118 lines
4.1 KiB
Plaintext
118 lines
4.1 KiB
Plaintext
[[mvc-servlet]]
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= DispatcherServlet
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[.small]#xref:web/webflux/dispatcher-handler.adoc[See equivalent in the Reactive stack]#
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Spring MVC, as many other web frameworks, is designed around the front controller
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pattern where a central `Servlet`, the `DispatcherServlet`, provides a shared algorithm
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for request processing, while actual work is performed by configurable delegate components.
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This model is flexible and supports diverse workflows.
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The `DispatcherServlet`, as any `Servlet`, needs to be declared and mapped according
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to the Servlet specification by using Java configuration or in `web.xml`.
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In turn, the `DispatcherServlet` uses Spring configuration to discover
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the delegate components it needs for request mapping, view resolution, exception
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handling, xref:web/webmvc/mvc-servlet/special-bean-types.adoc[and more].
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The following example of the Java configuration registers and initializes
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the `DispatcherServlet`, which is auto-detected by the Servlet container
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(see xref:web/webmvc/mvc-servlet/container-config.adoc[Servlet Config]):
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[tabs]
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======
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Java::
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+
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[source,java,indent=0,subs="verbatim,quotes"]
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----
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public class MyWebApplicationInitializer implements WebApplicationInitializer {
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@Override
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public void onStartup(ServletContext servletContext) {
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// Load Spring web application configuration
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AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
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context.register(AppConfig.class);
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// Create and register the DispatcherServlet
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DispatcherServlet servlet = new DispatcherServlet(context);
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ServletRegistration.Dynamic registration = servletContext.addServlet("app", servlet);
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registration.setLoadOnStartup(1);
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registration.addMapping("/app/*");
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}
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}
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----
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Kotlin::
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+
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[source,kotlin,indent=0,subs="verbatim,quotes"]
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----
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class MyWebApplicationInitializer : WebApplicationInitializer {
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override fun onStartup(servletContext: ServletContext) {
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// Load Spring web application configuration
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val context = AnnotationConfigWebApplicationContext()
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context.register(AppConfig::class.java)
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// Create and register the DispatcherServlet
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val servlet = DispatcherServlet(context)
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val registration = servletContext.addServlet("app", servlet)
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registration.setLoadOnStartup(1)
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registration.addMapping("/app/*")
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}
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}
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----
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======
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NOTE: In addition to using the ServletContext API directly, you can also extend
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`AbstractAnnotationConfigDispatcherServletInitializer` and override specific methods
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(see the example under xref:web/webmvc/mvc-servlet/context-hierarchy.adoc[Context Hierarchy]).
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NOTE: For programmatic use cases, a `GenericWebApplicationContext` can be used as an
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alternative to `AnnotationConfigWebApplicationContext`. See the
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{spring-framework-api}/web/context/support/GenericWebApplicationContext.html[`GenericWebApplicationContext`]
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javadoc for details.
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The following example of `web.xml` configuration registers and initializes the `DispatcherServlet`:
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[source,xml,indent=0,subs="verbatim,quotes"]
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----
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<web-app>
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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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<context-param>
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<param-name>contextConfigLocation</param-name>
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<param-value>/WEB-INF/app-context.xml</param-value>
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</context-param>
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<servlet>
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<servlet-name>app</servlet-name>
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<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
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<init-param>
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<param-name>contextConfigLocation</param-name>
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<param-value></param-value>
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</init-param>
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<load-on-startup>1</load-on-startup>
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</servlet>
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<servlet-mapping>
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<servlet-name>app</servlet-name>
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<url-pattern>/app/*</url-pattern>
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</servlet-mapping>
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</web-app>
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----
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NOTE: Spring Boot follows a different initialization sequence. Rather than hooking into
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the lifecycle of the Servlet container, Spring Boot uses Spring configuration to
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bootstrap itself and the embedded Servlet container. `Filter` and `Servlet` declarations
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are detected in Spring configuration and registered with the Servlet container.
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For more details, see the
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{spring-boot-docs-ref}/web/servlet.html#web.servlet.embedded-container[Spring Boot documentation].
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