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.

Learn more about Template Method

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.
In javax.servlet.http.HttpServlet class, all the doXXX() 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