User Manual

Croquet is all about configuration. Once it is properly configured, it should “just work.”

There are 3 steps to configuring Croquet:

  1. Configuring the application’s YAML file.
  2. Building the Croquet (or CroquetTester) object using the CroquetBuilder
  3. Adding any additional modules to the Croquet object created in step 2

With these 3 steps you can configure every aspect of Croquet. However, with sane defaults Croquet aims to require as little configuration as possible.

The following sections will explain all the configuration options in detail. If all of this scares you, look at croquet-example and see the Getting Started section of this guide.

Creating an Application Specific Configuration File

Application specific configuration files can easily be created by extending the Settings class. Properties are added using the (not very intuitive) @JsonProperty annotation. For example, to add a new setting called server you would simply add the following code to your settings class:

private String server;

public String getServer() {
    return server;

public void setServer(final String server) {
    this.server = server;

Croquet takes care of parsing the configuration file and using the getServer method you can access this value in your code. If you need to ensure the server value is specified in the configuration file, then add mark it as required: @JsonProperty(value = "server", required = true).

Configuring Wicket

Wicket is configured by the configuration file and through code using the CroquetBuilder class. The following aspects of Wicket can be configured via the configuration file:

  • CSS Resources (css_resources)
  • JavaScript Resources (js_resources)
  • Development vs Deployment

The following aspects of Wicket can be configured through the CroquetBuilder class:

  • Home page
  • Login page
  • Exception page
  • WebApplication class
  • Page mounts
  • Resources (both CSS & JavaScript can also be configured through CroquetBuilder)

Basic Configuration

The only required setting for Wicket is the home page class. Without this being set, CroquetBuilder cannot build a Croquet object. The Wicket home page is set via the setHomePageClass(Class<? extends WebPage>) method of the CroquetBuilder.

An exception page can be set to override Wicket’s default page using the setExceptionPageClass(Class<? extends WebPage>) method. (Note: exception pages are NOT set when in development mode as Wicket’s built-in exceptions pages are quite helpful.)

Creating an Authenticated Web Application

By default Croquet uses the CroquetApplication class as the Wicket WebApplication class. CroquetApplication extends AuthenticatedWebApplication making it easy to create an authenticated application with Croquet. To do so you need to override the getWebSessionClass() method of CroquetApplication to return a properly implemented AbstractAuthenticatedWebSession class. (More information on authenticated sessions can be found here.) Then set this new WebApplication class via the CroquetBuilder‘s setWebApplicationClass(final Class<? extends CroquetApplication>) method. You’ll also want to set the login page via the setLoginPageClass(Class<? extends WebPage>) method, otherwise it will default to the same page as the home page.

Configuring Resources

Resources can be configured via either the configuration file or via the CroquetBuilder class. CSS resources are set via the css_resource property in the YAML file. JavaScript resources are set via the js_resources property in the YAML file. Both local and hosted files can be specified as resources.

When specifying hosted resources, prefix them with // to ensure compatibility with http and https.

Resources can also be added via the CroquetBuilder class’s addResource(final String path, final Class<? extends IResource> resource) method. Because the second parameter of this method is a Class that extends IResource, any type of resource can be added.

Fine Grain Control

Normally you will want to set Croquet into either development mode or deployment mode and forget about the details. However, in some cases it can be useful to have more fine grain control over the different aspects of development vs deployment mode. Croquet enables this through a series of settings controlled by the YAML file:

  • minify_resources: false in development mode
  • strip_wicket_tags: false in development mode
  • stateless_checker: true in development mode
  • wicket_debug_toolbar: true in development mode

To override the default, simply specify the setting in the YAML file. Be careful as various configurations are a bit hacky.

Configuring Jetty

Jetty is configured via the application’s YAML file. Jetty only has one configuration option: the port it listens for connections on.

By default Jetty is configured with Wicket’s Jetty9WebSocketFilter, so you can use Web Sockets in Croquet. Jetty is also configured with a Guice and a Hibernate filter. Hibernate sessions are created with every request (when a database is configured). Jetty is also configured so that you will never see that annoying JSESSIONID parameter in any of your URLs.

If any of the Jetty configuration options do not meet your needs, they can be changed by overriding the configureJetty(final int port) method in the Croquet class.

We plan on adding additional configurations for Jetty. Please raise an issue for those you’d like to see added first.

Configuring Hibernate

Hibernate is used in Croquet as the JPA provider, and is setup to be as transparent as possible to the developer. It can be configured via either a persistence.xml file or via the Croquet YAML file, but not both. This makes it easy to transfer existing applications that might already have a persistence.xml file. If you’re starting from scratch though, it’s recommended that the Croquet YAML file be used so configurations are in as few places as possible.

Even though EntityManager does NOT implement Serializable, Croquet wraps the EntityManager in a proxy object that does implement Serializable. What this means is that you should NOT mark EntityManager fields with @Inject or transient! If you’re using FindBugs (which you should be), you’ll need to add the @edu.umd.cs.findbugs.annotations.SuppressWarnings("SE_BAD_FIELD") annotation to the field.

Croquet uses the Tomcat JDBC Connection Pool to provide connections to Hibernate. This connection pool implementation is more performant than the one that comes with Hibernate.

Configuring Logback

Logback is used for logging in Croquet. If no logging section is specified in the configuration file, then console logging is enabled using the format string: %-5level %date{ISO8601} %c:  %m%n.

You can override this default by specifying a logging section with 3 subsections:

  • loggers: specifies a list of loggers and their levels
  • file: specifies the configuration for logging to a file
  • console: specifies the configuration for logging to the console (enabled by default)

An example log configuration is shown below:

        "com.metrink.croquet": DEBUG
        "org.hibernate": WARN

        enabled: true
        currentLogFilename: ./croquet.log
        archivedLogFilenamePattern: ./croquet-%d.log.gz
        archiveFileCount: 5

        enabled: false

Adding Guice Modules

Guice is weaved throughout Croquet. There are very few things that are instantiated inside of Croquet without using Guice, and this should be carried through your application as well. With Croquet, Guice constructs every page of your application. This means you can and should inject all dependencies into the constructor of each page.

Note: Avoid field injection at all costs! It makes things MUCH harder to unit test. With Croquet, Guice is constructing every page, so there is no reason to use field injection. (See exceptions in the Overview section.)

Croquet will only accept two types of page constructors:

  1. Constructors with only dependencies that are @Injected.
  2. Constructors with dependencies that are @Injected and a PageParameters parameter.

Because of this, parameters that must be passed from page-to-page should be done via parameters (with the exception of sensitive information). This not only makes your application easier to bookmark (all the needed parameters for a page are in the URL), but it also severely reduces the size of the session, reducing the overall memory of your application. This does come at the cost of having to strictly verify all page parameters as they might have been changed/set by a malicious users. We think the trade-off is worth it which is why passing objects to pages in Croquet is prohibited.

Note: You can always store objects in the session; however, this comes at a larger memory cost.

Adding Managed Modules

Managed modules are modules that are started and stopped when Jetty starts and stops. These modules are very useful for dependencies that need to be started and stopped. Managed modules are added to Croquet via the addManagedModule(final Class<? extends ManagedModule> module) method. Settings (or other dependencies) should be bound with Guice and injected into the class.

Testing Croquet Applications

Unit tests are an integral part of good application development. However, web applications are often difficult to unit tests. Croquet attempts to make this easier by providing a CroquetTester class. This class configures a WicketTester instance using the same configuration as your application. To create a CroquetTester simply call the buildTester() method of CroquetBuilder instead of the build() method. To then obtain the WicketTester instance, call the getTester() method of the CroquetTester class. An example of these steps, taken from croquet-examples is shown below:

// create the croquet tester object through the builder
final CroquetTester<CrmSettings> croquetTester =
        CroquetBuilder.create(CrmSettings.class, new String[] { "application.yml" })
                      .addPageMount("/people", PeoplePage.class)
                      .addPageMount("/company", CompanyPage.class)
                      .addHealthCheck("/statuscheck", HealthCheck.class)

// get the custom settings for the application
final CrmSettings settings = croquetTester.getSettings();

// add in our Guice module
croquetTester.addGuiceModule(new CrmModule(settings));

// add in a managed module

// get the tester
tester = croquetTester.getTester();

Using the WicketTester you can easily ensure that your page will load:

public void test() {


For more information on using WicketTester see the Wicket documentation.

There is a known bug with the CroquetTester when using a persistence.xml file. The problem arises because a single instance of an EntityManagerFactoryRegistry is kept across unit tests. When a second unit test is run, the EntityManagerFactory is registered twice causing an issue. Using the YAML file does not have this problem. If you have a solution to this problem, we welcome all pull requests.