Enabling Spring Faces support

The main focus of the Spring Web Flow Framework is to deliver the infrastructure to describe the page flow of a web application. The flow itself is a very important element of a web application, because it describes its structure, particularly the structure of the implemented business use cases. But besides the flow which is only in the background, the user of your application is interested in the Graphical User Interface (GUI). Therefore, we need a solution of how to provide a rich user interface to the users. One framework which offers components is JavaServer Faces (JSF). With the release of Spring Web Flow 2, an integration module to connect these two technologies, called Spring Faces has been introduced. This article is no introduction to the JavaServer Faces technology. It is only a description about the integration of Spring Web Flow 2 with JSF. If you have never previously worked with JSF, please refer to the JSF reference to gain knowledge about the essential concepts of JavaServer Faces.

JavaServer Faces (JSF)—a brief introduction
The JavaServer Faces (JSF) technology is a web application framework with the goal to make the development of user interfaces for a web application (based on Java EE) easier. JSF uses a component-based approach with an own lifecycle model, instead of a request-driven approach used by traditional MVC web frameworks. The version 1.0 of JSF is specified inside JSR (Java Specification Request) 127 (http://jcp.org/en/jsr/detail?id=127).

To use the Spring Faces module, you have to add some configuration to your application. The diagram below depicts the single configuration blocks. These blocks are described in this article.

Enabling Spring Faces support

The first step in the configuration is to configure the JSF framework itself. That is done in the deployment descriptor of the web application—web.xml. The servlet has to be loaded at the startup of the application. This is done with the <load-on-startup>1</load-on-startup> element.

<!-- Initialization of the JSF implementation. The Servlet is not
 used at runtime -->
   <servlet>
       <servlet-name>Faces Servlet</servlet-name>
       <servlet-class>javax.faces.webapp.FacesServlet</servlet-class>
       <load-on-startup>1</load-on-startup>
   </servlet>
   <servlet-mapping>
       <servlet-name>Faces Servlet</servlet-name>
       <url-pattern>*.faces</url-pattern>
   </servlet-mapping>

For the work with the JavaServer Faces, there are two important classes. These are the javax.faces.webapp.FacesServlet and the javax.faces.context.FacesContext classes.
You can think of FacesServlet as the core base of each JSF application. Sometimes that servlet is called an infrastructure servlet. It is important to mention that each JSF application in one web container has its own instance of the FacesServlet class. This means that an infrastructure servlet cannot be shared between many web applications on the same JEE web container.
FacesContext is the data container which encapsulates all information that is necessary around the current request.
For the usage of Spring Faces, it is important to know that FacesServlet is only used to instantiate the framework. A further usage inside Spring Faces is not done.

To be able to use the components from Spring Faces library, it's required to use Facelets instead of JSP. Therefore, we have to configure that mechanism.

If you are interested in reading more about the Facelets technology, visit the Facelets homepage from java.net with the following URL: https://facelets.dev.java.net. A good introduction inside the Facelets technology is the "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html >
<body>
<form jsfc="h:form">
<span jsfc="h:outputText" value="Welcome to our page: #{user.name}"
disabled="#{empty user}" />
<input type="text" jsfc="h:inputText" value="#{bean.theProperty}" />
<input type="submit" jsfc="h:commandButton" value="OK"
action="#{bean.doIt}" />
</form>
</body>
</html>

The sample code snippet above uses the mentioned expression language (for example, the #{user.name} expression accesses the name property from the user instance) of the JSF technology to access the data.

What is component aliasing
One of the mentioned features of the Facelets technology is that it is possible to view a page directly in a browser without that the page is running inside a JEE container environment. This is possible through the component aliasing feature. With this feature, you can use normal HTML elements, for example an input element. Additionally, you can refer to the component which is used behind the scenes with the jsfc attribute. An example for that is <input type="text" jsfc="h:inputText" value="#{bean.theProperty}" /> . If you open this inside a browser, the normal input element is used. If you use it inside your application, the h:inputText element of the component library is used

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The ResourceServlet

One main part of the JSF framework are the components for the GUI. These components often consist of many files besides the class files. If you use many of these components, the problem of handling these files arises. To solve this problem, the files such as JavaScript and CSS (Cascading Style Sheets) can be delivered inside the JAR archive of the component.

If you deliver the file inside the JAR file, you can organize the components in one file and therefore it is easier for the deployment and maintenance of your component library.

Regardless of the framework you use, the result is HTML. The resources inside the HTML pages are required as URLs. For that, we need a way to access these resources inside the archive with the HTTP protocol. To solve that problem, there is a servlet with the name ResourceServlet (package org.springframework.js.resource).

The servlet can deliver the following resources:

Resources which are available inside the web application (for example, CSS files)

Resources inside a JAR archive

The configuration of the servlet inside web.xml is shown below:

<servlet>
<servlet-name>Resource Servlet</servlet-name>
<servlet-class>org.springframework.js.resource.ResourceServlet
</servlet-class>
<load-on-startup>0</load-on-startup>
</servlet>

<servlet-mapping>
<servlet-name>Resource Servlet</servlet-name>
<url-pattern>/resources/*</url-pattern>
</servlet-mapping>

It is important that you use the correct url-pattern inside servlet-mapping. As you can see in the sample above, you have to use /resources/*. If a component does not work (from the Spring Faces components), first check if you have the correct mapping for the servlet. All resources in the context of Spring Faces should be retrieved through this Servlet. The base URL is /resources.

Internals of the ResourceServlet

ResourceServlet can only be accessed via a GET request. The ResourceServlet servlet implements only the GET method. Therefore, it's not possible to serve POST requests. Before we describe the separate steps, we want to show you the complete process, illustrated in the diagram below:

For a better understanding, we choose an example for the explanation of the mechanism which is shown in the previous diagram. Let us assume that we have registered the ResourcesServlet as mentioned before and we request a resource by the following sample URL: http://localhost:8080/ flowtrac-web-jsf/resources/css/test1.css.

How to request more than one resource with one request
First, you can specify the appended parameter. The value of the parameter is the path to the resource you want to retrieve. An example for that is the following URL: http://localhost:8080/ flowtracweb-jsf/resources/css/test1.css?appended=/css/test2.css. If you want to specify more than one resource, you can use the delimiter comma inside the value for the appended parameter. A simple example for that mechanism is the following URL: http://localhost:8080/ flowtrac-web-jsf/resources/css/test1.css?appended=/css/test2.css, http://localhost:8080/flowtrac-web-jsf/resources/css/test1.css?appended=/css/test3.css. Additionally, it is possible to use the comma delimiter inside the PathInfo. For example: http://localhost:8080/flowtrac-web-jsf/resources/css/test1.css,/css/test2.css. It is important to mention that if one resource of the requested resources is not available, none of the requested resources is delivered. This mechanism can be used to deliver more than one CSS in one request. From the view of development, it can make sense to modularize your CSS files to get more maintainable CSS files. With that concept, the client gets one CSS, instead of many CSS files. From the view of performance optimization, it is better to have as few requests for rendering a page as possible. Therefore, it makes sense to combine the CSS files of a page. Internally, the files are written in the same sequence as they are requested.

To understand how a resource is addressed, we separate the sample URL into the specific parts. The example URL is a URL on a local servlet container which has an HTTP connector at port 8080. See the following diagram for the mentioned separation:

The table below describes the five sections of the URL that are shown in the previous diagram: