Intercepting Filter pattern

Intercepting Filter pattern (Intercepting Filter Pattern) for requesting an application or in response to do some pre-processing / post-processing. Define the filter, and before the request to the practical application of the target application on request. Filters can do authentication / authorization / logging or tracking request, then the request to the appropriate handler. The following is an entity of this design pattern.

• Filter (Filter) - filter before or after the execution of the request request handler to perform certain tasks.
• Filter chain (Filter Chain) - filter chain with a plurality of filters, and the implementation of these filters on Target in a defined sequence.
• Target - Target is the object request handler.
• Filter Manager (Filter Manager) - Filter Manager filters and filter chain.
• Client (Client) - Client object to Target object to send the request.

achieve

We will createFilterChain,FilterManager, Target, Client represents entities as various objects.AuthenticationFilterandDebugFilterrepresent entities filters.

InterceptingFilterDemo,we demonstrate the use ofClientclass to demonstrate the Intercepting Filter design pattern.

step 1

Create Filter Interface Filter.

Filter.java

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

Step 2

Create entity filter.

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 a 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 a client 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

UseClientto demonstrate the 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 output.

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