[[web-integration]]
= Other Web Frameworks

This chapter details Spring's integration with third-party web frameworks.

One of the core value propositions of the Spring Framework is that of enabling
_choice_. In a general sense, Spring does not force you 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 frameworks
(<<mvc, Spring MVC>> and <<webflux.adoc#webflux, Spring WebFlux>>) while, at the same time,
supporting integration with a number of popular third-party web frameworks.




[[web-integration-common]]
== Common Configuration

Before diving into the integration specifics of each supported web framework, let us
first take a look at common Spring configuration that is not specific to any one web
framework. (This section is equally applicable to Spring's own web framework variants.)

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) that are 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, and others 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 you can configure a Spring container (a
`WebApplicationContext`) that contains all of the 'business beans' in your application.

Moving on to specifics, all you one need to do is declare a
{api-spring-framework}/web/context/ContextLoaderListener.html[`ContextLoaderListener`]
in the standard Java EE servlet `web.xml` file of your web application and add a
`contextConfigLocation`<context-param/> section (in the same file) that defines which
set of Spring XML configuration files to load.

Consider the following `<listener/>` configuration:

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

Further consider the following `<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 do not specify the `contextConfigLocation` context parameter, the
`ContextLoaderListener` looks for a file called `/WEB-INF/applicationContext.xml` to
load. Once the context files are loaded, Spring creates a
{api-spring-framework}/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, so you can use the
following code snippet to get access to this "`business context`" `ApplicationContext`
created by the `ContextLoaderListener`.

The following example shows how to get the `WebApplicationContext`:

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

The
{api-spring-framework}/web/context/support/WebApplicationContextUtils.html[`WebApplicationContextUtils`]
class is for convenience, so you need not remember the name of the `ServletContext`
attribute. Its `getWebApplicationContext()` method returns `null` if an object
does not exist under the `WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE`
key. Rather than risk getting `NullPointerExceptions` in your application, it is 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 let you
use dependency injection on their controllers. Each web framework section has more detail
on its specific integration strategies.




[[jsf]]
== JSF

JavaServer Faces (JSF) is the JCP's standard component-based, event-driven web
user interface framework. It is an official part of the Java EE umbrella but also
individually usable, e.g. through embedding Mojarra or MyFaces within Tomcat.

Please note that recent versions of JSF became closely tied to CDI infrastructure
in application servers, with some new JSF functionality only working in such an
environment. Spring's JSF support is not actively evolved anymore and primarily
exists for migration purposes when modernizing older JSF-based applications.

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



[[jsf-springbeanfaceselresolver]]
=== Spring Bean Resolver

`SpringBeanFacesELResolver` is a JSF compliant `ELResolver` implementation,
integrating with the standard Unified EL as used by JSF and JSP. It delegates to
Spring's "`business context`" `WebApplicationContext` first and then to the
default resolver of the underlying JSF implementation.

Configuration-wise, you can define `SpringBeanFacesELResolver` in your JSF
`faces-context.xml` file, as the following example shows:

[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]]
=== Using `FacesContextUtils`

A custom `ELResolver` works well when mapping your properties to beans in
`faces-config.xml`, but, at times, you may need to explicitly grab a bean.
The {api-spring-framework}/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.

The following example shows how to use `FacesContextUtils`:

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




[[struts]]
== Apache Struts 2.x

Invented by Craig McClanahan, https://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 let the project grow and become popular among
Java web developers.

As a successor to the original Struts 1.x, check out Struts 2.x and the Struts-provided
https://struts.apache.org/release/2.3.x/docs/spring-plugin.html[Spring Plugin] for the
built-in Spring integration.




[[tapestry]]
== Apache Tapestry 5.x

https://tapestry.apache.org/[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 by using a combination of Tapestry
for the web user interface and the Spring container for the lower layers.

For more information, see Tapestry's dedicated
https://tapestry.apache.org/integrating-with-spring-framework.html[integration module for Spring].




[[web-integration-resources]]
== Further Resources

The following links go to further resources about the various web frameworks described in
this chapter.

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