Java Template Method Pattern Example

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Template Method in Java

Template Method is a behavioral design pattern that allows you to defines a skeleton of an algorithm in a base class and let subclasses override the steps without changing the overall algorithm's structure.

Usage of the pattern in Java

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.Reader and java.io.Writer.
All non-abstract methods of java.util.AbstractList, java.util.AbstractSet and java.util.AbstractMap.
javax.servlet.http.HttpServlet, all the doXXX() methods by default send a HTTP 405 "Method Not Allowed" error as a response. You're free to override any of them.

Identification: Template Method can be recognized by behavioral methods that already have a "default" behavior defined by the base class.

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