Block filter mode

Block filter mode

Intercept filter patterns are used to preprocess/post-process requests or responses to an application. D efine filters and apply them before passing them to the actual target application. F ilters can do authentication/authorization/logging, or track requests and then pass them on to the appropriate handler. The following are the entities of this design pattern.

• Filter - Filters perform certain tasks before or after the request handler executes the request.
• Filter Chain - The filter chain has multiple filters and executes them in the defined order on Target.
• The Target-Target object is the request handler.
• Filter Manager - Filter Manager manages filters and filter chains.
• Client - Client is the object that sends the request to the Target object.

Realize

We'll create FilterChain, FilterManager, Target, Client as various objects that represent entities. ElectronicFilter and DebugFilter represent entity filters.

InterceptingFilterDemo, our demo class uses Client to demonstrate intercept filter design patterns.

Step 1

Create a filter interface, Filter.

Filter.java

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

Step 2

Create an 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 filters = new ArrayList();
   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 a 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

Use Client to demonstrate intercept filter design patterns.

InterceptingFilterDemo.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