DATAMONGO-1317 - Assert compatibility with mongo-java-driver 3.2.

We now do a defensive check against the actual WObject of WriteConcern to avoid the IllegalStateException raised by the new java-driver in case _w is null or not an Integer. This allows us to run against recent 2.13, 2.14, 3.0, 3.1 and the latest 3.2.0.

Original pull request: #337.

Author: christophstrobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -775,11 +775,17 @@ protected void prepareCollection(DBCollection collection) {
 	protected WriteConcern prepareWriteConcern(MongoAction mongoAction) {
 
 		WriteConcern wc = writeConcernResolver.resolve(mongoAction);
+		return potentiallyForceAcknowledgedWrite(wc);
+	}
+
+	private WriteConcern potentiallyForceAcknowledgedWrite(WriteConcern wc) {
 
-		if (MongoClientVersion.isMongo3Driver()
-				&& ObjectUtils.nullSafeEquals(WriteResultChecking.EXCEPTION, writeResultChecking)
-				&& (wc == null || wc.getW() < 1)) {
-			return WriteConcern.ACKNOWLEDGED;
+		if (ObjectUtils.nullSafeEquals(WriteResultChecking.EXCEPTION, writeResultChecking)
+				&& MongoClientVersion.isMongo3Driver()) {
+			if (wc == null || wc.getWObject() == null
+					|| (wc.getWObject() instanceof Number && ((Number) wc.getWObject()).intValue() < 1)) {
+				return WriteConcern.ACKNOWLEDGED;
+			}
 		}
 		return wc;
 	}