Design Pattern - Intercepting Filter Pattern

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 performs certain task prior or after execution of request by request handler.
Filter - Filter which will performs 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.
Filter Chain - Filter Chain carries multiple filters and help to execute them in defined order on target.
Target - Target object is the request handler
Target - Target object is the request handler
Filter Manager - Filter Manager manages the filters and Filter Chain.
Filter Manager - Filter Manager manages the filters and Filter Chain.
Client - Client is the object who sends request to the Target object.
Client - Client is the object who sends request to the Target object.
We are going to create a FilterChain,FilterManager, Target, Client as various objects representing our entities.AuthenticationFilter and DebugFilter represent concrete filters.
InterceptingFilterDemo, our demo class, will use Client to demonstrate Intercepting Filter Design Pattern.
Create Filter interface.
Filter.java
public interface Filter {
   public void execute(String request);
}
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);
   }
}
Create Target
Target.java
public class Target {
   public void execute(String request){
      System.out.println("Executing request: " + request);
   }
}
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;
   }
}
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);
   }
}
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);
   }
}
Use the Client to demonstrate Intercepting Filter Design Pattern.
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");
   }
}
Verify the output.
Authenticating request: HOME
request log: HOME
Executing request: HOME


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