Template Method Pattern Overview

The Template Method pattern defines the skeleton of an algorithm in a base class, allowing subclasses to override specific steps without changing the algorithm's structure. This behavioral patttern encapsulates a fixed sequence of operations, where individual steps can be implemented differently by subclasses to produce varied outcomes.

Core Components

• Abstract Template: Defines the algorithm's framework with concrete and abstract methods
• Concrete Implementation: Provides specific implementations for the abstract steps defined in the template

Hook Methods in Template Pattern

public abstract class AlgorithmTemplate {
    
    public final void executeProcess() {
        initialize();
        processData();
        finalizeOperation();
        
        if (requiresValidation()) {
            validateResults();
        }
    }
    
    protected void initialize() {
        System.out.println("Initializing process");
    }
    
    protected void processData() {
        System.out.println("Processing data");
    }
    
    protected void finalizeOperation() {
        System.out.println("Finalizing operation");
    }
    
    public abstract void validateResults();
    
    protected boolean requiresValidation() {
        return false;
    }
}

Hook methods enable conditional execution of algorithm steps, providing flexibility to control the flow based on specific requirements. These methods typically return boolean values for conditional branching.

Framwork Implementations

Java Collections Framework

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
    public abstract E get(int index);
    // Template methods for list operations
}

Servlet API

• service() method as template with doGet(), doPost() as customizable steps

MyBatis Executor Hierarchy

public abstract class BaseExecutor implements Executor {
    protected abstract int performUpdate(MappedStatement statement, Object params) throws SQLException;
    protected abstract List<BatchResult> flushStatements(boolean rollbackFlag) throws SQLException;
    protected abstract <E> List<E> executeQuery(MappedStatement statement, Object params, 
                                              RowBounds bounds, ResultHandler handler, 
                                              BoundSql boundSql) throws SQLException;
}

Advantages and Limitations

Benefits:

• Promotes code reuse through common algorithm structure
• Enables easy extension by overriding specific steps
• Reduces code duplication by consolidating invariant behavior
• Supports open/closed principle through subclassing

Drawbacks:

• Increases class hierarchy complexity
• Requires subclass creation for each variation
• Parent class modifications impact all subclasses
• Can lead to rigid inheritance structures