Write documentation for Java actions

[glikson]

It seems that static fields in Java actions are initialized only on first invocation of an action.

• Environment: Bluemix
• Steps to reproduce:
  • create a Java action with the code below
  • invoke it multiple times
  • observe that the returned 'value' is increasing by one every invocation

import com.google.gson.JsonObject;
public class Static {
    static int field = 0;
    public static JsonObject main(JsonObject args) {
        JsonObject response = new JsonObject();
        response.addProperty("value", field++);
        return response;
    }
}

$ jar cf static.jar Static.class 
$ wsk action create static static.jar 
ok: created action static
$ wsk action invoke static --blocking --result
{
    "value": 0
}
$ wsk action invoke static --blocking --result
{
    "value": 1
}
$ wsk action invoke static --blocking --result
{
    "value": 2
}

Not entirely sure whether this is a bug or a feature (that should be properly documented), and whether it is environment-dependent.

[rabbah]

This is working as designed. The static field is "state" and if your action ends up reusing a container, state from previous invocations carries over to newer ones. You should not count on the container reuse but you can check for it (i.e. using a static). If you don't want this behavior then all static fields should be final and immutable.

[glikson]

OK, thanks. Sounds interesting. Is it documented somewhere?

[rabbah]

not yet.

[sjfink]

Changing title to reflect the actionable work: Document Java

[SyCode7]

Is there a basic example for deploying a java application somewhere yet ?

[glikson]

https://github.com/openwhisk/openwhisk/blob/master/docs/actions.md#creating-java-actions

[rabbah]

@psuter has a recent blog post as well: https://psuter.net/2017/01/20/openwhisk-java-gradle