Improve Spring Session validation message

Closes gh-9284

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/session/SessionAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 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.
@@ -38,7 +38,6 @@ import org.springframework.context.annotation.ImportSelector;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.session.Session;
 import org.springframework.session.SessionRepository;
-import org.springframework.util.Assert;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for Spring Session.
@@ -96,11 +95,17 @@ public class SessionAutoConfiguration {
 		@PostConstruct
 		public void checkSessionRepository() {
 			StoreType storeType = this.sessionProperties.getStoreType();
-			if (storeType != StoreType.NONE) {
-				Assert.notNull(this.sessionRepositoryProvider.getIfAvailable(),
-						"No session repository could be auto-configured, check your "
-								+ "configuration (session store type is '" + storeType
-								+ "')");
+			if (storeType != StoreType.NONE
+					&& this.sessionRepositoryProvider.getIfAvailable() == null) {
+				if (storeType != null) {
+					throw new IllegalArgumentException("No session repository could be "
+							+ "auto-configured, check your configuration (session store "
+							+ "type is '" + storeType.name().toLowerCase() + "')");
+				}
+				else {
+					throw new IllegalArgumentException("No Spring Session store is "
+							+ "configured: set the 'spring.session.store-type' property");
+				}
 			}
 		}
 

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/session/SessionAutoConfigurationTests.java

@@ -52,11 +52,19 @@ public class SessionAutoConfigurationTests extends AbstractSessionAutoConfigurat
 	@Test
 	public void contextFailsIfStoreTypeNotSet() {
 		this.thrown.expect(BeanCreationException.class);
-		this.thrown.expectMessage("No session repository could be auto-configured");
-		this.thrown.expectMessage("session store type is 'null'");
+		this.thrown.expectMessage("No Spring Session store is configured");
+		this.thrown.expectMessage("set the 'spring.session.store-type' property");
 		load();
 	}
 
+	@Test
+	public void contextFailsIfStoreTypeNotAvailable() {
+		this.thrown.expect(BeanCreationException.class);
+		this.thrown.expectMessage("No session repository could be auto-configured");
+		this.thrown.expectMessage("session store type is 'mongo'");
+		load("spring.session.store-type=mongo");
+	}
+
 	@Test
 	public void autoConfigurationDisabledIfStoreTypeSetToNone() {
 		load("spring.session.store-type=none");
@@ -116,14 +124,6 @@ public class SessionAutoConfigurationTests extends AbstractSessionAutoConfigurat
 				.isEqualTo("foobar");
 	}
 
-	@Test
-	public void validationFailsIfSessionRepositoryIsNotConfigured() {
-		this.thrown.expect(BeanCreationException.class);
-		this.thrown.expectMessage("No session repository could be auto-configured");
-		this.thrown.expectMessage("session store type is 'JDBC'");
-		load("spring.session.store-type=jdbc");
-	}
-
 	@Configuration
 	static class SessionRepositoryConfiguration {