Track change of MongoSession's id to properly delete.

When a session is made invalid and changed to a new one, the old one must be deleted from MongoDB at the next save().

Resolves #116.

src/main/java/org/springframework/session/data/mongo/MongoSession.java

@@ -43,6 +43,7 @@ public class MongoSession implements Session {
 	private static final char DOT_COVER_CHAR = '';
 
 	private String id;
+	private String originalSessionId;
 	private long createdMillis = System.currentTimeMillis();
 	private long accessedMillis;
 	private long intervalSeconds;
@@ -60,6 +61,7 @@ public class MongoSession implements Session {
 	public MongoSession(String id, long maxInactiveIntervalInSeconds) {
 
 		this.id = id;
+		this.originalSessionId = id;
 		this.intervalSeconds = maxInactiveIntervalInSeconds;
 		setLastAccessedTime(Instant.ofEpochMilli(this.createdMillis));
 	}
@@ -72,6 +74,7 @@ public class MongoSession implements Session {
 		return attributeName.replace(DOT_COVER_CHAR, '.');
 	}
 
+	@Override
 	public String changeSessionId() {
 
 		String changedId = UUID.randomUUID().toString();
@@ -85,10 +88,12 @@ public class MongoSession implements Session {
 		return (T) this.attrs.get(coverDot(attributeName));
 	}
 
+	@Override
 	public Set<String> getAttributeNames() {
 		return this.attrs.keySet().stream().map(MongoSession::uncoverDot).collect(Collectors.toSet());
 	}
 
+	@Override
 	public void setAttribute(String attributeName, Object attributeValue) {
 
 		if (attributeValue == null) {
@@ -98,10 +103,12 @@ public class MongoSession implements Session {
 		}
 	}
 
+	@Override
 	public void removeAttribute(String attributeName) {
 		this.attrs.remove(coverDot(attributeName));
 	}
 
+	@Override
 	public Instant getCreationTime() {
 		return Instant.ofEpochMilli(this.createdMillis);
 	}
@@ -110,24 +117,29 @@ public class MongoSession implements Session {
 		this.createdMillis = created;
 	}
 
+	@Override
 	public Instant getLastAccessedTime() {
 		return Instant.ofEpochMilli(this.accessedMillis);
 	}
 
+	@Override
 	public void setLastAccessedTime(Instant lastAccessedTime) {
 
 		this.accessedMillis = lastAccessedTime.toEpochMilli();
 		this.expireAt = Date.from(lastAccessedTime.plus(Duration.ofSeconds(this.intervalSeconds)));
 	}
 
+	@Override
 	public Duration getMaxInactiveInterval() {
 		return Duration.ofSeconds(this.intervalSeconds);
 	}
 
+	@Override
 	public void setMaxInactiveInterval(Duration interval) {
 		this.intervalSeconds = interval.getSeconds();
 	}
 
+	@Override
 	public boolean isExpired() {
 		return this.intervalSeconds >= 0 && new Date().after(this.expireAt);
 	}
@@ -140,14 +152,15 @@ public class MongoSession implements Session {
 		if (o == null || getClass() != o.getClass())
 			return false;
 		MongoSession that = (MongoSession) o;
-		return Objects.equals(id, that.id);
+		return Objects.equals(this.id, that.id);
 	}
 
 	@Override
 	public int hashCode() {
-		return Objects.hash(id);
+		return Objects.hash(this.id);
 	}
 
+	@Override
 	public String getId() {
 		return this.id;
 	}
@@ -159,4 +172,12 @@ public class MongoSession implements Session {
 	public void setExpireAt(final Date expireAt) {
 		this.expireAt = expireAt;
 	}
+
+	boolean hasChangedSessionId() {
+		return !getId().equals(this.originalSessionId);
+	}
+
+	String getOriginalSessionId() {
+		return this.originalSessionId;
+	}
 }

src/main/java/org/springframework/session/data/mongo/ReactiveMongoSessionRepository.java

@@ -15,6 +15,8 @@
  */
 package org.springframework.session.data.mongo;
 
+import static org.springframework.data.mongodb.core.query.Criteria.*;
+import static org.springframework.data.mongodb.core.query.Query.*;
 import static org.springframework.session.data.mongo.MongoSessionUtils.*;
 
 import java.time.Duration;
@@ -34,8 +36,6 @@ import org.springframework.session.ReactiveSessionRepository;
 import org.springframework.session.events.SessionCreatedEvent;
 import org.springframework.session.events.SessionDeletedEvent;
 
-import com.mongodb.DBObject;
-
 /**
  * A {@link ReactiveSessionRepository} implementation that uses Spring Data MongoDB.
  * 
@@ -92,12 +92,20 @@ public class ReactiveMongoSessionRepository
 	@Override
 	public Mono<Void> save(MongoSession session) {
 
-		DBObject dbObject = convertToDBObject(this.mongoSessionConverter, session);
-		if (dbObject != null) {
-			return this.mongoOperations.save(dbObject, this.collectionName).then();
-		} else {
-			return Mono.empty();
-		}
+		return Mono //
+				.justOrEmpty(convertToDBObject(this.mongoSessionConverter, session)) //
+				.flatMap(dbObject -> {
+					if (session.hasChangedSessionId()) {
+
+						return this.mongoOperations
+								.remove(query(where("_id").is(session.getOriginalSessionId())), this.collectionName) //
+								.then(this.mongoOperations.save(dbObject, this.collectionName));
+					} else {
+
+						return this.mongoOperations.save(dbObject, this.collectionName);
+					}
+				}) //
+				.then();
 	}
 
 	@Override