Dates Are Dates, Not Strings
You seem to be wanting to make a String of your date-time. Not necessary. JDBC is aware of the Java data type java.sql.Date which is a thin wrapper around java.util.Date.
See example in another question, Datetime in java or this java2s.com tutorial.
Joda-Time
By the way, if using Joda-Time, you can convert easily between a org.joda.time.DateTime and java.util.Date. Call the toDate()
method on DateTime class.
JSR 310 in Java 8
In the future, Java 8 includes a new set of java.time.* classes defined by JSR 310: Date and Time API to supplant the notoriously bad java.util.Date/Calendar classes. These classes are inspired by Joda-Time but are entirely re-architected.
ISO 8601 String Format
If you really want to pass a date-time as string, use format recognized by your database. For example, Postgres accepts ISO 8601 format and others. See "Date/Time Input" section of Date/Time Types page in Postgres doc.
Let Server Set Date-Time
Generally, it's a better idea to let the database engine insert the date-time rather than use your programming language. Most every database system will have various functions you can call to generate the current date-time. The SQL standard specifies a few such functions, but typically a database system offers various others in addition.
For example, Postgres 9 offers several ways to get current date-time.
Be sure to study the documentation. For example, in Postgres you may choose to get the date-time of the moment when the transaction began or you may get the moment when the date-time function is executed (later than the start of transaction). The transaction-start-time is useful when you are recording that time in multiple records and want them to all match on the same time value.