Behavioral Patterns : Memento

Properties:

-          Can be used when object state needs to be saved between interactions.

Implementation:

-          Originator class is the class of which state needs to be saved. It should be able to save its state into Memento objects and restore its state from Memento objects.

-          Memento objects keep state of originator object.

-          Caretaker is the client code which saves and restores state of originator using Memento objects.

Java Standard Library Implementations:

-          javax.faces.component. StateHolder implementations

-          java.sql.Connection

Example Usage:

try{

   //assume connection is acquired successfully

   conn.setAutoCommit(false);

   Statement statement = conn.createStatement();

  

   String DELETE_SQL = "delete from Person";

   statement.executeUpdate(DELETE_SQL);

   

   //set a Savepoint, we want to ensure that delete is done

   Savepoint savepoint = conn.setSavepoint("deleteSavePoint");

  

   //Execute an incorrect SQL statement which fails

   String INSERT_SQL = "INSERT INTO Person VALUES ('firstName', 'lastName', 'duplicate_candidat_key', 45)";

   statement.executeUpdate(INSERT_SQL);

  

   // If everything goes fine commit the changes.

   conn.commit();

}catch(SQLException se){

   // insert failed, return to deleteSavePoint

   conn.rollback(savepoint);

   conn.commit();

}