Question

There are many steps involved in executing one SQL statement in Java:

1. Create connection
2. Create statement
3. Execute statement, create resultset
4. Close resultset
5. Close statement
6. Close connection

At each of these steps SQLException can be thrown. If we to handle all exception and release all the resources correctly, the code will will look like this with 4 levels of TRY stacked on the top of each other.

try {
     Connection connection = dataSource.getConnection();
     try {
           PreparedStatement statement = connection.prepareStatement("SELECT 1 FROM myTable");
           try {
                ResultSet result = statement.executeQuery();
                try {
                     if (result.next()) {
                           Integer theOne = result.getInt(1);
                     }
                }
                finally {
                     result.close();
                }
           }
           finally {
                statement.close();
           }
     }
     finally {
           connection.close();
     }
}
catch (SQLException e) {
// Handle exception
}

Can you propose a better (shorter) way to execute a statement while still release all the consumed resources?

Answer 1

Check out Apache Commons DbUtils, and in particular the closeQuietly() method. It will handle the connection/statement/result set closing correctly, including the cases where one or more are null.

An alternative is Spring JdbcTemplate, which abstracts a lot of work away from you, and you handle your database queries in a much more functional fashion. You simply provide a class as a callback to be called on for every row of a ResultSet. It’ll handle iteration, exception handling and the correct closing of resources.