Package com.vaadin.observability.micrometer

Class ResyncDetectionFilter

java.lang.Object

com.vaadin.observability.micrometer.ResyncDetectionFilter

All Implemented Interfaces:

jakarta.servlet.Filter

public final class ResyncDetectionFilter
extends Object
implements jakarta.servlet.Filter

Portable, framework-agnostic servlet filter that observes UIDL message resends and resynchronization requests (prototype, kit-only, no Flow changes). It depends only on the servlet API and Micrometer, so it is meant for plain (non-Spring) deployments; a Spring application does not need this class and should use SpringResyncDetectionFilter instead.

Registering it in a plain servlet app. There is no auto-configuration outside Spring, so register the filter yourself against every request. It should run early (before anything else consumes the request body). For example, in a ServletContextListener or ServletContainerInitializer:

 FilterRegistration.Dynamic reg = servletContext.addFilter(
         "vaadinResyncDetection", new ResyncDetectionFilter(meterRegistry));
 // isMatchAfter=false so it precedes already-registered filters
 reg.addMappingForUrlPatterns(null, false, "/*");
 

or the equivalent <filter>/<filter-mapping> in web.xml. The MeterRegistry is whichever instance the application records into.

Flow recovers from lost responses entirely inside UidlRequestHandler by catching ClientResentPayloadException (replay the cached response) and ResynchronizationRequiredException (rebuild the UI state); neither surfaces to any Flow listener SPI the kit uses. This filter reconstructs the same signal by buffering the UIDL body (via CachedBodyHttpServletRequest so Flow can still read it) and handing it to a ResyncInspector.

Because it has no Spring APIs available it buffers the body eagerly; the Spring variant instead captures the bytes lazily as Flow reads them and only counts requests Flow actually consumed. Instrumentation never fails the request: any error while inspecting is swallowed.

Constructor Summary

Constructors

Constructor	Description
ResyncDetectionFilter(io.micrometer.core.instrument.MeterRegistry registry)	Creates the filter recording into the given registry.

Method Summary

Modifier and Type	Method	Description
void	doFilter(jakarta.servlet.ServletRequest request, jakarta.servlet.ServletResponse response, jakarta.servlet.FilterChain chain)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface jakarta.servlet.Filter

destroy, init

Constructor Details

ResyncDetectionFilter

public ResyncDetectionFilter(io.micrometer.core.instrument.MeterRegistry registry)

Creates the filter recording into the given registry.

Parameters:

registry - the meter registry, not null

Method Details

doFilter

public void doFilter(jakarta.servlet.ServletRequest request,
 jakarta.servlet.ServletResponse response,
 jakarta.servlet.FilterChain chain)
              throws IOException,
jakarta.servlet.ServletException

Specified by:

doFilter in interface jakarta.servlet.Filter

Throws:

IOException

jakarta.servlet.ServletException