I have the following and I get the error
java.lang.String cannot be cast to [Ljava.lang.String;
I have changed the Object[]
to String[]
because I faced the next error:
java.lang.Object cannot be cast to [Ljava.lang.String;
Any idea?
private Collection queryStatement(String SelectStatement) {
int colcount = 0;
int rowcount = 0;
int rowcounter = 0;
ArrayList a = new ArrayList();
Query query = getEntityManager().createNativeQuery(SelectStatement);
List<String[]> resultList = (List<String[]>) query.getResultList();
if (!resultList.equals(Collections.emptyList())) {
rowcount = resultList.size();
}
if (rowcount > 0) {
colcount = ((String[]) query.getResultList().get(0)).length;
}
rows = rowcount;
cols = colcount;
String[][] array = new String[rowcount][colcount];
for (String[] obj : resultList) {
String[] record = new String[colcount];
for (int colCounter = 0; colCounter < colcount; colCounter++) {
record[colCounter] = safeValue(obj[colCounter]+"");
}
array[ rowcounter++] = (String[]) record;
}
a.add(array);
return a;
}
java.lang.String cannot be cast to [Ljava.lang.String;
This error occurs when you try to cast a String
to an array of String
.
For example:
List list = new ArrayList<>();
list.add("foo");
String[] values = (String[])list.get(0); -> throws the exception
For me you get this error because query.getResultList()
returns a List<String>
or List<Object>
instead of List<String[]>
such that when you try to cast a value as a String[]
you get this exception.
According to the Javadoc createNativeQuery(String) returns a result of type Object[]
or a result of type Object
if there is only one column in the select list.
One simple way to fix it, could be to rely on the raw type for the result (it is not the most elegant approach but the simplest one) then later you can check the type of the content of the list to cast it properly.
List result = query.getResultList();
Then to check the type you can proceed as next:
if (resultList.isEmpty() || resultList.get(0) instanceof Object[]) {
// Several columns in the result
List<Object[]> resultList = (List<Object[]>) result;
// The rest of your current code here
} else {
// Only one column in the result
List<Object> resultList = (List<Object>) result;
...
}
A more elegant way could be to create an Entity
class and use createNativeQuery(String sqlString, Class entityClass)
to create your query, this way it will automatically map your columns with the fields of your Entity
Here is how it could look like
private Collection<T> queryStatement(String SelectStatement, Class<T> resultType) {
...
Query query = getEntityManager().createNativeQuery(SelectStatement, resultType);
List<T> resultList = (List<T>) query.getResultList();
...
}