apache/maven · error · IllegalArgumentException

Illegal event type: " + eventType

Error message

Illegal event type: " + eventType

What it means

Thrown by ArtifactTransferEvent.setEventType() when the value is not one of TRANSFER_INITIATED, TRANSFER_STARTED, TRANSFER_COMPLETED, TRANSFER_PROGRESS or TRANSFER_ERROR. The setter switch has a default arm rejecting everything else with IllegalArgumentException echoing the bad int. It protects listeners that dispatch on event type from receiving undefined states.

Source

Thrown at compat/maven-compat/src/main/java/org/apache/maven/repository/ArtifactTransferEvent.java:167

    }

    /**
     * @param eventType The eventType to set.
     */
    public void setEventType(final int eventType) {
        switch (eventType) {
            case TRANSFER_INITIATED:
                break;
            case TRANSFER_STARTED:
                break;
            case TRANSFER_COMPLETED:
                break;
            case TRANSFER_PROGRESS:
                break;
            case TRANSFER_ERROR:
                break;
            default:
                throw new IllegalArgumentException("Illegal event type: " + eventType);
        }

        this.eventType = eventType;
    }

    /**
     * @return Returns the local file.
     */
    public File getLocalFile() {
        return localFile;
    }

    /**
     * @param localFile The local file to set.
     */
    public void setLocalFile(File localFile) {
        this.localFile = localFile;
    }

View on GitHub (pinned to e4093d4e12)

Solutions

1. Use only the TransferEvent.TRANSFER_* constants for setEventType
2. Double-check argument order at event construction (eventType vs requestType are adjacent ints)
3. Create a fresh event per transfer state instead of mutating a shared instance
4. Migrate new code to org.eclipse.aether.TransferEvent with its enum-based EventTypes

Example fix

// before
event.setEventType(99);            // invented value
event.setEventType(REQUEST_GET);   // wrong constant family
// after
import static org.apache.maven.wagon.events.TransferEvent.TRANSFER_STARTED;
event.setEventType(TRANSFER_STARTED);

import static org.apache.maven.wagon.events.TransferEvent.*;
static boolean isValidEventType(int t) {
    return t == TRANSFER_INITIATED || t == TRANSFER_STARTED || t == TRANSFER_COMPLETED
        || t == TRANSFER_PROGRESS || t == TRANSFER_ERROR;
}

When it happens

Trigger: Calling setEventType() with an arbitrary int: a listener re-using an event object and passing a requestType (0/1) by mistake, a computed state machine value, or an unset 0 from a default-initialized event.

Common situations: Hand-written wagon listeners/adapters constructing or recycling ArtifactTransferEvent instances; copy-paste between setRequestType and setEventType; code compiled against wagon constants that changed meaning across versions.

Related errors

• Illegal request type: " + requestType
• artifactId can neither be null, empty nor blank
• version can neither be null, empty nor blank
• Unable to promptForPassword
• Unable to showMessage

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/9c222024d66e2c99. Report an issue: GitHub.