How do I create and store a global object that is accesible to all nodes?

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1

To be specific I want to (in a Java Snippet)

  • import a jar
  • initialize an object from that jar
  • and then make that object available to all nodes
2

How do you envision other nodes accessing this object? (e.g how would you have the Column Filter node access the object?) Or do you mean a specific subset of nodes that you want to access the object?

3

well the object is to be used by multiple Java Snippet nodes - I don’t want to output the object, I just need it to transform some data. But the creation of the object is costly so I should only do it once in the lifetime of the workflow.

4

I’ve done this sort of thing before by writing a custom Eclipse plugin, if you want to go that route.

I’m not familiar with how the Java Snippet node does class loading, but i take it that you’ve tried having a class in that jar you’re importing be a singleton, affecting that singleton in Java Snippet node 1 and then downstream seeing whether that singleton is the same instance affected by node 1?

Beyond that, in a pinch you could do some seriously hacky things like using the Eclipse IPreferenceStore to keep a ‘global’ object (if its really an object, as opposed to some values which could be represented as strings - you’ll need to do object serialization into and out of the preference store.)

5

Do you mean create my own node using the eclipse extension?

Here is more detail I should have provided in my post, the code looks like this - trying to use a .net object (I think Javonet is a singleton)

This works fine in a single Java Snippet node by the way.

//custom imports
import com.javonet.Javonet;
import com.javonet.JavonetException;
import com.javonet.JavonetFramework;
import com.javonet.api.NObject;

//custom code
Javonet.activate(“email”, “key”, JavonetFramework.v40);
Javonet.addReference(“D:\ClassLibrary.dll”);
NObject classLib = Javonet.New(“ClassLibrary.ClassLib”);
String value = classLib.invoke(“ReverseValue”,“Hello World”);

Javonet for sure only needs to be activated once, the references added one time as well.

6

I think you are likely to have to do this in your own node implementation. I think that the java snippet compiles the snippet code into an executable jar - one per node, and so singleton or not, you are going to recreate in each instance of the snippet, although I may be wrong on that.

It is possible to serialise objects to the knime workspace in your own node, which might also be a way to go.

Steve

7

I meant doing an Eclipse plugin, but not necessarily a KNIME node, depending on what you were trying to do.

I think you’re implying in the above cases, that a subsequent Java Snippet node executed after the JS node which enters the license information for Javonet, finds Javonet unlicensed? Aside from being gross, is there a significant time or processor or other penalty to having to do that activation in each JS node?

8

Every Java Snippet node has its own classloader. Therefore sharing data among several nodes will not work that way. And this is actually a good thing otherwise you could run into all kinds of nasty side-effects.

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