24. Integrating with other web frameworks
This chapter details Spring’s integration with third party web frameworks, such as JSF .
One of the core value propositions of the Spring Framework is that of enabling choice. In a general sense, Spring does not force one to use or buy into any particular architecture, technology, or methodology (although it certainly recommends some over others). This freedom to pick and choose the architecture, technology, or methodology that is most relevant to a developer and their development team is arguably most evident in the web area, where Spring provides its own web framework (Spring MVC), while at the same time providing integration with a number of popular third party web frameworks. This allows one to continue to leverage any and all of the skills one may have acquired in a particular web framework such as JSF, while at the same time being able to enjoy the benefits afforded by Spring in other areas such as data access, declarative transaction management, and flexible configuration and application assembly.
Having dispensed with the woolly sales patter (c.f. the previous paragraph), the remainder of this chapter will concentrate upon the meaty details of integrating your favorite web framework with Spring. One thing that is often commented upon by developers coming to Java from other languages is the seeming super-abundance of web frameworks available in Java. There are indeed a great number of web frameworks in the Java space; in fact there are far too many to cover with any semblance of detail in a single chapter. This chapter thus picks four of the more popular web frameworks in Java, starting with the Spring configuration that is common to all of the supported web frameworks, and then detailing the specific integration options for each supported web framework.
Please note that this chapter does not attempt to explain how to use any of the supported web frameworks. For example, if you want to use JSF for the presentation layer of your web application, the assumption is that you are already familiar with JSF itself. If you need further details about any of the supported web frameworks themselves, please do consult Section 24.6, “Further Resources” at the end of this chapter.
Before diving into the integration specifics of each supported web framework, let us first take a look at the Spring configuration that is not specific to any one web framework. (This section is equally applicable to Spring’s own web framework, Spring MVC.)
One of the concepts (for want of a better word) espoused by (Spring’s) lightweight application model is that of a layered architecture. Remember that in a 'classic' layered architecture, the web layer is but one of many layers; it serves as one of the entry points into a server side application and it delegates to service objects (facades) defined in a service layer to satisfy business specific (and presentation-technology agnostic) use cases. In Spring, these service objects, any other business-specific objects, data access objects, etc. exist in a distinct 'business context', which contains no web or presentation layer objects (presentation objects such as Spring MVC controllers are typically configured in a distinct 'presentation context'). This section details how one configures a Spring container (a
WebApplicationContext) that contains all of the 'business beans' in one’s application.
On to specifics: all that one need do is to declare a
ContextLoaderListener in the standard Java EE servlet
web.xml file of one’s web application, and add a
contextConfigLocation<context-param/> section (in the same file) that defines which set of Spring XML configuration files to load.
Find below the <listener/> configuration:
<listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener>
Find below the <context-param/> configuration:
<context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/applicationContext*.xml</param-value> </context-param>
If you don’t specify the
contextConfigLocation context parameter, the
ContextLoaderListener will look for a file called
/WEB-INF/applicationContext.xml to load. Once the context files are loaded, Spring creates a
WebApplicationContext object based on the bean definitions and stores it in the
ServletContext of the web application.
All Java web frameworks are built on top of the Servlet API, and so one can use the following code snippet to get access to this 'business context'
ApplicationContext created by the
WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);
WebApplicationContextUtils class is for convenience, so you don’t have to remember the name of the
ServletContext attribute. Its getWebApplicationContext() method will return
null if an object doesn’t exist under the
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE key. Rather than risk getting
NullPointerExceptions in your application, it’s better to use the
getRequiredWebApplicationContext() method. This method throws an exception when the
ApplicationContext is missing.
Once you have a reference to the
WebApplicationContext, you can retrieve beans by their name or type. Most developers retrieve beans by name and then cast them to one of their implemented interfaces.
Fortunately, most of the frameworks in this section have simpler ways of looking up beans. Not only do they make it easy to get beans from a Spring container, but they also allow you to use dependency injection on their controllers. Each web framework section has more detail on its specific integration strategies.
JavaServer Faces (JSF) is the JCP’s standard component-based, event-driven web user interface framework. As of Java EE 5, it is an official part of the Java EE umbrella.
For a popular JSF runtime as well as for popular JSF component libraries, check out the Apache MyFaces project . The MyFaces project also provides common JSF extensions such as MyFaces Orchestra : a Spring-based JSF extension that provides rich conversation scope support.
Spring Web Flow 2.0 provides rich JSF support through its newly established Spring Faces module, both for JSF-centric usage (as described in this section) and for Spring-centric usage (using JSF views within a Spring MVC dispatcher). Check out the Spring Web Flow website for details!
The key element in Spring’s JSF integration is the JSF
SpringBeanFacesELResolver is a JSF 1.2 compliant
ELResolver implementation, integrating with the standard Unified EL as used by JSF 1.2 and JSP 2.1. Like
SpringBeanVariableResolver, it delegates to the Spring’s 'business context'
WebApplicationContext first, then to the default resolver of the underlying JSF implementation.
Configuration-wise, simply define
SpringBeanFacesELResolver in your JSF 1.2 faces-context.xml file:
<faces-config> <application> <el-resolver>org.springframework.web.jsf.el.SpringBeanFacesELResolver</el-resolver> ... </application> </faces-config>
VariableResolver works well when mapping one’s properties to beans in faces-config.xml, but at times one may need to grab a bean explicitly. The
FacesContextUtils class makes this easy. It is similar to
WebApplicationContextUtils, except that it takes a
FacesContext parameter rather than a
ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());
Invented by Craig McClanahan, Struts is an open source project hosted by the Apache Software Foundation. At the time, it greatly simplified the JSP/Servlet programming paradigm and won over many developers who were using proprietary frameworks. It simplified the programming model, it was open source (and thus free as in beer), and it had a large community, which allowed the project to grow and become popular among Java web developers.
Check out the Struts Spring Plugin for the built-in Spring integration shipped with Struts.
From the Tapestry homepage :
Tapestry is a "Component oriented framework for creating dynamic, robust, highly scalable web applications in Java."
While Spring has its own powerful web layer, there are a number of unique advantages to building an enterprise Java application using a combination of Tapestry for the web user interface and the Spring container for the lower layers.
For more information, check out Tapestry’s dedicated integration module for Spring .