Posts Tagged ‘ Java ’

Flexible JUnit assertions with assertThat()

Over time I’ve found I end up with a gazillion permutation of assertion methods in JUnit: assertEquals, assertNotEquals, assertStringContains, assertArraysEqual, assertInRange, assertIn, etc.

Here’s a nicer way. jMock contains a constraint library for specifying precise expectations on mocks that can be reused in your own assertion method (and that’s the last time I’m going to mention mocks today, I promise – despite the frequent references to the jMock library).

By making a simple JUnit assertion method that takes a Constraint, it provides a replacement for all the other assert methods.

I call mine assertThat() because I think it reads well. Combined with the jMock syntactic sugar, you can use it like this:

assertThat(something, eq("Hello"));
assertThat(something, eq(true));
assertThat(something, isA(Color.class));
assertThat(something, contains("World"));
assertThat(something, same(Food.CHEESE));
assertThat(something, NULL);
assertThat(something, NOT_NULL);

Okay, that’s nice but nothing radical. A bunch of assert methods have been replaced with different methods that return constraint objects. But there’s more…

h3. Combining constraints

Constraints can be chained making it possible to combine them in different permutations. For instance, for virtually every assertion I do, I usually find that I need to test the negative equivalent at some point:

assertThat(something, not(eq("Hello")));
assertThat(something, not(contains("Cheese")));

Or maybe combinations of assertions:

assertThat(something, or(contains("color"), contains("colour")));

h3. Readable failure messages

The previous example can be written using the vanilla JUnit assert methods like this:

assertTrue(something.indexOf("color") > -1 || something.indexOf("colour") > -1);

Fine, the constraint based one is easier to read. But the real beauty is the failure message.

The vanilla JUnit assert fails with:


Useless! Means you have to put an explicit error message in the assertion:

assertTrue(something.indexOf("color") > -1 || something.indexOf("colour") > -1,
"Expected a string containing 'color' or 'colour'");

But the jMock constraint objects are self describing. So with this assertion:

assertThat(something, or(contains("color"), contains("colour")));

I get this useful failure message, for free:

Expected: (a string containing "color" or a string containing "colour")
but got : hello world

h3. Implementing it

The simplest way is to grab jMock and create your own base test class that extends MockObjectTestCase. This brings in convenience methods for free (I’m still not talking about mocks, honest). If you don’t want to extend this class, you can easily reimplement these methods yourself – it’s no biggie.

import org.jmock.MockObjectTestCase;
import org.jmock.core.Constraint;

public abstract class MyTestCase extends MockObjectTestCase {

protected void assertThat(Object something, Constraint matches) {
if (!matches.eval(something)) {
StringBuffer message = new StringBuffer("nExpected: ");
message.append("nbut got : ").append(something).append('n');


Now ensure all your test cases extend this instead of junit.framework.TestCase and you’re done.

h4. Defining custom constraints

Creating new constraints is easy. Let’s say I want something like:

assertThat(something, between(10, 20));

To do that I need to create a method that returns a Constraint object, requiring two methods; eval() for performing the actual assertion, and describeTo() for the self describing error message. This is something that can live in the base test class.

public Constraint between(final int min, final int max) {
return new Constraint() {
public boolean eval(Object object) {
if (!object instanceof Integer) {
return false;
int value = ((Integer)object).intValue();
return value > min && value < max;
public StringBuffer describeTo(StringBuffer buffer) {
return buffer.append("an int between ").append(min).append(" and ").append(max);

This can be combined with other constraints and still generate decent failure messages.

assertThat(something, or(eq(50), between(10, 20));
Expected: (50 or an int between 10 and 20)
but got : 43

In practice I find I only need to create a few of these constraints as the different combinations gives me nearly everything I need.

More about this in the jMock documentation.

h4. Summary

Since using this one assert method I’ve found my tests to be much easier to understand because of lack of noise and I’ve spent a lot less time creating ‘yet another assertion’ method for specific cases. And in most cases I never need to write a custom failure message as the failures are self describing.

h4. Updates

  1. The matchers from jMock have been pulled out into a new project, Hamcrest.
  2. A follow up to this post shows some creative uses of matchers, and talks a bit about when you shouldn’t use them.
  3. JUnit 4.4 now comes with assertThat()!

SiteMesh and Content Management @ O’Reilly OpenSource Conference

I’m talking at the O’Reilly OpenSource Conference (OSCON) – Wednesday Aug 3, Portland, Oregon.

Come and say hi.

A problem faced in every web application is how to separate style from content. SiteMesh is a framework that provides an elegant solution to this, resulting in a clean separation that is straightforward to work with, complements other web frameworks, and is easily applied to existing applications.

The first part of this session introduces SiteMesh, including an overview of the architecture and patterns, comparisons with other approaches, and how it can complement existing web frameworks (such as WebWork, Spring, and Struts).

The second part of this session demonstrates how SiteMesh can be blended with other technologies to form the foundation of a rich content management system that distinguishes between the specialized roles of users, their skills, and the most suitable tools. Content writers can use a word processor, web designers can use a WYSIWYG web development tool, and developers can use their IDE.

Allowing these different roles and tools to come together to produce one website is a trivial task with SiteMesh–allowing content management to be easily introduced to existing applications.

Finally, some of the advanced features of SiteMesh are discussed, such as real world tips and tricks, how to create custom strategies for which look and feel to apply, assembling pages from components and building portal style applications.

And for the first time, new features in SiteMesh 3 will be demonstrated, including extending the HTML processor, using it outside of SiteMesh, and offline support.

XStream 1.1.2 released. Java 5 Enums, JavaBeans, field aliasing, StAX, and more…

New features:

  • Java 5 Enum support.
  • JavaBeanConverter for serialization using getters and setters.
  • Aliasing of fields.
  • StAX integration, with namespaces.
  • Improved support on JDK 1.3 and IBM JDK.


Full download:

Jar only:

XStream 1.1.1 released

I’m pleased to announce the release of XStream 1.1.1 – the powerful, yet easy to use Java to XML serialization library.

Some of the improvements in this release:

  • Converters can be registered with a priority, allowing more generic filters to handle classes that don’t have more specific converters.
  • Converters can now access underlying HierarchicalStreamReader/Writer implementations to make implementation specific calls.
  • Improved support for classes using ObjectInputFields and ObjectInputValidation to follow the serialization specification.
  • Default ClassLoader may be changed using XStream.setClassLoader().
  • Loads of bugfixes and performance enhancements.

Full change log:

Accessing generic type information at runtime

A common misconception about generics in Java 5 is that you can’t access them at runtime.

What you can’t find out at runtime is which generic type is associated with an instance of an object. However you can use reflection to look at which types have been staticly associated with a member of a class.

public class GenericsTest extends TestCase {

class Thing {
public Map stuff;

public void test() throws Exception {
Field field = Thing.class.getField("stuff");
ParameterizedType type = (ParameterizedType) field.getGenericType();
assertEquals(Map.class, type.getRawType());
assertEquals(String.class, type.getActualTypeArguments()[0]);
assertEquals(Integer.class, type.getActualTypeArguments()[1]);


Just wanted to clear that up.

(This is something that I’ll probably exploit in XStream for J5 users to further simplify the XML.)

XStream 1.1 released

I’m pleased to announce the release of XStream 1.1.

New features include:

  • Improved support for serializing objects following the Java Serialization Specification:
    • Calls custom serialization methods, readObject(), writeObject(), readResolve() and writeReplace() in class, if defined.
    • Supports ObjectInputStream.getFields() and ObjectOutputStream.putFields() in custom serialization.
  • Provides implementations of ObjectInputStream and ObjectOutputStream, allowing drop in replacements for standard serialization,
    including support for streams of objects. [More…]
  • Reads and writes directly to most XML Java APIs: DOM, DOM4J, JDOM, XOM, Electric XML, StAX, Trax (write only), SAX (write only).

View the complete change log and

JUnit tip: Setting the default timezone with a TestDecorator

A problem I was finding when testing XStream is that many of the tests were timezone dependent. Initially I had some code in each setUp()/tearDown() method to set the default timezone and reset it afterwards.

This lead to a lot of duplication. Putting the common code in a super class was an option but this lead to a fragile base class.

Using composition allows this commonality to be put in one case and applied to the relevant test cases. This gets out of the ‘single inheritance’ issue.

JUnit provides an (often overlooked) decorator class to help with this. Here’s my TimeZoneTestSuite:

  public class TimeZoneTestSuite extends TestDecorator {

private final TimeZone timeZone;
private final TimeZone originalTimeZone;

public TimeZoneTestSuite(String timeZone, Test test) {
this.timeZone = TimeZone.getTimeZone(timeZone);
this.originalTimeZone = TimeZone.getDefault();

public void run(TestResult testResult) {
try {
} finally {
TimeZone.setDefault(originalTimeZone); // cleanup


To use it, you need to override the default test suite behavior by adding a method to your TestCase:

  public class MyTest extends TestCase {
public static Test suite() {
Test result = new TestSuite(MyTest.class); // default behavior
result = new TimeZoneTestSuite("EST", result); // ensure it runs in EST timezone
return result;

TestDecorators are a very powerful feature of JUnit – don’t forget about them.

XStream: how to serialize objects to non XML formats

As you know, XStream makes it easy to serialize objects to XML:

Person person = ...;





I often use this approach whilst debugging to dump out the contents of an object. It works, but my eyes just aren’t that good at parsing XML.

By creating an alternative writer implementation, XStream can be used to serialize objects in other formats:

Person person = ...;
xstream.marshal(stuff, new AnAlternativeWriter(out));

Producing the slightly more digestible:

firstName = Joe
lastName = Walnes
areaCode = 123
number = 433535
areaCode = 4545
number = 4534

To gain roundtrip serialization/deserialization support in alternative formats to XML, you need to provide your own implementations of both HierarchicalStreamWriter and HierarchicalStreamReader.

Looking back at the SiteMesh HTML parser

Before talking about how the new SiteMesh HTML processor works (to be released in SiteMesh 3), I thought I’d write a bit about how the current parser has evolved since it’s first attempt in 1999 – purely in the interest of nostalgia.

The original version used a bunch of regular expressions to extract the necessary chunks of text from the document. This was easy to get running, but very error prone as the matches had no context about where they were in a document. For example, a <title> element in a <head> block is very important to SiteMesh, however sometimes they appear elsewhere, such as in a comment, <script> or <xml> block.

This was dumped, in favour of a DOM based parser, which initially used JTidy to convert HTML to XHTML so it could be traversed as a standard DOM tree. Much nicer, but very slooow. Too slow, so I switched to OpenXML, an XML parser that was tolerant to nasty HTML, giving a slight boost to performance. I was much happier with OpenXML – even though it still added a fair amount of overhead and rewrote bits of HTML that I didn’t want it to.

Annoyingly, not long after that, the OpenXML project merged with the IBM XML4J parser project, rebranded itself as the mighty Apache Xerces and promptly dropped support for HTML parsing. So now I was dependant on a library that no longer existed.

By this time, SiteMesh had been open-sourced, and along came Victor Salaman, who was the third user to discover it (after Mike Cannon-Brookes and Joseph Ottinger). He saw the potential but hated the parser. About three hours later, he’d produced his own version that used low-level string manipulation. It wasn’t pretty, but it went like the clappers – twelve times faster than the OpenXML one, with the bonus feature of not rewriting great chunks of the document. This brought SiteMesh into the mainstream as it was now ready for use on high-traffic sites. 1.0 was released.

This parser really is the core of SiteMesh. It’s been our friend thanks to its speed and reliability. It’s been our enemy because of it’s awkwardness to understand and change. For a couple of years it remained barely untouched, except when we occasionally poked at it from afar with a long pointy stick for the odd change. Three years later, Chris Miller and Hani Suleiman took the plunge and gave its guts an overhaul – making it six times faster! Very brave.

Despite its awkwardness, it proudly lived on and is still the primary ingredient of SiteMesh today. It’s even been ported to VB.Net!

I’ve kept my eye on other HTML parsers, such as HotSAX, NekoHTML and TagSoup, always with the intention of implementing an easier to maintain parser, but I just couldn’t get the performance to be anything like what Victor, Chris and Hani achieved.

The problem is that most HTML parsers try to represent an HTML document as tree of nodes, like XML. This makes sense as that’s what HTML is meant to be, however, to do this, every single tag in a document must be analysed and balanced accordingly. This is hard, error-prone and adds a lot of overhead.

There’s another approach though. The new parser focusses on ease-of-use and ability to customize, without compromising on performance and robustness. I hope you’ll like it…

Update: Sorry, I forget to mention Hani in the original posting of this. how could I forget!

The road ahead for SiteMesh 3

Here’s an update of what’s in store for the upcoming SiteMesh releases and how they benefit you.

Firstly, there are a number of accumulated bugs that we’re steadily working our way through. The recent 2.1 and 2.2 releases have been mostly bugfixes, and this will continue for the 2.x series, including those related to using MVC frameworks such as Struts and WebWork.

Meanwhile, SiteMesh 3 has been brewing. It’s been four years since SiteMesh was first open-sourced (it existed for two years before that as closed-source) and in that time it hasn’t really changed significantly. SiteMesh 3 is going to see the largest set of improvements since it was initially released.

h3. Flexible HTML processing

The core of SiteMesh is based around an HTML parser that is very fast and tolerant to badly formed HTML, however at the cost of being extremely hard to extend.

SiteMesh 3 will contain a new parser, which is easy to customize, without compromising on performance and tolerance to malformed HTML. This will allow extensions to be written that can:

* Extract user-defined properties from the page beyond the predefined ones from <title>, <meta>, <content>, etc.
* Remove blocks of content from the page.
* Transform HTML as the page is parsed.

SiteMesh will come bundled with extensions for popular tasks and it will be trivial to add your own. More on this in a follow-up entry.

h3. Improved Velocity integration

This follows on from some work done by Atlassian and will allow a page to be generated using the Velocity API as an alternative to calling Servlet
RequestDispatchers and the Filter.

This offers significant performance improvements for applications that don’t use JSP and allows more of SiteMesh to be used in environments outside of the Servlet container, which leads nicely on to the next feature.

h3. Offline support with StaticMesh

There has been a lot of demand for using SiteMesh to generate web-sites in an offline manner. A common case for this is a simpler alternative to DocBook style tools, allowing documents to be authored in standard HTML capable word-processing tools (such as MS Word, OpenOffice and Mozilla Composer), giving you the full capabilities of a rich-text word-processor and without the need to learn a special markup/schema.

SiteMesh can then process these raw HTML files and generated another set of static HTML files with the appropriate presentation and navigation added.

Building upon the extended HTML processing capabilities, it will also be possible to do things like generate a table of contents, footnotes, and diagrams from inline syntax.

There have been at least three seperate incarnations of StaticMesh appear over the last few years. We hope to bring the best bits from each of these into the final version.

StaticMesh will have a simple API for configuration, bundled with a command-line wrapper and Ant task.

h2. Backwards compatability

Just to ease your minds, you’re not going to have to rewrite your applications to use SiteMesh 3. Great effort will be taken to ensure that backwards compatability is preserved. The library will have more features, but at the same time a lot of the old stuff can be simplified. Dependencies will be minimized and optional – for example, you will only need velocity.jar if you’re actually using the Velocity stuff.

I’ll be posting more information later.

Watch this space…