Generate FieldActions metadata offline

[igarashitm]

This is a...

[x] Feature request
[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[ ] Documentation issue or request

The problem

To achieve #204 we need to generate FieldActions metadata and deliver it into datamapper UI. Just like inspections, generate FieldActions metadata by invoking atlasmap maven plugin with feeding extension classpath, and store the metadata somewhere (as a part of extension metadata?). Then UI would feed them into datamapper step when initializing.

Note that there're built-in field actions in AtlasMap regardless of extension. It would be better also to generate those OOTB field actions metadata ahead to avoid online field action retrieval which happens everytime datamapper step opens.

[igarashitm]

GenerateFieldActionMojo generates field action metadata and save it into json file
https://github.com/atlasmap/atlasmap/blob/master/runtime/atlasmap-maven-plugin/src/main/java/io/atlasmap/maven/GenerateFieldActionsMojo.java

Example field action metadata

{
  "ActionDetails" : {
    "actionDetail" : [ {
      "name" : "Capitalize",
      "className" : "io.atlasmap.actions.StringSimpleFieldActions",
      "method" : "capitalize",
      "sourceType" : "STRING",
      "targetType" : "STRING",
      "sourceCollectionType" : "NONE",
      "targetCollectionType" : "NONE"
    }, {
..........
    }, {
      "name" : "DummyFieldAction",
      "custom" : true,
      "className" : "io.atlasmap.maven.test.DummyFieldActions",
      "method" : "dummy",
      "sourceType" : "BYTE",
      "targetType" : "NUMBER",
      "sourceCollectionType" : "MAP",
      "targetCollectionType" : "ARRAY"
    } ]
  }
}

[igarashitm]

@lburgazzoli where should we save those field action metadata? I found inspections are stored as a part of extension metadata here
https://github.com/syndesisio/syndesis/blob/master/app/extension/maven-plugin/src/main/java/io/syndesis/extension/maven/plugin/GenerateMetadataMojo.java#L504
but this is because they belong to the specific Action right? as opposed to the custom field actions should be available anytime user put a datamapper step.

[lburgazzoli]

We need to define a new extension type or amend the current model for library extensions.
I guess we also need to define an endpoint for the UI to retrieve the fields actions.

[igarashitm]

That makes sense. is it possible to bundle multiple extension types in a single archive and upload into Syndesis at once? If that's possible, I think whether to introduce a new extension type or update current model would be an internal & technical decision we can choose.

[lburgazzoli]

It is not possible to bundle multiple extension types in the same extension so I'd go for a new type, let me see how we can extend the model.

btw, do you have an example of a class that then generates the field action metadata definition ?

[igarashitm]

Here is an example field action, it only needs to extend AtlasFieldAction and put @AtlasFieldActionInfo annotation on the method.
atlasmap/atlasmap@ebd4aaa#diff-d985e3a4fe0762600044d3c4a6191c0b

Then AtlasMap will load them via ServiceLoader (META-INF/services)
atlasmap/atlasmap@ebd4aaa#diff-99c6b96449dd542593405cdf61e60269

The method parameter Action makes no sense for custom field actions, so we'll remove it (atlasmap/atlasmap#541)