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JSF 2.2: Theme

JSF 2.2: Theme

Richfaces and Primefaces have theme support, it is an attractive feature of the skin-able JSF components projects.
JSF 2.2 introduces a new feature named Resource Library Contracts which supports to apply different resources(css and js) and facelets template at runtime.
contracts resources files can be placed in /contracts folder under the web application root or /META-INF/contracts on classpath.

Using contracts in a web application

The following is an example of contracts resources structure in a web application.
/contracts
    /default
        /css
            defautl.css
            cssLayout.css
        template.xhtml
    /alternative
        /css
            defautl.css
            cssLayout.css
        template.xhtml
There are two contracts defined in the project, default and alternative.
The following is the content of /contracts/default/template.xhtml.
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://xmlns.jcp.org/jsf/facelets"
      xmlns:h="http://xmlns.jcp.org/jsf/html">
    
    <h:head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
        <link href="#{request.contextPath}/contracts/default/css/default.css" rel="stylesheet" type="text/css" />
        <link href="#{request.contextPath}/contracts/default/css/cssLayout.css" rel="stylesheet" type="text/css" />
        <title>Facelets Template</title>
    </h:head>
    
    <h:body>
        
        <div id="top" class="top">
            <ui:insert name="top">Top</ui:insert>
        </div>
        
        <div id="content" class="center_content">
            <ui:insert name="content">Content</ui:insert>
        </div>
        
    </h:body>
    
</html>
The content of /contracts/alternative/template.xhtml is similar, only the css reference path is changed.
<?xml version='1.0' encoding='UTF-8' ?>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:ui="http://xmlns.jcp.org/jsf/facelets"
      xmlns:h="http://xmlns.jcp.org/jsf/html">
    
    <h:head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
        <link href="#{request.contextPath}/contracts/alternative/css/default.css" rel="stylesheet" type="text/css" />
        <link href="#{request.contextPath}/contracts/alternative/css/cssLayout.css" rel="stylesheet" type="text/css" />
        <title>Facelets Template</title>
    </h:head>
    
    <h:body>
        
        <div id="top" class="top">
            <ui:insert name="top">Top</ui:insert>
        </div>
        
        <div id="content" class="center_content">
            <ui:insert name="content">Content</ui:insert>
        </div>
        
    </h:body>
    
</html>
In your facelets base template, you can use the contracts template directly.
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html" 
      xmlns:f="http://xmlns.jcp.org/jsf/core"
      xmlns:ui="http://xmlns.jcp.org/jsf/facelets">
        <f:view contracts="alternative">
            <ui:composition template="/template.xhtml"

                <ui:define name="content">    
                    <h1>Theme Switcher</h1>
                    <p>Sample of applying alternative.</p>
                </ui:define>
            </ui:composition>
        </f:view>
</ui:composition>
A new attribute contracts is added to f:view in JSF 2.2, which can specify the contracts name you will use, here the options are default and alternative.
NOTE: The template path is /template.xhtml, and there is no any contract prefix needed.
You can switch between different contracts dynamically through a backend bean.
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html" 
      xmlns:f="http://xmlns.jcp.org/jsf/core"
      xmlns:ui="http://xmlns.jcp.org/jsf/facelets">
        <f:view contracts="#{themeSwitcher.theme}">
            <ui:composition template="/template.xhtml">
                <ui:define name="content">    
                    <h1>Theme Switcher</h1>
                    <p>Current Theme:#{themeSwitcher.theme}</p>
                    <h:form>
                        <h:commandButton value="Default Theme" action="#{themeSwitcher.changeTheme('default')}">
                        </h:commandButton>    
                        <h:commandButton value="Alternative Theme" action="#{themeSwitcher.changeTheme('alternative')}">
                        </h:commandButton>    
                    </h:form>
                </ui:define>
            </ui:composition>
        </f:view>
</ui:composition>
In the template file, use two h:commandButton buttons to switch the contracts dynamically.
@Named
@SessionScoped
public class ThemeSwitcher implements Serializable {

    @Inject
    transient Instance<Logger> log;

    private String theme = "default";

    
    public void changeTheme( String _theme){
        log.get().log(Level.INFO, "call changeTheme{0}", _theme);
        switch (_theme) {
            case "alternative":
                this.theme = "alternative";
                break;
            default:
                this.theme = "default";
                break;
        }
    }

    public String getTheme() {
        return theme;
    }

    public void setTheme(String theme) {
        this.theme = theme;
    }
    
}
You can also configure the contracts in faces-config.xml file.
<application>
        <resource-library-contracts>
            <contract-mapping>
                <url-pattern>/themed-alt/*</url-pattern>
                <contracts>alternative</contracts>
            </contract-mapping>
            <contract-mapping>
                <url-pattern>/themed-default/*</url-pattern>
                <contracts>default</contracts>
            </contract-mapping>
        </resource-library-contracts>
</application>   
The /themed-alt will use the alternative and /themed-default will use default contracts.
Unfortunately, JSF 2.2 does not support EL as the value of contracts in faces-config.xml.
<contract-mapping>
    <url-pattern>/themed-dyn/*</url-pattern>
    <contracts>#{themeSwitcher.theme}</contracts>
</contract-mapping>
This feature is motioned in jdevelopment.nl website, and could be supported in a future version.

Building a contracts jar

Packaging the resources library contracts files into a jar file is easy to share the contracts among various projects.
Move the contracts resources into a standalone Maven module, and refactor the above war project into three Maven modules.
theme-library
    /theme-client
    /theme-resources
theme-library is a parent POM module, includes two sub modules, theme-client and theme-resources.
theme-resources is a jar module, including all resources library contracts files.
theme-resources
    /src
        /main
            /resoruces
                /META-INF
                    /contracts
                        /default
                            /css
                            template.xhtml
                            javax.faces.contract.xml
                        /alternative
                            /css
                            template.xhtml
                            javax.faces.contract.xml
javax.faces.contract.xml is an empty marker file, which is required to identify resource library contracts in a jar file.
theme-client is a war project, which will apply the contracts defined in theme-resources module. Include theme-resources as a Maven dependency in the pom.xml of theme-client.
<dependency>
            <groupId>com.hantsylabs.example.ee7</groupId>
            <artifactId>jsf-theme-resources</artifactId>
            <version>1.0-SNAPSHOT</version>
</dependency>
NOTE: In the Glassfish 4(Mojarra is upgraded to 2.2.1), I have tried package the contracts files with and without an empty javax.faces.contract.xml. If packaging them without the empty javax.faces.contract.xml marker file, the predefined contracts can not be recognized when applying the contract rule in faces-config.xml, but they can be used in Themeswitcher backend bean. It looks a little weird.

Sample codes

NOTE: In order to demonstrate the usage of Resources Library Contracts, I only changed the background color style in the css file. In the real world application, it could be much difference. For example, you can use different css and template layout before and after user is logged in.
Check out the complete codes from my github.com, and play it yourself.
https://github.com/hantsy/ee7-sandbox
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