This section discusses how to setup and configure a Click web application and covers the following topics:

  1. Servlet Configuration - how to setup the ClickServlet
  2. Application Configuration - how to configure the Click application descriptor
  3. Auto Deployed Files - automatically deployed Click files


The Click configuration files include:
Click application configuration files
  • WEB-INF/click.xml   -   Application Configuration (required)
  • WEB-INF/web.xml   -   Servlet Configuration (required)

1.  Servlet Configuration

For a Click web application to function the ClickServlet must be configured in the web application's /WEB-INF/web.xml file. A basic web application which maps all *.htm requests to a ClickServlet is provided below.


1.1  Servlet Mapping

By convention all Click page templates should have a .htm extension, and the ClickServlet should be mapped to process all *.htm URL requests. With this convention you have all the static HTML pages use a .html extension and they will not be processed as Click pages.

1.2  Load On Startup

Note you should always set load-on-startup element to be 0 so the servlet is initialized when the server is started. This will prevent any delay for the first client which uses the application.

The ClickServlet performs as much work as possible at startup to improve performance later on. The Click start up and caching strategy is configured with the Click application mode element in the "click.xml" config file, covered next.

2.  Application Configuration

The heart of a Click application is the click.xml configuration file. This file specifies the application pages, headers, the format object and the applications mode.

By default the ClickServlet will attempt to load the application configuration file using the path:   /WEB-INF/click.xml

If this file is not found under the WEB-INF directory, then ClickServlet will attempt to load it from the classpath as /click.xml.

See Click DTD for the click-app XML definition.

A complete Click configuration example is available here which can be used as a quick reference when configuring Click.

A basic Click app config file is provided below:


  <pages package=""/>
  <mode value="profile"/>

An example of an advanced config file is:

<click-app charset="UTF-8" locale="de"> 

  <pages package="">
    <page path="index.htm" classname="Home"/>

  <pages package=""/>

  <format classname="com.mycorp.util.Format"/>
  <mode value="profile"/>
  <log-service classname=""/>
The rest of this chapter cover Click configuration in detail.

2.1  Click App

The root click-app element defines two application localization attributes charset and locale.
<!ELEMENT click-app (pages*, headers?, format?, mode?, controls?, 
                     file-upload-service?, log-service?, template-service?)>
  <!ATTLIST click-app charset CDATA #IMPLIED>
  <!ATTLIST click-app locale CDATA #IMPLIED>
The charset attribute defines the character encoding set for: The locale attribute defines the default application Locale. If this value is defined it will override Locale returned by the request. Please see the Context getLocale() for details.

For example the folliwing configuration sets the application character set to UTF-8 and the default Locale as German (de):

<click-app charset="UTF-8" locale="de"> 

2.2  Pages

The first child element of the click-app is the mandatory pages element which defines the list of Click pages.
<!ELEMENT pages (page*)> 
   <!ATTLIST pages package CDATA #IMPLIED>
   <!ATTLIST pages automapping (true|false) "true"> 
   <!ATTLIST pages autobinding (true|false) "true"> 
The pages element can specify a default package name which is prepended to the classname of any pages defined.

The pages element also defines the automapping attribute which is discussed in the Page Automapping topic.

2.2.1  Multiple Pages Packages

Click can support multiple pages elements to enable the automapping of multiple packages.

  <pages package=""/>

  <pages package=""/>

With multiple pages elements, pages are loaded in the order of the page elements, with manual page elements being loaded before automapped pages. Once a page template has been mapped to a Page class it will not be replaced by a subsequent potential match. So pages elements at the top take priority over lower pages elements.

2.3  Page

The page element defines the Click application pages.
<!ELEMENT page (header*)>
   <!ATTLIST page classname CDATA #REQUIRED> 
Each page path must be unique, as the Click application maps HTTP requests to the page paths.

The Click application will create a new Page instance for the given request using the configured page classname. All pages must subclass Page and provide a public no arguments constructor, so they can be instantiated.

Pages can also define header values which are discussed in the next topic.

When the Click application starts up it will check all the page definitions. If there is a critical configuration error the ClickSerlvet will log an ERROR message and throw an UnavailableException. If this occurs the click application will be permanently unavailable until the error is fixed and the web app is restarted.

2.3.1  Page Automapping

Page automapping will automatically configure application pages using a simple set of rules. This enables you to greatly streamline your configuration file as you only need to define pages which don't fit the automapping rules.

Automapping will attempt to associate each page template (*.htm) and JSP file in the web application (excluding those under the WEB-INF and click directories) to a Page class. Automapped pages are loaded after the manually defined pages are loaded, and manually defined pages takes preference. When automapping is enabled the Click application will log the page mappings when in debug or trace mode.

For example given a page path to class mapping:

index.htm                     =>
search.htm                    =>
contacts/contacts.htm         =>
security/login.htm            =>
security/logout.htm           =>
security/change-password.htm  =>
This could be configured manually by setting the automapping attribute to "false" and using the package prefix, for example:
  <pages package="" automapping="false">
    <page path="index.htm"                    classname="Home"/>
    <page path="search.htm"                   classname="Search"/>
    <page path="contacts/contacts.htm"        classname="contacts.Contacts"/>
    <page path="security/login.htm"           classname="security.Login"/>
    <page path="security/logout.htm"          classname="security.Logout"/>    
    <page path="security/change-password.htm" classname="security.ChangePassword"/>    
Using automapping you only need to define the Home page which doesn't automatically map to index.html.
  <pages package="" automapping="true">
    <page path="index.htm" classname="Home"/>
Note automapping is true by default, so it could be omitted from the configuration file.

The page template name to classname convention is:

change-password.htm  =>  ChangePassword
change_password.htm  =>  ChangePassword
changePassword.htm   =>  ChangePassword
ChangePassword.htm   =>  ChangePassword
When automapping pages, if a class cannot be found Click will attempt to add the 'Page' suffix to the classname if not already present and map this. For example:
customer.htm         =>  CustomerPage
change-password.htm  =>  ChangePasswordPage

2.3.2  Automapping Excludes

With Page automapping there can be resources where you don't want automapping applied. For example when using a JavaScript library with lots of .htm files, you don't want automapping to try and find Page class for each of these files.

In these situations you can use the pages excludes element.

<!ELEMENT excludes (#PCDATA)>
   <!ATTLIST excludes pattern CDATA #REQUIRED>
For example if our application uses the TinyMCE JavaScript library we could configure our pages automapping to exclude all .htm files under the /tiny_mce directory.
  <pages package="">
    <excludes pattern="/tiny_mce/*"/>
The excludes pattern can specify multiple directories or files using a comma separated notation. For example:
  <pages package="">
    <excludes pattern="/dhtml/*, /tiny_mce/*, banner.htm, about.htm"/>
HTM files excluded from Page automapping are handled by an internal Page class with caching headers enabled.

2.3.3  Page Autobinding

By default all pages have autobinding enabled. With autobinding enabled the ClickServlet will automatically: For example:
public class EmployeePage extends Page {

    public Form employeeForm = new Form();
    public Table myTable = new Table();
In the example above the employeeForm and myTable controls were not added to the page. Also note that Form and Table does not have their names defined.

When autobinding is enabled, ClickServlet will create a new Page and add the public controls to the page. In the example above the employeeForm and myTable will be added to the page, as if you had invoked, addControl(employeeForm) and addControl(myTable).

The control's names were not defined so ClickServlet will set their names to the value of their field/variable name. In this case the Form name will be set to employeeForm while the Table name will set to myTable.

The above example is thus a shorthand way of writing the following:

public class EmployeePage extends Page {

    private Form employeeForm = new Form();
    private Table myTable = new Table();
    public void onInit() {

You can turn this behaviour off by setting the autobinding attribute to false, for example:
  <pages package="" autobinding="false"/>

2.4  Headers

The optional headers element defines a list of header elements which are applied to all pages.
<!ELEMENT headers (header*)> 
The header element defines header name and value pairs which are applied to the HttpServletResponse.
<!ELEMENT header (#PCDATA)>
   <!ATTLIST header name CDATA #REQUIRED>
   <!ATTLIST header value CDATA #REQUIRED>
   <!ATTLIST header type (String|Integer|Date) "String">
Page headers are set after the Page has been constructed and before onInit() is called. Pages can then modify their headers property using the setHeader() method.

2.4.1  Browser Caching

Headers are typically used to switch off browser caching. By default Click will use the following no caching header values if you don't define a headers element in your application:
    <header name="Pragma" value="no-cache"/>
    <header name="Cache-Control" 
            value="no-store, no-cache, must-revalidate, post-check=0, pre-check=0"/>
    <header name="Expires" value="1" type="Date"/>
Alternatively you can define your headers individually in pages or for all application pages by setting header values. For example to switch off caching in the login page, note the value for a Date type should be a long number value:
<page path="login.htm" classname="">
  <header name="Pragma" value="no-cache"/>
  <header name="Expires" value="1" type="Date"/>
If you wanted to enable caching for a particular page you could set the following page cache control header. This will mark the page as cachable for a period of 1 hour after which it should be reloaded.
<page path="home.htm" classname="">
  <header name="Cache-Control" value="max-age=3600, public, must-revalidate"/>
To apply header values globally define header values in the headers element. For example:
    <header name="Pragma" value="no-cache"/>
    <header name="Cache-Control" 
            value="no-store, no-cache, must-revalidate, post-check=0, pre-check=0"/>
    <header name="Expires" value="1" type="Date"/>

2.5  Format

The optional format element defines the Format object classname which is applied to all pages.
<!ELEMENT format (#PCDATA)>
    <ATTLIST format classname CDATA #FIXED ""> 
By default all Click pages are configured with a object. The format object is made available in the Velocity page templates using the name $format.

To specify a custom format class configure a format element in the click-app descriptor. For example:

  <format classname="com.mycorp.util.CustomFormat"/>

2.6  Mode

The optional mode element defines the application logging and caching mode.
    <ATTLIST mode value (production|profile|development|debug|trace) "development">
By default Click applications run in development mode, which switches off page template caching, and the logging level is set to INFO.

To change the default application mode configure a mode element in the click-app descriptor. For example to specify production mode you would add the following mode element:

  <mode value="production">
The application mode configuration can be overridden by setting the system property "click.mode". This can be use in the scenario of debugging a problem on a production system, where you change the mode to trace by setting the following system property and restarting the application.
The Click Application modes and their settings for Page auto loading, template caching and logging levels are:

Application mode Page auto loading Template caching Click logging level Velocity logging level
production No Yes WARN ERROR
profile No Yes INFO ERROR
development Yes No INFO ERROR
debug Yes No DEBUG ERROR
trace Yes No TRACE WARN

2.6.1  Page Auto Loading

When Page Auto Loading is enabled any new page templates and classes will be automatically loaded at runtime. These pages are loaded using the Page Automapping rules.

Page auto loading is a very handy feature for rapid development as you do not have to restart you application server to pick up new pages.

2.6.2  Click and Velocity Logging

The Click and Velocity runtimes use LogService for logging messages. The default LogService implementation is ConsoleLogService which will send messages to the console [System.out]. For example the following logging output is for a HomePage request when the application mode is trace:
[Click] [debug] GET http://localhost:8080/quickstart/home.htm
[Click] [trace]    invoked: HomePage.<<init>>
[Click] [trace]    invoked: HomePage.onSecurityCheck() : true
[Click] [trace]    invoked: HomePage.onInit()
[Click] [trace]    invoked: HomePage.onGet()
[Click] [trace]    invoked: HomePage.onRender()
[Click] [info ]    renderTemplate: /home.htm - 6 ms
[Click] [trace]    invoked: HomePage.onDestroy()
[Click] [info ] handleRequest:  /home.htm - 24 ms  
Any unhandled Throwable errors are logged by the ClickServlet.

Note that Click Extras also provide log adaptors for Log4J and the JDK Logging API.

When an application is not in production mode the error page displays detailed debugging information. When the application mode is production no debug information is displayed to prevent sensitive information being revealed. This behaviour can be changed by modifying the deployed click/error.htm page template.

2.7  Controls

The optional controls element defines a list of control elements which will be deployed on application startup.
<!ELEMENT controls (control*)> 
The control registers Control classes which will have their onDeploy() method invoked when the click application starts.
<!ELEMENT control (#PCDATA)>
   <!ATTLIST control classname CDATA #REQUIRED>
For example to have a CustomField control deploy its resources on application startup, you would add the following elements to your click.xml file:

     <control classname="com.mycorp.control.CustomField"/>

3.  Auto Deployed Files

To make pre-configured resources (templates, stylesheets, etc.) available to web applications, Click automatically deploys configured classpath resources to the /click directory at startup (if not already present).

You can modify these support files and Click will not overwrite them. These files include:

For example to customize the control styles you can place a customized copy (or even a brand new version) of control.css under the /click folder in your web project:

When Click starts up it will not override your copy of control.css with its own default version.

Different controls might deploy different stylesheet, javascript or image files, however the above principle still applies. By placing a customized copy of the stylesheet, javascript or image under the /click folder, you will override the default resource.

Be aware that some of the more complex controls (checklist, colorpicker, tree), deploys resources to subfolders under /click, for example /click/checklist/*.

A control's Javadoc will normally indicate what resources are deployed for that control.

It is generally easier to work with unpacked WARs and most servlet containers do just that. However some contains such as WebLogic (at least version 10) does not. To enable WebLogic to unpack the WAR go to the Admin Console > server node > Web Applications tab and check the Archived Real Path Enabled parameter.

If Click cannot deploy resources because of restricted file system permissions, warning messages will be logged.

If your application server does not unpack the WAR/EAR or has restricted permissions, you will need to package up these auto deployed files in your web applications WAR file. To do this you should run you application on a development machine without these restrictions and then package up the deployed files into the WAR/EAR before deployment.

3.1  Deploying Custom Resources

Click supports two ways of deploying pre-configured resources (templates, stylesheets, JavaScript etc.) from a Jar to a web applications.

  1. Through a Control's onDeploy() event handler. See the Controls section above.
  2. By packaging the resources (stylesheets, JavaScript, Images etc.) into a special folder called 'META-INF/web'.
As option #1 was already discussed above in section 2.7 Controls, lets look at option #2.

When Click starts up, it scans each Jar in the classpath for specially marked entries starting with 'META-INF/web/'. (Please note that even though Click will scan the entire classpath it is strongly recommended to host your Jar files inside your WAR lib folder e.g. WEB-INF/lib. Sharing Jars on the classpath can lead to class loading issues.)

Click will then copy all files found under 'META-INF/web/' to the web application folder.

For example, given a Jar file with the following entries:

Click will copy the files '/mycorp/edit_customer.js' and '/mycorp/edit_customer.css' to the web application folder.

Thus if the web application is called 'webapp', the files will be deployed as 'webapp/mycorp/edit_customer.js' and 'webapp/mycorp/edit_customer.css'.

Option #2 is especially useful when you need to deploy a large number of resources from a Jar. Note, only Jars placed under the 'WEB-INF/lib' folder will be deployed.