AJAX!

1. AJAX! KC Web & Java 29 november 2005

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

4. 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. Great Book: Head First Design Patterns • Observer • Decorator • Factory • Singleton • Command • Adapter and Façade • Iterator and Composite • State • Proxy • Compound

6. The Template Patternaka Don’t Call us, We will call You! TeaMaker CoffeeMaker CoffeeVerkeerdMaker • getCup • boilWater • steepTeaBag • pourInCup • optional addSugar • optional addLemon • getCup • boilWater • brewCoffee • pourInCup • optional addSugar • optional addMilk • getCup • boilWater • brewCoffee • pourInCup • addMilk • optional addSugar Generic pattern • getCup • boilWater • brew WHATEVER • pourInCup • addCondiments

7. Template Method Patterntemplate method: prepareRecipe

8. 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 final abstract algorithm hook (concrete) subclass (concrete) subclass

9. Template Method Patterntemplate method: prepareRecipe

10. 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. Template Method: BeverageMachine.prepareRecipe()

12. Using the Template MethodMy Little Coffeshop 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 }

13. Examples of the Template (Method) PatternDon’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. Examples of the Template (Method) PatternOutside 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. Architectuur Domain Object Domain Object Domain Object JNDI Service DAO

16. Example private Connection getConnection() throws SQLException { try { DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); return DriverManager.getConnection ("jdbc:oracle:thin:@localhost:1521:orcl“ ,"scott", "tiger"); } catch (SQLException sqle) { // handle exception return null; } } 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; } }

17. 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. 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"> <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver" /> <property name="url" value="jdbc:oracle:thin:@localhost:1521:BAARSJES1" /> <property name="username" value="scott" /> <property name="password" value="tiger" /> </bean> <bean id="employeeDAO" class="nl.amis.demo.dao.jdbc.EmployeeJdbcDao" > <property name="dataSource"> <ref local="dataSourceDBDirect" /> </property> </bean>

19. 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