Java Service Task in Designer / Modeler

I would like to create a Service Task which is implemented in Java. This service task should then be available in the modeler / designer (web application) for the customer so that he can drag and drop this service task without much configuration.

I develop a Java program as a Java Delegate: like this here:

After that I compile and deploy the jar file the WEB-INF/lib

What do I have to do the be able to use this service task in the designer “out-of-the-box”?
I want to know how to deploy/import/include my extension JAR to flowable-modeler so that I am able to see the custom service task in the flowable-modeler palette.

Hi John,

the similar question is:


Hi Martin,

I appreciate your answer. It is a bit hard to follow. Is there any official guide for this?
A little code example of a basic custom service task would help me greatly.

Thanks in advance.


Hi John,

The whole example is in the pull request

But let’s do it step by step.

  1. Add new node to stencilset_bpmn.json ServiceTask node is a good example. After this step new node is added to modeler paletes.
  2. Implement json -> bpmn and bpmn -> json converter and add it to the converters. The best example is org.flowable.editor.language.json.converter.ServiceTaskJsonConverter. (this step is needed only in the case when you want to change something in ServiceTask node in the stencil set.
  3. In your case this step is not needed, because you just need to use “default” service task behavior but you can also implement your own behavior to behave differently from service task (see e.g. org.flowable.engine.impl.bpmn.behavior.ServiceTaskJavaDelegateActivityBehavior)


1 Like

Dear Martin,

I’m new to Flowable so I might be wrong, but I think I’m trying to do something similar without success.

What I need to achieve is to make custom tasks available in the web based modeler so that users can create workflows starting from them.
Moreover I need these custom tasks to have a java delegate class associated by default.

I can easily achieve that with the eclipse editor but I don’t understand how to do that for the web based one.

What I did so far was: checking out the flowable engine from github (not even sure if this is needed), find the json file which should contain the tasks in the palette but I don’t even know which steps to follow in order to deploy them into the modeler.

Could you please guide me through that process?

Thanks a lot,


Hi Jacopo,

did you try to add new service task to palette?
after that you can add default value to java delegate class attribute.
Next task is to make non needed attributes hidden.


Hi Martin,

what I manage to do so far is:

  • checkout flowable-engine from github

  • find the stencilset_bpmn.json file in flowable-engine\modules\flowable-ui-modeler\flowable-ui-modeler-logic\src\main\resources

  • Add the following lines for a custom task:

    “type” : “node”,
    “id” : “CustomTask”,
    “title” : “Custom task”,
    “description” : “A service task with custom logic”,
    “icon” : “activity/list/type.service.png”,
    “groups” : [ “Activities” ],
    “propertyPackages” : [ “overrideidpackage”, “namepackage”, “documentationpackage”, “asynchronousdefinitionpackage”, “exclusivedefinitionpackage”, “servicetasktriggerablepackage”, “executionlistenerspackage”, “multiinstance_typepackage”, “multiinstance_cardinalitypackage”, “multiinstance_collectionpackage”, “multiinstance_variablepackage”, “multiinstance_conditionpackage”, “isforcompensationpackage”, “servicetaskclasspackage”, “servicetaskexpressionpackage”, “servicetaskdelegateexpressionpackage”, “servicetaskfieldspackage”, “servicetaskresultvariablepackage”, “skipexpressionpackage” ],
    “hiddenPropertyPackages” : [ ],
    “roles” : [ “Activity”, “sequence_start”, “sequence_end”, “ActivitiesMorph”, “all” ]


Hi Martin,

I have a small update:
I managed to build flowable-engine with ant on windows. I saw this generated the flwoable-modeler war.
Also, navigating into the modules to flowable-ui-modeler I see the various submodules (among which there is flowable-ui-modeler-logic which contains the stencil set json file.

I edited it and rebuild with maven, so when I deploy the new war I can see the new tasks as you can see from the picture.


What are the next steps now?
Which customization should I make in order to make this custom tasks ready to be put in a workflow?
How can I associate the java delegate to it?

Kind Regards,

add default value to e.g. java delegate class attribute.



where should I specify the delegate class?



    "name" : "claim_task_scripttextpackage",
    "properties" : [ {
      "id" : "scripttext_claim_task",
      "type" : "Text",
      "title" : "Script",
      "value" : "import static*;\n println 'Replace $USERID and $TASK_DEFINITION_KEY with proper value';\n processInstanceIds = getSubProcessInstanceIds(processInstanceId, execution);\n taskId = getVirtualProcessEngine(execution).getTaskService().createTaskQuery().processInstanceIdIn(processInstanceIds).taskDefinitionKey(\"$TASK_DEFINITION_KEY\").singleResult().getId();\n getVirtualProcessEngine(execution).getTaskService().claim(taskId, '$USER_ID');",
      "description" : "Script text of the script task.",
      "popular" : true
    } ]

shows how to create new package with default value. This package can be used in your custom task. In fact you have to create new package based on e.g servicetaskdelegateexpressionpackage.


Hi Martin,

I made some progress following your advice. Now I can drag the custom service tasks from the palette and have the proper delegate class associated with them.


When I try to validate the workflow I get some warnings concerning the tasks and some criticals concerning the link between them. As consequence when I try to export it I get an empty workflow. The only task ok is the receive task (which I did not customize).


This is an example of what I added in the stencilset for the custom tasks:

    "type" : "node",
    "id" : "CustomTask",
    "title" : "Custom Task",
    "description" : "A custom task",
    "view" : "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\"?>\n<svg\n   xmlns=\"\"\n   xmlns:svg=\"\"\n   xmlns:oryx=\"\"\n   xmlns:xlink=\"\"\n\n   width=\"102\"\n   height=\"82\"\n   version=\"1.0\">\n  <defs></defs>\n  <oryx:magnets>\n  \t<oryx:magnet oryx:cx=\"1\" oryx:cy=\"20\" oryx:anchors=\"left\" />\n  \t<oryx:magnet oryx:cx=\"1\" oryx:cy=\"40\" oryx:anchors=\"left\" />\n  \t<oryx:magnet oryx:cx=\"1\" oryx:cy=\"60\" oryx:anchors=\"left\" />\n  \t\n  \t<oryx:magnet oryx:cx=\"25\" oryx:cy=\"79\" oryx:anchors=\"bottom\" />\n  \t<oryx:magnet oryx:cx=\"50\" oryx:cy=\"79\" oryx:anchors=\"bottom\" />\n  \t<oryx:magnet oryx:cx=\"75\" oryx:cy=\"79\" oryx:anchors=\"bottom\" />\n  \t\n  \t<oryx:magnet oryx:cx=\"99\" oryx:cy=\"20\" oryx:anchors=\"right\" />\n  \t<oryx:magnet oryx:cx=\"99\" oryx:cy=\"40\" oryx:anchors=\"right\" />\n  \t<oryx:magnet oryx:cx=\"99\" oryx:cy=\"60\" oryx:anchors=\"right\" />\n  \t\n  \t<oryx:magnet oryx:cx=\"25\" oryx:cy=\"1\" oryx:anchors=\"top\" />\n  \t<oryx:magnet oryx:cx=\"50\" oryx:cy=\"1\" oryx:anchors=\"top\" />\n  \t<oryx:magnet oryx:cx=\"75\" oryx:cy=\"1\" oryx:anchors=\"top\" />\n  \t\n  \t<oryx:magnet oryx:cx=\"50\" oryx:cy=\"40\" oryx:default=\"yes\" />\n  </oryx:magnets>\n  <g pointer-events=\"fill\" oryx:minimumSize=\"50 40\">\n\t<rect id=\"text_frame\" oryx:anchors=\"bottom top right left\" x=\"1\" y=\"1\" width=\"94\" height=\"79\" rx=\"10\" ry=\"10\" stroke=\"none\" stroke-width=\"0\" fill=\"none\" />\n\t<rect id=\"bg_frame\" oryx:resize=\"vertical horizontal\" x=\"0\" y=\"0\" width=\"100\" height=\"80\" rx=\"10\" ry=\"10\" stroke=\"#bbbbbb\" stroke-width=\"1\" fill=\"#f9f9f9\" />\n\t\t<text \n\t\t\tfont-size=\"12\" \n\t\t\tid=\"text_name\" \n\t\t\tx=\"50\" \n\t\t\ty=\"40\" \n\t\t\toryx:align=\"middle center\"\n\t\t\toryx:fittoelem=\"text_frame\"\n\t\t\tstroke=\"#373e48\">\n\t\t</text>\n\t\n\t<g id=\"serviceTask\" transform=\"translate(3,3)\">\n\t<path oryx:anchors=\"top left\"\n\t\tstyle=\"fill:#72a7d0;stroke:none\"\n     d=\"M 8,1 7.5,2.875 c 0,0 -0.02438,0.250763 -0.40625,0.4375 C 7.05724,3.330353 7.04387,3.358818 7,3.375 6.6676654,3.4929791 6.3336971,3.6092802 6.03125,3.78125 6.02349,3.78566 6.007733,3.77681 6,3.78125 5.8811373,3.761018 5.8125,3.71875 5.8125,3.71875 l -1.6875,-1 -1.40625,1.4375 0.96875,1.65625 c 0,0 0.065705,0.068637 0.09375,0.1875 0.002,0.00849 -0.00169,0.022138 0,0.03125 C 3.6092802,6.3336971 3.4929791,6.6676654 3.375,7 3.3629836,7.0338489 3.3239228,7.0596246 3.3125,7.09375 3.125763,7.4756184 2.875,7.5 2.875,7.5 L 1,8 l 0,2 1.875,0.5 c 0,0 0.250763,0.02438 0.4375,0.40625 0.017853,0.03651 0.046318,0.04988 0.0625,0.09375 0.1129372,0.318132 0.2124732,0.646641 0.375,0.9375 -0.00302,0.215512 -0.09375,0.34375 -0.09375,0.34375 L 2.6875,13.9375 4.09375,15.34375 5.78125,14.375 c 0,0 0.1229911,-0.09744 0.34375,-0.09375 0.2720511,0.147787 0.5795915,0.23888 0.875,0.34375 0.033849,0.01202 0.059625,0.05108 0.09375,0.0625 C 7.4756199,14.874237 7.5,15.125 7.5,15.125 L 8,17 l 2,0 0.5,-1.875 c 0,0 0.02438,-0.250763 0.40625,-0.4375 0.03651,-0.01785 0.04988,-0.04632 0.09375,-0.0625 0.332335,-0.117979 0.666303,-0.23428 0.96875,-0.40625 0.177303,0.0173 0.28125,0.09375 0.28125,0.09375 l 1.65625,0.96875 1.40625,-1.40625 -0.96875,-1.65625 c 0,0 -0.07645,-0.103947 -0.09375,-0.28125 0.162527,-0.290859 0.262063,-0.619368 0.375,-0.9375 0.01618,-0.04387 0.04465,-0.05724 0.0625,-0.09375 C 14.874237,10.52438 15.125,10.5 15.125,10.5 L 17,10 17,8 15.125,7.5 c 0,0 -0.250763,-0.024382 -0.4375,-0.40625 C 14.669647,7.0572406 14.641181,7.0438697 14.625,7 14.55912,6.8144282 14.520616,6.6141566 14.4375,6.4375 c -0.224363,-0.4866 0,-0.71875 0,-0.71875 L 15.40625,4.0625 14,2.625 l -1.65625,1 c 0,0 -0.253337,0.1695664 -0.71875,-0.03125 l -0.03125,0 C 11.405359,3.5035185 11.198648,3.4455201 11,3.375 10.95613,3.3588185 10.942759,3.3303534 10.90625,3.3125 10.524382,3.125763 10.5,2.875 10.5,2.875 L 10,1 8,1 z m 1,5 c 1.656854,0 3,1.3431458 3,3 0,1.656854 -1.343146,3 -3,3 C 7.3431458,12 6,10.656854 6,9 6,7.3431458 7.3431458,6 9,6 z\" />\n\t</g>\n  \n\t<g id=\"parallel\">\n\t\t<path oryx:anchors=\"bottom\" fill=\"none\" stroke=\"#bbbbbb\" d=\"M46 70 v8 M50 70 v8 M54 70 v8\" stroke-width=\"2\" />\n\t</g>\n\t\n\t<g id=\"sequential\">\n\t\t<path oryx:anchors=\"bottom\" fill=\"none\" stroke=\"#bbbbbb\" stroke-width=\"2\" d=\"M46,76h10M46,72h10 M46,68h10\"/>\n\t</g>\n\t\n\t<g id=\"compensation\">\n\t\t<path oryx:anchors=\"bottom\" fill=\"none\" stroke=\"#bbbbbb\" d=\"M 62 74 L 66 70 L 66 78 L 62 74 L 62 70 L 58 74 L 62 78 L 62 74\" stroke-width=\"1\" />\n\t</g>\n  </g>\n</svg>",
    "icon" : "activity/list/custom/custom.png",
    "propertyPackages" : [ "CustomTaskNamePackage", "CustomTaskClassPackage", "CustomTaskOverrideIdPackage", "CustomTaskDocumentationPackage", "CustomTaskFieldsPackage", "custom_multiinstance_typepackage", "custom_isforcompensationpackage"],
    "hiddenPropertyPackages" : [ ],
    "roles" : [ "Activity", "sequence_start", "sequence_end", "ActivitiesMorph", "all" ]

What am I doing wrong? Is there a way to get more information out of the validation process?
Thanks a lot,


I had a look at the code of SequenceflowValidator. As far as I understood the sourceRef and targetRef are both empty for the custom tasks I added in the stencilset.

I don’t understand why it happens and how to avoid it. Could anybody help me with that? :pray:

Thanks a lot,

Hi Jacopo.

It’s hard to guess. It would be better if you provide small jUnit test for that.


Hi Martin,

what kind of jUnit test should I provide? I’m not yet to the point or running the workflow since it cannot be validated.

Is there a sample custom task that you can show me that works?
Is there any step I am missing maybe? The only thinkg I did was modifying the stencil set json.

Thanks a lot,

Hi Jacopo.

The test which shows how your model validation fails.

yes I posted the links to my pull request with the changes for simulation and testing framework in previous comment. may be I should write a short blog about it.


Hi Martin,

i am also trying to add custom task but always have many problem and did not find any proper steps guide that i can add custom task in flowable modeler.

Can you please guide me i just want to add custom task with custom dropdown properties, with associated java delegate.

so in delegate i can have all selected properties and userinput in that delegate after business logic move to next task.

please help me out from this problem.

Is there a way to externalize a custom task into a separate JAR? I’d like to avoid forking the engine and it seems that the converters are inside the engine.

I don’t think is possible to externalize a custom task into a separate JAR, because you need to modify several flowable-modules (listed in this post: How to extend Flowable to add "Business Domain" specific BPMN elements) to make it work.

Hi ,I am new to flowable.I am trying to customize the pallete.Require little clarification regarding the steps to be followed for the same.I am using apache tomcat server for flowable.I followed the steps mentioned above and was able to make changes in Stencilset_bpmn file.But while generating jar for the flowable-ui-modeler-logic using STS(spring tool) facing below issues:

[INFO] Scanning for projects…
[INFO] ---------------< org.flowable:flowable-ui-modeler-logic >---------------
[INFO] Building flowable-ui-modeler-logic 6.6.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[WARNING] The POM for org.flowable:flowable-ui-common:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-bpmn-model:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-bpmn-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-bpmn-layout:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-process-validation:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-image-generator:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-json-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-cmmn-model:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-cmmn-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-cmmn-json-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-cmmn-image-generator:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-dmn-xml-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-dmn-json-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-dmn-image-generator:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-form-model:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-form-json-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-event-registry-model:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-event-registry-json-converter:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[WARNING] The POM for org.flowable:flowable-app-engine-api:jar:6.6.0-SNAPSHOT is missing, no dependency information available
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 7.855 s
[INFO] Finished at: 2020-10-12T12:06:39+05:30
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal on project flowable-ui-modeler-logic: Could not resolve dependencies for project org.flowable:flowable-ui-modeler-logic:jar:6.6.0-SNAPSHOT: The following artifacts could not be resolved: org.flowable:flowable-ui-common:jar:6.6.0-SNAPSHOT, org.flowable:flowable-bpmn-model:jar:6.6.0-SNAPSHOT, org.flowable:flowable-bpmn-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-bpmn-layout:jar:6.6.0-SNAPSHOT, org.flowable:flowable-process-validation:jar:6.6.0-SNAPSHOT, org.flowable:flowable-image-generator:jar:6.6.0-SNAPSHOT, org.flowable:flowable-json-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-cmmn-model:jar:6.6.0-SNAPSHOT, org.flowable:flowable-cmmn-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-cmmn-json-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-cmmn-image-generator:jar:6.6.0-SNAPSHOT, org.flowable:flowable-dmn-xml-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-dmn-json-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-dmn-image-generator:jar:6.6.0-SNAPSHOT, org.flowable:flowable-form-model:jar:6.6.0-SNAPSHOT, org.flowable:flowable-form-json-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-event-registry-model:jar:6.6.0-SNAPSHOT, org.flowable:flowable-event-registry-json-converter:jar:6.6.0-SNAPSHOT, org.flowable:flowable-app-engine-api:jar:6.6.0-SNAPSHOT: Could not find artifact org.flowable:flowable-ui-common:jar:6.6.0-SNAPSHOT -> [Help 1]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1]

Help me to solve the issue so that I can generate jar.