Allow spring.config.location to be configured via servlet context

Previously, in a war deployment, the web environment’s property sources
were initialized using the servlet context after the application’s
configuration had been read by ConfigFileApplicationListener. This
meant that spring.config.location configured via the servlet context
had no effect.

This commit adds a new ApplicationListener,
ServletContextApplicationListener, that initialises the configurable
web environment’s property sources using the servlet context. It’s
ordered with higher precedence than ConfigFileApplicationListener to
ensure that any properties defined in the servlet context are available
when loading the application’s configuration.

Closes gh-6801

spring-boot/src/main/java/org/springframework/boot/context/web/ServletContextApplicationListener.java

+/*
+ * Copyright 2012-2016 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
+ *
+ *      http://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.context.web;
+
+import javax.servlet.ServletContext;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.context.config.ConfigFileApplicationListener;
+import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;
+import org.springframework.context.ApplicationListener;
+import org.springframework.core.Ordered;
+import org.springframework.web.context.ConfigurableWebEnvironment;
+
+/**
+ * An {@link ApplicationListener} that initializes the {@link SpringApplication} using the
+ * {@link ServletContext}.
+ *
+ * @author Andy Wilkinson
+ */
+final class ServletContextApplicationListener
+		implements ApplicationListener<ApplicationEnvironmentPreparedEvent>, Ordered {
+
+	private final ServletContext servletContext;
+
+	ServletContextApplicationListener(ServletContext servletContext) {
+		this.servletContext = servletContext;
+	}
+
+	@Override
+	public int getOrder() {
+		return ConfigFileApplicationListener.DEFAULT_ORDER - 1;
+	}
+
+	@Override
+	public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
+		if (event.getEnvironment() instanceof ConfigurableWebEnvironment) {
+			((ConfigurableWebEnvironment) event.getEnvironment())
+					.initPropertySources(this.servletContext, null);
+		}
+	}
+
+}

spring-boot/src/main/java/org/springframework/boot/context/web/SpringBootServletInitializer.java

@@ -112,6 +112,7 @@ public abstract class SpringBootServletInitializer implements WebApplicationInit
 		}
 		builder.initializers(
 				new ServletContextApplicationContextInitializer(servletContext));
+		builder.listeners(new ServletContextApplicationListener(servletContext));
 		builder.contextClass(AnnotationConfigEmbeddedWebApplicationContext.class);
 		builder = configure(builder);
 		SpringApplication application = builder.build();

spring-boot/src/test/java/org/springframework/boot/context/web/SpringBootServletInitializerTests.java

@@ -30,11 +30,14 @@ import org.junit.rules.ExpectedException;
 import org.springframework.beans.DirectFieldAccessor;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.context.ApplicationListener;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.mock.web.MockServletContext;
 import org.springframework.web.context.WebApplicationContext;
 
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.hasItem;
+import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.is;
 import static org.junit.Assert.assertThat;
 
@@ -102,6 +105,14 @@ public class SpringBootServletInitializerTests {
 				equalToSet(WithErrorPageFilterNotRegistered.class));
 	}
 
+	@Test
+	public void servletContextApplicationListenerIsAdded() {
+		new WithConfiguredSource().createRootApplicationContext(this.servletContext);
+		assertThat(this.application.getListeners(),
+				hasItem((Matcher<? super ApplicationListener<?>>) instanceOf(
+						ServletContextApplicationListener.class)));
+	}
+
 	private Matcher<? super Set<Object>> equalToSet(Object... items) {
 		Set<Object> set = new LinkedHashSet<Object>();
 		Collections.addAll(set, items);