001/* 002 * Copyright 2002-2016 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.web; 018 019import java.lang.reflect.Modifier; 020import java.util.LinkedList; 021import java.util.List; 022import java.util.ServiceLoader; 023import java.util.Set; 024import javax.servlet.ServletContainerInitializer; 025import javax.servlet.ServletContext; 026import javax.servlet.ServletException; 027import javax.servlet.annotation.HandlesTypes; 028 029import org.springframework.core.annotation.AnnotationAwareOrderComparator; 030 031/** 032 * Servlet 3.0 {@link ServletContainerInitializer} designed to support code-based 033 * configuration of the servlet container using Spring's {@link WebApplicationInitializer} 034 * SPI as opposed to (or possibly in combination with) the traditional 035 * {@code web.xml}-based approach. 036 * 037 * <h2>Mechanism of Operation</h2> 038 * This class will be loaded and instantiated and have its {@link #onStartup} 039 * method invoked by any Servlet 3.0-compliant container during container startup assuming 040 * that the {@code spring-web} module JAR is present on the classpath. This occurs through 041 * the JAR Services API {@link ServiceLoader#load(Class)} method detecting the 042 * {@code spring-web} module's {@code META-INF/services/javax.servlet.ServletContainerInitializer} 043 * service provider configuration file. See the 044 * <a href="https://download.oracle.com/javase/6/docs/technotes/guides/jar/jar.html#Service%20Provider"> 045 * JAR Services API documentation</a> as well as section <em>8.2.4</em> of the Servlet 3.0 046 * Final Draft specification for complete details. 047 * 048 * <h3>In combination with {@code web.xml}</h3> 049 * A web application can choose to limit the amount of classpath scanning the Servlet 050 * container does at startup either through the {@code metadata-complete} attribute in 051 * {@code web.xml}, which controls scanning for Servlet annotations or through an 052 * {@code <absolute-ordering>} element also in {@code web.xml}, which controls which 053 * web fragments (i.e. jars) are allowed to perform a {@code ServletContainerInitializer} 054 * scan. When using this feature, the {@link SpringServletContainerInitializer} 055 * can be enabled by adding "spring_web" to the list of named web fragments in 056 * {@code web.xml} as follows: 057 * 058 * <pre class="code"> 059 * {@code 060 * <absolute-ordering> 061 * <name>some_web_fragment</name> 062 * <name>spring_web</name> 063 * </absolute-ordering> 064 * }</pre> 065 * 066 * <h2>Relationship to Spring's {@code WebApplicationInitializer}</h2> 067 * Spring's {@code WebApplicationInitializer} SPI consists of just one method: 068 * {@link WebApplicationInitializer#onStartup(ServletContext)}. The signature is intentionally 069 * quite similar to {@link ServletContainerInitializer#onStartup(Set, ServletContext)}: 070 * simply put, {@code SpringServletContainerInitializer} is responsible for instantiating 071 * and delegating the {@code ServletContext} to any user-defined 072 * {@code WebApplicationInitializer} implementations. It is then the responsibility of 073 * each {@code WebApplicationInitializer} to do the actual work of initializing the 074 * {@code ServletContext}. The exact process of delegation is described in detail in the 075 * {@link #onStartup onStartup} documentation below. 076 * 077 * <h2>General Notes</h2> 078 * In general, this class should be viewed as <em>supporting infrastructure</em> for 079 * the more important and user-facing {@code WebApplicationInitializer} SPI. Taking 080 * advantage of this container initializer is also completely <em>optional</em>: while 081 * it is true that this initializer will be loaded and invoked under all Servlet 3.0+ 082 * runtimes, it remains the user's choice whether to make any 083 * {@code WebApplicationInitializer} implementations available on the classpath. If no 084 * {@code WebApplicationInitializer} types are detected, this container initializer will 085 * have no effect. 086 * 087 * <p>Note that use of this container initializer and of {@code WebApplicationInitializer} 088 * is not in any way "tied" to Spring MVC other than the fact that the types are shipped 089 * in the {@code spring-web} module JAR. Rather, they can be considered general-purpose 090 * in their ability to facilitate convenient code-based configuration of the 091 * {@code ServletContext}. In other words, any servlet, listener, or filter may be 092 * registered within a {@code WebApplicationInitializer}, not just Spring MVC-specific 093 * components. 094 * 095 * <p>This class is neither designed for extension nor intended to be extended. 096 * It should be considered an internal type, with {@code WebApplicationInitializer} 097 * being the public-facing SPI. 098 * 099 * <h2>See Also</h2> 100 * See {@link WebApplicationInitializer} Javadoc for examples and detailed usage 101 * recommendations.<p> 102 * 103 * @author Chris Beams 104 * @author Juergen Hoeller 105 * @author Rossen Stoyanchev 106 * @since 3.1 107 * @see #onStartup(Set, ServletContext) 108 * @see WebApplicationInitializer 109 */ 110@HandlesTypes(WebApplicationInitializer.class) 111public class SpringServletContainerInitializer implements ServletContainerInitializer { 112 113 /** 114 * Delegate the {@code ServletContext} to any {@link WebApplicationInitializer} 115 * implementations present on the application classpath. 116 * <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)}, 117 * Servlet 3.0+ containers will automatically scan the classpath for implementations 118 * of Spring's {@code WebApplicationInitializer} interface and provide the set of all 119 * such types to the {@code webAppInitializerClasses} parameter of this method. 120 * <p>If no {@code WebApplicationInitializer} implementations are found on the classpath, 121 * this method is effectively a no-op. An INFO-level log message will be issued notifying 122 * the user that the {@code ServletContainerInitializer} has indeed been invoked but that 123 * no {@code WebApplicationInitializer} implementations were found. 124 * <p>Assuming that one or more {@code WebApplicationInitializer} types are detected, 125 * they will be instantiated (and <em>sorted</em> if the @{@link 126 * org.springframework.core.annotation.Order @Order} annotation is present or 127 * the {@link org.springframework.core.Ordered Ordered} interface has been 128 * implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)} 129 * method will be invoked on each instance, delegating the {@code ServletContext} such 130 * that each instance may register and configure servlets such as Spring's 131 * {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener}, 132 * or any other Servlet API componentry such as filters. 133 * @param webAppInitializerClasses all implementations of 134 * {@link WebApplicationInitializer} found on the application classpath 135 * @param servletContext the servlet context to be initialized 136 * @see WebApplicationInitializer#onStartup(ServletContext) 137 * @see AnnotationAwareOrderComparator 138 */ 139 @Override 140 public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) 141 throws ServletException { 142 143 List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>(); 144 145 if (webAppInitializerClasses != null) { 146 for (Class<?> waiClass : webAppInitializerClasses) { 147 // Be defensive: Some servlet containers provide us with invalid classes, 148 // no matter what @HandlesTypes says... 149 if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) && 150 WebApplicationInitializer.class.isAssignableFrom(waiClass)) { 151 try { 152 initializers.add((WebApplicationInitializer) waiClass.newInstance()); 153 } 154 catch (Throwable ex) { 155 throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex); 156 } 157 } 158 } 159 } 160 161 if (initializers.isEmpty()) { 162 servletContext.log("No Spring WebApplicationInitializer types detected on classpath"); 163 return; 164 } 165 166 servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath"); 167 AnnotationAwareOrderComparator.sort(initializers); 168 for (WebApplicationInitializer initializer : initializers) { 169 initializer.onStartup(servletContext); 170 } 171 } 172 173}