flowable/flowable-engine · error · FlowableConflictException

A group with id '' already exists.

Error message

A group with id '' already exists.

What it means

createGroup checks identityService.createGroupQuery().groupId(id).count() before creating, and throws FlowableConflictException when a group with that id already exists. This pre-check exists because the underlying identity API does not throw a typed duplicate-key exception, so the REST layer maps it to HTTP 409.

Solutions

1. Check existence first (GET /identity/groups/{id}) and skip or update instead of POSTing a duplicate.
2. Make seed scripts idempotent: create only when the group is absent.
3. If the existing group should receive new attributes, use PUT /identity/groups/{id} rather than POST.

Example fix

// before
client.post("/identity/groups", group); // may 409 on retry
// after
if (client.get("/identity/groups/" + group.getId()) == null) {
    client.post("/identity/groups", group);
} else {
    client.put("/identity/groups/" + group.getId(), group);
}

boolean exists = client.list("/identity/groups").stream()
    .anyMatch(g -> groupRequest.getId().equals(g.getId()));
if (exists) { /* update or skip instead of POST */ }

try {
    client.post("/identity/groups", groupRequest);
} catch (HttpClientErrorException e) {
    if (e.getStatusCode() == HttpStatus.CONFLICT) {
        client.put("/identity/groups/" + groupRequest.getId(), groupRequest); // upsert
    } else throw e;
}

When it happens

Trigger: POST /identity/groups with an "id" that already exists in ACT_ID_GROUP, including a retry of a successful create or a re-seeded demo group id such as from the Flowable demo data setup.

Common situations: Non-idempotent bootstrap/seed scripts run twice; race between two admins creating the same group concurrently; migration script re-inserting groups from an old system without checking existence.

Understand the failure class

Background: "already exists" / EEXIST / FileAlreadyExistsException: what the 'file already exists' error means and how to fix it — this error's family across 37 libraries.

Related errors

• Engine property already exists
• User '' is already part of group ''.
• Variable ' ' is already present on task ' '.
• Could not find a group with id ''.
• Id cannot be null.

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/a9cdcb501716a438. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-rest/src/main/java/org/flowable/rest/service/api/identity/GroupCollectionResource.java:133

    @ApiOperation(value = "Create a group", tags = { "Groups" }, code = 201)
    @ApiResponses(value = {
            @ApiResponse(code = 201, message = "Indicates the group was created."),
            @ApiResponse(code = 400, message = "Indicates the id of the group was missing.")
    })
    @PostMapping(value = "/identity/groups", produces = "application/json")
    @ResponseStatus(HttpStatus.CREATED)
    public GroupResponse createGroup(@RequestBody GroupRequest groupRequest) {
        if (groupRequest.getId() == null) {
            throw new FlowableIllegalArgumentException("Id cannot be null.");
        }
        
        if (restApiInterceptor != null) {
            restApiInterceptor.createGroup(groupRequest);
        }

        // Check if a user with the given ID already exists so we return a CONFLICT
        if (identityService.createGroupQuery().groupId(groupRequest.getId()).count() > 0) {
            throw new FlowableConflictException("A group with id '" + groupRequest.getId() + "' already exists.");
        }

        Group created = identityService.newGroup(groupRequest.getId());
        created.setId(groupRequest.getId());
        created.setName(groupRequest.getName());
        created.setType(groupRequest.getType());
        identityService.saveGroup(created);

        return restResponseFactory.createGroupResponse(created);
    }

}

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