Unhandled checked exception handled in enclosing function

Question

I have a great number of methods for a class that require catching some checked exceptions, where they will all be handled the same way. Hence, I want to write a method to enclose all of the functions with the try catch. Here is the full code, using JDBC:

private static <T> T HandleResultSet(ResultSet rs, Function<ResultSet, T> fn) {
    T returnValue = null;

    try {
        while (rs.next()) {
            returnValue = fn.apply(rs);
        }
    }
    catch(SQLException se)
    {
        se.printStackTrace();
    }
    finally
    {
        try {
            if (rs != null)
                rs.close();
        }
        catch(SQLException se) {
            se.printStackTrace();
        }

        return returnValue;
    }
}

public static String MySQLMethod(int param)
{
    Function<ResultSet, String> getProperty = (ResultSet set) ->
    {
        if (set.next())
            return set.getString("Property");
        return "ERR";
    };

    ResultSet rs = CallSQL("SELECT * FROM [User] WHERE Param = '" + param + "';");
    return HandleResultSet(rs, getProperty);
}

For those unfamiliar with JDBC, the important part is that the methods "set.next()" and "set.getString()" in my "getProperty" function require a catch on SQLException. This catch is included in "HandleResultSet", but the compiler doesn't seem smart enough to know that, and I can't seem to get around the issue. Any thoughts on ways to handle this?

I am using the latest version of IntelliJ IDEA.

Answer 1

If you look at signature of java.util.function.Function#apply it doesn't throw any exception. So you have to create your own interface which throws SQLException:

@FunctionalInterface
public interface CheckedFunction<T, R> {
    R apply(T t) throws SQLException;
}

and then:

CheckedFunction<ResultSet, String> getProperty = (ResultSet set) -> {
        if (set.next())
            return set.getString("Property");
        return "ERR";
};

Also use try-with-resources for ResultSet