Change preference of session store implementations

The order has been determined based on usage statistics.

Closes gh-27756

Author: mbhave

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

@@ -116,8 +116,8 @@ DefaultCookieSerializerCustomizer rememberMeServicesCookieSerializerCustomizer()
 
 		@Configuration(proxyBeanMethods = false)
 		@ConditionalOnMissingBean(SessionRepository.class)
-		@Import({ RedisSessionConfiguration.class, MongoSessionConfiguration.class, HazelcastSessionConfiguration.class,
-				JdbcSessionConfiguration.class })
+		@Import({ RedisSessionConfiguration.class, JdbcSessionConfiguration.class, HazelcastSessionConfiguration.class,
+				MongoSessionConfiguration.class })
 		static class ServletSessionRepositoryConfiguration {
 
 		}

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

@@ -58,9 +58,9 @@ void defaultConfig() {
 	}
 
 	@Test
-	void hazelcastTakesPrecedenceOverJdbc() {
+	void hazelcastTakesPrecedenceOverMongo() {
 		this.contextRunner.withClassLoader(
-				new FilteredClassLoader(RedisIndexedSessionRepository.class, MongoIndexedSessionRepository.class))
+				new FilteredClassLoader(RedisIndexedSessionRepository.class, JdbcIndexedSessionRepository.class))
 				.run(this::validateDefaultConfig);
 	}
 

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

@@ -74,6 +74,12 @@ void defaultConfig() {
 		this.contextRunner.run(this::validateDefaultConfig);
 	}
 
+	@Test
+	void jdbcTakesPrecedenceOverMongoAndHazelcast() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader(RedisIndexedSessionRepository.class))
+				.run(this::validateDefaultConfig);
+	}
+
 	private void validateDefaultConfig(AssertableWebApplicationContext context) {
 		JdbcIndexedSessionRepository repository = validateSessionRepository(context,
 				JdbcIndexedSessionRepository.class);

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

@@ -63,12 +63,6 @@ void defaultConfig() {
 		this.contextRunner.run(validateSpringSessionUsesMongo("sessions"));
 	}
 
-	@Test
-	void mongoTakesPrecedenceOverJdbcAndHazelcast() {
-		this.contextRunner.withClassLoader(new FilteredClassLoader(RedisIndexedSessionRepository.class))
-				.run(validateSpringSessionUsesMongo("sessions"));
-	}
-
 	@Test
 	void defaultConfigWithCustomTimeout() {
 		this.contextRunner.withPropertyValues("spring.session.timeout=1m")

spring-boot-project/spring-boot-docs/src/docs/asciidoc/web/spring-session.adoc

@@ -4,9 +4,9 @@ Spring Boot provides {spring-session}[Spring Session] auto-configuration for a w
 When building a servlet web application, the following stores can be auto-configured:
 
 * Redis
-* MongoDB
-* Hazelcast
 * JDBC
+* Hazelcast
+* MongoDB
 
 Additionally, {spring-boot-for-apache-geode}[Spring Boot for Apache Geode] provides {spring-boot-for-apache-geode-docs}#geode-session[auto-configuration for using Apache Geode as a session store].
 
@@ -16,10 +16,10 @@ If a single Spring Session module is present on the classpath, Spring Boot uses
 If you have more than one implementation, Spring Boot uses the following order for choosing a specific implementation:
 
 . Redis
-. MongoDB
-. Hazelcast
 . JDBC
-. If none of Redis, MongoDB, Hazelcast and JDBC are available, we do not configure a `SessionRepository`.
+. Hazelcast
+. MongoDB
+. If none of Redis, JDBC, Hazelcast and MongoDB are available, we do not configure a `SessionRepository`.
 
 
 When building a reactive web application, the following stores can be auto-configured: