I am trying to connect to run a query to fetch all the records in MongoDB and then convert the records into a list ofthe reference object type I am taking as a generic to my calling class. The code is running fine and achieving the desired result in Eclipse but gives a compilation error during a maven build , both maven and eclipse are referencing the same JDK(1.8). can someone please help me resolve this issue
public class MongoPersistenceImpl<T> {
MongoDatabase database=(MongoDatabase)MongoConnectImpl.getInstance().getConnection();
public List<T> getAll(T modelObject){
MongoCollection<Document> collection=database.getCollection(MongoConnectImpl.MONGO_COLLECTION);
List<T> reportList=new ArrayList<>();
Gson gson=new Gson();
MongoCursor<Document> cursor = collection.find().iterator();
try {
while (cursor.hasNext()) {
T report=gson.fromJson(cursor.next().toJson(),modelObject.getClass());
reportList.add(report);
}
return reportList;
}catch(Exception e){
CatsLogger.printLogs(3, "30016", e, MongoPersistenceImpl.class,new Object[]{"get all"} );
return null;
} finally {
cursor.close();
}
}
}
Logs :-
[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] incompatible types: inference variable T has incompatible bounds
equality constraints: capture#1 of ? extends java.lang.Object
upper bounds: T,java.lang.Object
The complete message on reproducing the same being :-
UPDATE : explicitly type casting the an Object variable worked , but I still need to understand how?
public List<T> getAll(T modelObject){
MongoCollection<Document> collection=database.getCollection(MongoConnectImpl.MONGO_COLLECTION);
List<T> reportList=new ArrayList<T>();
Gson gson=new Gson();
MongoCursor<Document> cursor = collection.find().iterator();
try {
while (cursor.hasNext()) {
Object rep=gson.fromJson(cursor.next().toJson(),modelObject.getClass());
T report=(T)rep;//explicit type cast
reportList.add(report);
}
return reportList;
}catch(Exception e){
CatsLogger.printLogs(3, "30016", e, MongoPersistenceImpl.class,new Object[]{"get all"} );
return null;
} finally {
cursor.close();
}
}
While you are trying to cast an object to a specific Type
of report
, try changing
T report = gson.fromJson(cursor.next().toJson(), modelObject.getClass());
to
T report = gson.fromJson(cursor.next().toJson(), (java.lang.reflect.Type) modelObject.getClass());
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