Scott Leberknight's Weblog

A recent project started out life as an all-Java project that used Maven as the build tool. Initially we used Atlassian Clover to measure unit test coverage. Clover is a great product for Java code, but unfortunately it only works with Java code because it works at the Java source level. (This was the case as of Spring 2009, and I haven't checked since then.) As we started migrating existing code from Java to Groovy and writing new code in Groovy, we started to lose data about unit test coverage because Clover does not understand Groovy code. To remedy this problem we switched from Clover to Cobertura, which instruments at the bytecode level and thus works with Groovy code. Theoretically it would also work with any JVM-based language but I'm not sure whether or not it could handle something like Clojure or not.

In any case, we only cared about Groovy so Cobertura was a good choice. With the Cobertura Maven plugin we quickly found a problem, which was that even though the code coverage was running, the reports only showed coverage for Java code, not Groovy. This blog shows you how to display coverage on Groovy code when using Maven and the Cobertura plugin. In other words, I'll show how to get Cobertura reports to link to the real Groovy source code in Maven, so you can navigate Cobertura reports as you normally would.

The core problem is pretty simple, though it took me a while to figure out how to fix it. Seems to be pretty standard in Maven: I know what I want to do, but finding out how to do it is the really hard part. The only thing you need to do is tell Maven about the Groovy source code and where it lives. The way I did this is to use the Codehaus build-helper-maven-plugin which has an add-source goal. The add-source goal does just what you would expect; it adds a specified directory (or directories) as a source directory in your Maven build. Here's how you use it in your Maven pom.xml file:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <executions>
        <execution>
            <phase>generate-sources</phase>
            <goals>
                <goal>add-source</goal>
            </goals>
            <configuration>
                <sources>
                    <source>src/main/groovy</source>
                </sources>
            </configuration>
        </execution>
    </executions>
</plugin>

In the above code snippet, we're using the "build-helper-maven-plugin" to add the src/main/groovy directory. That's pretty much it. Run Cobertura as normal, view the reports, and you should now see coverage on Groovy source code as well as Java.

I've just published an article in the November 2009 NFJS Magazine on Hibernate Performance Tuning. Here's the abstract:

Many developers treat Hibernate like a "black box" and assume it will simply "Do the Right Thing" when it comes to all things related to the underlying database. This is a faulty assumption because, while Hibernate is great at the mechanics of database interaction, it cannot and will likely not ever be able to figure out the specific details of your domain model and discern the most efficient and best performing data access strategies. In this first article of a two part series, I'll show you how to achieve better performance in your Hibernate applications by focusing on tuning object retrieval, which forms the basis of your "fetch plan" for finding and storing objects in the database.

If you are using Hibernate and want to know more about how to change how objects are fetched from the database, check it out and let me know what you think. Note that NFJS Magazine does require a subscription.

Java and Evolution

The Java language has been around for a pretty long time, and in my view is now a stagnant language. I don't consider it dead because I believe it will be around for probably decades if not longer. But it appears to have reached its evolutionary peak, and it doesn't look it's going to be evolved any further. This is not due to problems inherent in the language itself. Instead it seems the problem lies with Java's stewards (Sun and the JCP) and their unwillingness to evolve the language to keep it current and modern, and more importantly the goal to keep backward compatibility at all costs. Not just Sun, but also it seems the large corporations with correspondingly large investments in Java like IBM and Oracle aren't exactly chomping at the bit to improve Java. I don't even know if they think it even needs improvement at all. So really, the ultra-conservative attitude towards change and evolution is the problem with Java from my admittedly limited view of things.

That's why I don't hate Java. But, I do hate the way it has been treated by the people charged with improving it. It is clear many in the Java community want things like closures and a native property syntax but instead we got Project Coin. This, to me, is sad really. It is a shame that things like closures and native properties were not addressed in Java/JDK/whatever-it-is-called 7.

Why Not?

I want to know why Java can't be improved. We have concrete examples that it is possible to change a major language in major ways. Even in ways that break backward compatibility in order to evolve and improve. Out with the old, in with the new. Microsoft with C# showed that you can successfully evolve a language over time in major ways. For example C# has always had a property syntax but it now also has many features found in dynamically typed and functional languages such as type inference and, effectively, closures. With LINQ it introduced functional concepts. When C# added generics they did it correctly and retained the type information in the compiled IL, whereas Java used type-erasure and simply dropped the types from the compiled bytecode. There is a great irony here: though C# began life about five or six years after Java, it not only has caught up but has surpassed Java in most if not all ways, and has continued to evolve while Java has become stagnant.

C# is not the only example. Python 3 is a major overhaul of the Python language, and it introduced breaking changes that are not backwards compatible. I believe they provide a migration tool to assist you should you want to move from the 2.x series to version 3 and beyond. Microsoft has done this kind of thing as well. I remember when they made Visual Basic conform to the .NET platform and introduced some rather gut wrenching (for VB developers anyway) changes, and they also provided a tool to aid the transition. One more recent example is Objective-C which has experienced a resurgence in importance mainly because of the iPhone. Objective-C has been around longer than all of Java, C#, Ruby, Python, etc. since the 1980s. Apple has made improvements to Objective-C and it now sports a way to define and synthesize properties and most recently added blocks (effectively closures). If a language that pre-dates Java (Python also pre-dates Java by the way) can evolve, I just don't get why Java can't.

While it is certainly possible to remain on older versions of software, forcing yourself to upgrade can be a Good Thing, because it ensures you don't get the "COBOL Syndrome" where you end up with nothing but binaries that have to run on a specific hardware platform forever and you are trapped until you rewrite or you go out of business. The other side of this, of course, is that organizations don't have infinite time, money, and resources to update every single application. Sometimes this too can be good, because it forces you to triage older systems, and possibly consolidate or outright eliminate them if they have outlived their usefulness. In order to facilitate large transitions, I believe it is very important to use tools that help automate the upgrade process, e.g. tools that analyze code and fix it if possible (reporting all changes in a log) and which provide warnings and guidance when a simple fix isn't possible.

The JVM Platform

Before I get into the changes I'd make to Java to make it not feel like I'm developing with a straightjacket on while having to type masses of unnecessary boilerplate code, I want to say that I think the JVM is a great place to be. Obviously the JVM itself facilitates developing all kinds of languages as evidenced by the huge number of languages that run on the JVM. The most popular ones and most interesting ones these days are probably JRuby, Scala, Groovy, and Clojure though there are probably hundreds more. So I suppose you could make an argument that Java doesn't need to evolve any more because we can simply use a more modern language that runs on the JVM.

The main problem I have with that argument is simply that there is already a ton of Java code out there, and there are many organizations who are simply not going to allow other JVM-based languages; they're going to stick with Java for the long haul, right or wrong. This means there is a good chance that even if you can manage convince someone to try writing that shiny new web app using Scala and its Lift framework, JRuby on Rails, Grails, or Clojure, chances are at some point you'll also need to maintain or enhance existing large Java codebases. Wouldn't you like to be able to first upgrade to a version of Java that has closures, native property syntax, method/property handles, etc?

Next I'll choose what would be my top three choices to make Java much better immediately.

Top Three Java Improvements

If given the chance to change just three things about Java to make it better, I would choose these:

• Remove checked exceptions
• Add closures
• Add formal property support

I think these three changes along would make coding in Java much, much better. Let's see how.

Remove Checked Exceptions

By removing checked exceptions you eliminate a ton of boilerplate try/catch clauses that do nothing except log a message, wrap and re-throw as a RuntimeException, pollute the API with throws clauses all over the place, or worst of all empty catch blocks that can cause very subtle and evil bugs. With unchecked exceptions, developers still have the option to catch exceptions that they can actually handle. It would be interesting to see how many times in a typical Java codebase people actually handle exceptions and do something at the point of exception, or whether they simply punt it away for the caller to handle, who in turn also punts, and so forth all the way up the call stack until some global handler catches it or the program crashes. If I were a betting man, I'd bet a lot of money that for most applications, developers punt the vast majority of the time. So why force people to handle something they cannot possible handle?

Add Closures

I specifically listed removing checked exceptions first, because to me it is the first step to being able to have a closure/block syntax that isn't totally horrendous. If you remove checked exceptions, then adding closures would seem to be much easier since you don't need to worry at all about what exceptions could possibly be thrown and there is obviously no need to declare exceptions. Closures/blocks would lead to better ability to handle collections, for example as in Groovy but in Java you would still have types (note I'm also using a literal property syntax here):

// Find all people whose last name is "Smith"
List<Person> peeps = people.findAll { Person person -> person.lastName.equals("Smith");   } 

// Create a list of names by projecting the name property of a bunch of Person objects
List<String> names = people.collect { Person person -> person.name; }

Not quite as clean as Groovy but still much better than the for loops that would traditionally be required (or trying to shoehorn functional-style into Java using the Jakarta Commons Collections or Google Collections). Removal of checked exceptions would allow, as mentioned earlier, the block syntax to not have to deal with declaring exceptions all over the place. Having to declare checked exceptions in blocks makes the syntax worse instead of better, at least when I saw the various closure proposals for Java/JDK/whatever 7 which did not get included. Requiring types in the blocks is still annoying, especially once you get used to Ruby and Groovy, but it would be passable.

Native Property Syntax

The third change should do essentially what Groovy for properties does but should introduce a "property" keyword (i.e. don't rely on whether someone accidentally put an access modifier in there as Groovy does). The syntax could be very clean:

property String firstName;
property String lastName;
property Date dateOfBirth;

The compiler could automatically generate the appropriate getter/setter for you like Groovy does. This obviates the need to manually code the getter/setter. Like Groovy you should be able to override either or both. It de-clutters code enormously and removes a ton of lines of silly getter/setter code (plus JavaDocs if you are actually still writing them for every get/set method). Then you could reference properties as you would expect: person.name is the "getter" and person.name = "Fred" is the "setter." Much cleaner syntax, way less boilerplate code. By the way, if someone used the word "property" in their code, i.e. as a variable name, it is just not that difficult to rename refactor, especially with all the advanced IDEs in the Java community that do this kind of thing in their sleep.

Lots of other things could certainly be done, but if just these three were done I think Java would be much better off, and maybe it would even come into the 21st century like Objective-C. (See the very long but very good Ars Technica Snow Leopard review for information on Objective-C's new blocks feature.)

Dessert Improvements

If (as I suspect they certainly will :-) ) Sun/Oracle/whoever takes my suggestions and makes these changes and improves Java, then I'm sure they'll want to add in a few more for dessert. After the main course which removes checked exceptions, adds closures, and adds native property support, dessert includes the following:

• Remove type-erasure and clean up generics
• Add property/method handles
• String interpolation
• Type inference
• Remove "new" keyword

Clean Up Generics

Generics should simply not remove type information when compiled. If you're going to have generics in the first place, do it correctly and stop worrying about backward compatibility. Keep type information in the bytecode, allow reflection on it, and allow me to instantiate a "new T()" where T is some type passed into a factory method, for example. I think an improved generics implementation could basically copy the way C# does it and be done.

Property/Method Handles

Property/method handles would allow you to reference a property or method directly. They would make code that now must use strings strongly typed and refactoring-safe (IDEs like IntelliJ already know how to search in text and strings but can never be perfect) much nicer. For example, a particular pet peeve of mine and I'm sure a lot of other developers is writing Criteria queries in Hibernate. You are forced to reference properties as simple strings. If the lastName property is changed to surname then you better make sure to catch all the places the String "lastName" is referenced. So you could replace code like this:

session.createCriteria(Person.class)
	.add(Restrictions.eq("lastName", "Smith")
	.addOrder(Order.asc("firstName")
	.list();

with this using method/property handles:

session.createCriteria(Person.class)
	.add(Restrictions.eq(Person.lastName, "Smith")
	.addOrder(Order.asc(Person.firstName)
	.list();

Now the code is strongly-typed and refactoring-safe. JPA 2.0 tries mightily to overcome having strings in the new criteria query API with its metamodel. But I find it pretty much appalling to even look at, what with having to create or code-generate a separate "metamodel" class which you reference like "_Person.lastName" or some similar awful way. This metamodel class lives only to represent properties on your real model object for the sole purpose of making JPA 2.0 criteria queries strongly typed. It just isn't worth it and is total overkill. In fact, it reminds me of the bad-old days of rampant over-engineering in Java (which apparently is still alive and well in many circles but I try to avoid it as best I can). The right thing is to fix the language, not to invent something that adds yet more boilerplate and more complexity to an already overcomplicated ecosystem.

Method handles could also be used to make calling methods using reflection much cleaner than it currently is, among other things. Similarly it would make accessing properties via reflection easier and cleaner. And with only unchecked exceptions you would not need to catch the four or five kinds of exceptions reflective code can throw.

String Interpolation

String interpolation is like the sorbet that you get at fancy restaurants to cleanse your palate. This would seem to be a no-brainer to add. You could make code like:

log.error("The object of type  ["
    + foo.getClass().getName()
    + "] and identifier ["
    + foo.getId()
    + "] does not exist.", cause);

turn into this much more palatable version (using the native property syntax I mentioned earlier):

log.error("The object of type [${foo.class.name}] and identifier [${foo.id}] does not exist.", cause);

Type Inference

I'd also suggest adding type inference, if only for local variables like C# does. Why do we have to repeat ourselves? Instead of writing:

Person person = new Person();

why can't we just write:

var person = new Person();

I have to believe the compiler and all the tools are smart enough to infer the type from the "new Person()". Especially since other strongly-typed JVM languages like Scala do exactly this kind of thing.

Elminate "new"

Last but not least, and actually not the last thing I can think of but definitely the last I'm writing about here, let's get rid of the "new" keyword and either go with Ruby's new method or Python's constructor syntax, like so:

// Ruby-like new method
var person = Person.new()

// or Python-like construction
var person = Person()

This one came to me recently after hearing Bruce Eckel give an excellent talk on language evolution and archaeology. He had a ton of really interesting examples of why things are they way they are, and how Java and other languages like C++ evolved from C. One example was the reason for "new" in Java. In C++ you can allocate objects on the stack or the heap, so there is a stack-based constructor syntax that does not use "new" while the heap-based constructor syntax uses the "new" operator. Even though Java only has heap-based object allocation, it retained the "new" keyword which is not only boilerplate code but also makes the entire process of object construction pretty much immutable: you cannot change anything about it nor can you easily add hooks into the object creation process.

I am not an expert at all in the low-level details, and Bruce obviously knows what he is talking about way more than I do, but I can say that I believe the Ruby and Python syntaxes are not only nicer but more internally consistent, especially in the Ruby case because there is no special magic or sauce going on. In Ruby, new is just a method, on a class, just like everything else.

Conclusion to this Way Too Long Blog Entry

I did not actually set out to write a blog whose length is worthy of a Ted Neward blog. It just turned out that way. (And I do in fact like reading Ted's long blogs!) Plus, I found out that speculative fiction can be pretty fun to write, since I don't think pretty much any of these things are going to make it into Java anytime soon, if ever, and I'm sure there are lots of people in the Java world who hate things like Ruby won't agree anyway.

When you have collections of associated objects in domain objects, you generally want to specify some kind of default sort order. For example, suppose I have domain objects Timeline and Event:

@Entity
class Timeline {

    @Required 
    String description

    @OneToMany(mappedBy = "timeline")
    @javax.persistence.OrderBy("startYear, endYear")
    Set<Event> events
}

@Entity
class Event {

    @Required
    Integer startYear

    Integer endYear

    @Required
    String description

    @ManyToOne
    Timeline timeline
}

In the above example I've used the standard JPA (Java Persistence API) @OrderBy annotation which allows you to specify the order of a collection of objects via object properties, in this example a @OneToMany association . I'm ordering first by startYear in ascending order and then by endYear, also in ascending order. This is all well and good, but note that I've specified that only the start year is required. (The @Required annotation is a custom Hibernate Validator annotation which does exactly what you would expect.) How are the events ordered when you have several events that start in the same year but some of them have no end year? The answer is that it depends on how your database sorts null values by default. Under Oracle 10g nulls will come last. For example if two events both start in 2001 and one of them has no end year, here is how they are ordered:

2001 2002  Some event
2001 2003  Other event
2001       Event with no end year

What if you want to control how null values are ordered so they come first rather than last? In Hibernate there are several ways you could do this. First, you could use the Hibernate-specific @Sort annotation to perform in-memory (i.e. not in the database) sorting, using natural sorting or sorting using a Comparator you supply. For example, assume I have an EventComparator helper class that implements Comparator. I could change Timeline's collection of events to look like this:

@OneToMany(mappedBy = "timeline")
@org.hibernate.annotations.Sort(type = SortType.COMPARATOR, comparator = EventCompator)
 Set<Event> events

Using @Sort will perform sorting in-memory once the collection has been retrieved from the database. While you can certainly do this and implement arbitrarily complex sorting logic, it's probably better to sort in the database when you can. So we now need to turn to Hibernate's @OrderBy annotation, which lets you specify a SQL fragment describing how to perform the sort. For example, you can change the events mapping to :

@OneToMany(mappedBy = "timeline")
@org.hibernate.annotations.OrderBy("start_year, end_year")
 Set<Event> events

This sort order is the same as using the JPA @OrderBy with "startYear, endYear" sort order. But since you write actual SQL in Hibernate's @OrderBy you can take advantage of whatever features your database has, at the possible expense of portability across databases. As an example, Oracle 10g supports using a syntax like "order by start_year, end_year nulls first" to order null end years before non-null end years. You could also say "order by start_year, end year nulls last" which sorts null end years last as you would expect. This syntax is probably not portable, so another trick you can use is the NVL function, which is supported in a bunch of databases. You can rewrite Timeline's collection of events like so:

@OneToMany(mappedBy = "timeline")
@org.hibernate.annotations.OrderBy("start_year, nvl(end_year , start_year)")
 Set<Event> events

The expression "nvl(end_year , start_year)" simply says to use end_year as the sort value if it is not null, and start_year if it is null. So for sorting purposes you end up treating end_year as the same as the start_year if end_year is null. In the contrived example earlier, applying the nvl-based sort using Hibernate's @OrderBy to specify SQL sorting criteria, you now end with the events sorted like this:

2001       Event with no end year
2001 2002  Some event
2001 2003  Other event

Which is what you wanted in the first place. So if you need more complex sorting logic than what you can get out of the standard JPA @javax.persistence.OrderBy, try one of the Hibernate sorting options, either @org.hibernate.annotations.Sort or @org.hibernate.annotations.OrderBy. Adding a SQL fragment into your domain class isn't necessarily the most elegant thing in the world, but it might be the most pragmatic thing.

Last week I tweeted about groovification, which is defined thusly:

groovification. noun. the process of converting java source code into groovy source code (usually done to make development more fun)

On my main day-to-day project, we've been writing unit tests in Groovy for quite a while now, and recently we decided to start implementing new code in Groovy rather than Java. The reason for doing this is to gain more flexibility in development, to make testing easier (i.e. in terms of the ability to mock dependencies in a trivial fashion), to eliminate a lot of Java boilerplate code and thus write less code, and of course to make developing more fun. It's not that I hate Java so much as I feel Java simply isn't innovating anymore and hasn't for a while, and isn't adding features that I simply don't want to live without anymore such as closures and the ability to do metaprogramming when I need to. In addition, it isn't removing features that I don't want, such as checked exceptions. If I know, for a fact, that I can handle an exception, I'll handle it appropriately. Otherwise, when there's nothing I can do anyway, I want to let the damn thing propagate up and just show a generic error message to the user, log the error, and send the admin team an email with the problem details.

This being, for better or worse, a Maven project, we've had some interesting issues with mixed compilation of Java and Groovy code. The GMaven plugin is easy to install and works well but currently has some outstanding issues related to Groovy stub generation, specifically it cannot handle generics or enums properly right now. (Maybe someone will be less lazy than me and help them fix it instead of complaining about it.) Since many of our classes use generics, e.g. in service classes that return domain objects, we currently are not generating stubs. We'll convert existing classes and any other necessary dependencies to Groovy as we make updates to Java classes, and we are implementing new code in Groovy. Especially in the web controller code, this becomes trivial since the controllers generally depend on other Java and/or Groovy code, but no other classes depend on the controllers. So starting in the web tier seems to be a good choice. Groovy combined with implementing controllers using the Spring @MVC annotation-based controller configuration style (i.e. no XML configuration), is making the controllers really thin, lightweight, and easy to read, implement, and test.

I estimate it will take a while to fully convert all the existing Java code to Groovy code. The point here is that we are doing it piecemeal rather than trying to do it all at once. Also, whenever we convert a Java file to a Groovy one, there are a few basics to make the classes Groovier without going totally overboard and spending loads of time. First, once you've used IntelliJ's move refactoring to move the .java file to the Groovy source tree (since we have src/main/java and src/main/groovy) you can then use IntelliJ's handy-dandy "Rename to Groovy" refactoring. In IntelliJ 8.1 you need to use the "Search - Find Action" menu option or keystroke and type "Rename to..." and select "Rename to Groovy" since they goofed in version 8 and that option was left off a menu somehow. Once that's done you can do a few simple things to make the class a bit more groovy. First, get rid of all the semi-colons. Next, replace getter/setter code with direct property access. Third, replace for loops with "each"-style internal iterators when you don't need the loop index and "eachWithIndex" where you do. You can also get rid of some of the redundant modifiers like "public class" since that is the Groovy default. That's not too much at once, doesn't take long, and makes your code Groovier. Over time you can do more groovification if you like.

The most common gotchas I've found have to do with code that uses anonymous or inner classes since Groovy doesn't support those Java language features. In that case you can either make a non-public named class (and it's OK to put it in the same Groovy file unlike Java as long as it's not public) or you can refactor the code some other way (using your creativity and expertise since we are not monkeys, right?). This can sometimes be a pain, especially if you are using a lot of them. So it goes. (And yes, that is a Slaughterhouse Five reference.)

Happy groovification!

If you want/need to run VisualVM on a 32-bit Macbook Pro you'll need to do a couple of things. First, download and install Soy Latte, using these instructions - this gets you a Java 6 JDK/JRE on your 32-bit Macbook Pro. Second, download VisualVM and extract it wherever, e.g. /usr/local/visualvm. If you now try to run VisualVM you'll get the following error message:

$ ./visualvm
./..//platform9/lib/nbexec: line 489: /System/Library/Frameworks/JavaVM.framework/
Versions/1.6/Home/bin/java: Bad CPU type in executable

Oops. After looking at the bin/visualvm script I noticed it is looking for an environment variable named "jdkhome." So the third step is to export an environment variable named 'jdkhome' that points to wherever you installed Soy Latte:

export jdkhome=/usr/local/soylatte16-i386-1.0.3

Now run the bin/visualvm script from the command line. Oh, almost forgot to mention that you should also have X11 installed, which it will be by default on Mac OS X Leopard. Now if all went well, you should have VisualVM up and running!

If you're into Groovy and Spring, check out my two-part series on IBM developerWorks on using Groovy together with Spring's dynamic language support for potentially more flexible (and interesting) applications. In Part 1 I show how to easily integrate Groovy scripts (i.e. .groovy files containing one or more classes) into Spring-based applications. In Part 2 I show how to use the "refreshable beans" feature in Spring to automatically and transparently reload Spring beans implemented in Groovy from pretty much anywhere including a relational database, and why you might actually are to do something like that!

If you are (stuck) in Javaland, which for my main project I currently am, and you'd like a little of the closure-like goodness you get from, well, lots of other languages like Ruby, Groovy, C#, Scala, etc. then you can get a tad bit closer by using the Apache Commons Collections library. Ok, scratch that. You aren't going to get much closer but at least for some problems the extensive set of utilities available can make your life at least a little easier when dealing with collections, in that you don't need to code the same stuff over and over again, or create your own library of collection-related utilities for many common tasks. Note also I am not intending to start any kind of religious war here abut Java vs. Java.next, which is how Stu aptly refers to languages like Grooovy, JRuby, Scala, and Clojure.

As a really quick and simple example, say you have a collection of Foo objects and that you need to extract the value of the bar property of every one of those objects, and you want all the values in a new collection that you can use for whatever you need to. In that case you can use the collect method of the CollectionUtils class to do this pretty easily.

List<Foo> foos = getListOfFoosSomehow();
Collection<String> bars = CollectionUtils.collect(foos, TransformerUtils.invokerTransformer("getBar"));

This simple code is equivalent to the following:

List<Foo> foos = getListOfFoosSomehow();
Collection<String> bars = new ArrayList<String>();
for (Foo foo : foos) {
    bars.add(foo.getBar());
}

Depending on your viewpoint and how willing you are to ignore the ugliness of passing a method name into a method as in the first example, you can write less code for common scenarios such as this using the Commons Collections utilities. If Java gets method handles in Java 7, the first example could possibly be more elegantly rewritten like this:

List<Foo> foos = getListOfFoosSomehow();
// Making a HUGE assumption here about how method handles could possibly work...
Collection<String> bars = CollectionUtils.collect(foos, TransformerUtils.invokerTransformer(Foo.getBar));

Of course, if Java 7 also gets closures then everything I just wrote is moot and irrelevant (which it might be anyway even as I write this). Regardless, with the current state of Java (no closures and no method handles) the Commons Collections library just might have some things to make your life a bit easier when dealing with collections using good old pure Java code.

EasyMock is a Java dynamic mocking framework that allows you to record expected behavior of mock objects, play them back, and finally verify the results. As an example, say you have an interface FooService with a method List<Foo> findFoos(FooSearchCriteria criteria, Integer maxResults, String[] sortBy) and that you have a FooSearcher class which uses a FooService to perform the actual searching. With EasyMock you could test that the FooSearcher uses the FooService as it should without needing to also test the actual FooService implementation. It is important in unit tests to isolate dependent collaborators so they can be tested independently. One thing I pretty much always forget when using EasyMock is that if you use any IArgumentMatchers in your expectations, then all the arguments must use an IArgumentMatcher. Going back to the FooSearcher example, you might start out with the following test (written in Groovy for convenience):

void testSearch() {
  def service = createMock(FooService)
  def searcher = new FooSearcher(fooService: service, maxAllowedResults: 10)
  def criteria = new FooSearchCriteria()
  def sortCriteria = ["bar", "baz"] as String[]
  def expectedResult = [new Foo(), new Foo()]
  expect(service.findFoos(criteria, 10, sortCriteria)).andReturn(expectedResult)
  replay service
  def result = searcher.search(criteria, "bar", "baz")
  assertSame expectedResult, result
  verify service
}

The above test fails with the following error message:

java.lang.AssertionError: 
  Unexpected method call findFoos(com.acme.FooSearchCriteria@ea443f, 10, [Ljava.lang.String;@e41d4a):
    findFoos(com.acme.FooSearchCriteria@ea443f, 10, [Ljava.lang.String;@268cc6): expected: 1, actual: 0
	at org.easymock.internal.MockInvocationHandler.invoke(MockInvocationHandler.java:29)
	at org.easymock.internal.ObjectMethodsFilter.invoke(ObjectMethodsFilter.java:45)
	at $Proxy0.findFoos(Unknown Source)
	at com.acme.FooSearcher.search(FooSearcher.java:19)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    ...

We expected a call to findFoos which takes a FooSearchCriteria, an integer, and a string array describing the sort conditions. But from the error message, EasyMock told us that the expected method was not called and so verification of the mock behavior failed. What happened? Well, basically the string array that was expected was not the string array actually passed as the argument. Look back at the stack trace and specifically the array arguments: the actual argument was [Ljava.lang.String;@e41d4a while the expected argument was [Ljava.lang.String;@268cc6. The FooSearcher.search method's signature is List<Foo> FooSearchCriteria criteria, String... sortBy) - the varargs that are passed to FooSearcher.search are getting packed into a new array when called and that new array is subsequently passed into the FooService which is what causes the difference between the expected and actual array arguments!

To make sure that arguments such as arrays and other complex objects are matched properly by the mock object, EasyMock provides IArgumentMatcher to compare the expected and actual arguments to method calls. Essentially, it is like performing a logical "assertEquals" on the arguments. One of the matchers EasyMock provides is obtained via the static aryEq method in the EasyMock class. So for example if you had a method that took a single array argument, you could make an expectation of mock behavior like this:

def myArray = ["foo", "bar", "baz"] as String[]
expect(someObject.someMethod(EasyMock.aryEq(myArray)).andReturn(anotherObject)

Here you tell EasyMock to expect a call to someMethod on someObject with myArray as the sole argument, and to return anotherObject. Cool, so let's try to fix the failing test above using EasyMock.aryEq (which was imported statically using import static):

void testSearch() {
  def service = createMock(FooService)
  def searcher = new FooSearcher(fooService: service, maxAllowedResults: 10)
  def criteria = new FooSearchCriteria()
  def sortCriteria = ["bar", "baz"] as String[]
  def expectedResult = [new Foo(), new Foo()]
  // Try to use EasyMock's aryEq() to ensure the expected array argument equals the actual argument...
  expect(service.findFoos(criteria, 10, aryEq(sortCriteria))).andReturn(expectedResult)
  replay service
  def result = searcher.search(criteria, "bar", "baz")
  assertSame expectedResult, result
  verify service
}

This test also fails with the following error message:

java.lang.IllegalStateException: 3 matchers expected, 1 recorded.
	at org.easymock.internal.ExpectedInvocation.createMissingMatchers(ExpectedInvocation.java:41)
	at org.easymock.internal.ExpectedInvocation.(ExpectedInvocation.java:33)
	at org.easymock.internal.ExpectedInvocation.(ExpectedInvocation.java:26)
	at org.easymock.internal.RecordState.invoke(RecordState.java:64)
	at org.easymock.internal.MockInvocationHandler.invoke(MockInvocationHandler.java:24)
	at org.easymock.internal.ObjectMethodsFilter.invoke(ObjectMethodsFilter.java:45)
	at $Proxy0.findFoos(Unknown Source)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    ...

Wait, shouldn't that have made EasyMock ensure that the supplied argument was verified using an IArgumentMatcher, specifically an ArrayEquals matcher? Well, sort of. And this is where I always forget what the "N matchers expected, M recorded" error message means and fumble around for a few minutes while I remember. In short, the rule is this:

If you use an argument matcher for one argument, you must use an argument matcher for all the arguments.

So in the above example, we recorded one matcher via the call to aryEq. Now EasyMock will expect an argument matcher for all the arguments in the expectation, and there are three arguments. Now this makes sense. We need to add argument matchers for the other arguments as well. So let's now fix the test:

void testSearch() {
  def service = createMock(FooService)
  def maxResults = 10
  def searcher = new FooSearcher(fooService: service, maxAllowedResults: maxResults)
  def criteria = new FooSearchCriteria()
  def sortCriteria = ["bar", "baz"] as String[]
  def expectedResult = [new Foo(), new Foo()]
  // If you define one matcher for an expected argument, you need to define them for all the arguments!
  expect(service.findFoos(isA(FooSearchCriteria), eq(maxResults), aryEq(sortCriteria))).andReturn(expectedResult)
  replay service
  def result = searcher.search(criteria, "bar", "baz")
  assertSame expectedResult, result
  verify service
}

Now the test passes as we expect it to. We used several other common types of argument matchers here via the static isA and eq argument matchers. The isA matcher ensures the argument is an instance of the specified class, while the eq matcher checks that the actual argument equals the expected argument via the normal Java equality check, i.e. expected.equals(actual). So in summary, if you ever receive the dreaded "N matchers expected, M recorded" error message from EasyMock, you know you need to ensure that all arguments to an expectation use a matcher. And, if you got this far and were dying to mention that if you're using Groovy to test Java code there are easier ways in Groovy to test than using a framework like EasyMock, you're right for the most part. There are still some things you cannot do when testing Java code using Groovy. I plan to go into that more in a future blog post.