interface WebApplicationInitializer
Interface to be implemented in Servlet 3.0+ environments in order to configure the ServletContext programmatically -- as opposed to (or possibly in conjunction with) the traditional web.xml
-based approach.
Implementations of this SPI will be detected automatically by , which itself is bootstrapped automatically by any Servlet 3.0 container. See SpringServletContainerInitializer for details on this bootstrapping mechanism.
Example The traditional, XML-based approach Most Spring users building a web application will need to register Spring'sDispatcherServlet
. For reference, in WEB-INF/web.xml, this would typically be done as follows: <servlet> <servlet-name>dispatcher</servlet-name> <servlet-class> org.springframework.web.servlet.DispatcherServlet </servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/spring/dispatcher-config.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>dispatcher</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping>
The code-based approach with WebApplicationInitializer
Here is the equivalent DispatcherServlet
registration logic, WebApplicationInitializer
-style: public class MyWebAppInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { XmlWebApplicationContext appContext = new XmlWebApplicationContext(); appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml"); ServletRegistration.Dynamic dispatcher = container.addServlet("dispatcher", new DispatcherServlet(appContext)); dispatcher.setLoadOnStartup(1); dispatcher.addMapping("/"); } }
As an alternative to the above, you can also extend from . As you can see, thanks to Servlet 3.0's new ServletContext#addServlet
method we're actually registering an instance of the DispatcherServlet
, and this means that the DispatcherServlet
can now be treated like any other object -- receiving constructor injection of its application context in this case.
This style is both simpler and more concise. There is no concern for dealing with init-params, etc, just normal JavaBean-style properties and constructor arguments. You are free to create and work with your Spring application contexts as necessary before injecting them into the DispatcherServlet
.
Most major Spring Web components have been updated to support this style of registration. You'll find that DispatcherServlet
, FrameworkServlet
, ContextLoaderListener
and DelegatingFilterProxy
all now support constructor arguments. Even if a component (e.g. non-Spring, other third party) has not been specifically updated for use within WebApplicationInitializers
, they still may be used in any case. The Servlet 3.0 ServletContext
API allows for setting init-params, context-params, etc programmatically.
WEB-INF/web.xml
was successfully replaced with code in the form of a WebApplicationInitializer
, but the actual dispatcher-config.xml
Spring configuration remained XML-based. WebApplicationInitializer
is a perfect fit for use with Spring's code-based @Configuration
classes. See @ Javadoc for complete details, but the following example demonstrates refactoring to use Spring's org.springframework.web.context.support.AnnotationConfigWebApplicationContext in lieu of XmlWebApplicationContext
, and user-defined @Configuration
classes AppConfig
and DispatcherConfig
instead of Spring XML files. This example also goes a bit beyond those above to demonstrate typical configuration of the 'root' application context and registration of the ContextLoaderListener
: public class MyWebAppInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { // Create the 'root' Spring application context AnnotationConfigWebApplicationContext rootContext = new AnnotationConfigWebApplicationContext(); rootContext.register(AppConfig.class); // Manage the lifecycle of the root application context container.addListener(new ContextLoaderListener(rootContext)); // Create the dispatcher servlet's Spring application context AnnotationConfigWebApplicationContext dispatcherContext = new AnnotationConfigWebApplicationContext(); dispatcherContext.register(DispatcherConfig.class); // Register and map the dispatcher servlet ServletRegistration.Dynamic dispatcher = container.addServlet("dispatcher", new DispatcherServlet(dispatcherContext)); dispatcher.setLoadOnStartup(1); dispatcher.addMapping("/"); } }
As an alternative to the above, you can also extend from . Remember that WebApplicationInitializer
implementations are detected automatically -- so you are free to package them within your application as you see fit. Ordering WebApplicationInitializer
execution WebApplicationInitializer
implementations may optionally be annotated at the class level with Spring's @org.springframework.core.annotation.Order annotation or may implement Spring's org.springframework.core.Ordered interface. If so, the initializers will be ordered prior to invocation. This provides a mechanism for users to ensure the order in which servlet container initialization occurs. Use of this feature is expected to be rare, as typical applications will likely centralize all container initialization within a single WebApplicationInitializer
. Caveats web.xml versioning
WEB-INF/web.xml
and WebApplicationInitializer
use are not mutually exclusive; for example, web.xml can register one servlet, and a WebApplicationInitializer
can register another. An initializer can even modify registrations performed in web.xml
through methods such as ServletContext#getServletRegistration(String)
. However, if WEB-INF/web.xml
is present in the application, its version
attribute must be set to "3.0" or greater, otherwise ServletContainerInitializer
bootstrapping will be ignored by the servlet container.
Apache Tomcat maps its internal DefaultServlet
to "/", and on Tomcat versions <= 7.0.14, this servlet mapping cannot be overridden programmatically. 7.0.15 fixes this issue. Overriding the "/" servlet mapping has also been tested successfully under GlassFish 3.1.
Author
Chris Beams
Since
3.1
See Also
SpringServletContainerInitializerorg.springframework.web.context.AbstractContextLoaderInitializerorg.springframework.web.servlet.support.AbstractDispatcherServletInitializerorg.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer
abstract fun onStartup(servletContext: ServletContext): Unit
Configure the given ServletContext with any servlets, filters, listeners context-params and attributes necessary for initializing this web application. See examples WebApplicationInitializer. |
abstract class AbstractContextLoaderInitializer : WebApplicationInitializer
Convenient base class for WebApplicationInitializer implementations that register a ContextLoaderListener in the servlet context. The only method required to be implemented by subclasses is |
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abstract class AbstractReactiveWebInitializer : WebApplicationInitializer
Base class for a org.springframework.web.WebApplicationInitializer that installs a Spring Reactive Web Application on a Servlet container. Spring configuration is loaded and given to |
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abstract class AbstractServletHttpHandlerAdapterInitializer : WebApplicationInitializer
Base class for org.springframework.web.WebApplicationInitializer implementations that register a ServletHttpHandlerAdapter in the servlet context. |