Buy my House!

My apologies for posting something almost personal, but this is mostly as a note for myself.

If you live in the Austin in area and are looking for a good house, mine is for sale.

When to go dynamic

The most typical complaint I hear from Java developers about Groovy is, "I spent X hours trying to figure out this problem that would've been a compile time error in Java." And they're right. Very little compile time checking is done in Groovy. It can't be done because methods may be available at runtime that aren't resolvable at compile time. That's part of what it means to be a dynamic language.

Some developers seem to think using the optional types will save them. e.g.,

int foo (String bar) {
 return bar.size()
}

Looks good, right? Try running this script:

int foo (String bar) {
 return bar.size()
}
if(false) {
 String s = foo(123)
 println s
}
println "Done"

Go ahead. Run that script. No error. Types aren't checked at compile time. If we change false to true, we get a groovy.lang.MissingMethodException at runtime, but that's it. Your compiler can't save you here. Good unit tests will catch some errors if you use the optional types, but you have to know what the error is before you can test for it, so you've already spent the X hours trying to track it down.

What makes Java so good for enterprise work is the static types. Static types enforce a contract. Static types make it possible for Eclipse to take you to the exact method that will be invoked by a particular line in the source. If the method is on an interface, Eclipse can tell you all types that implement that interface method and take you to any implementation you choose immediately. This is extremely useful when you're trying to navigate a complex, unfamiliar system. While a human may be able to easily figure out what file to open, having a tool that can do it for you automatically allows your concentration to remain on what the code does and lets you work at a higher mental level of abstraction.

If I have to learn a new framework that someone has written, I'll get through it 10x faster if it's in Java. No/bad documentation? Not a problem, I'll just look at the code for that method. Whereas if I come upon an undocumented Groovy method, what do I do? Ugh, I have to grep through all of the source to figure out where it's defined, how it's used, yada yada. Not quick. Breaks my concentration.

Java is very good at making large systems manageable. However, the trade off is that
any system that has been under active development for more than 2 weeks quickly becomes a large system. There is nothing concise about Java. There are very few shortcuts. The simplicity of the language and the rigidity of types means you have to write more code and produce more classes to get things done and God help you if you want anything remotely flexible. Code that needs to do something even slightly dynamic can quickly become unreadable and strewn with all kinds of reflection objects, odd exceptions and other nastiness. Or worse. You could end up in XML hell.

Enter Groovy. Dynamic languages do best when there are conventions and consistent ways of doing things. Grails is proof of this. Controllers are in the controllers folder, services in the services folder, etc. Each class follows a certain arechtype and there are good idioms in place that imply what is going on. However, when you start writing plugins, or doing things outside of the normal scope of Grails, things can get messy fast.

Anytime you're coding in uncharted territory, consider going back to Java. Writing a plugin? Implement as much of it as you can in Java. Only go back to Groovy if the equivalent Java code gets too ugly or would be many times longer. Most of your plugin/framework/new invention's plumbing should be in Java. The plumbing is where you connect everything together, and it's important to verify that thingDoer is of type ThingDoer, and that all interceptors properly implement the ThingDoerInterceptor interface. You want your API to fail fast so your users don't end up with a NPE exception deep in your code that they have no hope of debugging.

Keep Groovy at the fringes, handling the nasty implementation details, and protected by static types and good assertions. Make sure your Groovy class implements an interface, or better yet, have a Java class implement the interface and wrap the Groovy implementation so you can jump to it in Eclipse. Use Java to provide enforce the type contracts and provide a well defined framework. Use Groovy to make the implementation readable.

Mock object are making your tests stupid

Mock objects were created because when you're writing unit tests (especially in a statically typed language), it can be a pain to create a subclass/implementations to use for your tests. You need a mock whenever the class you are testing depends on another class. You want to guarantee that changes to the other class don't break your tests for this class, because that would defeat one of the purposes of unit testing: isolation of the failure to a particular class/method. So you want an object that, whenever getTemperatureOutside is called, returns 32 degrees.

Sometimes you also want to make sure that the method you are testing causes some side effect. e.g., if the temperature outside is less than 32 degrees, it should call deployIceScraperNarwhals(). So, you want a method that records that deployIceScraperNarwhals() was called (but doesn't actually deploy the Narwhals) and something that checks that it actually was called, failing the test if it wasn't. Thus, the idea of verifying method calls was inextricably bound to the idea of providing fake methods to isolate behavior and every genius-pants writing a mock object framework decided that the verification was the most important part, to be emphasized throughout the documentation.

Then you came along, read the mock object documentation and proceed to go and write unit tests like this (mock object syntax is made up):

class UnderTest {
 int calculate(Foo foo,Bar bar) {
    int a = foo.getA()
    int b = bar.getB()
    return a + b
 }
}

class UnderTestTest {
  void testCalculate() {
     Foo foo = createMock(Foo).getA().andReturn(3)
     Bar bar = createMock(Bar).getB().andReturn(2)
     assertEquals(5,instance.calculate(foo,bar))
  }
}

Honestly, I'm looking for the stupid thing you did here, and I can't find it. The test passes, you didn't have to write MockFoo and MockBar classes, and all is right with the world. Until you decide to make an optimization:

class UnderTest {
 int calculate(Foo foo,Bar bar) {
    if(foo.getA() == bar.getB()) {
      return foo.getA() << 1 // a+b = a*2 = a left shifted 1 bit     
    }     
    int a = foo.getA()     
    int b = bar.getB()
     return a + b
 }
}

Ignoring the fact that this probably hurts performance instead of helping, lets rerun the test and see what we get (error message made up because I'm lazy): "Unexpected call to getA." That's right, you only told it to expect one call to getA, not two. You didn't change the result, you didn't remove an important side effect, in short, you did nothing that should break a test. Everything is still working perfectly. But it broke the test.

This is the part where I get to tell you you're an idiot. Instead of realizing that what you really want is a stub object, you decided that you must have written the test wrong so you rewrite it to expect between 1 and 2 calls to getA(). Because these mock object things can be tricky, you proceed to write all of your unit tests from then on by examining the source of the method you are testing, creating a mock for each dependency, adding a method call for each method call in the source, and basically rewriting the method in mock form. You idiot. You just wrote a test that confirms that the method was coded a particular way, not that the method behaves correctly.

Here's an example:

class OtherUnderTest {
 /**
  * @return a Map with a result entry, which is a message to the user.
  */
 Map deployNarhwals(Foo foo,Bar bar,Narwhals narwhals) {
    if( underTest.calculate(foo,bar) < 32 ) {
       narwhals.deploy()
       return [result: narwhals.getStatus()+' narwhals deployed']
    }
    return [result:'ok']
 }
}

class OtherUnderTestTest {
  void testDeployNarwhals() {
     Foo foo = createMock(Foo).getA().andReturn(3)
     Bar bar = createMock(Bar).getB().andReturn(2)
     Narwhals narwhals = createMock(Narwhals).getStatus().andReturn('Deadly')
     narwhals.deploy()
     Map result = instance.deployNarwhals(foo,bar,narwhals)
     assertEquals([result:'Deadly narwhals deployed'],result)
  }
}

You did so many things wrong here I'm going to have to make a list:

• You mocked the parameters, but didn't stub the internal dependency. See that instance of UnderTest in there? You're not testing it's calculate method, you're testing deployNarwhals, so you need to replace it with an instance that returns something like 31 so that you'll always be testing the condition (which should be a part of your API documentation) "if the temperature outside is less than 32 degrees, the narwhals will be deployed." Stupid.


• You verify that the side effect occurs, but you also couple your test to your implementation.What if I decide that the user doesn't need to know the Narwhal's status, I change the wording of the message, or make an extra call to getStatus()? Broken test. But the test shouldn't break just because your marketing department decided that 'released' was a more green term than 'deployed', or you cleaned up your code and change the number or order of non-side-effect-causing method calls.


• You check for equality on a MapDo you really care if there are extra keys in the Map? Probably not. Instead, check that all the key value pairs you expect are there.

This is how you should have written your test:

class OtherUnderTestTest {
  void testDeployNarwhals() {
     boolean deployed = false
     Narwhals narwhals = [
        getStatus: { return "Deadly" },
        deployNarwhals: {
          deployed = true
        }
     ] as Narwhals
     instance.setUnderTest([calculate:{ return 31 }] as UnderTest)
     Map result = instance.deployNarwhals(new Foo(),new Bar(),narwhals)
     assertTrue(deployed)
     assertNotNull(result.result)
  }
}

You could use a mock object framework for the Narwhals object, but you should configure it to only require the call to deployNarwhals, and not to fail when other methods are called. The above test will not fail unless the API contract is broken. I only assert that the expected side effect occurred, and that a non-null message was returned.

The problem is that you morons seem to think that more assertions == better test. That's simply not true. A good test covers as many cases as possible, but only asserts what is defined in the API contract. If you start asserting things that are not part of the API, like getA() is called, you make the test brittle. Even worse, someone could come along and see your assertion and think that getA() being called is part of the API and code accordingly! Now you've introduced a bug somewhere else in the code that your tests wont catch and could become a complete mess if it isn't caught quickly. The reality is you should assert only what you have to to catch a bug. Sometimes tests don't even need assertions, or it's not worth the effort to write them. It's enough that they show that the code under test ran without error, which is no small matter. Knowing that retrieveNarwhals(null,null,null) doesn't throw an exception can be very important.

Now, get back to work and try to stop writing brain dead tests. You thick ninny.

EDIT: Here's a good alternative: Mockito.

Kill the Singletons. (And those things you thought were Singletons too)

You guys think you're so smart. You read something about design patterns once, and now you can justify any code you write by showing the pattern it implements. Except you only remember the Singleton, and a few others. You probably remember the Factory, because you usually implement it as a Singleton. Maybe you remember the Facade and/or the Adapter pattern. You may even have some code somewhere that implements the Visitor pattern, probably where it was not at all appropriate. But Singleton is the one that everyone knows. Even those of you who never even read a poorly written article on design patterns. And you use it everywhere.

Or you think that you do. Probably you're using it as a Factory or a Locator. Or you have a class with static methods that you use to load resources or something like that. Those are singletons right? No, but you thought they were. There are even some clever and occasionally useful Singletonish things implemented using ThreadLocals, but that's for later. The point is, you've used Singletons as an excuse for what amounts to a bunch of global variables and methods. Bad programmer! No copy and paste for you!

The real problem is in how you're using them. Singletons can't (easily or at all) be proxied, decorated, replaced or mocked. You're losing all kinds of flexibility, without gaining any sort of benefit. This is your code:

public void doSomething() {
MyConfig config = MyConfig.getConfiguration();
config.doSomething();
// etc....
}

This is your code on inversion of control:

private MyConfig config;

public void doSomething() {
config.doSomething();
// etc....
}

public void setConfig(MyConfig config) {
this.config = config;
}

Of course, somewhere else you need to myClassThatDoSomething.setConfig(configInstance);, or have your container do it. This pattern is also called dependency injection, but unlike the Singleton, it's easy to get right. Don't call static lookup methods (or any lookup methods if you can avoid it) and make everything you need an object property. It's a simple change, but it gives you tons of flexibility. The only downside is that you have to learn how to use an IoC container. Fortunately, they're getting more idiot proof by the day, so with a little work, you can probably figure it out.

Now, before you go and delete every last one of your singletons, there are a few situations where IoC wont work. For IoC to work, you have to have control of the creation of the object, or at least be able to get a reference to it before it's used. A good example is logging. Logging has to be available before the container even initalizes, so you can't dependency inject logging components (easily). And sometimes, the thing you need to inject can't be managed by the container. For example, suppose you need access to the current HTTP request object, or the session object? Ignore for a second that your container can usually mange to inject special objects like these and recognize that what makes these object special is that, in a particular scope, there is only one of them at a time. By their very definition, there can only be one HTTP Request and one Session at a time. To have two requests, or two session doesn't make any sense. That means you actually have a good candidate for a singleton. A filter like this can be very helpful (some types & casts omitted for brevity):

private static ThreadLocal request = new ThreadLocal();

public static HttpRequest getRequest() {
return request.get();
}

public void doFilter(request,response,chain) {
request.set(request);
try {
 chain.doFilter(request,response);
} finally {
 request.clear();
}
}

That lets anything that's executed inside the filter call MyFilter.getRequest() to get the current HTTP request object, regardless of whether the framework was kind enough to pass it in. Even this should only be a last resort. There may be a legitimate case where someone needs to wrap, replace or mock the request, but your singleton code gets in the way. How will you unit test code that accesses the request in this way? There is no real HTTP request when you're running unit tests. Dependency injection solves a lot of problems.

Sometimes you can't avoid the Singleton, but considering the mess that you've made of things so far, maybe you should ask someone smarter than you next time you think you really need a Singleton. You probably don't. Now get back to work, and when you have some time, get the original (and best) design patterns book, read it, and stop abusing them. Design patterns are meant to describe good code, not magical pixie dust that you sprinkle on to make your crappy code suddenly good. Alas, that is another post.

JS Tips & Tricks

http://javascript.crockford.com, Secrets of the JavaScript Ninja and JavaScript: The Good Parts will cover almost everything you need to know about JavaScript. Still, there are a few tricks that I use almost every day that I feel are often underrated:

• && and || aren't your father's boolean operators. Thanks to JavaScript's notion of truth (anything but false, null, 0, undefined and the empty string), they don't have to return boolean value, and will not unless you coerce it into one with !!. That means you can use them inline as part of assignments and in parameter lists. e.g,

  function(someParam) {
   // provide a default value
   someParam = someParam || {};
   // ...
  }
  
  // guard against null objects
  var count = foo && foo.count || 0; // if foo is null, count == 0, else foo.count
  

• function scope:

  (function($){
  $('#foo').doSomething();
  // ...
  })(jQuery);

  The key here is that you're taking a global/wider scoped variable and making it a local variable, which allows you to rename/replace the original variable with little to no impact to your code. For example, suppose you need to use 2 versions of jQuery in your page. If you have the good sense to wrap all of your scripts in a function, you can include jQuery version A, then include your scripts that need version A, then include jQuery version B and your other scripts. Or if you wrote all of your scripts using $ as a reference to jQuery and then wanted to use Prototype in the same page.
  
  The other nice thing about wrapping your scripts is that any vars and function your define wont bleed into the window scope unless you specifically assign them to window. e.g., window.GLOBAL_FOO = 123;
  

Sorry for the short post. I have some more code heavy stuff I think I'm working on for next time, I promise.

Quit being lazy. lern2javascript noob

[Note: This is a blog post from a year ago, but I'm reviving it because I'm seeing developers and companies lose work because they don't have JavaScript experience. If you work on web applications, you need to learn JavaScript. In addition to this post, which targets Java developers, I've added links to good getting started resources at the end.]

Prologue: Why you need to learn JavaScript

For the foreseeable future (probably the next 5-10 years), the majority of software development will be done on web applications. Many of these will be ports of existing desktop applications or designed to replace such applications. Developing desktop-like applications on the web is going to require that Ajax thing you've been hearing about, something called DHTML, DOM, etc. That means you'll be using JavaScript.

We Java developers have been conditioned to flee at the first mention of JavaScript which has meant that it has long been the job of the 'creatives' to do the JavaScript work. That's not going to cut it anymore. While the work UX experts do is crucial to developing any application, they have different training, priorities and experiences. RIAs need solid technical developers who understand best practices, patterns, unit testing, etc. and can apply them to JavaScript.

One way Java developers try to avoid having to deal with JavaScript is through frameworks like JSF or GWT. There are certainly advantages to using a framework, but they are no substitute for being comfortable with JavaScript. Developing RIAs through a framework without knowing JavaScript is like using Hibernate without a solid understanding of SQL and relational databases. You may get by, but it wont be easy and it wont be pretty.

Hopefully you're now convinced that JavaScript is in your future. I want you to know that you don't have to be dragged into it kicking and screaming. It will be fun. You know those closure things that they're talking about putting in Java 7? JavaScript has always had them. Ever get tired of writing the same Java code over and over? JavaScript code is far shorter and less repetitive.

Differences: The Good, The Bad, and The Ugly

I'm going to focus on the immediately important differences for now. We'll pick up the more subtle ones as we go.

• JavaScript, like Java, has a C like syntax so you should feel pretty much at home. It has fewer keywords than Java, but adds a few new ones. The most important one is function, which we'll talk about more in the next chapter, but there's also var(declares a variable), with (to generally be avoided), and in (multiple uses).


• JavaScript is loosely (weak) typed. For a UI, that's a good thing, because most of the data you're working with is string data, so you don't have to declare String everywhere and if you need a string to occasionally be a number, it happens automatically. Every object has a boolean value of true except 0,the empty string and false. An undefined or null variable also evaluates to false, so you can check to see if an object has the method/property that you want like so:
  

  if(!foo.bar) {
   throw "foo must have bar";
   // you can throw anything to raise an error
  }
  

  Of course, you can do whatever you like if the object you were passed doesn't have a particular method.


• There are only Numbers in JavaScript. There is no distinction between int,float, double and long. Math.round, Math.floor and Math.ceil are there if you need them. The maximum value is 1.7976931348623157e+308 so don't worry too much about overflowing. You shouldn't be doing any heavy computation on the client anyways. If you try to do arithmetic with something that isn't a number, the result will be NaN (not a number). NaN and anything is NaN. That includes undefined variables:

  var foo = 1;
  foo + bar; // == NaN, since bar is undefined

• There is no char type. You can use either single or double quotes to delimit a string. 'f' is always the string "f". charCodeAt(index) on strings will give you the character code as a number.
  


• In addition to functions, objects and arrays are first class citizens (technically functions and arrays are also objects). You can define array literals using the [] syntax: var myArray = [1,2,3];. For objects you use {} and provide a list of name:value pairs: var myObj = { foo: "bar", baz: [1,2,3] }. Both array and object literals can span multiple lines. It's generally good form to break lines after a comma (if you must break lines):
  

  var foo = {
   bar: "baz", qux: 123,
   quxx: { a: 1, b: 2, c: 3}
  };

• Perhaps the most important JavaScript data type is the function. We wont get into it now, but you need to know that you can treat functions like any other variable. e.g.,
  

  var foo = function(a,b) {
   return a + b;
  };
  
  foo(1,2); // == 3

• When a function is called as a property of an object, it gets access to this. e.g.,

  var foo = new Object();
  foo.bar = function(a) {
   return a + this.b;
  };
  foo.b = 2;
  foo.bar(1); // == 3
  foo.bar(2); // == 4



• Note that while you can get put a reference to foo's bar function in a variable, it will no longer have access to foo via this.

  var bar = foo.bar;
  bar(2); // == NaN (not a number)

  Since this.b is undefined, 2 + undefined is NaN. You might be wondering why this.bar doesn't result in an error. Well, it's because this is always defined. Since JavaScript executes in the context of the browser window, the default this is the window. This is where all global variables live. Incidentally, you can reference the window explicitly with the window object.
  


• There is a difference in scoping in JavaScript as well. You're used to having block local variables. Well, in JavaScript variables are either global or function local. Blocks share their enclosing scope, so
  

  var foo;
  if(true) {
   foo = 1;
  }

  is the same as

  if(true) {
   var foo = 1;
  }

  foo will still be visible after the else block. If you fail to define a var inside a function, a global variable is created (or if it exists it is overwritten). e.g.,

  
  function() {
   foo = 1; // sets window.foo = 1
  }

  So, think carefully about scope when you declare and use variables.
  


• JavaScript is interpreted, which means that you don't even know 100% if a line of your script is valid until it actually runs. That makes unit testing crucial. Fortunately tools like JUnit, Javadoc, etc. all have JavaScript equivalents that will seem very familiar. There are also a host of development tools including Eclipse plugins, Aptana, IntelliJ support, etc. to help you along.
  


• Lastly, you should know that JavaScript inheritance is prototypal. It is fully possible to achieve class based inheritance, which we will do with the help of a library called Prototype, but the prototypal nature of JavaScript gives us some interesting options which we will explore later.

Your Environment

We're Java developers, so we know the power of a good IDE. Eclipse, NetBeans and IntelliJ all have decent JavaScript support. There are a variety of plug-ins for Eclipse (I use JSEclipse), but I'm going to tell you right now that none of them will give you the code completion that you're used to. It's simply not possible with a dynamic, weakly typed language. You'll have to learn APIs the old fashioned way, by reading the docs and using them.

Fortunately, JavaScript gives you an amazing debugging and exploratory tool that you have never had and likely will never have with Java. Its name is Firebug. Go ahead and install it. Done? You need to restart Firefox. OK. Good. Now see in the bottom right corner? Click it. This is Firebug. It does a lot of things, but for now we're just going to mess around with the 'command line'. Do the following:

1. Click the in the bottom right corner of Firebug.
2. Paste this into the command line and press Ctrl+Enter or click 'Run':
   

   $('demoSteps').childElements().each(function(item,i) {
    item.insert("("+i+")");
   });
   

OK, it's not the most impressive example, but you did just execute code without having to reload the page or anything. Here we're making use of a library called Prototype. Bookmark the API immediately. What the above code does is call a function named '$' (yes, that's a valid variable name in JavaScript) with the argument 'demoSteps'. When $ is given a string, it looks for the element in the HTML with id="demoSteps". We get the child elements and iterate over them, calling the anonymous function we defined there on each element, along with it's index. We then append the index in parentheses to the body of each element.

The equivalent JavaScript without Prototype is a lot longer. You could start learning JavaScript without any libraries, but then you'd quickly get caught up in fixing bugs and writing the same code over an over. Fixing bugs doesn't give you a good appreciation for a language, nor does clunky repetitive code. In any serious web project you will use Prototype or a similar library, so it doesn't hurt to know it. After you're comfortable, we will delve deeper into the JavaScript language and you'll learn what Prototype hides from you.

Before we go, drag this onto your bookmarks toolbar: Insert Prototype. Now you can go to any web page, click that bookmarklet, pop open the console and start using Prototype to play. For homework, explore the Prototype API, especially the utility functions and the Enumerable methods. Try to write as many snippets using the API as you can.

Resources

• http://javascript.crockford.com/ Read these essays. They're all pretty short, but they are essential. Also, get a copy of Crockford's book.
  
• http://jquery.com/ jQuery is very popular. It has tons of plug-ins, with new ones popping up everyday. You will need it.
  

You don't know what a controller is for, do you?

This is my second post in what I'm going to call the "You deserve verbal abuse because your code is dumb" series. These are things that frustrate me greatly, like creating spaghetti code because you don't understand CSS. (In fairness, my solution may not be obvious, but there is no excuse for highly fragmented spaghetti code in the view layer; someone should have come up with something better).

Last time I talked about how you can use CSS to get rid of most of that if/else logic you have in your page templates. Today, I'm going to explain controllers to you. That's the C in MVC. You should know this stuff. The controller is the thing that receives the HTTP request and decides what to do with it. Most frameworks will map URLs to different controller classes and methods. The controller is responsible for picking the view to render and loading the right data based on the request (and maybe the URL).

Most of you seem to think that it ends there, and that it's OK to take whatever convulted data structure your service layer spits out and pass that right on to the view. Lean in really close so I can hit you. No! Bad developer! The whole reason that we moved away from CGI/Servlets is because mixing the processing code and the view markup is a bad idea. Unfortunately, you Philistines didn't get it, so you invented crap like Struts that just puts a layer of abstraction around HTML code and then get yourselves back into the same mess.

This is what your templates look like:

<div id="${result.product.productInfo.productId.toString()}">
<h4> ${result.product.productInfo.productName.getLocalizedString(request.client.language)} </h4>
etc....

and here is how they should look:

<div id="${productId}">
<h4> ${productName} </h4>
etc....

The controller is responsible for getting and creating a model that makes sense for the view. Even the most technically averse designer can look at a view with a smart controller and figure out what's going on and how to edit it. It's when the expressions start to get long and the if/else logic creeps in that they start to get confused and scared. So, have pity on the designers, keep the logic in the controller. If you're careful, maybe someday the designers can get in there and actually change the templates themselves, instead of having to file a bug report for every single HTML change. Wouldn't that be nice?