A better solution

Use SOAPMessage API instead of DOM.

  private void alterSoapEnvelope(SaajSoapMessage soapResponse) {    try {      SOAPMessage soapMessage = soapResponse.getSaajMessage();      SOAPPart soapPart = soapMessage.getSOAPPart();      SOAPEnvelope envelope = soapPart.getEnvelope();      SOAPHeader header = soapMessage.getSOAPHeader();      SOAPBody body = soapMessage.getSOAPBody();      SOAPFault fault = body.getFault();      envelope.removeNamespaceDeclaration(envelope.getPrefix());      envelope.addNamespaceDeclaration(PREFERRED_PREFIX, SOAP_ENV_NAMESPACE);      envelope.setPrefix(PREFERRED_PREFIX);      header.setPrefix(PREFERRED_PREFIX);      body.setPrefix(PREFERRED_PREFIX);      if (fault != null) {        fault.setPrefix(PREFERRED_PREFIX);      }    } catch (SOAPException e) {      e.printStackTrace();    }  }

It's much faster now.

I use SAAJ. Try this.

1. soapEnvelope.removeNamespaceDeclaration("SOAP-ENV");
2. soapEnvelope.addNamespaceDeclaration("soapenv", "http://schemas.xmlsoap.org/soap/envelope/");
3. soapEnvelope.setPrefix("soapenv");
4. soapHeader.setPrefix("soapenv");
5. soapBody.setPrefix("soapenv");

Don't forget:soapMessage.saveChanges();

Reference:Changing the default XML namespace prefix generated with JAXWS

Additional Point :

you have to extend your Webservice config class with WsConfigurationAdapter and add your CustomEndpointInterceptor in the webservice config class as stated below.

Then only the interceptor works.

Refer below link for more details

https://memorynotfound.com/spring-ws-intercept-request-response-soap-messages/