apache/flink · error · IllegalArgumentException

Configuration cannot evaluate value %s as a byte[] value

Error message

Configuration cannot evaluate value %s as a byte[] value

What it means

Configuration.getBytes(key, default) is the legacy typed getter: it looks up the raw stored value and, unless the stored object's class is exactly byte[], throws IllegalArgumentException 'Configuration cannot evaluate value %s as a byte[] value'. Unlike modern ConfigOption getters it does no string coercion — the value must have been put as a byte array via setBytes/setValue(byte[]) or parsed as TYPE_BYTES.

Source

Thrown at flink-core/src/main/java/org/apache/flink/configuration/Configuration.java:156

    }

    /**
     * Returns the value associated with the given key as a byte array.
     *
     * @param key The key pointing to the associated value.
     * @param defaultValue The default value which is returned in case there is no value associated
     *     with the given key.
     * @return the (default) value associated with the given key.
     */
    @Internal
    public byte[] getBytes(String key, byte[] defaultValue) {
        return getRawValue(key)
                .map(
                        o -> {
                            if (o.getClass().equals(byte[].class)) {
                                return (byte[]) o;
                            } else {
                                throw new IllegalArgumentException(
                                        String.format(
                                                "Configuration cannot evaluate value %s as a byte[] value",
                                                o));
                            }
                        })
                .orElse(defaultValue);
    }

    /**
     * Adds the given byte array to the configuration object. If key is <code>null</code> then
     * nothing is added.
     *
     * @param key The key under which the bytes are added.
     * @param bytes The bytes to be added.
     */
    @Internal
    public void setBytes(String key, byte[] bytes) {
        setValueInternal(key, bytes);

View on GitHub (pinned to 2f3c205e92)

Solutions

Store the value as byte[] (conf.setBytes(key, bytes)) instead of a string, if you must use getBytes.
Migrate to the ConfigOption API: define ConfigOption<byte[]> or parse explicitly: BaseEncoding.base64().decode(conf.getString(key)).
If the value may legitimately be a string encoding of bytes, read it with getString and decode it yourself.

Example fix

// before
byte[] secret = conf.getBytes("security.secret", null); // key came from YAML as String -> throws

// after
byte[] secret = java.util.Base64.getDecoder().decode(conf.getString("security.secret", ""));

Defensive patterns

Strategy: type-guard

Validate before calling

Object raw = conf.getRawValue(key).orElse(null);
if (raw != null && !raw.getClass().equals(byte[].class)) {
    throw new IllegalArgumentException("Key '" + key + "' is " + raw.getClass().getSimpleName() + ", not byte[]");
}

Type guard

boolean isByteValue(Configuration conf, String key) {
    return conf.getRawValue(key).map(o -> o.getClass().equals(byte[].class)).orElse(true);
}

Prevention

Do not use the legacy getBytes on YAML-loaded configuration — values there are Strings.
Standardize on the ConfigOption API for new code.
Encode binary data as base64 strings if it must round-trip through config files.

When it happens

Trigger: Calling getBytes on a key whose value was stored as String, Integer, Boolean, or any non-byte[] type (e.g. read from flink-conf.yaml where everything parses to a String); mixing the old String-keyed API with YAML-loaded values.

Common situations: Legacy code paths calling conf.getBytes("some.key", null) on keys defined in the YAML config file; internal utilities expecting byte[] set programmatically but the key was overridden in configuration files.

Related errors

AI-assisted analysis of apache/flink@2f3c205e92 (2026-08-14). Data as JSON: /api/errors/6d0d42745a46ec85. Report an issue: GitHub.