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DeutschIntercepting 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
[edit]Filter manager, filter chain, filters and target are components of the pattern.
Filter manager
[edit]This manages filter processing and creates the filter chain with the appropriate filters, in the correct order, and initiates processing.[1]
Filter chain
[edit]A Filter Chain is a specific series of filters, composed so as to form a logical chain.[1]
Filters
[edit]These are the individual filters that are mapped to a target and their processing is coordinated by filter chain.[1]
Target
[edit]This is the resource requested by the client.[1]
Consequences
[edit]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
[edit]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); } } 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 // apply filters for (final Filter filter : filters) { // pass request & response through various // filters filter.execute(request, response); } } }