1. Structure
    Filter manager  Filter chain  Filters  Target 

2. Consequences

3. Sample code

4. See also

5. References

Structure

Filter manager, filter chain, filters and target are components of the pattern.

Filter manager

This manages filter processing and creates the filter chain with the appropriate filters, in the correct order, and initiates processing.^[1]

Filter chain

A Filter Chain is a specific series of filters, composed so as to form a logical chain.^[1]

Filters

These are the individual filters that are mapped to a target and their processing is coordinated by filter chain.^[1]

Target

This is the resource requested by the client.^[1]

Consequences

Following benefits can be considered:

• Improved reusability: Common code is centralized in pluggable components enhancing reuse.
• Increased flexibility: Generic common components can be applied and removed declaratively, improving flexibility.^[1][2]

Reduced performance can be concerned as unnecessarily long chains of interceptors and filters may hurt performance.^[2]

Sample code

Sample code implementation for filters with custom filter strategy is given below.

Code for implementing a filter - debugging filter:

public class DebuggingFilter implements Processor {

  public DebuggingFilter(Processor myTarget) {    target = myTarget;  }

  public void execute(ServletRequest req,   ServletResponse res) throws IOException,     ServletException    {    //Do some filter processing here, such as     // displaying request parameters    target.execute(req, res);  }

}

Code for implementing a filter - core processor:

public class CoreProcessor implements Processor {

  private Processor target;  public CoreProcessor()   {    this(null);  }

  public CoreProcessor(Processor myTarget)   {    target = myTarget;  }

  public void execute(ServletRequest req,       ServletResponse res) throws IOException,       ServletException   {    //Do core processing here  }

}

Code for handling requests:

public void processRequest(ServletRequest req,

  ServletResponse res)   throws IOException, ServletException {  Processor processors = new DebuggingFilter(     new AuthenticationFilter(new CoreProcessor()));  processors.execute(req, res);

  //Then dispatch to next resource, which is probably   // the View to display  dispatcher.dispatch(req, res);

}

Code for filter manager:

public void processRequest(ServletRequest req,

  ServletResponse res)   throws IOException, ServletException {  Processor processors = new DebuggingFilter(     new AuthenticationFilter(new CoreProcessor()));  processors.execute(req, res);

  //Then dispatch to next resource, which is probably   // the View to display  dispatcher.dispatch(req, res);

}

Code for filter chain:

public class FilterChain {

  // filter chain   private List myFilters = new ArrayList<>();

  // Creates new FilterChain   public FilterChain()  {    // plug-in default filter services for example     // only. This would typically be done in the     // FilterManager, but is done here for example     // purposes    myFilters.add(new DebugFilter());    myFilters.add(new LoginFilter());    myFilters.add(new AuditFilter());  }

  public void processFilter(     javax.servlet.http.HttpServletRequest request,    javax.servlet.http.HttpServletResponse response)  throws javax.servlet.ServletException,     java.io.IOException         {    Filter filter;

    // apply filters    for (final Filter filter : filters)    {      // pass request & response through various       // filters      filter.execute(request, response);    }  }

}

See also

• Front controller
• Decorator pattern
• Template method pattern
• Interceptor pattern
• Pipeline (software)

References

• People's judge
• People's Key
• People's Khural of Buryatia
• People's Khural of the Republic of Buryatia
• People skill
• People skills
• People's Labor Party
• People's Labour Party (Cuba)
• People's Labour Party (disambiguation)
• People's League (Alberta)
• People's Liberal Action
• People's Liberation Army and Partisan Detachments of Yugoslavia
• People's Liberation Army at the 1989 Tiananmen Square protests
• People's Liberation Army General Armaments Department
• People's Liberation Army General Logistics Department
• People's Liberation Army General Political Department
• People's Liberation Army Invasion/Liberation of Xinjiang (1949)
• People's Liberation Army invasion of Tibet
• People's Liberation Army invasion of Tibet (1950–1951)
• People's Liberation Army Invasion of Xinjiang (1949)
• People's Liberation Army liberation of Tibet (1950–1951)
• People's Liberation Army Macao Garrison
• People's Liberation Army (Nepal)
• People's Liberation Army, Nepal
• People's Liberation Army Nepal