Java tutorial
/* * Copyright 2012-2019 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 * limitations under the License. */ package org.springframework.boot.web.servlet.support; import java.util.Collections; import javax.servlet.Filter; import javax.servlet.Servlet; import javax.servlet.ServletContext; import javax.servlet.ServletContextEvent; import javax.servlet.ServletException; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.boot.SpringApplication; import org.springframework.boot.builder.ParentContextApplicationContextInitializer; import org.springframework.boot.builder.SpringApplicationBuilder; import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent; import org.springframework.boot.web.servlet.ServletContextInitializer; import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext; import org.springframework.context.ApplicationContext; import org.springframework.context.ApplicationListener; import org.springframework.context.annotation.Configuration; import org.springframework.core.Ordered; import org.springframework.core.annotation.MergedAnnotations; import org.springframework.core.annotation.MergedAnnotations.SearchStrategy; import org.springframework.core.env.ConfigurableEnvironment; import org.springframework.util.Assert; import org.springframework.web.WebApplicationInitializer; import org.springframework.web.context.ConfigurableWebEnvironment; import org.springframework.web.context.ContextLoaderListener; import org.springframework.web.context.WebApplicationContext; /** * An opinionated {@link WebApplicationInitializer} to run a {@link SpringApplication} * from a traditional WAR deployment. Binds {@link Servlet}, {@link Filter} and * {@link ServletContextInitializer} beans from the application context to the server. * <p> * To configure the application either override the * {@link #configure(SpringApplicationBuilder)} method (calling * {@link SpringApplicationBuilder#sources(Class...)}) or make the initializer itself a * {@code @Configuration}. If you are using {@link SpringBootServletInitializer} in * combination with other {@link WebApplicationInitializer WebApplicationInitializers} you * might also want to add an {@code @Ordered} annotation to configure a specific startup * order. * <p> * Note that a WebApplicationInitializer is only needed if you are building a war file and * deploying it. If you prefer to run an embedded web server then you won't need this at * all. * * @author Dave Syer * @author Phillip Webb * @author Andy Wilkinson * @since 2.0.0 * @see #configure(SpringApplicationBuilder) */ public abstract class SpringBootServletInitializer implements WebApplicationInitializer { protected Log logger; // Don't initialize early private boolean registerErrorPageFilter = true; /** * Set if the {@link ErrorPageFilter} should be registered. Set to {@code false} if * error page mappings should be handled via the server and not Spring Boot. * @param registerErrorPageFilter if the {@link ErrorPageFilter} should be registered. */ protected final void setRegisterErrorPageFilter(boolean registerErrorPageFilter) { this.registerErrorPageFilter = registerErrorPageFilter; } @Override public void onStartup(ServletContext servletContext) throws ServletException { // Logger initialization is deferred in case an ordered // LogServletContextInitializer is being used this.logger = LogFactory.getLog(getClass()); WebApplicationContext rootAppContext = createRootApplicationContext(servletContext); if (rootAppContext != null) { servletContext.addListener(new ContextLoaderListener(rootAppContext) { @Override public void contextInitialized(ServletContextEvent event) { // no-op because the application context is already initialized } }); } else { this.logger.debug("No ContextLoaderListener registered, as createRootApplicationContext() did not " + "return an application context"); } } protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) { SpringApplicationBuilder builder = createSpringApplicationBuilder(); builder.main(getClass()); ApplicationContext parent = getExistingRootWebApplicationContext(servletContext); if (parent != null) { this.logger.info("Root context already created (using as parent)."); servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null); builder.initializers(new ParentContextApplicationContextInitializer(parent)); } builder.initializers(new ServletContextApplicationContextInitializer(servletContext)); builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class); builder = configure(builder); builder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext)); SpringApplication application = builder.build(); if (application.getAllSources().isEmpty() && MergedAnnotations .from(getClass(), SearchStrategy.TYPE_HIERARCHY).isPresent(Configuration.class)) { application.addPrimarySources(Collections.singleton(getClass())); } Assert.state(!application.getAllSources().isEmpty(), "No SpringApplication sources have been defined. Either override the " + "configure method or add an @Configuration annotation"); // Ensure error pages are registered if (this.registerErrorPageFilter) { application.addPrimarySources(Collections.singleton(ErrorPageFilterConfiguration.class)); } return run(application); } /** * Returns the {@code SpringApplicationBuilder} that is used to configure and create * the {@link SpringApplication}. The default implementation returns a new * {@code SpringApplicationBuilder} in its default state. * @return the {@code SpringApplicationBuilder}. * @since 1.3.0 */ protected SpringApplicationBuilder createSpringApplicationBuilder() { return new SpringApplicationBuilder(); } /** * Called to run a fully configured {@link SpringApplication}. * @param application the application to run * @return the {@link WebApplicationContext} */ protected WebApplicationContext run(SpringApplication application) { return (WebApplicationContext) application.run(); } private ApplicationContext getExistingRootWebApplicationContext(ServletContext servletContext) { Object context = servletContext.getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE); if (context instanceof ApplicationContext) { return (ApplicationContext) context; } return null; } /** * Configure the application. Normally all you would need to do is to add sources * (e.g. config classes) because other settings have sensible defaults. You might * choose (for instance) to add default command line arguments, or set an active * Spring profile. * @param builder a builder for the application context * @return the application builder * @see SpringApplicationBuilder */ protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) { return builder; } private static final class WebEnvironmentPropertySourceInitializer implements ApplicationListener<ApplicationEnvironmentPreparedEvent>, Ordered { private final ServletContext servletContext; private WebEnvironmentPropertySourceInitializer(ServletContext servletContext) { this.servletContext = servletContext; } @Override public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) { ConfigurableEnvironment environment = event.getEnvironment(); if (environment instanceof ConfigurableWebEnvironment) { ((ConfigurableWebEnvironment) environment).initPropertySources(this.servletContext, null); } } @Override public int getOrder() { return Ordered.HIGHEST_PRECEDENCE; } } }