Provide Session Id Generation Strategy

spring-session-core/src/main/java/org/springframework/session/MapSession.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2014-2022 the original author or authors.
+ * Copyright 2014-2023 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.
@@ -21,9 +21,10 @@
 import java.time.Instant;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.Map;
+import java.util.ServiceLoader;
 import java.util.Set;
-import java.util.UUID;
 
 /**
  * <p>
@@ -44,6 +45,7 @@
  *
  * @author Rob Winch
  * @author Vedran Pavic
+ * @author Yanming Zhou
  * @since 1.0
  */
 public final class MapSession implements Session, Serializable {
@@ -229,7 +231,14 @@ public int hashCode() {
 	}
 
 	private static String generateId() {
-		return UUID.randomUUID().toString();
+		return sessionIdGenerator.generateId();
+	}
+
+	private static final SessionIdGenerator sessionIdGenerator;
+
+	static {
+		Iterator<SessionIdGenerator> generators = ServiceLoader.load(SessionIdGenerator.class).iterator();
+		sessionIdGenerator = generators.hasNext() ? generators.next() : SessionIdGenerator.DEFAULT;
 	}
 
 	private static final long serialVersionUID = 7160779239673823561L;

spring-session-core/src/main/java/org/springframework/session/SessionIdGenerator.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2014-2023 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
+ *
+ *      https://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.session;
+
+import java.util.UUID;
+
+/**
+ * <p>
+ * Id generator for creating new session.
+ * </p>
+ *
+ * @author Yanming Zhou
+ */
+@FunctionalInterface
+public interface SessionIdGenerator {
+
+	/**
+	 * Using random UUID as default id generator.
+	 */
+	SessionIdGenerator DEFAULT = () -> UUID.randomUUID().toString();
+
+	/**
+	 * Generate and return a new session identifier.
+	 * @return the newly generated session id
+	 */
+	String generateId();
+
+}

spring-session-core/src/test/java/org/springframework/session/SessionIdGeneratorTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2014-2023 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
+ *
+ *      https://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.session;
+
+import java.util.concurrent.atomic.AtomicLong;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author Yanming Zhou
+ */
+class SessionIdGeneratorTests {
+
+	static final String prefix = "sessionid-";
+
+	@Test
+	void sessionIdShouldStartsWithCustomizedPrefix() {
+		MapSession session = new MapSession();
+		assertThat(session.getId()).startsWith(prefix);
+		session.changeSessionId();
+		assertThat(session.getId()).startsWith(prefix);
+	}
+
+	public static class MySessionIdGenerator implements SessionIdGenerator {
+
+		private final AtomicLong counter = new AtomicLong();
+
+		@Override
+		public String generateId() {
+			return prefix + this.counter.incrementAndGet();
+		}
+
+	}
+
+}

spring-session-core/src/test/resources/META-INF/services/org.springframework.session.SessionIdGenerator

@@ -0,0 +1 @@
+org.springframework.session.SessionIdGeneratorTests$MySessionIdGenerator