Intercepting Filter Pattern

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The intercepting filter design pattern is used when we want to do some pre-processing / post-processing with request or response of the application. Filters are defined and applied on the request before passing the request to actual target application. Filters can do the authentication/ authorization/ logging or tracking of request and then pass the requests to corresponding handlers. Following are the entities of this type of design pattern.

  • Filter - Filter which will perform certain task prior or after execution of request by request handler.

  • Filter Chain - Filter Chain carries multiple filters and help to execute them in defined order on target.

  • Target - Target object is the request handler

  • Filter Manager - Filter Manager manages the filters and Filter Chain.

  • Client - Client is the object who sends request to the Target object.

Implementation

We're going to create a FilterChain,FilterManager, Target, Client as various objects representing our entities.AuthenticationFilter and DebugFilter represents concrete filters.

InterceptingFilterDemo, our demo class will use Client to demonstrate Intercepting Filter Design Pattern.

Intercepting Filter Pattern UML Diagram

Step 1

Create Filter interface.

Filter.java

public interface Filter {
   public void execute(String request);
}

Step 2

Create concrete filters.

AuthenticationFilter.java

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

DebugFilter.java

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

Step 3

Create Target

Target.java

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

Step 4

Create Filter Chain

FilterChain.java

import java.util.ArrayList;
import java.util.List;

public class FilterChain {
   private List<Filter> filters = new ArrayList<Filter>();
   private 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 void setTarget(Target target){
      this.target = target;
   }
}

Step 5

Create Filter Manager

FilterManager.java

public class FilterManager {
   FilterChain filterChain;

   public FilterManager(Target target){
      filterChain = new FilterChain();
      filterChain.setTarget(target);
   }
   public void setFilter(Filter filter){
      filterChain.addFilter(filter);
   }

   public void filterRequest(String request){
      filterChain.execute(request);
   }
}

Step 6

Create Client

Client.java

public class Client {
   FilterManager filterManager;

   public void setFilterManager(FilterManager filterManager){
      this.filterManager = filterManager;
   }

   public void sendRequest(String request){
      filterManager.filterRequest(request);
   }
}

Step 7

Use the Client to demonstrate Intercepting Filter Design Pattern.

FrontControllerPatternDemo.java

public class InterceptingFilterDemo {
   public static void main(String[] args) {
      FilterManager filterManager = new FilterManager(new Target());
      filterManager.setFilter(new AuthenticationFilter());
      filterManager.setFilter(new DebugFilter());

      Client client = new Client();
      client.setFilterManager(filterManager);
      client.sendRequest("HOME");
   }
}

Step 8

Verify the output.

Authenticating request: HOME
request log: HOME
Executing request: HOME


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