spring-framework/src/asciidoc/web-integration.adoc

[[web-integration]]
= Integrating with other web frameworks


[[intro]]
== Introduction

.Spring Web Flow
****
Spring Web Flow (SWF) aims to be the best solution for the management of web application
page flow.

SWF integrates with existing frameworks like Spring MVC and JSF, in both Servlet and
Portlet environments. If you have a business process (or processes) that would benefit
from a conversational model as opposed to a purely request model, then SWF may be the
solution.

SWF allows you to capture logical page flows as self-contained modules that are reusable
in different situations, and as such is ideal for building web application modules that
guide the user through controlled navigations that drive business processes.

For more information about SWF, consult the
http://projects.spring.io/spring-webflow/[Spring Web Flow website].
****

This chapter details Spring's integration with third party web frameworks, such as
http://www.oracle.com/technetwork/java/javaee/javaserverfaces-139869.html[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
(<<mvc,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.

[NOTE]
====
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 <<web-integration-resources>> at the end of this chapter.
====




[[web-integration-common]]
== Common configuration
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
{javadoc-baseurl}/org/springframework/web/context/ContextLoaderListener.html[`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:

[source,xml,indent=0]
[subs="verbatim,quotes"]
----
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>
----

Find below the <context-param/> configuration:

[source,xml,indent=0]
[subs="verbatim,quotes"]
----
	<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
{javadoc-baseurl}/org/springframework/web/context/WebApplicationContext.html[`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 `ContextLoaderListener`.

[source,java,indent=0]
[subs="verbatim,quotes"]
----
	WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext);
----

The
{javadoc-baseurl}/org/springframework/web/context/support/WebApplicationContextUtils.html[`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.




[[jsf]]
== JavaServer Faces 1.2
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
http://myfaces.apache.org/[Apache MyFaces project]. The MyFaces project also provides
common JSF extensions such as http://myfaces.apache.org/orchestra/[MyFaces Orchestra]:
a Spring-based JSF extension that provides rich conversation scope support.

[NOTE]
====
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
http://projects.spring.io/spring-webflow[Spring Web Flow website] for details!
====

The key element in Spring's JSF integration is the JSF `ELResolver` mechanism.

[[jsf-springbeanfaceselresolver]]
=== SpringBeanFacesELResolver (JSF 1.2+)
`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:

[source,xml,indent=0]
[subs="verbatim,quotes"]
----
	<faces-config>
		<application>
			<el-resolver>org.springframework.web.jsf.el.SpringBeanFacesELResolver</el-resolver>
			...
		</application>
	</faces-config>
----


[[jsf-facescontextutils]]
=== FacesContextUtils
A custom `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
{javadoc-baseurl}/org/springframework/web/jsf/FacesContextUtils.html[`FacesContextUtils`]
class makes this easy. It is similar to `WebApplicationContextUtils`, except that it
takes a `FacesContext` parameter rather than a `ServletContext` parameter.

[source,java,indent=0]
[subs="verbatim,quotes"]
----
	ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance());
----



[[struts]]
== Apache Struts 2.x
Invented by Craig McClanahan, http://struts.apache.org[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
https://struts.apache.org/release/2.3.x/docs/spring-plugin.html[Spring Plugin] for the
built-in Spring integration shipped with Struts.



[[tapestry]]
== Tapestry 5.x
From the http://tapestry.apache.org/[Tapestry homepage]:

Tapestry is a "__Component oriented framework for creating dynamic, robust,
highly scalable web applications in Java.__"

While Spring has its own <<mvc,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
https://tapestry.apache.org/integrating-with-spring-framework.html[integration module for
Spring].



[[web-integration-resources]]
== Further Resources
Find below links to further resources about the various web frameworks described in this
chapter.

* The http://www.oracle.com/technetwork/java/javaee/javaserverfaces-139869.html[JSF] homepage
* The http://struts.apache.org/[Struts] homepage
* The http://tapestry.apache.org/[Tapestry] homepage