pentaho/pentaho-kettle · error · KettleException

UserDefinedJavaClassDialog.Exception.CouldNotGetFields

Error message

UserDefinedJavaClassDialog.Exception.CouldNotGetFields

What it means

In UserDefinedJavaClassDialog's field-preview (test) path, getFields() on the step meta did not succeed (returned false), so a KettleException 'CouldNotGetFields' is thrown and shown in a 'Test failed' ErrorDialog. It means the UDJC step could not determine its output fields for the preview.

Solutions

1. Fix compile errors in the UDJC Java code shown in the dialog (check generated code for syntax/typing mistakes).
2. Ensure the step has a valid input hop and the previous step produces the expected fields.
3. Check 'Fields' grid entries: referenced input field names must match actual upstream fields exactly.
4. Compile a minimal version of the class (remove added code) to isolate the failing statement, then re-add incrementally.

Example fix

// before
Object[] r = new Object[data.outputRowMeta.size()]; // uses wrong meta
// after
Object[] r = RowDataUtil.allocateRowData(data.outputRowMeta.size());

// before testing the class, confirm input meta resolves
if (transMeta.getPrevStepFields(stepMeta) == null || transMeta.getPrevStepFields(stepMeta).isEmpty()) {
  throw new KettleException("UDJC step has no input fields; connect a previous step first");
}

boolean canGetFields(TransMeta tm, StepMeta sm) { try { return tm.getStepFields(sm) != null; } catch (Exception e) { return false; } }

try { testClass(); } catch (KettleException e) { new ErrorDialog(shell, "Test failed", "Could not get fields — check UDJC code compiles and input fields exist", e); }

When it happens

Trigger: Clicking 'Test class' / preview in the UDJC dialog when the step's getFields() returns false — typically because the generated class failed to compile or the input fields could not be resolved.

Common situations: Java code with compile errors (bad imports, undefined variables); referencing input fields that do not exist in the previous step; no previous step connected so input row meta is empty.

Related errors

• Could not initialize from codeSnippets.xml
• Error executing UserDefinedJavaClass.getFields():
• Error initializing UserDefinedJavaClass to get fields:
• GetXMLDataDialog.Exception.FileDoesNotExist
• GetXMLDateLoopNodesImportProgressDialog.Exception.ErrorScann…

AI-assisted analysis of pentaho/pentaho-kettle@f3058517a1 (2026-09-13). Data as JSON: /api/errors/dd56b9b4dd0847e7. Report an issue: GitHub.

Appendix: source

Thrown at ui/src/main/java/org/pentaho/di/ui/trans/steps/userdefinedjavaclass/UserDefinedJavaClassDialog.java:1429

              etd.setReadOnly();
              etd.open();
            }
          }

          RowMetaInterface previewRowsMeta = progressDialog.getPreviewRowsMeta( wStepname.getText() );
          List<Object[]> previewRows = progressDialog.getPreviewRows( wStepname.getText() );

          if ( previewRowsMeta != null && previewRows != null && previewRows.size() > 0 ) {
            PreviewRowsDialog prd =
              new PreviewRowsDialog(
                shell, transMeta, SWT.NONE, wStepname.getText(), previewRowsMeta, previewRows, loggingText );
            prd.open();
          }
        }

        return true;
      } else {
        throw new KettleException( BaseMessages.getString(
          PKG, "UserDefinedJavaClassDialog.Exception.CouldNotGetFields" ) );
      }
    } catch ( Exception e ) {
      new ErrorDialog(
        shell, BaseMessages.getString( PKG, "UserDefinedJavaClassDialog.TestFailed.DialogTitle" ), BaseMessages
          .getString( PKG, "UserDefinedJavaClassDialog.TestFailed.DialogMessage" ), e );
      return false;
    }

  }

  private void buildSnippitsTree() {

    TreeItem item = new TreeItem( wTree, SWT.NULL );
    item.setImage( guiResource.getImageBol() );
    item.setText( BaseMessages.getString( PKG, "UserDefinedJavaClassDialog.Snippits.Label" ) );

    Map<Category, TreeItem> categoryTreeItems = new EnumMap<Category, TreeItem>( Category.class );

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