so.
16 Feb 2016
If you are like me, you tend to work on open source using your personal email and at YP using your enterprise email. But
git doesn’t handle that well so you need to never forget to do
git config user.email henri.tremblay@somewhere.com
after each git init
or git clone
.
I finally had the time for work on an almost satisfying solution.
07 Sep 2015
This version has finally removed the old (and ugly) partial mocking methods. You are now required to use the
partialMockBuilder
.
In exchange, you get really nice short methods to create your mocks: mock
, niceMock
and strictMock
.
You also get a better stability since cglib and ASM are now embedded to remove a possible version mismatch with
your own dependencies. Note that Objenesis will stay as an explicit dependency.
Change log