quarkusio/quarkus · error · ClassCastException

Cannot compare

Error message

Cannot compare 

What it means

MultiByteHttpData.compareTo(InterfaceHttpData) requires the other object to also be a MultiByteHttpData; otherwise it throws ClassCastException. This mirrors Netty's ordering contract where mixed data types cannot be meaningfully ordered.

Source

Thrown at independent-projects/resteasy-reactive/client/runtime/src/main/java/org/jboss/resteasy/reactive/client/impl/multipart/MultiByteHttpData.java:301

    public FileUpload touch(Object hint) {
        buffer.touch(hint);
        return this;
    }

    @Override
    public int hashCode() {
        return System.identityHashCode(this);
    }

    @Override
    public boolean equals(Object o) {
        return System.identityHashCode(this) == System.identityHashCode(o);
    }

    @Override
    public int compareTo(InterfaceHttpData o) {
        if (!(o instanceof MultiByteHttpData)) {
            throw new ClassCastException("Cannot compare " + getHttpDataType() +
                    " with " + o.getHttpDataType());
        }
        return compareTo((MultiByteHttpData) o);
    }

    public int compareTo(MultiByteHttpData o) {
        return Integer.compare(System.identityHashCode(this), System.identityHashCode(o));
    }

    @Override
    public HttpDataType getHttpDataType() {
        return HttpDataType.FileUpload;
    }

    @Override
    public String getFilename() {
        return filename;
    }

View on GitHub (pinned to e1c734241f)

Solutions

1. Ensure compared parts are all MultiByteHttpData, or implement a Comparator that falls back to comparing by name/type
2. Use IdentityHashMap or a list instead of sorted collections for mixed parts
3. Catch ClassCastException and fall back to name-based comparison

Example fix

// before
parts.sort(Comparator.naturalOrder());
// after
parts.sort(Comparator.comparing(InterfaceHttpData::getName));

if (!(a instanceof MultiByteHttpData) || !(b instanceof MultiByteHttpData)) { /* use name-based comparator */ }

boolean bothMultiByte(InterfaceHttpData a, InterfaceHttpData b) { return a instanceof MultiByteHttpData && b instanceof MultiByteHttpData; }

try { return data.compareTo(other); } catch (ClassCastException e) { return data.getName().compareTo(other.getName()); }

When it happens

Trigger: Sorting or comparing multipart HttpData collections that mix MultiByteHttpData with other InterfaceHttpData types (e.g. MemoryFileUpload, attributes).

Common situations: Using TreeSet/TreeMap or Collections.sort on multipart parts; Netty's internal HttpData ordering when a request mixes plain and multi-byte parts.

Related errors

• setting content of MultiByteHttpData is not supported
• adding content to MultiByteHttpData is not supported
• getting all the contents of a MultiByteHttpData is not suppo
• Reading MultiByteHttpData as String is not supported
• Renaming destination file for MultiByteHttpData is not suppo

AI-assisted analysis of quarkusio/quarkus@e1c734241f (2026-09-05). Data as JSON: /api/errors/e4234427f7ea81c4. Report an issue: GitHub.