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 apppcation. Filters are defined and appped on the request before passing the request to actual target apppcation. 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 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.

Cpent - Cpent is the object who sends request to the Target object.

Implementation

We are going to create a FilterChain,FilterManager, Target, Cpent as various objects representing our entities.AuthenticationFilter and DebugFilter represent concrete filters.

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

Step 1

Create Filter interface.

Filter.java

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

Step 2

Create concrete filters.

AuthenticationFilter.java

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

DebugFilter.java

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

Step 3

Create Target

Target.java

pubpc class Target {
   pubpc 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;

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

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

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

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

Step 5

Create Filter Manager

FilterManager.java

pubpc class FilterManager {
   FilterChain filterChain;

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

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

Step 6

Create Cpent

Cpent.java

pubpc class Cpent {
   FilterManager filterManager;

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

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

Step 7

Use the Cpent to demonstrate Intercepting Filter Design Pattern.

InterceptingFilterDemo.java

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

      Cpent cpent = new Cpent();
      cpent.setFilterManager(filterManager);
      cpent.sendRequest("HOME");
   }
}

Step 8

Verify the output.

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