flowable/flowable-engine · error · FlowableException

Unexpected exception getting variable data

Error message

Unexpected exception getting variable data

What it means

This FlowableException wraps an IOException thrown while reading the binary/stream content of a runtime variable in the REST API. It indicates the server failed at the I/O level when serializing or deserializing the variable's data (e.g. reading a byte array or serializable object), not that the variable is missing. The original IOException is attached as the cause.

Source

Thrown at modules/flowable-rest/src/main/java/org/flowable/rest/service/api/runtime/VariableInstanceDataResource.java:89

                result = (byte[]) variable.getValue();
                response.setContentType("application/octet-stream");

            } else if (RestResponseFactory.SERIALIZABLE_VARIABLE_TYPE.equals(variable.getType())) {
                try (ByteArrayOutputStream buffer = new ByteArrayOutputStream();
                     ObjectOutputStream outputStream = new ObjectOutputStream(buffer)) {
                    outputStream.writeObject(variable.getValue());
                    result = buffer.toByteArray();
                    response.setContentType("application/x-java-serialized-object");
                }

            } else {
                throw new FlowableObjectNotFoundException("The variable does not have a binary data stream.", null);
            }
            return result;

        } catch (IOException ioe) {
            // Re-throw IOException
            throw new FlowableException("Unexpected exception getting variable data", ioe);
        }
    }

    public RestVariable getVariableFromRequest(boolean includeBinary, String varInstanceId) {
        VariableInstance varObject = runtimeService.createVariableInstanceQuery().id(varInstanceId).singleResult();

        if (varObject == null) {
            throw new FlowableObjectNotFoundException("Historic variable instance '" + varInstanceId + "' could not be found.", VariableInstanceEntity.class);
        } else {
            
            if (restApiInterceptor != null) {
                restApiInterceptor.accessVariableInfoById(varObject);
            }
            
            return restResponseFactory.createRestVariable(varObject.getName(), varObject.getValue(), null, varInstanceId, RestResponseFactory.VARIABLE_VARINSTANCE, includeBinary);
        }
    }
}

View on GitHub (pinned to d6d39ce1c6)

Solutions

1. Inspect the wrapped IOException cause in logs to find the real I/O failure
2. Re-set the variable with fresh binary/serializable content via the REST API to replace corrupted data
3. Verify the flowable variable storage (DB blob columns) is intact and not truncated
4. Upgrade/align Flowable version to get fixes for variable stream handling

Example fix

// before
RestVariable result = getVariableData(...); // throws opaque FlowableException
// after
try {
    RestVariable result = getVariableData(...);
} catch (FlowableException e) {
    logger.error("variable data I/O failed", e.getCause());
    // re-set the variable or return 500 with cause detail
}

VariableInstance v = runtimeService.createVariableInstanceQuery().id(id).singleResult();
boolean safe = v != null && (v.getValue() instanceof byte[] || "serializable".equals(v.getType()));

boolean hasBinaryStream(VariableInstance v) {
    return v != null && v.getValue() instanceof byte[];
}

try {
    RestVariable data = resource.getVariableData(...);
} catch (FlowableException e) {
    log.error("variable data I/O failure", e.getCause());
    throw new ResponseStatusException(HttpStatus.INTERNAL_SERVER_ERROR, "variable data unavailable");
}

When it happens

Trigger: Calling GET on a variable instance data endpoint (VariableInstanceDataResource.getVariableData) where the variable holds binary or serializable data and the underlying stream read/write throws IOException, e.g. corrupted or unavailable variable byte content during toByteArray/writeObject.

Common situations: Large serialized variables whose stream fails mid-read; database storing truncated byte arrays; serialization incompatibility when the stored object graph cannot be written; environment/classloader issues during object serialization.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• Unexpected exception getting variable data
• Error getting variable " + variableName
• Unexpected exception getting variable data
• Error getting variable ${variable.getName()}
• Unexpected exception getting variable data

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/c593f99dc465ce4d. Report an issue: GitHub.