Template Method in Java
Template Method is a behavioral design pattern that allows you to define a skeleton of an algorithm in a base class and let subclasses override the steps without changing the overall algorithm’s structure.
Complexity:
Popularity:
Usage examples: The Template Method pattern is quite common in Java frameworks. Developers often use it to provide framework users with a simple means of extending standard functionality using inheritance.
Here are some examples of Template Methods in core Java libraries:
-
All non-abstract methods of
java.io.InputStream,java.io.OutputStream,java.io.Readerandjava.io.Writer. -
All non-abstract methods of
java.util.AbstractList,java.util.AbstractSetandjava.util.AbstractMap. -
In
javax.servlet.http.HttpServletclass, all thedoXXX()methods send the HTTP 405 “Method Not Allowed” error by default. However, you can override any of those methods to send a different response.
Identification: Template Method can be recognized if you see a method in base class that calls a bunch of other methods that are either abstract or empty.
Overriding standard steps of an algorithm
In this example, the Template Method pattern defines an algorithm of working with a social network. Subclasses that match a particular social network, implement these steps according to the API provided by the social network.
networks
networks/Network.java: Base social network class
package refactoring_guru.template_method.example.networks; /** * Base class of social network. */ public abstract class Network { String userName; String password; Network() {} /** * Publish the data to whatever network. */ public boolean post(String message) { // Authenticate before posting. Every network uses a different // authentication method. if (logIn(this.userName, this.password)) { // Send the post data. boolean result = sendData(message.getBytes()); logOut(); return result; } return false; } abstract boolean logIn(String userName, String password); abstract boolean sendData(byte[] data); abstract void logOut(); } networks/Facebook.java: Concrete social network
package refactoring_guru.template_method.example.networks; /** * Class of social network */ public class Facebook extends Network { public Facebook(String userName, String password) { this.userName = userName; this.password = password; } public boolean logIn(String userName, String password) { System.out.println("\nChecking user's parameters"); System.out.println("Name: " + this.userName); System.out.print("Password: "); for (int i = 0; i < this.password.length(); i++) { System.out.print("*"); } simulateNetworkLatency(); System.out.println("\n\nLogIn success on Facebook"); return true; } public boolean sendData(byte[] data) { boolean messagePosted = true; if (messagePosted) { System.out.println("Message: '" + new String(data) + "' was posted on Facebook"); return true; } else { return false; } } public void logOut() { System.out.println("User: '" + userName + "' was logged out from Facebook"); } private void simulateNetworkLatency() { try { int i = 0; System.out.println(); while (i < 10) { System.out.print("."); Thread.sleep(500); i++; } } catch (InterruptedException ex) { ex.printStackTrace(); } } } networks/Twitter.java: One more social network
package refactoring_guru.template_method.example.networks; /** * Class of social network */ public class Twitter extends Network { public Twitter(String userName, String password) { this.userName = userName; this.password = password; } public boolean logIn(String userName, String password) { System.out.println("\nChecking user's parameters"); System.out.println("Name: " + this.userName); System.out.print("Password: "); for (int i = 0; i < this.password.length(); i++) { System.out.print("*"); } simulateNetworkLatency(); System.out.println("\n\nLogIn success on Twitter"); return true; } public boolean sendData(byte[] data) { boolean messagePosted = true; if (messagePosted) { System.out.println("Message: '" + new String(data) + "' was posted on Twitter"); return true; } else { return false; } } public void logOut() { System.out.println("User: '" + userName + "' was logged out from Twitter"); } private void simulateNetworkLatency() { try { int i = 0; System.out.println(); while (i < 10) { System.out.print("."); Thread.sleep(500); i++; } } catch (InterruptedException ex) { ex.printStackTrace(); } } } Demo.java: Client code
package refactoring_guru.template_method.example; import refactoring_guru.template_method.example.networks.Facebook; import refactoring_guru.template_method.example.networks.Network; import refactoring_guru.template_method.example.networks.Twitter; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; /** * Demo class. Everything comes together here. */ public class Demo { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); Network network = null; System.out.print("Input user name: "); String userName = reader.readLine(); System.out.print("Input password: "); String password = reader.readLine(); // Enter the message. System.out.print("Input message: "); String message = reader.readLine(); System.out.println("\nChoose social network for posting message.\n" + "1 - Facebook\n" + "2 - Twitter"); int choice = Integer.parseInt(reader.readLine()); // Create proper network object and send the message. if (choice == 1) { network = new Facebook(userName, password); } else if (choice == 2) { network = new Twitter(userName, password); } network.post(message); } } OutputDemo.txt: Execution result
Input user name: Jhonatan Input password: qswe Input message: Hello, World! Choose social network for posting message. 1 - Facebook 2 - Twitter 2 Checking user's parameters Name: Jhonatan Password: **** .......... LogIn success on Twitter Message: 'Hello, World!' was posted on Twitter User: 'Jhonatan' was logged out from Twitter 
