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Tutorials : Managing DAO transactions in Java :

Testing the Transaction Handler

JUnit is the obvious choice when testing whether the transaction handling works as intended. Here's some code that will try to insert the same DVD twice. This results in an error and forces a rollback. The test determines whether the first—correctly inserted—DVD has been rolled back and is no longer in the database:

public void testTransaction4() throws DAOException {
  trans.begin();

  String id = "ID3";
  String title = "Troy";
  manager.createDVD(id, title);

  // Check for correct insert
  DVD dvd = manager.getDVD(id);
  assertNotNull("Test for ID3", dvd);

  // Try a double insert
  try {
    manager.createDVD(id, title);
    fail("Double create must throw an exception");
  } catch (DAOException e) {
    trans.rollback();
  }

  // Check that the inserted record has been rolled back
  dvd = manager.getDVD(id);
  assertNull("Test for ID3", dvd);
}

If the test is successful, the JUnit will show a "green bar."

Flexibility Through Interfaces

Now you know how to use a Transaction object to manage DAO transactions in a simple and back-end neutral way. There is a set of conventions that have to be followed: the business logic must call the begin/end/rollback methods on the Transaction object, but that's all. By using interfaces to define DAOs and the Transaction object, it's a simple thing to replace the back-end system. This is especially useful during testing, since this allows you to use a mock-up of the back-end.

Happy coding!

Related Resources

All the programs and files from the article are in this zip-file.
The examples use MySQL as the JDBC implementation. See "Installation of MySQL" in this article for information on how to install and use MySQL.
Sun's "Core J2EE Patterns: Data Access Object"
Handling transactions, logging, and exceptions with DAOs: "Advanced DAO Programming"
DAO Code Examples
Links to Other DAO Articles.

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