Add support for configuring Spring Session JDBC flush mode

See gh-17797

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

@@ -67,6 +67,7 @@ class JdbcSessionConfiguration {
 			}
 			setTableName(jdbcSessionProperties.getTableName());
 			setCleanupCron(jdbcSessionProperties.getCleanupCron());
+			setFlushMode(jdbcSessionProperties.getFlushMode());
 			setSaveMode(jdbcSessionProperties.getSaveMode());
 		}
 

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

@@ -18,6 +18,7 @@ package org.springframework.boot.autoconfigure.session;
 
 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.boot.jdbc.DataSourceInitializationMode;
+import org.springframework.session.FlushMode;
 import org.springframework.session.SaveMode;
 
 /**
@@ -56,6 +57,12 @@ public class JdbcSessionProperties {
 	 */
 	private DataSourceInitializationMode initializeSchema = DataSourceInitializationMode.EMBEDDED;
 
+	/**
+	 * Sessions flush mode. Determines when session changes are written to the session
+	 * store.
+	 */
+	private FlushMode flushMode = FlushMode.ON_SAVE;
+
 	/**
 	 * Sessions save mode. Determines how session changes are tracked and saved to the
 	 * session store.
@@ -94,6 +101,14 @@ public class JdbcSessionProperties {
 		this.initializeSchema = initializeSchema;
 	}
 
+	public FlushMode getFlushMode() {
+		return this.flushMode;
+	}
+
+	public void setFlushMode(FlushMode flushMode) {
+		this.flushMode = flushMode;
+	}
+
 	public SaveMode getSaveMode() {
 		return this.saveMode;
 	}

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

@@ -30,6 +30,7 @@ import org.springframework.boot.test.context.runner.WebApplicationContextRunner;
 import org.springframework.boot.web.servlet.FilterRegistrationBean;
 import org.springframework.jdbc.BadSqlGrammarException;
 import org.springframework.jdbc.core.JdbcOperations;
+import org.springframework.session.FlushMode;
 import org.springframework.session.SaveMode;
 import org.springframework.session.data.mongo.MongoOperationsSessionRepository;
 import org.springframework.session.data.redis.RedisOperationsSessionRepository;
@@ -130,6 +131,19 @@ class SessionAutoConfigurationJdbcTests extends AbstractSessionAutoConfiguration
 				});
 	}
 
+	@Test
+	void customFlushMode() {
+		this.contextRunner
+				.withPropertyValues("spring.session.store-type=jdbc", "spring.session.jdbc.flush-mode=immediate")
+				.run((context) -> {
+					assertThat(context.getBean(JdbcSessionProperties.class).getFlushMode())
+							.isEqualTo(FlushMode.IMMEDIATE);
+					SpringBootJdbcHttpSessionConfiguration configuration = context
+							.getBean(SpringBootJdbcHttpSessionConfiguration.class);
+					assertThat(configuration).hasFieldOrPropertyWithValue("flushMode", FlushMode.IMMEDIATE);
+				});
+	}
+
 	@Test
 	void customSaveMode() {
 		this.contextRunner