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Showing posts from 2010

Speeding up Spring integration tests

The biggest problem with unit testing using Spring testing support* is the time it takes to initialize the Spring framework context. Every new test case adds precious seconds to overall build time. After a while it will take minutes or even hours to fully build the application, while most of this time is consumed by Spring itself. But we'll start from the basics.
In order to make JUnit aware of Spring framework test support, simply add these annotations on test case class:
@RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration @Transactional public class MainControllerTest { //... }
While @Transactional is not necessary, it will greatly simplify testing when database is involved (details here). In IntelliJ IDEA 10 (I just took this brand new version for a test drive) these annotations will raise the following error to occur:

And suggested solution:

Functional Java Developers’ Day 2010

Ted Newards’ talk about functional programming in Java and his workshop on Scala (hence the article title) were the most memorable events during the third JDD conference that I attended last week. Sadly most memorable, and almost the only ones. But first things first.

After spending endless hours with great Enterprise JavaBeans 3.0 book by Bill Burke I’ve expected something fabulous, but Bills’ lecture about JAX-RS was just average, with no coding, only plain API introduction. Scott Davis' presenting REST and ROA last year was way much better. Thankfully Angelika Langer talk about Java concurrency pitfalls was much more interesting, although one might argue that she just gave a summary of marvelous Java Concurrency in Practice book, that I have recommended long time ago. One new thing I’ve learnt is that updating volatile variable guarantees all other non-volatile variable updated earlier by the same thread to be visible by other threads, as if they were volatile as well (are you …

Testing for exceptions in JUnit revised

In his recent post the author of fantastic mocking framework Mockito collected few rules about testing exceptions. What caught my attention is the advice to use JUnit rules (nomen est omen!) for testing exceptions. ExpectedException rule gathers advantages of both expected@Test attribute clarity and try-catch strictness. Here is the example:

public class DefaultFooServiceTest { private FooService fooService = new DefaultFooService(); @Rule public ExpectedException exception = new ExpectedException(); @Test public void shouldThrowNpeWhenNullName() throws Exception { //given String name = null; //when exception.expect(NullPointerException.class); fooService.echo(name); //then } }

Szczepan claims that ExpectedException fits into given/when/then test template nicely. I disagree! Look at the code snippet above – what is the most natural place to put assertions on exception being thrown? From the obvious reasons it must be the last line before the line that actuall…

JavaScript dynamic language support in Spring framework

Miško Hevery’s blog post about JavaScript opened my eyes and changed the way I thought about this language completely. Miško practices TDD and advices this technique at every occasion. JavaScript, being dynamic language, needs tests even more than statically and strongly typed languages. This immediately invalidates main objections against JavaScript and dynamic languages at all – that lack of compile time checks inevitably lead to poor quality and runtime bugs instead of compile time. But what is more convincing to you: that your code passes very strict compile time rules or that it passes unit tests covering all the use cases?

After going through the first few chapters of Object-Oriented JavaScript... I couldn’t help myself to try this new, very productive language with functional aspirations. But then I realized that, unlike Java, JavaScript misses:

good runtime environment: it’s hard to name handful of web browsers, each implementing different dialect of the language, decent runtim…

Creating prototype Spring beans on demand using lookup-method

The strength of the Spring Framework is its emphasis on stateless services. Being totally against OOP, this approach has many pragmatic advantages, with low memory consumption, no cost of pooling and multithreaded safety at the top of the list. But sometimes you really need the context and having non-singleton beans with different state attached to each instance makes your code a lot cleaner and easier to read. Let’s start from stateless code and do some consecutive refactorings.

Every time a new flight is entered into the system, we validate it with multiple business rules using FlightValidator class (please forgive my complete absence of domain knowledge):

public class FlightValidator { @Resource //Many services public boolean validate(Flight flight) { return validateSourceAndTarget(flight) && isAirplaneAvailable(flight) && isAirportFree(flight) && !buyerBlackListed(flight) && reservationLimitReached(flight); } //Many more methods }

There is someth…

Few words after Javarsovia 2010

It is never too late to mention about such a great event like Javarsovia 2010 conference. The conference was really successful, even though I was one of the speakers ;-). If you were near Warsaw on 26th of June and missed the conference I feel really sorry for you. But first things first.

I was really surprised not seeing long queues for the registration, so not wasting a lot of time, equipped with good-looking conference T-shirt, we went to see the first presentation. Tomasz Bujok with his From zero to jBPM hero! lecture did a great job introducing jBPM framework. I have seen quite a few presentations about this engine already, thankfully Tomasz made one step further in the topic and have shown some anti-patterns and other tips for jBPM developers. This was really interesting as anyone, after reading a book or two, can have a "How-to" talk. But having "How-not-to" talk requires knowledge and experience in the technology far beyond the typical tutorial-driven &quo…

Hades: DRY principle in JPA/Spring development

It's almost two weeks after great Javarsovia 2010 conference, but before I write few words about this event, let me mention about really clever library called Hades. I owe you this after my attendance in GeeCON 2010, where I discovered this tool during its author talk.

DRY stands for Don't Repeat Yourself and if you were developing in JPA for a while you have violated this principal several times. Take for example this piece of code:

Although IntelliJ IDEA has a wonderful support for JPA (have you noticed this little popup suggesting me the proper named query parameter name since?), I still have to write the same boilerplate code over and over. Basically for each entity object I need a DAO class and 90% of them look the same except they have different entity type. Same CRUD, same paging and sorting logic, same unit tests, similar queries. We are getting bored after writing fifth or tenth DAO like this, especially if we are lazy (which is good!) So Hades provides nice abstractio…

Clean code, clean logs: easy to read, easy to parse (10/10)

There are two groups of receivers particularly interested in your application logs: human beings (you might disagree, but programmers belong to this group as well) and computers (typically shell scripts written by system administrators). Logs should be suitable for both of these groups. If someone looking from behind your back at your application logs sees:

from Wikipedia

then you were probably not reading my tips carefully enough. The reference to famous Clean code book in the title of this series is not accidental: logs should be readable and easy to understand just like the code should.

On the other hand, if your application produces half GiB of logs each hour, no man and no graphical text editor will ever manage to read them entirely. This is where old-school grep, sed and awk come in handy. If it is possible, try to write logging messages in such a way, that they could be understood both by humans and computers, e.g. avoid formatting of numbers, use patterns that can be easily recog…

Clean code, clean logs: log exceptions properly (9/10)

First of all, avoid logging exceptions, let your framework or container (whatever it is) do it for you*. Logging exceptions is one of the most important roles of logging at all, but many programmers tend to treat logging as a way to handle the exception. They sometimes return default value (typically null, 0 or empty string) and pretend that nothing has happened. Other times they first log the exception and then wrap it and throw back:

log.error("IO exception", e);
throw new MyCustomException(e);

This construct will almost always print the same stack trace two times, because something will eventually catch MyCustomException and log its cause. Log or wrap and throw back (which is preferable), never both, otherwise your logs will be confusing.

But if we really do WANT to log the exception? For some reason (because we don’t read APIs and documentation?), about half of the logging statements I see are wrong. Quick quiz, which of the following log the NPE properly?

try {
Integer x…

Clean code, clean logs: watch out for external systems (8/10)

This is the special case of the previous tip: if you communicate with any external system, consider logging every piece of data that comes out from your application and gets in. Period. Integration is a tough job and diagnosing problems between two applications (think two different vendors, environments, technology stacks and teams) is particularly hard. Recently, for example, we've discovered that logging full messages contents, including SOAP and HTTP headers in Apache CXF web services is extremely useful during integration and system testing.

This is a big overhead and if performance is an issue, you can always disable logging. But what is the point of having fast, but broken application, that no one can fix? Be extra careful when integrating with external systems and prepare to pay that cost. If you are lucky and all your integration is handled by ESB, bus is probably the best place to log every incoming request and response. See for example Mules' <log-component/>.


Impressions after GeeCON 2010

Two days ago I came back from Poznań, Poland, where second edition of GeeCON conference took place. After attending the first edition my expectations were very high and sadly I left Poznań a bit disappointed. It is most likely a matter of my personal taste, but still just a few presentations are worth mentioning.

The biggest surprise and most fabulous piece of lecture has been given by Dawid Weiss on Java in high-performance computing. He managed to combine great show with lots of non-trivial examples. Lots of humour, brilliant slides and great contact with the audience. One of the most charismatic speakers I have seen. But on the other hand it was not a stand-up comedy, where you have lots of fun during the lecture but you don’t gain anything useful after them. Dawid given plenty of examples and micro-benchmarks during his speech, making us believe that tuning, benchmarking and even studying bytecode and assembly language might be interesting. Bravo for Dawid, I was really proud to s…

Clean code, clean logs: log method arguments and return values (7/10)

When you find a bug during development, you typically run a debugger trying to track down the potential cause*. Now imagine for a while you can’t use a debugger. For example, because the bug manifested itself on a customer environment few days ago and everything you have are logs. Would be able to find anything in them?

If you follow the simple rule of logging each method input and output (arguments and return values), you don’t even need debugger any more. Of course, you must be reasonable but every method that: accesses external system (including database), blocks, waits, etc. should be considered. Simply follow this pattern:

public String printDocument(Document doc, Mode mode) {
log.debug("Entering printDocument(doc={}, mode={})", doc, mode);
String id = //Lengthy printing operation
log.debug("Leaving printDocument(): {}", id);
return id;

Because you are logging both the beginning and the end of method invocation, you can manually discover inefficient …

Clean code, clean logs: tune your pattern (6/10)

Logging pattern is a wonderful tool, that transparently adds meaningful context to every logging statement you make. But you must consider very carefully which information to include in your pattern. For example, logging date when your logs roll every hour is pointless as the date is already included in the log file name. On the contrary, without logging thread name you would be unable to track any process using logs when two threads work concurrently – the logs will overlap. This might be fine in single-threaded applications – that are almost dead nowadays.

From my experience, ideal logging pattern should include (of course except the logged message itself): current time (without date, milliseconds precision), logging level (if you pay attention to it), name of the thread, simple logger name (not fully qualified) and the message. In Logback it is something like:

<appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">

Clean code, clean logs: concise and descriptive (5/10)

Each logging statement should contain both data and description. Consider the following examples:

log.debug("Message processed");
log.debug("Message with id '{}' processed", message.getJMSMessageID());

Which log would you like to see while diagnosing failure in an unknown application? Believe me, all the examples above are almost equally common. Another anti-pattern:

if(message instanceof TextMessage)
log.warn("Unknown message type");

Was it so hard to include actual message type, message id, etc. in warning string? I know something went wrong, but what, what was the context? Third anti-pattern is "magic-log". Real life example: most programmers in the team knew that 3 ampersands followed by exclamation mark, followed by hash, followed by pseudorandom alphanumeric string log means "Message with XYZ id received". Nobody bothered to change the log, simply someone hit the keyboard an…

Clean code, clean logs: avoid side effects (4/10)

Logging statements should have no or little impact on application behavior. Recently a friend of mine gave an example of a system that threw Hibernates' LazyInitializationException only on some particular environment. As you’ve probably guessed from the context, some logging statement caused lazy initialized collection to be loaded when session was attached. On this environment the logging levels were increased and collection was no longer initialized. Think how long would it take you to find a bug without knowing this context?

Another side effect is slowing the application down. Quick answer: if you log too much or improperly use toString()/string concatenation, logging has a performance side effect. How big? Well, I have seen server restarting every 15 minutes because of a thread starvation caused by excessive logging. Now this is a side effect! From my experience, few hundreds of MiB is probably the upper limit of how much you can log onto disk per hour.

Of course if logging stat…

Clean code, clean logs: do you know what you are logging? (3/10)

Every time you issue a logging statement, take a moment and have a look what exactly will land in your log file. Read your logs afterwards and spot malformed sentences. First of all, avoid NPEs like this:

log.debug("Processing request with id: {}", request.getId());

Are you absolutely sure that request is not null here? Another pitfall is logging collections. If you fetched collection of domain objects from the database using Hibernate and carelessly log them like here:

log.debug("Returning users: {}", users);

SLF4J will call toString() only when the statement is actually printed, which is quite nice. But if it does... Out of memory error, N+1 select problem, thread starvation (logging is synchronous!), lazy initialization exception, logs storage filled completely – each of these might occur.

It is a much better idea to log, for example, only ids of domain objects (or even only size of the collection). But making a collection of ids when having a collection of objects h…

Clean code, clean logs: logging levels are there for you (2/10)

Every time you are making a logging statement, you think hard which logging level is appropriate for this type of event, do you? Somehow 90% of programmers never pay attention to logging levels, simply logging everything on the same level, typically INFO or DEBUG. Why? Logging frameworks have two major benefits over System.out: categories and levels. Both allow you to selectively filter logging statements permanently or only for diagnostics time. If you really can’t see the difference, print this table and look at it every time you start typing "log." in your IDE:

ERROR – something terribly wrong had happened, that must be investigated immediately. No system can tolerate items logged on this level. Example: NPE, database unavailable, mission critical use case cannot be continued.

WARN – the process might be continued, but take extra caution. Actually I always wanted to have two levels here: one for obvious problems where work-around exists (for example: "Current data unav…

Clean code, clean logs: use appropriate tools (1/10)

Many programmers seem to forget how logging application behavior and its current activity is important. When somebody puts:"!@#$%");

happily somewhere in the code, he probably don't realize the importance of application logs during maintenance, tuning and failure identification. Underestimating the value of good logs is a terrible mistake. I have collected few random advices that I find especially useful when it comes to writing logging routines and I will present them in a series of short articles. First tip (out of ten) is about logging libraries and tools.

In my opinion, SLF4J is the best logging API available, mostly because of a great pattern substitution support:

log.debug("Found {} records matching filter: '{}'", records, filter);

In Log4j you would have to use:

log.debug("Found " + records + " records matching filter: '" + filter + "'");

This is not only longer and less readable, but also inefficient bec…

Elegance vs. simplicity

Few weeks ago I had pleasure to give a speech "Mule ESB vs. Apache ServiceMix" at Warsaw Java Users Group, together with Łukasz Dywicki. During this live coding session I have been implementing some simple integration logic using Mule ESB, while Łukasz did the same with ServiceMix. The presentation went pretty good, you can find source code here.

While preparing for the speech I have discovered some bug (see MULE-4708) in Mule ESB 2.2.1. My patch has been applied in less than 10 hours after submitting, which is quite impressive. Sadly, the ESB’s code I had to study to track down the bug was not so impressive, at least that was my first impression. Just take a look at this excerpt from org.mule.transport.jms.JmsMessageUtils, that takes literally any object and converts it into proper JMS message type:

public static Message toMessage(Object object, Session session) throws JMSException {
if (object instanceof Message) {
return (Message) object;
} else if (objec…