Workflow - help

[Patrícia Sousa]

I'm trying to create a workflow that have multiple assignees (done) and launch to them, a task. When I start the workflow, I want to run a java code that makes modifications on file that the task has been assigned. How can I run this java code on "Start Workflow"? 

And then, I want that each assignee have a task to approve (this moment, the assignees don't have task to approve, appear task done, how can I do that), and to approve I want to run other java code. 

How can I make this ? Assign this java codes to workflow?

I don't know how to define bpmn too.