What causes "Cannot add converters" in pentaho/pentaho-kettle?

Do not call addConverter on ContentConverterHandler; register custom converters before constructing the handler if the constructor allows it

pentaho/pentaho-kettle · error · UnsupportedOperationException

Cannot add converters

Error message

Cannot add converters

What it means

addConverter() is rejected because the converter map in ContentConverterHandler is fixed at construction; extensions cannot be extended at runtime. This is an explicit API contract guarding the immutable converter registry.

Solutions

Do not call addConverter on ContentConverterHandler; register custom converters before constructing the handler if the constructor allows it
Use getConverter for lookups and rely on the preconfigured set
Fork/wrap the handler if you genuinely need dynamic converter registration

Example fix

// before
handler.addConverter( "xml", new XmlConverter() );
// after
Converter conv = handler.getConverter( "ktr" ); // use preconfigured converters only

Defensive patterns

Strategy: validation

Validate before calling

// Registration is not supported; verify converters are preconfigured
Converter c = handler.getConverter( extension );
if ( c == null ) {
  throw new IllegalStateException( "No preconfigured converter for " + extension + "; addConverter is unsupported" );
}

Try / catch

try {
  handler.addConverter( ext, conv );
} catch ( UnsupportedOperationException e ) {
  log.warn( "Converter registration unsupported: use preconfigured converters" );
}

Prevention

Treat the converter registry as immutable after construction
Configure needed converters before constructing the handler if the API allows
Use existing extension mappings rather than registering new ones

When it happens

Trigger: Calling addConverter(String extension, Converter) on a ContentConverterHandler instance, e.g. custom code trying to register a handler for a new file extension.

Common situations: Developers attempting to plug in support for additional repository file types; framework code that tries to register default converters after creation.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/ad5b3b9a002b2059. Report an issue: GitHub.

Appendix: source

Thrown at plugins/repo-vfs/repo-vfs-pur/src/main/java/org/pentaho/di/plugins/repofvs/pur/converter/ContentConverterHandler.java:56

  public Converter getConverter( String extension ) {
    if ( extension == null ) {
      return simpleConverter;
    }
    return switch ( extension.toLowerCase() ) {
      case Const.STRING_JOB_DEFAULT_EXT -> jobConverter;
      case Const.STRING_TRANS_DEFAULT_EXT -> transConverter;
      default -> simpleConverter;
    };
  }

  @Override
  public Map<String, Converter> getConverters() {
    throw new UnsupportedOperationException( "Use getConverter" );
  }

  @Override
  public void addConverter( String extension, Converter converter ) {
    throw new UnsupportedOperationException( "Cannot add converters" );
  }


}

View on GitHub (pinned to f3058517a1)