/*
* Copyright 2002-2020 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
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package org.springframework.web;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.ServiceLoader;
import java.util.Set;
import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.HandlesTypes;
import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;
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<Object>) 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.
In combination with web.xml
A web application can choose to limit the amount of classpath scanning the Servlet container does at startup either through the metadata-complete attribute in web.xml, which controls scanning for Servlet annotations or through an <absolute-ordering> element also in web.xml, which controls which web fragments (i.e. jars) are allowed to perform a ServletContainerInitializer scan. When using this feature, the SpringServletContainerInitializer can be enabled by adding "spring_web" to the list of named web fragments in web.xml as follows: <absolute-ordering>
<name>some_web_fragment</name>
<name>spring_web</name>
</absolute-ordering>
Relationship to Spring's WebApplicationInitializer
Spring's WebApplicationInitializer SPI consists of just one method: WebApplicationInitializer.onStartup(ServletContext). The signature is intentionally quite similar to onStartup.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. In other words, any servlet, listener, or filter may be registered within a WebApplicationInitializer, not just Spring MVC-specific components.
This class is neither designed for extension 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.
Author: Chris Beams, Juergen Hoeller, Rossen Stoyanchev See Also: - onStartup(Set, ServletContext)
- WebApplicationInitializer
Since: 3.1
/**
* Servlet 3.0 {@link ServletContainerInitializer} designed to support code-based
* configuration of the servlet container using Spring's {@link WebApplicationInitializer}
* SPI as opposed to (or possibly in combination with) the traditional
* {@code web.xml}-based approach.
*
* <h2>Mechanism of Operation</h2>
* This class will be loaded and instantiated and have its {@link #onStartup}
* method invoked by any Servlet 3.0-compliant container during container startup assuming
* that the {@code spring-web} module JAR is present on the classpath. This occurs through
* the JAR Services API {@link ServiceLoader#load(Class)} method detecting the
* {@code spring-web} module's {@code META-INF/services/javax.servlet.ServletContainerInitializer}
* service provider configuration file. See the
* <a href="https://download.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#Service%20Provider">
* JAR Services API documentation</a> as well as section <em>8.2.4</em> of the Servlet 3.0
* Final Draft specification for complete details.
*
* <h3>In combination with {@code web.xml}</h3>
* A web application can choose to limit the amount of classpath scanning the Servlet
* container does at startup either through the {@code metadata-complete} attribute in
* {@code web.xml}, which controls scanning for Servlet annotations or through an
* {@code <absolute-ordering>} element also in {@code web.xml}, which controls which
* web fragments (i.e. jars) are allowed to perform a {@code ServletContainerInitializer}
* scan. When using this feature, the {@link SpringServletContainerInitializer}
* can be enabled by adding "spring_web" to the list of named web fragments in
* {@code web.xml} as follows:
*
* <pre class="code">
* <absolute-ordering>
* <name>some_web_fragment</name>
* <name>spring_web</name>
* </absolute-ordering>
* </pre>
*
* <h2>Relationship to Spring's {@code WebApplicationInitializer}</h2>
* Spring's {@code WebApplicationInitializer} SPI consists of just one method:
* {@link WebApplicationInitializer#onStartup(ServletContext)}. The signature is intentionally
* quite similar to {@link ServletContainerInitializer#onStartup(Set, ServletContext)}:
* simply put, {@code SpringServletContainerInitializer} is responsible for instantiating
* and delegating the {@code ServletContext} to any user-defined
* {@code WebApplicationInitializer} implementations. It is then the responsibility of
* each {@code WebApplicationInitializer} to do the actual work of initializing the
* {@code ServletContext}. The exact process of delegation is described in detail in the
* {@link #onStartup onStartup} documentation below.
*
* <h2>General Notes</h2>
* In general, this class should be viewed as <em>supporting infrastructure</em> for
* the more important and user-facing {@code WebApplicationInitializer} SPI. Taking
* advantage of this container initializer is also completely <em>optional</em>: 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
* {@code WebApplicationInitializer} implementations available on the classpath. If no
* {@code WebApplicationInitializer} types are detected, this container initializer will
* have no effect.
*
* <p>Note that use of this container initializer and of {@code WebApplicationInitializer}
* is not in any way "tied" to Spring MVC other than the fact that the types are shipped
* in the {@code spring-web} module JAR. Rather, they can be considered general-purpose
* in their ability to facilitate convenient code-based configuration of the
* {@code ServletContext}. In other words, any servlet, listener, or filter may be
* registered within a {@code WebApplicationInitializer}, not just Spring MVC-specific
* components.
*
* <p>This class is neither designed for extension nor intended to be extended.
* It should be considered an internal type, with {@code WebApplicationInitializer}
* being the public-facing SPI.
*
* <h2>See Also</h2>
* See {@link WebApplicationInitializer} Javadoc for examples and detailed usage
* recommendations.<p>
*
* @author Chris Beams
* @author Juergen Hoeller
* @author Rossen Stoyanchev
* @since 3.1
* @see #onStartup(Set, ServletContext)
* @see WebApplicationInitializer
*/
@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
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.
Params: - webAppInitializerClasses – all implementations of
WebApplicationInitializer found on the application classpath - servletContext – the servlet context to be initialized
See Also: - WebApplicationInitializer.onStartup(ServletContext)
- AnnotationAwareOrderComparator
/**
* Delegate the {@code ServletContext} to any {@link WebApplicationInitializer}
* implementations present on the application classpath.
* <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)},
* Servlet 3.0+ containers will automatically scan the classpath for implementations
* of Spring's {@code WebApplicationInitializer} interface and provide the set of all
* such types to the {@code webAppInitializerClasses} parameter of this method.
* <p>If no {@code 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 {@code ServletContainerInitializer} has indeed been invoked but that
* no {@code WebApplicationInitializer} implementations were found.
* <p>Assuming that one or more {@code WebApplicationInitializer} types are detected,
* they will be instantiated (and <em>sorted</em> if the @{@link
* org.springframework.core.annotation.Order @Order} annotation is present or
* the {@link org.springframework.core.Ordered Ordered} interface has been
* implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)}
* method will be invoked on each instance, delegating the {@code ServletContext} such
* that each instance may register and configure servlets such as Spring's
* {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener},
* or any other Servlet API componentry such as filters.
* @param webAppInitializerClasses all implementations of
* {@link WebApplicationInitializer} found on the application classpath
* @param servletContext the servlet context to be initialized
* @see WebApplicationInitializer#onStartup(ServletContext)
* @see AnnotationAwareOrderComparator
*/
@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {
List<WebApplicationInitializer> initializers = Collections.emptyList();
if (webAppInitializerClasses != null) {
initializers = new ArrayList<>(webAppInitializerClasses.size());
for (Class<?> waiClass : webAppInitializerClasses) {
// Be defensive: Some servlet containers provide us with invalid classes,
// no matter what @HandlesTypes says...
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
try {
initializers.add((WebApplicationInitializer)
ReflectionUtils.accessibleConstructor(waiClass).newInstance());
}
catch (Throwable ex) {
throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
}
}
}
}
if (initializers.isEmpty()) {
servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
return;
}
servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
AnnotationAwareOrderComparator.sort(initializers);
for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext);
}
}
}