1 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method AJAX! KC Web & Java 29 november 2005

2 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method 1-0

3 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method J2SE Design Patterns: Het Template Pattern Lucas Jellema KC Web & Java – 10 Minute Talks, Donderdag 29 november 2005

4 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Introducing Design Patterns Recurring algorithms, construction, designs Best practices Associated with various technologies  ERD  Database Design  J2EE Architecture MVC, Business Delegate, Façade, …  Non IT environments  J2SE – Java Programming Most famous: ….  Singleton

5 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Great Book: Head First Design Patterns Observer Decorator Factory Singleton Command Adapter and Façade Iterator and Composite State Proxy Compound

6 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method The Template Pattern aka Don’t Call us, We will call You! TeaMaker getCup boilWater steepTeaBag pourInCup optional addSugar optional addLemon CoffeeMaker getCup boilWater brewCoffee pourInCup optional addSugar optional addMilk CoffeeVerkeerdMaker getCup boilWater brewCoffee pourInCup addMilk optional addSugar getCup boilWater brew WHATEVER pourInCup addCondiments Generic pattern

7 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Template Method Pattern template method: prepareRecipe

8 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method The Template Pattern The Template (Method) Pattern  Defines the skeleton of an algorithm in a method, deferring some steps or pieces to sub-classes  Lets subclasses (re)define part of an algorithm without changing its structure (abstract) superclass algorithm final abstract hook (concrete) subclass

9 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Template Method Pattern template method: prepareRecipe

10 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method The Template Pattern The Template (Method) Pattern  Three modes Forcing subclasses to implement certain steps (abstract or interface) Allowing subclasses to complement certain steps (through overridable hooks) Allowing subclasses to redefine steps (through overridable algorithm methods)  Non-overridable steps are defined final in the superclass

11 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Template Method: BeverageMachine.prepareRecipe()

12 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method package nl.amis.shop.mypackage; public class CoffeeShop { public CoffeeShop() { } public void drinkBeverage( BeverageMachine bm) { bm.prepareRecipe(); System.out.println("Enjoy your drink\n"); } public static void main(String[] args) { CoffeeShop coffeeShop = new CoffeeShop(); coffeeShop.drinkBeverage(new CoffeeMachine()); coffeeShop.drinkBeverage(new TeaMachine()); coffeeShop.drinkBeverage(new CoffeeWrongMachine()); }//main } Using the Template Method My Little Coffeshop

13 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Examples of the Template (Method) Pattern Don’t Call Us – We Will Call You Spring JDBC Arrays.sort(Object[] a)  Not a Superclass/Subclass situation  To use sort on an array, the array elements must implement the Comparable interface by defining the compareTo() method java.io.InputStream – abstract read() method that subclasses must implement Swing  JFrame – paint() method: a hook with an empty default implementation  Applet – start(), stop(), destroy(): hooks ADF DataAction  override onCommit, add onMyEvent

14 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Examples of the Template (Method) Pattern Outside the Java Arena Oracle Forms event-triggers  Pre-Insert, Post-Insert – hooks surrounding the Insert algorithm  even On-Insert that allows overriding of the core of the the Insert algoritm but even then the other hooks will exist Database DML Event Triggers  Before insert statement, before insert row  After insert row, After insert statement

15 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Architectuur Service DAO Domain Object Domain Object Domain Object JNDI

16 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Example import java.sql.*; import javax.sql.*; public class EmpDao { public List getAllEmployees() { Connection con = null; PreparedStatement pstmt = null; ResultSet rs = null; List emps = new ArrayList(); try { con = getConnection(); pstmt = con.prepareStatement ("select * from emp"); rs = pstmt.executeQuery(); while (rs.next()) { Employee e = new Employee(); e.setId (rs.getLong(1)); e.setName (rs.getString(2)); //... emps.add(e); } } catch (SQLException e) { // handle exception } finally { try { rs.close(); pstmt.close(); con.close(); } catch (SQLException e1) { // no action needed } return emps; } private Connection getConnection() throws SQLException { try { Context ic = new InitialContext(); DataSource ds = (DataSource) ic.lookup ("java:comp/env/jdbc/myDatabase"); return ds.getConnection(); } catch (NamingException e) { // handle exception return null; } private Connection getConnection() throws SQLException { try { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); return DriverManager.getConnection "tiger"); } catch (SQLException sqle) { // handle exception return null; }

17 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Template Pattern Operation largely follows a standard algorithm At certain steps, specialization or customization is required Several implementations  Abstract ‘hook’ methods that sub-class may override  Parametrize behaviour and have invoker provide the details Such as the SQL Query Spring JDBC Templates  Implement all JDBC wiring  Parametrize the query and the result-handling

18 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Example of Spring JDBC Template public interface empDao { public List getAllEmployees (); } public class EmployeeJdbcDao extends JdbcDaoSupport implements EmpDao { public List getAllEmployees() { JdbcTemplate jt = getJdbcTemplate(); return jt.queryForList (“select * from emp”); } <bean id="dataSourceDBDirect" class="org.springframework.jdbc.datasource.DriverManagerDataSource" destroy-method="close">

19 KC Web & Java – 29 november 2005 – Design Patterns – The Template Method Conclusions Template Method Pattern  Instead of overriding and reimplementing the algorithm in a subclass  The algorithms has predefined call outs To abstract method that subclasses MUST implement To concrete, overridable methods to change parts of the algorithm – but not the overall structure! To hooks (optionally implemented by subclasses to complement the steps of the algoritm Easy to apply Recognized from duplication of algorithm across classes  You frequently override a method and duplicate most of its implementation Read – and enjoy – Head First Design Patterns