alibaba/arthas · error · IllegalArgumentException

Source is not an array: {}

Error message

Source is not an array: {}

What it means

ObjectUtils.toObjectArray() throws IllegalArgumentException when the source object is non-null, is not already an Object[], and is not recognized by Class.isArray() as any kind of array. The method's contract is to convert primitive or object arrays into Object[]; a non-array object violates that precondition.

Source

Thrown at core/src/main/java/com/taobao/arthas/core/util/ObjectUtils.java:109

                    break;
                }
            } else if(candidate.toString().equalsIgnoreCase(constant)) {
                break;
            }

            ++var5;
        }

        return true;
    }

    public static Object[] toObjectArray(Object source) {
        if(source instanceof Object[]) {
            return (Object[])((Object[])source);
        } else if(source == null) {
            return new Object[0];
        } else if(!source.getClass().isArray()) {
            throw new IllegalArgumentException("Source is not an array: " + source);
        } else {
            int length = Array.getLength(source);
            if(length == 0) {
                return new Object[0];
            } else {
                Class wrapperType = Array.get(source, 0).getClass();
                Object[] newArray = (Object[])((Object[])Array.newInstance(wrapperType, length));

                for(int i = 0; i < length; ++i) {
                    newArray[i] = Array.get(source, i);
                }

                return newArray;
            }
        }
    }

    public static boolean nullSafeEquals(Object o1, Object o2) {

View on GitHub (pinned to 21cf2e9ba5)

Solutions

1. Convert the Collection to an array before calling: list.toArray() instead of passing the list directly.
2. Add an instanceof check before calling toObjectArray and handle non-array inputs separately.
3. If the input may legitimately be non-array, guard with source.getClass().isArray() and branch.

Example fix

// before
List<String> items = Arrays.asList("a", "b");
Object[] arr = ObjectUtils.toObjectArray(items); // throws

// after
Object[] arr = items.toArray();
// or, if you must route through toObjectArray:
Object[] arr = items.toArray(new Object[0]);

Object source = getValue();
if (source == null || !source.getClass().isArray()) {
    // handle non-array: convert collection, or return empty
    return new Object[0];
}
ObjectUtils.toObjectArray(source);

public static boolean isArray(Object o) {
    return o != null && o.getClass().isArray();
}

try {
    arr = ObjectUtils.toObjectArray(source);
} catch (IllegalArgumentException e) {
    if (source instanceof Collection) {
        arr = ((Collection<?>) source).toArray();
    } else {
        arr = new Object[]{source};
    }
}

When it happens

Trigger: Calling toObjectArray(source) where source is a Collection, Map, String, or any plain object rather than an actual Java array (int[], Object[], etc.).

Common situations: A caller passed a List or Set expecting array conversion; a generic code path received a boxed scalar or string and forwarded it here; the method is used as a utility without checking the input type first.

Related errors

• {iface} is not an interface
• model class is null
• create view instance failure, viewClass:{}
• Couldn't find rpcmethod: {}
• Arthas server port binding failed! Please check $HOME/logs/a

AI-assisted analysis of alibaba/arthas@21cf2e9ba5 (2026-08-14). Data as JSON: /api/errors/c785030f47f4e6ba. Report an issue: GitHub.