Checking for a null int value from a Java ResultSe

Question

In Java I'm trying to test for a null value, from a ResultSet, where the column is being cast to a primitive int type.

int iVal;
ResultSet rs = magicallyAppearingStmt.executeQuery(query);
if (rs.next()) {
  if (rs.getObject("ID_PARENT") != null && !rs.wasNull()) {
    iVal = rs.getInt("ID_PARENT");
  }
}

From the code fragment above, is there a better way to do this, and I assume that the second wasNull() test is redundant?

Educate us, and Thanks

Answer 1

Another solution:

public class DaoTools {
    static public Integer getInteger(ResultSet rs, String strColName) throws SQLException {
        int nValue = rs.getInt(strColName);
        return rs.wasNull() ? null : nValue;
    }
}

Answer 2

Just an update with Java Generics.

You could create an utility method to retrieve an optional value of any Java type from a given ResultSet, previously casted.

Unfortunately, getObject(columnName, Class) does not return null, but the default value for given Java type, so 2 calls are required

public <T> T getOptionalValue(final ResultSet rs, final String columnName, final Class<T> clazz) throws SQLException {
    final T value = rs.getObject(columnName, clazz);
    return rs.wasNull() ? null : value;
}

In this example, your code could look like below:

final Integer columnValue = getOptionalValue(rs, Integer.class);
if (columnValue == null) {
    //null handling
} else {
    //use int value of columnValue with autoboxing
}

Happy to get feedback

Answer 3

Another nice way of checking, if you have control the SQL, is to add a default value in the query itself for your int column. Then just check for that value.

e.g for an Oracle database, use NVL

SELECT NVL(ID_PARENT, -999) FROM TABLE_NAME;

then check

if (rs.getInt('ID_PARENT') != -999)
{
}

Of course this also is under the assumption that there is a value that wouldn't normally be found in the column.

Answer 4

For convenience, you can create a wrapper class around ResultSet that returns null values when ResultSet ordinarily would not.

public final class ResultSetWrapper {

    private final ResultSet rs;

    public ResultSetWrapper(ResultSet rs) {
        this.rs = rs;
    }

    public ResultSet getResultSet() {
        return rs;
    }

    public Boolean getBoolean(String label) throws SQLException {
        final boolean b = rs.getBoolean(label);
        if (rs.wasNull()) {
            return null;
        }
        return b;
    }

    public Byte getByte(String label) throws SQLException {
        final byte b = rs.getByte(label);
        if (rs.wasNull()) {
            return null;
        }
        return b;
    }

    // ...

}

Answer 5

AFAIK you can simply use

iVal = rs.getInt("ID_PARENT");
if (rs.wasNull()) {
  // do somthing interesting to handle this situation
}

even if it is NULL.

Answer 6

With java 8 you can do this:

Long nVal = Optional.ofNullable(resultSet.getBigDecimal("col_name"))
                    .map(BigDecimal::longValue).orElse(null));

In that case you ensure that the nVal will be null (and not zero) if the SQL value is NULL