Here's a working demo

Your error boils down to mixing APIs in an unsupported way.

If you have a look at the documentation for PostProcessors you will see that it states:

Pre-processors and post-processors are different to processors in that instead of executing on a single event or on an event model (a fragment of a template), they apply to the entire template execution process as an additional step in the engine’s processing chain. Therefore they follow an API completely different to that of processors, much more event-oriented, defined by the lower-level ITemplateHandler interface.

a) ITextProcessor cannot be used in conjunction with IPostProcessorDialect.

b) The method getHandlerClass() defines the implementation of your PostProcessor, so it fails in your case because of

return ITemplateHandler.class;

ITemplateHandler is an interface and does not have a constructor, thus the exception java.lang.NoSuchMethodException: org.thymeleaf.engine.ITemplateHandler.<init>()

How can it be fixed?

public class StripElementWhiteSpaceDialect implements IPostProcessorDialect {

    Set<IPostProcessor> processors = new HashSet<>();

    {
       processors.add(new PostProcessor(TemplateMode.HTML, StripElementWhiteSpaceHandler.class, Integer.MAX_VALUE));
    }

    @Override
    public int getDialectPostProcessorPrecedence() {
        return 0;
    }

    @Override
    public Set<IPostProcessor> getPostProcessors() {
        return processors;
    }

    @Override
    public String getName() {
        return "Minifier";
    }

    public static class StripElementWhiteSpaceHandler extends AbstractTemplateHandler {

       @Override
       public void handleText(IText textNode) {
          
           //update the text
           
           super.handleText(...);
       }

    }

}

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@duoduobingbing thanks for the demo. But actually textNode.getText() is not the final complete processed output but rather chuncks. So doesnt fit what i was looking for. Thanks very much anyway.

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