"Incorrect string value" when trying to insert UTF-8 into MySQL via JDBC?

This is how my connection is set:
Connection conn = DriverManager.getConnection(url + dbName +"?useUnicode=true&characterEncoding=utf-8", userName, password);

And I'm getting the following error when tyring to add a row to a table:
Incorrect string value: '\xF0\x90\x8D\x83\xF0\x90...' for column 'content' at row 1

I'm inserting thousands of records, and I always get this error when the text contains \xF0 (i.e. the the incorrect string value always starts with \xF0).

The column's collation is utf8_general_ci.

What could be the problem?