Intercepting Filter Pattern

1. Introduction

The Intercepting Filter Pattern is a design pattern that allows you to intercept requests and responses in a web application, enabling you to apply additional processing before or after the main business logic. This pattern is often used for tasks such as logging, authentication, and authorization.

2. Key Concepts

• **Filter**: An interface or abstract class defining a method for processing requests and responses.
• **Target**: The main business logic that processes the request.
• **Chain**: A series of filters that can be applied to requests and responses.

3. Implementation

Here’s how to implement the Intercepting Filter Pattern in a typical application:

1. Define the Filter interface.
2. Implement concrete filters that apply specific processing.
3. Create a Target interface for the business logic.
4. Implement the Target interface.
5. Create a FilterChain to manage filters.
6. Implement the InterceptingFilter class to manage the request processing.

interface Filter {
    void execute(String request);
}

class AuthenticationFilter implements Filter {
    public void execute(String request) {
        System.out.println("Authenticating request: " + request);
    }
}

class LoggingFilter implements Filter {
    public void execute(String request) {
        System.out.println("Logging request: " + request);
    }
}

class Target {
    public void execute(String request) {
        System.out.println("Executing request: " + request);
    }
}

class FilterChain {
    private List filters = new ArrayList<>();
    private Target target;

    public void setTarget(Target target) {
        this.target = target;
    }

    public void addFilter(Filter filter) {
        filters.add(filter);
    }

    public void execute(String request) {
        for (Filter filter : filters) {
            filter.execute(request);
        }
        target.execute(request);
    }
}

public class InterceptingFilterDemo {
    public static void main(String[] args) {
        FilterChain filterChain = new FilterChain();
        filterChain.addFilter(new AuthenticationFilter());
        filterChain.addFilter(new LoggingFilter());

        Target target = new Target();
        filterChain.setTarget(target);

        filterChain.execute("HOME");
    }
}

4. Best Practices

• Keep filters independent: Ensure that filters do not depend on each other to promote reusability.
• Order matters: Be mindful of the order in which filters are applied as it can affect the outcome.
• Limit filter scope: Only apply filters where necessary to avoid performance overhead.

5. FAQ