#1514 [java] False positive when ResultSet.wasNull() is used

[Slava Semushin]

import java.sql.ResultSet;
import java.sql.SQLException;

public final class JdbcUtils {

    public static Integer getInteger(final ResultSet resultSet, final String fieldName) throws SQLException {
        final int value = resultSet.getInt(fieldName);
        if (resultSet.wasNull()) {
            return null;
        }

        return value;
    }

}
$ ./pmd-bin-5.5.1/bin/run.sh pmd -d example -R java-optimizations -f csv
"Problem","Package","File","Priority","Line","Description","Rule set","Rule"
"1","","/home/coder/example/JdbcUtils.java","3","7","Avoid declaring a variable if it is unreferenced before a possible exit point.","Optimization","PrematureDeclaration"

But it's not an error, because I can't declare variable later. I have to invoke ResultSet.getInt() first and later check whether it was NULL or not with ResultSet.wasNull() method.

[Andreas Dangel]

Hi,
you could write it in a different way and avoiding multiple returns, too:

import java.sql.ResultSet;
import java.sql.SQLException;

public final class JdbcUtils {
    public static Integer getInteger(final ResultSet resultSet, final String fieldName) throws SQLException {
        Integer value = resultSet.getInt(fieldName);
        if (resultSet.wasNull()) {
            value = null;
        }
        return value;
    }
}

Would that work for you?

I'm actually trying to avoid adjusting the rule PrematureOptimization with too specific cases like this one for ResultSet...

Regards,
Andreas

[Slava Semushin]

Here I've shown a bit simplified code. In reality I'm not returning this value as-is but modifying it and this means that I should add another if for checking for null again.

[Andreas Dangel]

Can you post the not-simplified-code, please? It's hard for me to understand your use case otherwise...

[Slava Semushin]

Yes, you can find it here: https://github.com/php-coder/mystamps/blob/b7fe1dac7a7f0bc09e9e153a8408687fd899c79f/src/main/java/ru/mystamps/web/dao/impl/JdbcUtils.java#L32-L52

[Andreas Dangel]

Thanks for your patience. I've got it now.
However, I don't think, we should change the rule for this use case. We currently have no exceptions for this rule and I'm hesitating to start adding a list of allowed violations (which could grow over time...)

Here are three workarounds/alternatives:

1. Since ResultSet.getInt(String) never returns null (it returns 0 if the column was NULL), we could just rely on autoboxing:

        Integer value = resultSet.getInt(fieldName);
        if (resultSet.wasNull()) {
            value = null;
        }

        return value;

1. Or we could explicitly convert it to an Integer reference type:

        Integer value = Integer.valueOf(resultSet.getInt(fieldName));
        if (resultSet.wasNull()) {
            value = null;
        }

        return value;

1. Using the ternary operator

        int value = resultSet.getInt(fieldName);
        return resultSet.wasNull() ? null : Integer.valueOf(value);

Or you could leave your implementation just as-is with the suppression in place. Remember, not all rules of PMD can be applied to every use case - sometimes, there are good reasons to violate rules - and here the JDBC API makes it necessary to have this specific call flow.

Therefore I'm closing this issue as "won't fix".