Sébastien Deleuze
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[[web-integration]] |
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= Other Web Frameworks |
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This chapter details Spring's integration with third-party web frameworks. |
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One of the core value propositions of the Spring Framework is that of enabling |
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_choice_. In a general sense, Spring does not force you to use or buy into any |
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particular architecture, technology, or methodology (although it certainly recommends |
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some over others). This freedom to pick and choose the architecture, technology, or |
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methodology that is most relevant to a developer and their development team is |
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arguably most evident in the web area, where Spring provides its own web frameworks |
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(xref:web/webmvc.adoc#mvc[Spring MVC] and xref:web/webflux.adoc#webflux[Spring WebFlux]) |
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while, at the same time, supporting integration with a number of popular third-party |
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web frameworks. |
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[[web-integration-common]] |
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== Common Configuration |
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Before diving into the integration specifics of each supported web framework, let us |
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first take a look at common Spring configuration that is not specific to any one web |
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framework. (This section is equally applicable to Spring's own web framework variants.) |
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One of the concepts (for want of a better word) espoused by Spring's lightweight |
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application model is that of a layered architecture. Remember that in a "classic" |
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layered architecture, the web layer is but one of many layers. It serves as one of the |
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entry points into a server-side application, and it delegates to service objects |
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(facades) that are defined in a service layer to satisfy business-specific (and |
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presentation-technology agnostic) use cases. In Spring, these service objects, any other |
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business-specific objects, data-access objects, and others exist in a distinct "business |
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context", which contains no web or presentation layer objects (presentation objects, |
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such as Spring MVC controllers, are typically configured in a distinct "presentation |
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context"). This section details how you can configure a Spring container (a |
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`WebApplicationContext`) that contains all of the 'business beans' in your application. |
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Moving on to specifics, all you need to do is declare a |
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{spring-framework-api}/web/context/ContextLoaderListener.html[`ContextLoaderListener`] |
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in the standard Jakarta EE servlet `web.xml` file of your web application and add a |
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`contextConfigLocation` `<context-param/>` section (in the same file) that defines which |
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set of Spring XML configuration files to load. |
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Consider the following `<listener/>` configuration: |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<listener> |
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<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> |
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</listener> |
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---- |
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Further consider the following `<context-param/>` configuration: |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<context-param> |
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<param-name>contextConfigLocation</param-name> |
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<param-value>/WEB-INF/applicationContext*.xml</param-value> |
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</context-param> |
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---- |
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If you do not specify the `contextConfigLocation` context parameter, the |
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`ContextLoaderListener` looks for a file called `/WEB-INF/applicationContext.xml` to |
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load. Once the context files are loaded, Spring creates a |
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{spring-framework-api}/web/context/WebApplicationContext.html[`WebApplicationContext`] |
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object based on the bean definitions and stores it in the `ServletContext` of the web |
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application. |
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All Java web frameworks are built on top of the Servlet API, so you can use the |
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following code snippet to get access to this "business context" `ApplicationContext` |
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created by the `ContextLoaderListener`. |
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The following example shows how to get the `WebApplicationContext`: |
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[source,java,indent=0,subs="verbatim,quotes"] |
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---- |
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WebApplicationContext ctx = WebApplicationContextUtils.getWebApplicationContext(servletContext); |
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---- |
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The |
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{spring-framework-api}/web/context/support/WebApplicationContextUtils.html[`WebApplicationContextUtils`] |
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class is for convenience, so you need not remember the name of the `ServletContext` |
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attribute. Its `getWebApplicationContext()` method returns `null` if an object |
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does not exist under the `WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE` |
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key. Rather than risk getting `NullPointerExceptions` in your application, it is better |
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to use the `getRequiredWebApplicationContext()` method. This method throws an exception |
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when the `ApplicationContext` is missing. |
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Once you have a reference to the `WebApplicationContext`, you can retrieve beans by their |
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name or type. Most developers retrieve beans by name and then cast them to one of their |
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implemented interfaces. |
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Fortunately, most of the frameworks in this section have simpler ways of looking up beans. |
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Not only do they make it easy to get beans from a Spring container, but they also let you |
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use dependency injection on their controllers. Each web framework section has more detail |
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on its specific integration strategies. |
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[[jsf]] |
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== JSF |
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JavaServer Faces (JSF) is the JCP's standard component-based, event-driven web |
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user interface framework. It is an official part of the Jakarta EE umbrella but also |
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individually usable, for example, through embedding Mojarra or MyFaces within Tomcat. |
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Please note that recent versions of JSF became closely tied to CDI infrastructure |
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in application servers, with some new JSF functionality only working in such an |
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environment. Spring's JSF support is not actively evolved anymore and primarily |
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exists for migration purposes when modernizing older JSF-based applications. |
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The key element in Spring's JSF integration is the JSF `ELResolver` mechanism. |
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[[jsf-springbeanfaceselresolver]] |
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=== Spring Bean Resolver |
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`SpringBeanFacesELResolver` is a JSF compliant `ELResolver` implementation, |
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integrating with the standard Unified EL as used by JSF and JSP. It delegates to |
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Spring's "business context" `WebApplicationContext` first and then to the |
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default resolver of the underlying JSF implementation. |
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Configuration-wise, you can define `SpringBeanFacesELResolver` in your JSF |
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`faces-context.xml` file, as the following example shows: |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<faces-config> |
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<application> |
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<el-resolver>org.springframework.web.jsf.el.SpringBeanFacesELResolver</el-resolver> |
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... |
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</application> |
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</faces-config> |
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---- |
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[[jsf-facescontextutils]] |
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=== Using `FacesContextUtils` |
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A custom `ELResolver` works well when mapping your properties to beans in |
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`faces-config.xml`, but, at times, you may need to explicitly grab a bean. |
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The {spring-framework-api}/web/jsf/FacesContextUtils.html[`FacesContextUtils`] |
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class makes this easy. It is similar to `WebApplicationContextUtils`, except that |
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it takes a `FacesContext` parameter rather than a `ServletContext` parameter. |
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The following example shows how to use `FacesContextUtils`: |
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[source,java,indent=0,subs="verbatim,quotes"] |
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---- |
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ApplicationContext ctx = FacesContextUtils.getWebApplicationContext(FacesContext.getCurrentInstance()); |
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---- |
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[[struts]] |
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== Apache Struts |
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Invented by Craig McClanahan, https://struts.apache.org[Struts] is an open-source project |
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hosted by the Apache Software Foundation. Struts 1.x greatly simplified the |
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JSP/Servlet programming paradigm and won over many developers who were using proprietary |
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frameworks. It simplified the programming model; it was open source; and it had a large |
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community, which let the project grow and become popular among Java web developers. |
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As a successor to the original Struts 1.x, check out Struts 2.x or more recent versions |
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as well as the Struts-provided |
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https://struts.apache.org/plugins/spring/[Spring Plugin] for built-in Spring integration. |
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[[tapestry]] |
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== Apache Tapestry |
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https://tapestry.apache.org/[Tapestry] is a "Component oriented framework for creating |
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dynamic, robust, highly scalable web applications in Java." |
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While Spring has its own xref:web/webmvc.adoc#mvc[powerful web layer], there are a number of unique |
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advantages to building an enterprise Java application by using a combination of Tapestry |
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for the web user interface and the Spring container for the lower layers. |
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For more information, see Tapestry's dedicated |
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https://tapestry.apache.org/integrating-with-spring-framework.html[integration module for Spring]. |
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[[web-integration-resources]] |
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== Further Resources |
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The following links go to further resources about the various web frameworks described in |
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this chapter. |
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* The https://www.oracle.com/java/technologies/javaserverfaces.html[JSF] homepage |
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* The https://struts.apache.org/[Struts] homepage |
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* The https://tapestry.apache.org/[Tapestry] homepage |
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