apache/maven · error · XmlWriterException

Unable to write settings

Error message

Unable to write settings: {}

What it means

Wrapper thrown by DefaultSettingsXmlFactory.write when serializing a Settings document fails: STaX writer errors, IOException on the target stream, or failures thrown by the configured InputLocationFormatter. The cause is preserved and its message appended.

Solutions

1. Unwrap getCause() to identify the stream/IO versus formatter versus STaX failure
2. Verify the stream is open and writable before the call
3. Test the InputLocationFormatter separately if one is configured

Example fix

// before
try {
    settingsXmlFactory.write(req);
} catch (XmlWriterException e) {
    throw new RuntimeException(e); // real cause hidden
}

// after
try {
    settingsXmlFactory.write(req);
} catch (XmlWriterException e) {
    log.error("settings write failed: {}", e.getCause().getMessage(), e.getCause());
}

try {
    settingsXmlFactory.write(req);
} catch (XmlWriterException e) {
    Throwable cause = e.getCause();
    // distinguish stream failure vs formatter failure before deciding to retry
    log.error("settings write failed", cause);
}

When it happens

Trigger: Output stream already closed or read-only; an InputLocationFormatter that throws on null locations; STaX implementation failures during write.

Common situations: Writing settings back to a read-only file; custom location formatters used for round-tripping settings with comments.

Related errors

• Unable to write model:
• Unable to write plugin:
• Unable to write toolchains
• Problem during inlining POM
• reader or inputStream must be non null

AI-assisted analysis of apache/maven@e4093d4e12 (2026-08-21). Data as JSON: /api/errors/d954c05ba7611ef0. Report an issue: GitHub.

Appendix: source

Thrown at impl/maven-impl/src/main/java/org/apache/maven/impl/DefaultSettingsXmlFactory.java:100

        }
        try {
            SettingsStaxWriter xmlWriter = new SettingsStaxWriter();
            xmlWriter.setAddLocationInformation(false);

            Function<Object, String> formatter = request.getInputLocationFormatter();
            if (formatter != null) {
                xmlWriter.setAddLocationInformation(true);
                Function<InputLocation, String> adapter = formatter::apply;
                xmlWriter.setStringFormatter(adapter);
            }

            if (writer != null) {
                xmlWriter.write(writer, content);
            } else {
                xmlWriter.write(outputStream, content);
            }
        } catch (Exception e) {
            throw new XmlWriterException("Unable to write settings: " + getMessage(e), getLocation(e), e);
        }
    }

    static <T> T nonNull(T t, String name) {
        if (t == null) {
            throw new IllegalArgumentException(name + " cannot be null");
        }
        return t;
    }
}

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