Question

Objective: ensure all code paths either throw or return a valid connection; I am trying to explicitly avoid at all costs the connection object to ever return as “null”.

This is the best I could come up with:

public class JdbcConnectionManager {
  public static class JdbcConnectionFailureException extends Exception {
    private static final String JDBC_CONNECTION_INVALID_MESSAGE =
        "JDBC connection invalid, checked with timeout value of: "
            + JdbcConnectionManager.JDBC_CONNECTION_VALIDATION_TIMEOUT_IN_SECONDS;
    private static final long serialVersionUID = 1L;
    public JdbcConnectionFailureException(String message) {
      super(message);
    }
    public JdbcConnectionFailureException(Throwable throwable) {
      super(throwable);
    }
  }
  private static int JDBC_CONNECTION_VALIDATION_TIMEOUT_IN_SECONDS = 3;
  public static Connection getJdbcConnection(
      JdbcConnectionParameters jdbcConnectionParameters)
      throws JdbcConnectionFailureException {
    try {
      if (jdbcConnectionParameters
          .driverNeedsHelpRegisteringUsingClassForName()) {
        Class.forName(jdbcConnectionParameters
            .getClassForNameDriverRegistrationString());
      }
      Connection jdbcConnection =
          DriverManager.getConnection(jdbcConnectionParameters
              .getJbdcConnectionUrl());
      if (!jdbcConnection
          .isValid(JdbcConnectionManager.JDBC_CONNECTION_VALIDATION_TIMEOUT_IN_SECONDS)) {
        throw new JdbcConnectionManager.JdbcConnectionFailureException(
            JdbcConnectionManager.JdbcConnectionFailureException.JDBC_CONNECTION_INVALID_MESSAGE);
      }
      // TODO: perform further validation on the connection
      return jdbcConnection;
    } catch (ClassNotFoundException classNotFoundException) {
      throw new JdbcConnectionManager.JdbcConnectionFailureException(
          classNotFoundException);
    } catch (SQLException sqlException) {
      throw new JdbcConnectionManager.JdbcConnectionFailureException(
          sqlException);
    }
  }
}

Am I rock-solid here? Is there a better, more concise/elegant/robust way to ensure “connection” is never “null”?

EDIT:

I added a jdbcConnection.isValid() check but I have left out input validation. I’ll do that in the actual code.

Answer 1

It would be much clearer to just return the connection from inside the try block:

public static Connection getJdbcConnection(
              JdbcConnectionParameters jdbcConnectionParameters)
                                     throws JdbcConnectionFailureException {
    try {
        if (jdbcConnectionParameters.driverNeedsHelpRegisteringUsingClassForName()) {
            Class.forName(jdbcConnectionParameters
                                .getClassForNameDriverRegistrationString());
        }
        return DriverManager.getConnection(jdbcConnectionParameters
                   .getJbdcConnectionUrl());
        // TODO: perform further validation on the connection
    } 
    catch (ClassNotFoundException classNotFoundException) {
        throw new JdbcConnectionManager.JdbcConnectionFailureException(
            classNotFoundException);
    } 
    catch (SQLException sqlException) {
        throw new JdbcConnectionManager.JdbcConnectionFailureException(
            sqlException);
    }
}

EDIT : to answer your question about dead code:

jdbcConnection can NOT be null at this place, because if it was null, a NPE would have been thrown at the line

if (!jdbcConnection.isValid(...))