DATAMONGO-641 - Fixed potential NullPointerException in MongoLog4jAppender.

Log4j appender now only closes Mongo instance if available.

spring-data-mongodb-log4j/src/main/java/org/springframework/data/mongodb/log4j/MongoLog4jAppender.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011 by the original author(s).
+ * Copyright 2011-2013 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.
@@ -13,7 +13,6 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.data.mongodb.log4j;
 
 import java.net.UnknownHostException;
@@ -34,7 +33,10 @@ import com.mongodb.Mongo;
 import com.mongodb.WriteConcern;
 
 /**
- * @author Jon Brisbin <jbrisbin@vmware.com>
+ * Log4j appender writing log entries into a MongoDB instance.
+ * 
+ * @author Jon Brisbin
+ * @author Oliver Gierke
  */
 public class MongoLog4jAppender extends AppenderSkeleton {
 
@@ -130,8 +132,12 @@ public class MongoLog4jAppender extends AppenderSkeleton {
 		this.db = mongo.getDB(database);
 	}
 
-	@SuppressWarnings({ "unchecked" })
+	/*
+	 * (non-Javadoc)
+	 * @see org.apache.log4j.AppenderSkeleton#append(org.apache.log4j.spi.LoggingEvent)
+	 */
 	@Override
+	@SuppressWarnings({ "unchecked" })
 	protected void append(final LoggingEvent event) {
 		if (null == db) {
 			try {
@@ -199,10 +205,21 @@ public class MongoLog4jAppender extends AppenderSkeleton {
 		db.getCollection(coll).insert(dbo, wc);
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.apache.log4j.AppenderSkeleton#close()
+	 */
 	public void close() {
+
+		if (mongo != null) {
 			mongo.close();
 		}
+	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.apache.log4j.AppenderSkeleton#requiresLayout()
+	 */
 	public boolean requiresLayout() {
 		return true;
 	}

spring-data-mongodb-log4j/src/test/java/org/springframework/data/mongodb/log4j/MongoLog4jAppenderUnitTests.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2013 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
+ *
+ *      http://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.data.mongodb.log4j;
+
+import org.junit.Test;
+
+/**
+ * Unit tests for {@link MongoLog4jAppender}.
+ * 
+ * @author Oliver Gierke
+ */
+public class MongoLog4jAppenderUnitTests {
+
+	/**
+	 * @see DATAMONGO-641
+	 */
+	@Test
+	public void closesWithoutMongoInstancePresent() {
+		new MongoLog4jAppender().close();
+	}
+}