Intercepting filter pattern

Intercepting Filter is a JavaEE pattern which creates pluggable filters to process common services in a standard manner without requiring changes to core request processing code. The filters intercept incoming requests and outgoing responses, allowing preprocessing and post-processing, and these filters can be added or removed unobtrusively without changing existing code.[1] This pattern applies reusable processing transparently before and after the actual request execution by the front and page controllers.[2]

Structure

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

Filter manager

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

Filter chain

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

Filters

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

Target

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

Consequences

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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 a concern, as unnecessarily long chains of interceptors and filters may hurt performance.[2]

Sample code

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

Code for implementing a filter - debugging filter:

public class DebuggingFilter implements Processor {     private Processor target;      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);     } } 

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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     } } 

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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); } 

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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); } 

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Code for filter chain:

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

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See also

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References

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  1. ^ a b c d e f g h i j k "Core J2EE Patterns - Intercepting Filter". Oracle. Oracle. Retrieved 6 February 2016.
  2. ^ a b c Kayal, D. (2008). Pro Java EE Spring Patterns. New York: Apress. pp. 98–106.