Spring Framework

org.springframework.web
Class SpringServletContainerInitializer

java.lang.Object
  extended by org.springframework.web.SpringServletContainerInitializer
All Implemented Interfaces:
javax.servlet.ServletContainerInitializer

public class SpringServletContainerInitializer
extends java.lang.Object
implements javax.servlet.ServletContainerInitializer

Servlet 3.0 ServletContainerInitializer designed to support code-based configuration of the servlet container using Spring's WebApplicationInitializer SPI as opposed to (or possibly in combination with) the traditional web.xml-based approach.

Mechanism of Operation

This class will be loaded and instantiated and have its onStartup method invoked by any Servlet 3.0-compliant container during container startup assuming that the spring-web module JAR is present on the classpath. This occurs through the JAR Services API ServiceLoader.load(Class) method detecting the spring-web module's META-INF/services/javax.servlet.ServletContainerInitializer service provider configuration file. See the JAR Services API documentation as well as section 8.2.4 of the Servlet 3.0 Final Draft specification for complete details.

when in combination with web.xml

If a web application does include a WEB-INF/web.xml file, it is important to understand that neither this nor any other ServletContextInitializer will be processed unless the <web-app> element's version attribute is >= "3.0" and the xsi:schemaLocation for "http://java.sun.com/xml/ns/javaee" is set to "http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd".

Relationship to Spring's WebApplicationInitializer

Spring's WebApplicationInitializer SPI consists of just one method: WebApplicationInitializer.onStartup(ServletContext). The signature is intentionally quite similar to ServletContainerInitializer.onStartup(Set, ServletContext): simply put, SpringServletContainerInitializer is responsible for instantiating and delegating the ServletContext to any user-defined WebApplicationInitializer implementations. It is then the responsibility of each WebApplicationInitializer to do the actual work of initializing the ServletContext. The exact process of delegation is described in detail in the onStartup documentation below.

General Notes

In general, this class should be viewed as supporting infrastructure for the more important and user-facing WebApplicationInitializer SPI. Taking advantage of this container initializer is also completely optional: while it is true that this initializer will be loaded and invoked under all Servlet 3.0+ runtimes, it remains the user's choice whether to make any WebApplicationInitializer implementations available on the classpath. If no WebApplicationInitializer types are detected, this container initializer will have no effect.

Note that use of this container initializer and of WebApplicationInitializer is not in any way "tied" to Spring MVC other than the fact that the types are shipped in the spring-web module JAR. Rather, they can be considered general-purpose in their ability to facilitate convenient code-based configuration of the ServletContext. Said another way, any servlet, listener, or filter may be registered within a WebApplicationInitializer, not just Spring MVC-specific components.

This class is not designed for nor intended to be extended. It should be considered an internal type, with WebApplicationInitializer being the public-facing SPI.

See Also

See WebApplicationInitializer Javadoc for examples and detailed usage recommendations.

Since:
3.1
Author:
Chris Beams, Juergen Hoeller
See Also:
onStartup(Set, ServletContext), WebApplicationInitializer

Constructor Summary
SpringServletContainerInitializer()
           
 
Method Summary
 void onStartup(java.util.Set<java.lang.Class<?>> webAppInitializerClasses, javax.servlet.ServletContext servletContext)
          Delegate the ServletContext to any WebApplicationInitializer implementations present on the application classpath.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

SpringServletContainerInitializer

public SpringServletContainerInitializer()
Method Detail

onStartup

public void onStartup(java.util.Set<java.lang.Class<?>> webAppInitializerClasses,
                      javax.servlet.ServletContext servletContext)
               throws javax.servlet.ServletException
Delegate the ServletContext to any WebApplicationInitializer implementations present on the application classpath.

Because this class declares @HandlesTypes(WebApplicationInitializer.class), Servlet 3.0+ containers will automatically scan the classpath for implementations of Spring's WebApplicationInitializer interface and provide the set of all such types to the webAppInitializerClasses parameter of this method.

If no WebApplicationInitializer implementations are found on the classpath, this method is effectively a no-op. An INFO-level log message will be issued notifying the user that the ServletContainerInitializer has indeed been invoked, but that no WebApplicationInitializer implementations were found.

Assuming that one or more WebApplicationInitializer types are detected, they will be instantiated (and sorted if the @Order annotation is present or the Ordered interface has been implemented). Then the WebApplicationInitializer.onStartup(ServletContext) method will be invoked on each instance, delegating the ServletContext such that each instance may register and configure servlets such as Spring's DispatcherServlet, listeners such as Spring's ContextLoaderListener or any other Servlet API componentry such as filters.

Specified by:
onStartup in interface javax.servlet.ServletContainerInitializer
Parameters:
webAppInitializerClasses - all implementations of WebApplicationInitializer found on the application classpath
servletContext - the servlet context to be initialized
Throws:
javax.servlet.ServletException
See Also:
WebApplicationInitializer.onStartup(ServletContext), AnnotationAwareOrderComparator

Spring Framework